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Chemistry notes for SSC CGL exam: Pinnacle Coaching Centre

Chemistry notes for SSC CGL exam: Pinnacle Coaching Centre

Chemistry notes for SSC CGL exam: Pinnacle Coaching Centre

Dear readers, In this article, we are providing Chemistry notes for SSC CGL exam. These notes has been collected from 7th -10 th Class NCERT + Other sources. We are sharing these materials with you because these are really helpful for SSC exam aspirants.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

NCERT Class 7, Chapter 5 (Acids, Bases and Salt)



  • Curd, lemon juice, orange juice and vinegar taste sour. These substances taste sour because they contain acids.
  • The chemical nature
    of such substances is acidic.
  • The word acid comes from the Latin word acere which means sour.
  • The acids in these substances are natural acids

Substances like these which are bitter in taste and feel soapy on touching are known as bases.

The nature of such substances is said to be basic.

Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators


The indicators change their colour when added to a solution containing an acidic or a basic substance. Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.


Litmus: A natural dye

The most commonly used natural indicator is litmus. It is extracted from lichens .It has a mauve (purple) color in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper

The solutions which do not change the color of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.

  • Turmeric is another natural indicator
    • Why a turmeric stain on my white shirt is turned to red when it is washed with soap. It is because the soap solution is basic

To prepare limewater, dissolve some lime (chuna) in water in a bottle. Stir the solution and keep it for some time. Pour a little from the top. This is lime water.

  • China Rose as Indicator (China rose 9Gudhal) petals

China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.

Acid rain

As the name indicates the rain containing excess of acids is called an acid rain

Where do these acids come from? The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively. Acid rain can cause damage to buildings, historical monuments, plants and animals.


Phenolphthalein as an Indicator

In neutralization reaction a new substance is formed. This is called salt

Salt may be acidic, basic or neutral in nature. Thus, neutralization can be defined as follows:

The reaction between an acid and a base is known as neutralization. Salt and water are produced in this process with the evolution of heat. Acid+Base  Salt+Water (Heat is evolved) The following reaction is an example: Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) Sodium chloride (NaCl) + Water (H2 O)



Our stomach contains hydrochloric acid. It helps us to digest food, but too much of acid in the stomach causes indigestion. Sometimes indigestion is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralizes the effect of excessive acid.

Ant sting The sting of an ant contains formic acid. When an ant bites, it injects the acidic liquid into the skin. The effect of the sting can be neutralized by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

Soil treatment

Excessive use of chemical fertilizers makes the soil acidic. Plants do not grow well when the soil is either too acidic or too basic. When the soil is too acidic, it is treated with bases like quick lime (calcium oxide) or slaked lime (calcium hydroxide). If the soil is basic, organic matter is added to it. Organic matter releases acids which neutralizes the basic nature of the soil.

Factory wastes

The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralized by adding basic substances.


  • Acid
  • Acidic
  • Base
  • Basic
  • Indicator
  • Neutral
  • Neutralization
  • Salt

What you have learnt

  1. Acids are sour in taste. Bases are bitter in taste and soapy to touch.
  2. Acid turns blue litmus red. Bases turn red litmus blue.
  3. Substances which are neither acidic nor basic are called neutral.
  4. Solutions of substances that show different colour in acidic, basic and neutral solutions are called indicators.
  5. An acid and a base neutralize each other and form a salt.
  6. A salt may be acidic, basic or neutral in nature.

Did you know? 

Each cell in our body contains an acid, the deoxyribonucleic acid or DNA . It controls every feature of the body such as our looks, colour of our eyes, our height etc. Proteins that build part of our cells are also made of amino acids. The fats in our body contain fatty acids.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

NCERT Class 7 Chapter 6 : Physical and Chemical Changes


Properties such as shape, size, colour and state of a substance are called its physical properties.

A change in which a substance undergoes a change in its physical properties is called a physical change.

A physical change is generally reversible. In such a change no new substance is formed

Chemical change

A change with which you are quite familiar is the rusting of iron. If you leave a piece of iron in the open for some time, it acquires a film of brownish substance. This substance is called rust and the process is called rusting.

Magnesium oxide (MgO) + Water (H 2 O) → Magnesium hydroxide [Mg(OH)2 ]

Magnesium hydroxide is a base. So, magnesium oxide is a new substance formed on burning of magnesium. The equations here are different from those in mathematics. In equations of this kind, the arrow implies ‘becomes’. No attempt should be made to balance chemical equations at this stage.

Chemistry notes for SSC CGL exam: Pinnacle Coaching Centre
A change in which one or more new substances are formed is called a chemical change. A chemical change is also called a chemical reaction.

Chemical changes are very important in our lives. All new substances are formed as a result of chemical changes. For example, if a metal is to be extracted from an ore, such as iron from iron ore, we need to carry out a series of chemical changes

We have seen that one or more new substances are produce in a chemical change. In addition to new products, the following may accompany a chemical change: „ Heat, light or any other radiation (ultraviolet, for example) may be given off or absorbed. „ Sound may be produced. „ A change in smell may take place or a new smell may be given off. „ A colour change may take place . „ A gas may be formed.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar

When carbon dioxide is passed through lime water, calcium carbonate is formed, which makes lime water milky. The turning of lime water into milky is a standard test of carbon dioxide

burning of magnesium ribbon is a chemical change.

Burning of coal, wood or leaves is also a chemical change. In fact, burning of any substance is a chemical change. Burning is always accompanied by production of heat.

Explosion of a firework is a chemical change.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

You must have noticed that a slice of an apple acquires a brown colour if it is not consumed immediately. If you have not seen this change in colour, cut a fresh slice of apple and keep it away for some time. Repeat the same activity with a slice of potato or brinjal. The change of colour in these cases is due to the formation of new substances. Are not these changes chemical changes?

You neutralized an acid with a base. Is neutralization a chemical change?

A protective shield
  • You must have heard of the ozone layer in our atmosphere. It protects us from the harmful ultraviolet radiation which comes from the sun. Ozone absorbs this radiation and breaks down to oxygen. Oxygen is different from ozone. Can we call the breaking down of ozone a chemical change? If ultraviolet radiation were not absorbed by ozone, it would reach the earth’s surface and cause harm to us and other life forms. Ozone acts as a natural shield against this radiation.
  • Plants produce their food by a process called photosynthesis. Can we call photosynthesis a chemical change?
  • Even digestion is a chemical change


RUSTING OF IRON Let us get back to rusting. This is one change that affects iron articles and slowly destroys them. Since iron is used in making bridges, ships, cars, truck bodies and many other articles, the monetary loss is huge.

The process of rusting can be represented by the following equation: Iron (Fe) + Oxygen (O 2 , from the air) + water (H 2 O) → rust (iron oxide Fe 2O3 ) For rusting, the presence of both oxygen and water (or water vapour) is essential

In fact, if the content of moisture in air is high, which means if it is more humid, rusting becomes faster

So, how do we prevent rusting? Prevent iron articles from coming in contact with oxygen, or water, or both. One simple way is to apply a coat of paint or grease. In fact, these coats should be applied regularly to prevent rusting. Another way is to deposit a layer of a metal like chromium or zinc on iron

This process of depositing a layer of zinc on iron is called galvanization. The iron pipes we use in our homes to carry water are galvanized to prevent rusting.

Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese. It does not rust


You have learnt that salt can be obtained by the evaporation of sea water. The salt obtained in this manner is not pure and its crystals are small. The shape of the crystals cannot be seen clearly. However, large crystals of pure substances can be formed from their solutions. The process is called crystallization.  It is an example of a physical change

Keywords in the chapter

  • Chemical change
  • Chemical reaction
  • Crystallization
  • Galvanization
  • Physical change
  • Rusting
What you have learnt
  • Changes can be of two types, physical and chemical.
  • Physical changes are changes in the physical properties of substances. No new substances are formed in these changes. These changes may be reversible.
  • In chemical changes new substances are produced.
  • Some substances can be obtained in pure state from their solutions by crystallization.




  • Natural fibres like cotton, wool, silk, etc., are obtained from plants or animals.
  • The synthetic fibres, on the other hand, are made by human beings. That is why these are called synthetic or man-made fibres.

A synthetic fibre is also a chain of small units joined together. Each small unit is actually a chemical substance. Many such small units combine to form a large single unit called a polymer. The word ‘polymer’ comes from two Greek words; poly meaning many and mer meaning part/unit. So, a polymer is made of many repeating units.

Polymers occur in nature also. Cotton, for example, is a polymer called cellulose. Cellulose is made up of a large number of glucose units.

Types of Synthetic Fibres

  1. Rayon

Silk fiber obtained from silkworm was discovered in China and was kept as a closely guarded secret for a long time.

Fabric obtained from silk fibre was very costly. But its beautiful texture fascinated everybody. Attempts were made to make silk artificially. Towards the end of the nineteenth century, scientists were successful in obtaining a fibre having properties similar to that of silk. Such a fibre was obtained by chemical treatment of wood pulp. This fibre was called rayon or artificial silk. Although rayon is obtained from a natural source, wood pulp, yet it is a man-made fibre. It is cheaper than silk and can be woven like silk fibres. It can also be dyed in a wide variety of colours. Rayon is mixed with cotton to make bed sheets or mixed with wool to make carpets.

  1. Nylon

Nylon is another man-made fibre. In 1931, it was made without using any natural raw material (from plant or animal). It was prepared from coal, water and air. It was the first fully synthetic fibre. Nylon fibre was strong, elastic and light. It was lustrous and easy to wash. So, it became very popular for making clothes. We use many articles made from nylon, such as socks, ropes, tents, toothbrushes, car seat belts, sleeping bags, curtains etc. Nylon is also used for making parachutes and ropes for rock climbing.

A nylon thread is actually stronger than a steel wire.

  1. Polyester and Acrylic

Polyester is another synthetic fibre. Fabric made from this fibre does not get wrinkled easily. It remains crisp and is easy to wash. So, it is quite suitable for making dress material. You must have seen people wearing nice polyester shirts and other dresses. Terylene is a popular polyester. It can be drawn into very fine fibres that can be woven like any other yarn.

PET is a very familiar form of polyester. It is used for making bottles, utensils, films, wires and many other useful products.

Polyester (Poly+ester) is actually made up of the repeating units of a chemical called an ester. Esters are the chemicals which give fruits their smell. Fabrics are sold by names like polycot, polywool, terrycot etc. As the name suggests, these are made by mixing two types of fibres. Polycot is a mixture of polyester and cotton. Polywool is a mixture of polyester and wool.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

We wear sweaters and use shawls or blankets in the winter. Many of these are actually not made from natural wool, though they appear to resemble wool. These are prepared from another type of synthetic fibre called  acrylic. The wool obtained from natural sources is quite expensive, whereas clothes made from acrylic are relatively cheap. They are available in a variety of colours. Synthetic fibres are more durable and affordable which makes them more popular than natural fibres.

When you burn synthetic fibres you find that their behaviour is different from that of the natural fibres. You must have noticed that synthetic fibres melt on heating. This is actually a disadvantage of synthetic fibres. If the clothes catch fire, it can be disastrous. The fabric melts and sticks to the body of the person wearing it. We should, therefore, not wear synthetic clothes while working in the kitchen or in a laboratory.

All the synthetic fibres are prepared by a number of processes using raw materials of petroleum origin, called petrochemicals.

Characteristics of Synthetic Fibres

Imagine that it is a rainy day. What kind of umbrella would you use and why? Synthetic fibres possess unique characteristics which make them popular dress materials. They dry up quickly, are durable, less expensive, readily available and easy to maintain.


You must be familiar with many plastic articles used everyday

Plastic is also a polymer like the synthetic fibre. All plastics do not have the same type of arrangement of units. In some it is linear, whereas in others it is cross-linked.

Plastic articles are available in all possible shapes and sizes

The fact is that plastic is easily mouldable i.e. can be shaped in any form. Plastic can be recycled, reused, coloured, melted, rolled into sheets or made into wires. That is why it finds such a variety of uses.

Polythene(Poly+ethene) is an example of a plastic. It is used for making commonly used polythene bags.

You will observe that some plastic articles can bend easily while some break when forced to bend. When we add hot water to a plastic bottle, it gets deformed. Such plastic which gets deformed easily on heating and can be bent easily are known as thermoplastics. Polythene and PVC are some of the examples of thermoplastics. These are used for manufacturing toys, combs and various types of containers.

On the other hand, there are some plastics which when moulded once, can not be softened by heating. These are called thermosetting plastics.

Two examples are bakelite and melamine. Bakelite is a poor conductor of heat and electricity. It is used for making electrical switches, handles of various utensils, etc. Melamine is a versatile material. It resists fire and can tolerate heat better than other plastics. It is used for making floor tiles, kitchenware and fabrics which resist fire.

Plastics as Materials of Choice

Today if we think of storing a food item, water, milk, pickles, dry food, etc., plastic containers seem most convenient. This is because of their light weight, lower price, good strength and easy handling. Being lighter as compared to metals, plastics are used in cars, aircrafts and spacecrafts, too. The list is endless if we start counting articles like slippers, furniture and decoration pieces, etc.

Characteristic properties of plastics.

  1. Plastic is non-reactive .You know that metals like iron get rusted when left exposed to moisture and air. But plastics do not react with water and air. They are not corroded easily. That is why they are used to store various kinds of material, including many chemicals.
  2. Plastic is light, strong and durable plastic is very light, strong, durable and can be moulded into different shapes and sizes, it is used for various purposes. Plastics are generally cheaper than metals. They are widely used in industry and for household articles.
  3. Plastics are poor conductors

Plastics are poor conductors of heat and electricity. That is why electrical wires have plastic covering, and handles of screw drivers are made of plastic. Handles of frying pans are also made of plastic.

Plastics find extensive use in the health-care industry. Some examples of their use are the packaging of tablets, threads used for stitching wounds, syringes, doctors’ gloves and a number of medical instruments. Special plastic cookware is used in microwave ovens for cooking food. In microwave ovens, the heat cooks the food but does not affect the plastic vessel. Teflon is a special plastic on which oil and water do not stick. It is used for nonstick coating on cookwares.

Fire-proof plastics: Although synthetic fibre catches fire easily, it is interesting to know that the uniforms of firemen have coating of melamine plastic to make them flame resistant.

Plastics and the Environment

Disposal of plastic is a major problem. Why? A material which gets decomposed through natural processes, such as action by bacteria, is called biodegradable. A material which is not easily decomposed by natural processes is termed as non-biodegradable.

Type of waste Approximate time Taken to degenerate Nature of material
Peels of vegetable and fruits, 1 to 2 weeks. Biodegradable
leftover foodstuff, etc.
Paper 10–30 days Biodegradable
Cotton  cloth 2 to 5 months Biodegradable
Wood 10 to15 years Biodegradable
Woollen clothes About a year Biodegradable
Tin, aluminium, and other metal cans 100 to 500 years Non-biodegradable
Plastic bags Several years Non-biodegradable


Since plastic takes several years to decompose, it is not environment friendly. It causes environmental pollution. Besides, the burning process in the synthetic material is quite slow and it does not get completely burnt easily. In the process it releases lots of poisonous fumes into the atmosphere causing air pollution.

It is better to recycle the plastic waste. Most of the thermoplastics can be recycled. However, during recycling certain colouring agents are added. This limits its usage especially for storage of food.

As a responsible citizen remember the 4 R principles. Reduce, Reuse, Recycle and Recover.


  • Synthetic fibres and plastics, like natural fibres, are made of very large units called polymers. Polymers are made up of many smaller units.
  • While natural fibres are obtained from plants and animals, synthetic fibres are obtained by chemical processing of petrochemicals. Like natural fibres, these fibres can also be woven into fabrics.
  • Synthetic fibres find uses ranging from many household articles like ropes, buckets, furniture, containers, etc. to highly specialized uses in aircrafts, ships, spacecrafts, healthcare, etc.
  • Depending upon the types of chemicals used for manufacturing synthetic fibres, they are named as Rayon, Nylon, Polyester and Acrylic.
  • The different types of fibres differ from one another in their strength, water absorbing capacity, nature of burning, cost, durability, etc.
  • Today, life without plastics cannot be imagined. Be it home, or outside, plastic is every where.
  • The waste created by plastics is not environment friendly. On burning plastics release poisonous gases. On dumping in the ground they may take years to degenerate. This is because of their non-biodegradable nature.
  • We need to use synthetic fibres and plastics in such a manner that we can enjoy their good qualities and at the same time minimise the environmental hazards for the living communities.
Historical Nylon Riots:

Nylon appears like silk. It is strong and flexible. These endearing qualities of nylon created a public sensation, or nylon mania, when it was introduced in 1939. Women’s stockings made from this new fibre were in great demand.7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar


  • Metals can be distinguished from non-metals on the basis of their physical and chemical properties.
  • The property of metals by which they can be beaten into thin sheets is called malleability.
  • This is a characteristic property of metals. As you must have noticed, materials like coal and pencil lead do not show this property
  • Iron rod, nail and copper wire are good conductors while rolled sulphur piece and coal piece are poor conductors.
  • The property of metal by which it can be drawn into wires is called ductility
  • The things made of metals produce ringing sound when struck hard. Suppose you have two boxes similar in appearance, one made of wood and the other of metal. Can you tell which box is made of metal by striking both the boxes? Since metals produce ringing sounds, they are said to be The materials other than metals are not sonorous.
  • Some materials are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity.

The materials which generally posses these properties are called metals. The examples of metals are iron, copper, aluminum, calcium, magnesium, etc. In contrast, materials like coal and sulphur are soft and dull in appearance. They break down into powdery mass on tapping with hammer. They are not sonorous and are poor conductors of heat and electricity. These materials are called non-metals. The examples of non-metals are sulphur, carbon, oxygen, phosphorus, etc.

Metals like sodium and potassium are soft and can be cut with a knife. Mercury is the only metal which is found in liquid state at room temperature. These are exceptions.

Chemical Properties of Metals and Non-metals
  1. Reaction with Oxygen

You are familiar with the phenomenon of rusting of iron. Recall the reaction by which rust is formed. Burning a magnesium ribbon in air. In both the processes oxide formation takes place.

Does copper also get rusted?

When a copper vessel is exposed to moist air for long, it acquires a dull green coating. The green material is a mixture of copper hydroxide (Cu(OH) 2 ) and copper carbonate (CuCO 3 ). The following is the reaction 2Cu+H 2O+CO2+O 2→Cu (OH)2+ CuCO 3 moist air

Now recall the activity of burning magnesium ribbon. The ash obtained on burning magnesium ribbon is dissolved in water and tested for its acidic / basic nature. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

In general, metallic oxides are basic in nature

Let us now observe the reaction of non-metals with oxygen.

The name of the product formed in the reaction of sulphur and oxygen is sulphur dioxide gas. When sulphur dioxide is dissolved in water sulphurous acid is formed. The reaction can be given as follows: Sulphur dioxide (SO 2) + Water (H 2 O) → Sulphurous acid (H 2SO 3 )

The sulphurous acid turns blue litmus paper red. Generally, oxides of non-metals are acidic in nature.

  1. Reaction with Water

Let us see how metals and non-metals react with water.

Sodium metal is very reactive. It reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. It is, therefore, stored in kerosene.

You observed that sodium reacts vigorously with water. Some other metals do not do so. For example, iron reacts with water slowly.

Generally, non-metals do not react with water though they may be very reactive in air. Such non-metals are stored in water. For example, phosphorus is a very reactive non-metal. It catches fire if exposed to air. To prevent the contact of phosphorus with atmospheric oxygen, it is stored in water.

  1. Reactions with Acids

Let us see how metals and non-metals behave with acids.

You must have noticed that copper does not react with dilute hydrochloric acid even on heating but it reacts with sulphuric acid.

You must have found that nonmetals generally do not react with acids but metals react with acids and produce hydrogen gas that burns with a ‘pop’ sound.

  1. Reactions with Bases

Metals react with sodium hydroxide to produce hydrogen gas. Reactions of non-metals with bases are complex.

  1. Displacement Reactions

A more reactive metal can replace a less reactive metal, but a less reactive one cannot replace a more reactive metal.

Uses of Metals and Nonmetals

Metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils, water boilers, etc.

Non-metal essential for our life which all living beings inhale during breathing, Non-metals used in fertilisers to enhance the growth of plants, Non-metal used in water purification process, Non-metal used in the purple coloured solution which is applied on wounds as an antiseptic, Non-metals used in crackers.

In a chemical reaction, new substances are formed. These substances are different from those which underwent the reaction. Now, if a substance cannot be broken down further by chemical reactions, by cooling, heating, or by electrolysis, it is called ‘element’. Sulphur is an element. So is iron. Carbon, too, is an element. The smallest unit of an element is atom. A sample of an element contains only one kind of atoms. The atom of an element remains unaffected by physical changes in the element. For example, an atom of liquid sulphur would be exactly the same as the atom of solid or vapour sulphur. Although we have an infinite variety of substances in the universe, the number of elements forming these substances is limited. There are no more than 92 naturally occurring elements. An important classification of elements is in terms of metals and non-metals. Most of the elements are metals. Less than 20 are non-metals. A few are metalloids which possess characters of both metals and non-metals.




  • Metals are lustrous whereas non-metals have no lustre.
  • Generally, metals are malleable and ductile. Non-metals do not have these properties.
  • Generally, metals are good conductors of heat and electricity but non-metals are poor conductors.
  • On burning, metals react with oxygen to produce metal oxides which are basic in nature. Non-metals react with oxygen to produce non- metallic oxides which are acidic in nature.
  • Some metals react with water to produce metal hydroxides and hydrogen gas. Generally, nonmetals do not react with water.
  • Metals react with acids and produce metal salts and hydrogen gas. Generally, non-metals do not react with acids.
  • Some metals react with bases to produce hydrogen gas.
  • More reactive metals displace less reactive metals from their compounds in aqueous solutions.
  • Metals and non-metals are used widely in everyday life


  • Natural resources can be broadly classified into two kinds
  • Inexhaustible Natural Resources– These resources are present in unlimited quantity in nature and are not likely to be exhausted by human activities. Examples are: sunlight, air.
  • Exhaustible Natural Resources The amount of these resources in nature is limited. They can be exhausted by human activities. Examples of these resources are forests, wildlife, minerals, coal, petroleum, natural gas etc.
  • In this chapter we will learn about some exhaustible natural resources like coal, petroleum and natural gas. These were formed from the dead remains of living organisms (fossils). So, these are all known as fossil fuels.


  • It is as hard as stone and is black in colour.
  • Coal is one of the fuels used to cook food. Earlier, it was used in railway engines to produce steam to run the engine. It is also used in thermal power plants to produce electricity. Coal is also used as a fuel in various industries. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

Story of Coal

About 300 million years ago the earth had dense forests in low lying wetland areas. Due to natural processes, like flooding, these forests got buried under the soil. As more soil deposited over them, they were compressed. The temperature also rose as they sank deeper and deeper. Under high pressure and high temperature, dead plants got slowly converted to coal. As coal contains mainly carbon, the slow process of conversion of dead vegetation into coal is called carbonisation. Since it was formed from the remains of vegetation, coal is also called a fossil fuel.

When heated in air, coal burns and produces mainly carbon dioxide gas. Coal is processed in industry to get some useful products such as coke, coal tar and coal gas.

  1. Coke

It is a tough, porous and black substance. It is almost pure form of carbon. Coke is used in the manufacture of steel and in the extraction of many metals.

  1. Coal tar

It is a black, thick liquid unpleasant smell. It is a mixture of about 200 substances. Products obtained from coal tar are used as starting materials for manufacturing various substances used in everyday life and in industry, like synthetic dyes, drugs, explosives, perfumes, plastics, paints, photographic materials, roofing materials, etc. Interestingly, naphthalene balls used to repel moths and other insects are also obtained from coal tar.

These days, bitumen, a petroleum product, is used in place of coal-tar for metalling the roads.

  1. Coal gas

Coal gas is obtained during the processing of coal to get coke. It is used as a fuel in many industries situated near the coal processing plants.

Coal gas was used for street lighting for the first time in London in 1810 and in New York around 1820. Now days, it is used as a source of heat rather than light.


You know that petrol is used as a fuel in light automobiles such as motor cycles/ scooters and cars. Heavy motor vehicles like trucks and tractors run on diesel. Petrol and diesel are obtained from a natural resource called petroleum

Petroleum was formed from organisms living in the sea. As these organisms died, their bodies settled at the bottom of the sea and got covered with layers of sand and clay. Over millions of years, absence of air, high temperature and high pressure transformed the dead organisms into petroleum and natural gas.

You see that the layer containing petroleum oil and gas is above that of water. Why is it so? Recall that oil and gas are lighter than water and do not mix with it.

The world’s first oil well was drilled in Pennsylvania, USA, in 1859. Eight years later, in 1867, oil was stuck at Makum in Assam. In India, oil is found in Assam, Gujarat, Mumbai High and in the river basins of Godavari and Krishna.

Refining of Petroleum

Petroleum is a dark oily liquid. It has an unpleasant odour. It is a mixture of various constituents such as petroleum gas, petrol, diesel, lubricating oil, paraffin wax, etc. The process of separating the various constituents/fractions of petroleum is known as refining. It is carried out in a petroleum refinery.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar

Many useful substances are obtained from petroleum and natural gas. These are termed as ‘Petrochemicals’. These are used in the manufacture of detergents, fibres (polyester, nylon, acrylic etc.), polythene and other man-made plastics. Hydrogen gas obtained from natural gas, is used in the production of fertilisers (urea). Due to its great commercial importance, petroleum is also called ‘black gold’.

Various constituents of petroleum and their use

Natural Gas

Natural gas is a very important fossil fuel because it is easy to transport through pipes. Natural gas is stored under high pressure as compressed natural gas (CNG). CNG is used for power generation. It is now being used as a fuel for transport vehicles because it is less polluting. It is a cleaner fuel. The great advantage of CNG is that it can be used directly for burning in homes and factories where it can be supplied through pipes. Such a network of pipelines exists in Vadodara (Gujarat), some parts of Delhi and other places

Natural gas is also used as a starting material for the manufacture of a number of chemicals and fertilisers. India has vast reserves of natural gas. In our country, natural gas has been found in Tripura, Rajasthan, Maharashtra and in the Krishna Godavari delta.

Some Natural Resources are Limited

You know that coal and petroleum are fossil fuels. It required the dead organisms millions of years to get converted into these fuels. On the other hand, the known reserves of these will last atmost a few hundred years. Moreover, burning of these fuels is a major cause of air pollution. Their use is also linked to global warming. It is therefore necessary that we use these fuels only when absolutely necessary. This will result in better environment, smaller risk of global warming and their availability for a longer period of time. In India, the Petroleum Conservation Research Association (PCRA) advises people how to save petrol/diesel while driving. Their tips are:  Drive at a constant and moderate speed as far as possible,  Switch off the engine at traffic lights or at a place where you have to wait,  Ensure correct tyre pressure, and  Ensure regular maintenance of the vehicle




  • Coal, petroleum and natural gas are fossil fuels.
  • Fossil fuels were formed from the dead remains of living organisms millions of years ago.
  • Fossil fuels are exhaustible resources.
  • Coke, coal tar and coal gas are the products of coal.
  •  Petroleum gas, petrol, diesel, kerosene, paraffin wax, lubricating oil are obtained by refining petroleum.
  • Coal and petroleum resources are limited. We should use them judiciously


You are familiar with the burning of a candle. What is the difference between the burning of a candle and the burning of a fuel like coal? May be you were able to guess right: candle burns with a flame whereas coal does not.

Let us study the chemical process of burning and the types of flame produced during this process.

What is Combustion?

We learnt that magnesium burns to form magnesium oxide and produces heat and light

Charcoal burns in air. We know that coal, too, burns in air producing carbon dioxide, heat and light

A chemical process in which a substance reacts with oxygen to give off heat is called combustion.

Chemistry notes for SSC CGL exam: Pinnacle Coaching Centre
The substance that undergoes combustion is said to be combustible. It is also called a fuel. The fuel may be solid, liquid or gas. Sometimes, light is also given off during combustion, either as a flame or as a glow.

In our body food is broken down by reaction with oxygen and heat is produced.

We find that for combustion, air is necessary

The lowest temperature at which a substance catches fire is called its ignition temperature.

The history of the matchstick is very old. More than five thousand years ago small pieces of pinewood dipped in sulphur were used as matches in ancient Egypt. The modern safety match was developed only about two hundred years ago

A mixture of antimony trisulphide, potassium chlorate and white phosphorus with some glue and starch was applied on the head of a match made of suitable wood. When struck against a rough surface, white phosphorus got ignited due to the heat of friction. This started the combustion of the match. However, white phosphorus proved to be dangerous both for the workers involved in the manufacturing of matches and for the users. These days the head of the safety match contains only antimony trisulphide and potassium chlorate. The rubbing surface has powdered glass and a little red phosphorus (which is much less dangerous). When the match is struck against the rubbing surface, some red phosphorus gets converted into white phosphorus. This immediately reacts with potassium chlorate in the matchstick head to produce enough heat to ignite antimony trisulphide and start the combustion

We find that a combustible substance cannot catch fire or burn as long as its temperature is lower than its ignition temperature.

The substances which have very low ignition temperature and can easily catch fire with a flame are called inflammable substances.

Examples of inflammable substances are petrol, alcohol, Liquified Petroleum Gas (LPG), etc. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

There are three essential requirements for producing fire.

These are: fuel, air (to supply oxygen) and heat (to raise the temperature of the fuel beyond the ignition temperature)

Fire can be controlled by removing one or more of these requirements. The job of a fire extinguisher is to cut off the supply of air, or to bring down the temperature of the fuel, or both

The most common fire extinguisher is water. But water works only when things like wood and paper are on fire. If electrical equipment is on fire, water may conduct electricity and harm those trying to douse the fire. Water is also not suitable for fires involving oil and petrol. Do you recall that water is heavier than oil? So, it sinks below the oil, and oil keeps burning on top.

For fires involving electrical equipment and inflammable materials like petrol, carbon dioxide (CO 2) is the best extinguisher. CO2, being heavier than oxygen, covers the fire like a blanket. Since the contact between the fuel and oxygen is cut off, the fire is controlled. The added advantage of CO 2 is that in most cases it does not harm the electrical equipment.

How do we get the supply of carbon dioxide? It can be stored at high pressure as a liquid in cylinders. In what form is the LPG stored in cylinders? When released from the cylinder, CO 2 expands enormously in volume and cools down. So, it not only forms a blanket around the fire, it also brings down the temperature of the fuel. That is why it is an excellent fire extinguisher. Another way to get CO2 is to release a lot of dry powder of chemicals like sodium bicarbonate (baking soda) or potassium bicarbonate. Near the fire, these chemicals give off CO2 .

Types of Combustion

Bring a burning matchstick or a gas lighter near a gas stove in the kitchen. Turn on the knob of the gas stove.

We find that the gas burns rapidly and produces heat and light. Such combustion is known as rapid combustion

There are substances like phosphorus which burn in air at room temperature. The type of combustion in which a material suddenly bursts into flames, without the application of any apparent cause is called spontaneous combustion.

Spontaneous combustion of coal dust has resulted in many disastrous fires in coal mines. Spontaneous forest fires are sometimes due to the heat of the sun or due to lightning strike. However, most forest fires are due to the carelessness of human beings. When a cracker is ignited, a sudden reaction takes place with the evolution of heat, light and sound. A large amount of gas formed in the reaction is liberated. Such a reaction is called explosion. Explosion can also take place if pressure is applied on the cracker.


The substances which vapourise during burning, give flames. For example, kerosene oil and molten wax rise through the wick and are vapourised during burning and form flames. Charcoal, on the other hand, does not vapourise and so does not produce a flame.

Non-luminous zone of the flame has a high temperature? In fact, this part of the flame is the hottest part .

Goldsmiths blow the outermost zone of a flame with a metallic blow-pipe for melting gold and silver . Why do they use the outermost zone of the flame?

What is a Fuel

The sources of heat energy for domestic and industrial purposes are mainly wood, charcoal, petrol, kerosene, etc. These substances are called fuels. A good fuel is one which is readily available. It is cheap. It burns easily in air at a moderate rate. It produces a large amount of heat. It does not leave behind any undesirable substances.

There is probably no fuel that could be considered as an ideal fuel.

Fuel Efficiency

The amount of heat energy produced on complete combustion of 1 kg of a fuel is called its calorific value. The calorific value of a fuel is expressed in a unit called kilojoule per kg(kJ/kg)

Burning of Fuels Leads to Harmful Products

  1. Carbon fuels like wood, coal, petroleum release unburnt carbon particles. These fine particles are dangerous pollutants causing respiratory diseases, such as asthma
  2. 2. Incomplete combustion of these fuels gives carbon monoxide gas. It is a very poisonous gas. It is dangerous to burn coal in a closed room. The carbon monoxide gas produced can kill persons sleeping in that room
  3. Combustion of most fuels releases carbon dioxide in the environment. Increased concentration of carbon dioxide in the air is believed to cause global warming.

Global warming is the rise in temperature of the atmosphere of the earth. This results, among other things, in the melting of polar glaciers, which leads to a rise in the sea level, causing floods in the coastal areas. Low lying coastal areas may even be permanently submerged under water

  1. Burning of coal and diesel releases sulphur dioxide gas. It is an extremely suffocating and corrosive gas. Moreover, petrol engines give off gaseous oxides of nitrogen. Oxides of sulphur and nitrogen dissolve in rain water and form acids. Such rain is called acid rain. It is very harmful for crops, buildings and soil.

The use of diesel and petrol as fuels in automobiles is being replaced by CNG (Compressed Natural Gas), because CNG produces the harmful products in very small amounts.

CNG is a cleaner fuel.




  • The substances which burn in air are called combustible.
  • Oxygen (in air) is essential for combustion.
  • During the process of combustion, heat and light are given out.
  • Ignition temperature is the lowest temperature at which a combustible substance catches fire.
  • Inflammable substances have very low ignition temperature.
  • Fire can be controlled by removing one or more requirements essential for producing fire.
  • Water is commonly used to control fires.
  • Water cannot be used to control fires involving electrical equipments or oils.
  • There are various types of combustions such as rapid combustion, spontaneous combustion, explosion, etc.
  • There are three different zones of a flame -dark zone, luminous zone and non-luminous zone.
  • An ideal fuel is cheap, readily available, readily combustible and easy to transport. It has high calorific value. It does not produce gases or residues that pollute the environment.
  • Fuels differ in their efficiency and cost.
  • Fuel efficiency is expressed in terms of its calorific value which is expressed in units of kilojoule per kg.
  • Unburnt carbon particles in air are dangerous pollutants causing respiratory problems.
  •  Incomplete combustion of a fuel gives poisonous carbon monoxide gas.
  • Increased percentage of carbon dioxide in air has been linked to global warming.
  • Oxides of sulphur and nitrogen produced by the burning of coal, diesel and petrol cause acid rain which is harmful for crops, buildings and soil.


  • Everything in this universe is made up of material which scientists have named “matter”
  • All the things occupy space, that is, volume*and have mass.

Physical Nature of Matter


The particles of matter are very small – they are small beyond our imagination!!!!

Characteristics of Particles of Matter


Particles of matter are continuously moving, that is, they possess what we call the kinetic energy.

As the temperature rises, particles move faster. So, we can say that with increase in temperature the kinetic energy of the particles also increases.

Particles of matter intermix on their own with each other. They do so by getting into the spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion. We also observe that on heating, diffusion becomes faster.


Particles of matter have force acting between them. This force keeps the particles together. The strength of this force of attraction varies from one kind of matter to another.

States of Matter

Matter around us exists in three different states– solid, liquid and gas.

These states of matter arise due to the variation in the characteristics of the particles of matter.


All these have a definite shape, distinct boundaries and fixed volumes, that is, have negligible compressibility. Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.


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Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid. The gases from the atmosphere diffuse and dissolve in water. These gases, especially oxygen and carbon dioxide, are essential for the survival of aquatic animals and plants. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

All living creatures need to breathe for survival. The aquatic animals can breathe under water due to the presence of dissolved oxygen in water. Thus, we may conclude that solids, liquids and gases can diffuse into liquids.

The rate of diffusion of liquids is higher than that of solids

This is due to the fact that in the liquid state, particles move freely and have greater space between each other as compared to particles in the solid state


We have observed that gases are highly compressible as compared to solids and liquids.

The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed natural gas (CNG) is used as fuel these days in vehicles. Due to its high compressibility, large volumes of a gas can be compressed into a small cylinder and transported easily.

The smell of hot cooked food reaches us in seconds; compare this with the rate of diffusion of solids and liquids. Due to high speed of particles and large space between them, gases show the property of diffusing very fast into other gases.

In the gaseous state, the particles move about randomly at high speed. Due to this random movement, the particles hit each other and also the walls of the container. The pressure exerted by the gas is because of this force exerted by gas particles per unit area on the walls of the container.

The mass per unit volume of a substance is called density. (Density = mass/volume). Arrange the following in order of increasing density – air, exhaust from chimneys, honey, water, chalk, cotton and iron

Can Matter Change its State?

Water can exist in three states of matter– • solid, as ice, • liquid, as the familiar water, and • gas, as water vapour. What happens inside the matter during this change of state? How does this change of state take place?


On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particles start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point

The melting point of a solid is an indication of the strength of the force of attraction between its particles

The melting point of ice is 273.16 K*. The process of melting, that is, change of solid state into liquid state is also known as fusion

When a solid melts, its temperature remains the same, so where does the heat energy go?

You must have observed, during the experiment of melting, that the temperature of the system does not change after the melting point is reached, till all the ice melts. This happens even though we continue to heat the beaker, that is, we continue to supply heat. This heat gets used up in changing the state by overcoming the forces of attraction between the particles. As this heat energy is absorbed by ice without showing any rise in temperature, it is considered that it gets hidden into the contents of the beaker and is known as the latent heat. The word latent means hidden. The amount of heat energy that is required to change 1 kg of a solid into liquid at atmospheric pressure at its melting point is known as the latent heat of fusion. So, particles in water at 0 0  C (273 K) have more energy as compared to particles in ice at the same temperature.

When we supply heat energy to water, particles start moving even faster. At a certain temperature, a point is reached when the particles have enough energy to break free from the forces of attraction of each other. At this temperature the liquid starts changing into gas. The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point. Boiling is a bulk phenomenon. Particles from the bulk of the liquid gain enough energy to change into the vapour state.

For water this temperature is 373 K (100  0 C = 273 + 100 = 373 K).

Can you define the latent heat of vaporisation? Do it in the same way as we have defined the latent heat of fusion. Particles in steam, that is, water vapour at 373 K (100 0  C) have more energy than water at the same temperature. This is because particles in steam have absorbed extra energy in the form of latent heat of vaporisation.

So, we infer that the state of matter can be changed into another state by changing the temperature.

A change of state directly from solid to gas without changing into liquid state (or vice versa) is called sublimation.


We have already learnt that the difference in various states of matter is due to the difference in the distances between the constituent particles. What will happen when we start putting pressure and compress a gas enclosed in a cylinder?

Have you heard of solid carbon dioxide (CO2 )?It is stored under high pressure. Solid CO2 gets converted directly to gaseous state on decrease of pressure to 1 atmosphere* without coming into liquid state. This is the reason that solid carbon dioxide is also known as dry ice.

Thus, we can say that pressure and temperature determine the state of a substance, whether it will be solid, liquid or gas.


We know that particles of matter are always moving and are never at rest.

At a given temperature in any gas, liquid or solid, there are particles with different amounts of kinetic energy. In the case of liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.


You must have observed that the rate of evaporation increases with–

An increase of surface area:

We know that evaporation is a surface phenomenon. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.

An increase of temperature: With the increase of temperature, more number of particles get enough kinetic energy to go into the vapour state.

A decrease in humidity: Humidity is the amount of water vapour present in air. The air around us cannot hold more than a definite amount of water vapour at a given temperature. If the amount of water in air is already high, the rate of evaporation decreases.

An increase in wind speed: It is a common observation that clothes dry faster on a windy day. With the increase in wind speed, the particles of water vapour move away with the wind, decreasing the amount of water vapour in the surrounding.


In an open vessel, the liquid keeps on evaporating. The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.

What happens when you pour some acetone (nail polish remover) on your palm? The particles gain energy from your palm or surroundings and evaporate causing the palm to feel cool.

After a hot sunny day, people sprinkle water on the roof or open ground because the large latent heat of vaporisation of water helps to cool the hot surface.

Why should we wear cotton clothes in summer?

During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

Why do we see water droplets on the outer surface of a glass containing ice-cold water?

Let us take some ice-cold water in a tumbler. Soon we will see water droplets on the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.

Now scientists are talking of five states of matter: Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate.

Plasma: The state consists of super energetic and super excited particles. These particles are in the form of ionised gases. The fluorescent tube and neon sign bulbs consist of plasma. Inside a neon sign bulb there is neon gas and inside a fluorescent tube there is helium gas or some other gas. The gas gets ionised, that is, gets charged when electrical energy flows through it. This charging up creates a plasma glowing inside the tube or bulb. The plasma glows with a special colour depending on the nature of gas. The Sun and the stars glow because of the presence of plasma in them. The plasma is created in stars because of very high temperature.

Bose-Einstein Condensate: In 1920, Indian physicist Satyendra Nath Bose had done some calculations for a fifth state of matter. Building on his calculations, Albert Einstein predicted a new state of matter – the BoseEinstein Condensate (BEC). In 2001, Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman of USA received the Nobel prize in physics for achieving “Bose-Einstein condensation”. The BEC is formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to super low temperatures.

What you have learnt

  • Matter is made up of small particles.
  • The matter around us exists in three states— solid, liquid and gas.
  • The forces of attraction between the particles are maximum in solids, intermediate in liquids and minimum in gases.
  • The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.
  • The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.
  • The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
  • Sublimation is the change of gaseous state directly to solid state without going through liquid state, and vice versa.
  • Boiling is a bulk phenomenon. Particles from the bulk (whole) of the liquid change into vapour state.
  • Evaporation is a surface phenomenon. Particles from the surface gain enough energy to overcome the forces of attraction present in the liquid and change into the vapour state.
  • The rate of evaporation depends upon the surface area exposed to the atmosphere, the temperature, the humidity and the wind speed.
  • Evaporation causes cooling.
  • Latent heat of vaporisation is the heat energy required to change 1 kg of a liquid to gas at atmospheric pressure at its boiling point.
  • Latent heat of fusion is the amount of heat energy required to change 1 kg of solid into liquid at its melting point.


NCERT Class 9 Chapter 2: Is Matter around us pure


When a scientist says that something is pure, it means that all the constituent particles of that substance are the same in their chemical nature. A pure substance consists of a single type of particles

What is a Mixture?

Mixtures are constituted by more than one kind of pure form of matter, known as a substance. A substance cannot be separated into other kinds of matter by any physical process.

We know that dissolved sodium chloride can be separated from water by the physical process of evaporation.

  • A mixture contains more than one substance.



Mixture which has a uniform composition throughout. Such mixtures are called homogeneous mixtures or solutions.

Examples of such mixtures are: (i) salt in water and (ii) sugar in water.

A homogeneous mixture can have a variable composition.

Mixtures, which contain physically distinct parts and have non-uniform compositions. Such mixtures are called heterogeneous mixtures. Mixtures of sodium chloride and iron filings, salt and sulphur, and oil and water are examples of heterogeneous mixtures.

What is a Solution?

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A solution is a homogeneous mixture of two or more substances.

Lemonade, soda water etc. are all examples of solutions

We can also have solid solutions (alloys) and gaseous solutions (air).

In a solution there is homogeneity at the particle level. For example, lemonade tastes the same throughout. This shows that particles of sugar or salt are evenly distributed in the solution

Alloys: Alloys are homogeneous mixtures of metals and cannot be separated into their components by physical methods. But still, an alloy is considered as a mixture because it shows the properties of its constituents and can have variable composition. For example, brass is a mixture of approximately 30% zinc and 70% copper.

A solution has a solvent and a solute as its components. The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent. The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

Examples: (i) A solution of sugar in water is a solid in liquid solution. In this solution, sugar is the solute and water is the solvent. (ii) A solution of iodine in alcohol known as ‘tincture of iodine’, has iodine (solid) as the solute and alcohol (liquid) as the solvent. (iii) Aerated drinks like soda water etc., are gas in liquid solutions. These contain carbon dioxide (gas) as solute and water (liquid) as solvent. (iv) Air is a mixture of gas in gas. Air is a homogeneous mixture of a number of gases. Its two main constituents are: oxygen (21%) and nitrogen (78%). The other gases are present in very small quantities. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

Properties of a solution

  • A solution is a homogeneous mixture.
  • The particles of a solution are smaller than 1 nm (10 -9 meters) in diameter. So, they cannot be seen by naked eyes.
  • Because of very small particle size, they do not scatter a beam of light passing through the solution. So, the path of light is not visible in a solution.
  • The solute particles cannot be separated from the mixture by the process of filtration. The solute particles do not settle down when left undisturbed, that is, a solution is stable.


In a solution the relative proportion of the solute and solvent can be varied. Depending upon the amount of solute present in a solution, it can be called a dilute, concentrated or a saturated solution.

At any particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be a saturated solution.

In other words, when no more solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

The amount of the solute present in the saturated solution at this temperature is called its solubility.

If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.

The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution, or the amount of solute dissolved in a given mass or volume of solvent. Concentration of solution = Amount of solute/ Amount of solution

Or Amount of solute/Amount of solvent

There are various ways of expressing the concentration of a solution, but here we will learn only two methods. (i) Mass by mass percentage of a solution Mass of solute = ×100 Mass of solution (ii) Mass by volume percentage of a solution Mass of solute = ×100 Volume of solution

What is a suspension?

Non-homogeneous systems in which solids are dispersed in liquids, are called suspensions. A suspension is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Particles of a suspension are visible to the naked eye.

Properties of a Suspension

  • Suspension is a heterogeneous mixture. The particles of a suspension can be seen by the naked eye.
  • The particles of a suspension scatter a beam of light passing through it and make its path visible.
  • The solute particles settle down when a suspension is left undisturbed, that is, a suspension is unstable.
  • They can be separated from the mixture by the process of filtration.


The particles of a colloid are uniformly spread throughout the solution. Due to the relatively smaller size of particles, as compared to that of a suspension, the mixture appears to be homogeneous. But actually, a colloidal solution is a heterogeneous mixture, for example, milk.

Because of the small size of colloidal particles, we cannot see them with naked eyes. But, these particles can easily scatter a beam of visible light

This scattering of a beam of light is called the Tyndall effect after the name of the scientist who discovered this effect. Tyndall effect can also be observed when a fine beam of light enters a room through a small hole. This happens due to the scattering of light by the particles of dust and smoke in the air.

Properties of a colloid

  • A colloid is a heterogeneous mixture.
  • The size of particles of a colloid is too small to be individually seen by naked eyes.
  • Colloids are big enough to scatter a beam of light passing through it and make its path visible.
  • They do not settle down when left undisturbed, that is, a colloid is quite stable.
  • They cannot be separated from the mixture by the process of filtration. But, a special technique of separation known as centrifugation can be used to separate the colloidal particles

The components of a colloidal solution are the dispersed phase and the dispersion medium.

The solute-like component or the dispersed particles in a colloid form the dispersed phase, and the component in which the dispersed phase is suspended is known as the dispersing medium. Colloids are classified according to the state (solid, liquid or gas) of the dispersing medium and the dispersed phase.

Separating the Components of a Mixture

  • We have learnt that most of the natural substances are not chemically pure.
  • Different methods of separation are used to get individual components from a mixture.
  • Separation makes it possible to study and use the individual components of a mixture.
  • Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration that we use in our day-to-day life.
  • Sometimes special techniques have to be used for the separation of the components of a mixture.


We find that ink is a mixture of a dye in water. Thus, we can separate the volatile component (solvent) from its non-volatile solute by the method of evaporation


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Now-a-days, we get full-cream, toned and double-toned varieties of milk packed in polypacks or tetra packs in the market. These varieties of milk contain different amounts of fat.

Sometimes the solid particles in a liquid are very small and pass through a filter paper. For such particles the filtration technique cannot be used for separation.

Such mixtures are separated by centrifugation. The principle is that the denser particles are forced to the bottom and the lighter particles stay at the top when spun rapidly


  • Used in diagnostic laboratories for blood and urine tests.
  • Used in dairies and home to separate butter from cream.
  • Used in washing machines to squeeze out water from wet clothes.



  • To separate mixture of oil and water.
  • In the extraction of iron from its ore, the lighter slag is removed from the top by this method to leave the molten iron at the bottom in the furnace.

The principle is that immiscible liquids separate out in layers depending on their densities.


Ammonium chloride changes directly from solid to gaseous state on heating. So, to separate such mixtures that contain a sublimable volatile component from a non-sublimable impurity (salt in this case), the sublimation process is used.

Some examples of solids which sublime are ammonium chloride, camphor, naphthalene and anthracene.


The ink that we use has water as the solvent and the dye is soluble in it. As the water rises on the filter paper it takes along with it the dye particles. Usually, a dye is a mixture of two or more colours. The coloured component that is more soluble in water, rises faster and in this way the colours get separated. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

This process of separation of components of a mixture is known as chromatography. Kromain Greek means colour. This technique was first used for separation of colours, so this name was given. Chromatography is the technique used for separation of those solutes that dissolve in the same solvent. With the advancement in technology, newer techniques of chromatography have been developed.


To separate

  • colours in a dye
  • pigments from natural colours
  • drugs from blood.


This method is called distillation. It is used for the separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.

To separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K, fractional distillation process is used, for example, for the separation of different gases from air, different factions from petroleum products etc.

The apparatus is similar to that for simple distillation, except that a fractionating column is fitted in between the distillation flask and the condenser. A simple fractionating column is a tube packed with glass beads. The beads provide surface for the vapours to cool and condense repeatedly, as shown in Figure.


Flow diagram shows the process of obtaining gases from air. If we want oxygen gas from air (Figure), we have to separate out all the other gases present in the air. The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air. This liquid air is allowed to warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.


The crystallisation method is used to purify solids. For example, the salt we get from sea water can have many impurities in it. To remove these impurities, the process of crystallisation is used. Crystallisation is a process that separates a pure solid in the form of its crystals from a solution. Crystallisation technique is better than simple evaporation technique as –

  • Some solids decompose or some, like sugar, may get charred on heating to dryness.
  • Some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid.


  • Purification of salt that we get from sea water.
  • Separation of crystals of alum (phitkari) from impure samples.

Thus, by choosing one of the above methods according to the nature of the components of a mixture, we get a pure substance

What are the Types of Pure Substances?


Robert Boyle was the first scientist to use the term element in 1661. Antoine Laurent Lavoisier (1743-94), a French chemist, was the first to establish an experimentally useful definition of an element. He defined an element as a basic form of matter that cannot be broken down into simpler substances by chemical reactions. Elements can be normally divided into metals, non-metals and metalloids. We have already discussed in the previous chapters.

  • The number of elements known at present are more than 100.
  • Ninety-two elements are naturally occurring and the rest are manmade. Majority of the elements are solid.
  • Eleven elements are in gaseous state at room temperature.
  • Two elements are liquid at room temperature.
  • Two elements are liquid at room temperature–mercury and bromine.
  • Elements, gallium and cesium become liquid at a temperature slightly above room temperature (303 K)


A compound is a substance composed of two or more elements, chemically combined with one another in a fixed proportion

Mixtures and Compounds

What you have learnt

  • A mixture contains more than one substance (element and/or compound) mixed in any proportion.
  • Mixtures can be separated into pure substances using appropriate separation techniques.
  • A solution is a homogeneous mixture of two or more substances. The major component of a solution is called the solvent, and the minor, the solute.
  • The concentration of a solution is the amount of solute present per unit volume or per unit mass of the solution/solvent.
  • Materials that are insoluble in a solvent and have particles that are visible to naked eyes, form a suspension. A suspension is a heterogeneous mixture.
  • Colloids are heterogeneous mixtures in which the particle size is too small to be seen with the naked eye, but is big enough to scatter light. Colloids are useful in industry and daily life. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium.
  • Pure substances can be elements or compounds. An element is a form of matter that cannot be broken down by chemical reactions into simpler substances. A compound is a substance composed of two or more different types of elements, chemically combined in a fixed proportion.
  • Properties of a compound are different from its constituent elements, whereas a mixture shows the properties of its constituting elements or compounds.


Laws of Chemical Combination

experimentations by Lavoisier and Joseph L. Proust.


Law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction


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Many compounds were composed of two or more elements and each such compound had the same elements in the same proportions, irrespective of where the compound came from or who prepared it

“In a chemical substance the elements are always present in definite proportions by mass”.

According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms.

The postulates of this theory may be stated as follows:

(i) All matter is made of very tiny particles called atoms.

(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction

iii) Atoms of a given element are identical in mass and chemical properties

(iv) Atoms of different elements have different masses and chemical properties.

(v) Atoms combine in the ratio of small whole numbers to form compounds.

(vi) The relative number and kinds of atoms are constant in a given compound.

What you have learnt

During a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is known as the Law of Conservation of Mass. In a pure chemical compound, elements are always present in a definite proportion by mass. This is known as the Law of Definite Proportions.

  • An atom is the smallest particle of the element that can exist independently and retain all its chemical properties.
  • A molecule is the smallest particle of an element or a compound capable of independent existence under ordinary conditions. It shows all the properties of the substance.
  • A chemical formula of a compound shows its constituent elements and the number of atoms of each combining element.
  • Clusters of atoms that act as an ion are called polyatomic ions. They carry a fixed charge on them. The chemical formula of a molecular compound is determined by the valency of each element.
  • In ionic compounds, the charge on each ion is used to determine the chemical formula of the compound.
  • Scientists use the relative atomic mass scale to compare the masses of different atoms of elements. Atoms of carbon-12 isotopes are assigned a relative atomic mass of 12 and the relative masses of all other atoms are obtained by comparison with the mass of a carbon-12 atom.
  • The Avogadro constant 6.022 ×10 23 is defined as the number of atoms in exactly 12 g of carbon-12.
  • The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.
  • Mass of 1 mole of a substance is called its molar mass.


NCERT Class 9, Chapter 4 Structure of the atom


In nature, a number of atoms of some elements have been identified, which have the same atomic number but different mass numbers. For example, take the case of hydrogen atom, it has three atomic species, namely protium (  H), deuterium ( 2 1 H or D) and tritium ( 3 1 H or T).

Many elements consist of a mixture of isotopes. Each isotope of an element is a pure substance. The chemical properties of isotopes are similar but their physical properties are different

Applications Since the chemical properties of all the isotopes of an element are the same, normally we are not concerned about taking a mixture. But some isotopes have special properties which find them useful in various fields. Some of them are : (i) An isotope of uranium is used as a fuel in nuclear reactors. (ii) An isotope of cobalt is used in the treatment of cancer. (iii) An isotope of iodine is used in the treatment of goitre. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes


Let us consider two elements — calcium, atomic number 20, and argon, atomic number 18. The number of electrons in these atoms is different, but the mass number of both these elements is 40. That is, the total number of nucleons is the same in the atoms of this pair of elements. Atoms of different elements with different atomic numbers, which have the same mass number, are known as isobars.

What you have learnt

  • Credit for the discovery of electron and proton goes to J.J. Thomson and E.Goldstein, respectively.
  • J.J. Thomson proposed that electrons are embedded in a positive sphere.
  • Rutherford’s alpha-particle scattering experiment led to the discovery of the atomic nucleus.
  • Rutherford’s model of the atom proposed that a very tiny nucleus is present inside the atom and electrons revolve around this nucleus. The stability of the atom could not be explained by this model.
  • Neils Bohr’s model of the atom was more successful. He proposed that electrons are distributed in different shells with discrete energy around the nucleus. If the atomic shells are complete, then the atom will be stable and less reactive.
  • J. Chadwick discovered presence of neutrons in the nucleus of an atom. So, the three sub-atomic particles of an atom are: (i) electrons, (ii) protons and (iii) neutrons. Electrons are negatively charged, protons are positively charged and neutrons have no charges. The mass of an electron is about  1 2000 times the mass of an hydrogen atom. The mass of a proton and a neutron is taken as one unit each.
  • Shells of an atom are designated as K,L,M,N,….
  • Valency is the combining capacity of an atom.
  • The atomic number of an element is the same as the number of protons in the nucleus of its atom.
  • The mass number of an atom is equal to the number of nucleons in its nucleus.
  • Isotopes are atoms of the same element, which have different mass numbers.
  • Isobars are atoms having the same mass number but different atomic numbers.
  • Elements are defined by the number of protons they possess.


NCERT Class 10, Chapter1: Chemical Reactions and Equations

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Chemical Reactions and Equations

A solution of slaked lime produced by the reaction

is used for white washing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also CaCO2 .

Reactions in which heat is released along with the formation of products are called exothermic chemical reactions

Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses – one is in the manufacture of cement. When a decomposition reaction is carried out by heating, it is called thermal decomposition.

Decomposition reactions require energy either in the form of heat, light or electricity for breaking down the reactants. Reactions in which energy is absorbed are known as endothermic reactions.

Why does the iron nail become brownish in colour and the blue colour of copper sulphate solution fade? The following chemical reaction takes place in this Activity–

In this reaction, iron has displaced or removed another element, copper, from copper sulphate solution. This reaction is known as displacement reaction.

Oxidation and Reduction

The surface of copper powder becomes coated with black copper(II) oxide. Why has this black substance formed? This is because oxygen is added to copper and copper oxide is formed.

If hydrogen gas is passed over this heated material (CuO), the black coating on the surface turns brown as the reverse reaction takes place and copper is obtained.

If a substance gains oxygen during a reaction, it is said to be oxidised. If a substance loses oxygen during a reaction, it is said to be reduced. During this reaction,  the copper(II) oxide is losing oxygen and is being reduced. The hydrogen is gaining oxygen and is being oxidised. In other words, one reactant gets oxidized while the other gets reduced during a reaction. Such reactions are called oxidation-reduction reactions or redox reactions.



You must have observed that iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Some other metals also get tarnished in this manner. Have you noticed the colour of the coating formed on copper and silver? When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the green coating on copper are other examples of corrosion. Corrosion causes damage to car bodies, bridges, iron railings, ships and to all objects made of metals, specially those of iron. Corrosion of iron is a serious problem. Every year an enormous amount of money is spent to replace damaged iron.


When fats and oils are oxidised, they become rancid and their smell and taste change. Usually substances which prevent oxidation (antioxidants) are added to foods containing fats and oil. Keeping food in air tight containers helps to slow down oxidation. Do you know that chips manufacturers usually flush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised ?

What you have learnt

  • A complete chemical equation represents the reactants, products and their physical states symbolically.
  • A chemical equation is balanced so that the numbers of atoms of each type involved in a chemical reaction are the same on the reactant and product sides of the equation. Equations must always be balanced.
  • In a combination reaction two or more substances combine to form a new single substance.
  • Decomposition reactions are opposite to combination reactions. In a decomposition reaction, a single substance decomposes to give two or more substances.
  • Reactions in which heat is given out along with the products are called exothermic reactions.
  • Reactions in which energy is absorbed are known as endothermic reactions.
  • When an element displaces another element from its compound, a displacement reaction occurs.
  • Two different atoms or groups of atoms (ions) are exchanged in double displacement reactions.
  • Precipitation reactions produce insoluble salts.
  • Reactions also involve the gain or loss of oxygen or hydrogen by substances. Oxidation is the gain of oxygen or loss of hydrogen. Reduction is the loss of oxygen or gain of hydrogen.

NCERT Class10, Chapter2: Acids, Bases and Salts

Acids, Bases and Salts

  • You already know that acids are sour in taste and change the colour of blue litmus to red, whereas, bases are bitter and change the colour of the red litmus to blue.
  • Litmus is a natural indicator, turmeric is another such indicator.
  • Have you noticed that a stain of curry on a white cloth becomes reddish-brown when soap, which is basic in nature, is scrubbed on it? It turns yellow again when the cloth is washed with plenty of water.
  • You can also use synthetic indicators such as methyl orange and phenolphthalein to test for acids and bases.


How do Acids and Bases React with Metals?

The reaction that takes place can be written as follows.

How do Metal Carbonates and Metal Hydrogencarbonates React with Acids?

On passing the carbon dioxide gas evolved through lime water,

On passing excess carbon dioxide the following reaction takes place:

How do Acids and Bases React with each other?

Base + Acid →Salt + Water

Reaction of Metallic Oxides with Acids

Metal oxide + Acid →Salt + Water

Reaction of a Non-metallic Oxide with Base

Calcium hydroxide, which is a base, reacts with carbon dioxide to produce a salt and water. Since this is similar to the reaction between a base and an acid, we can conclude that nonmetallic oxides are acidic in nature.


All acids generate hydrogen gas on reacting with metals, so hydrogen seems to be common to all acids

What Happens to an Acid or a Base in a Water Solution?

We have seen that acids give H3O+ or H+ (aq) ion in water.

Let us see what happens when a base is dissolved in water.

Bases generate hydroxide (OH–) ions in water. Bases which are soluble in water are called alkalis. Water.

All bases do not dissolve in water. An alkali is a base that dissolves in water. They are soapy to touch, bitter and corrosive. Never taste or touch them as they may cause harm.

Now as we have identified that all acids generate H+ (aq) and all bases generate OH – (aq), we can view the neutralisation reaction as follows –

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The process of dissolving an acid or a base in water is a highly exothermic one. Care must be taken while mixing concentrated nitric acid or sulphuric acid with water. The acid must always be added slowly to water with constant stirring. If water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating. Mixing an acid or base with water results in decrease in the concentration of ions (H3O+/OH­­­-) per unit volume. Such a process is called dilution and the acid or the base is said to be diluted. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes


A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. The p in pH stands for ‘potenz’ in German, meaning power. On the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). pH should be thought of simply as a number which indicates the acidic or basic nature of a solution. Higher the hydronium ion concentration, lower is the pH value.

Importance of pH in Everyday Life

Are plants and animals pH sensitive?

Our body works within the pH range of 7.0 to 7.8. Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

Acids in other planets The atmosphere of venus is made up of thick white and yellowish clouds of sulphuric acid.

pH in our digestive system

It is very interesting to note that our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. To get rid of this pain, people use bases called antacids. These antacids neutralise the excess acid. Magnesium hydroxide (Milk of magnesia), a mild base, is often used for this purpose.

pH change as the cause of tooth decay

Tooth decay starts when the pH of the mouth is lower than 5.5. Tooth enamel, made up of calcium phosphate is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.

Self defence by animals and plants through chemical warfare.

Have you ever been stung by a honey-bee? Bee-sting leaves an acid which causes pain and irritation. Use of a mild base like baking soda on the stung area gives relief. Stinging hair of nettle leaves inject methanoic acid causing burning pain.

Nature provides neutralisation options Nettle is a herbaceous plant which grows in the wild. Its leaves have stinging hair, which cause painful stings when touched accidentally. This is due to the methanoic acid secreted by them. A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle in the wild. Can you guess the nature of the dock plant?


The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and many more.

Sodium hydroxide

When electricity is passed through an aqueous solution of sodium chloride (called brine), it decomposes to form sodium hydroxide. The process is called the chlor-alkali process because of the products formed– chlor for chlorine and alkali for sodium hydroxide.

Above Shown: Important products from the chlor-alkali process

Bleaching powder

Bleaching powder is used –

  • for bleaching cotton and linen in the textile industry, for bleaching wood pulp in paper factories and for bleaching washed clothes in laundry;
  • as an oxidising agent in many chemical industries; and
  • for disinfecting drinking water to make it free of germs.

Baking soda

The soda commonly used in the kitchen for making tasty crispy pakoras is baking soda. Sometimes it is added for faster cooking. The chemical name of the compound is sodium hydrogencarbonate (NaHCO3). It is produced using sodium chloride as one of the raw materials.

Can you correlate why it can be used to neutralise an acid? It is a mild non-corrosive base. The following reaction takes place when it is heated during cooking –

Sodium hydrogencarbonate has got various uses in the household

Uses of sodium hydrogencarbonate (NaHCO3)

  • For making baking powder, which is a mixture of baking soda (sodium hydrogencarbonate) and a mild edible acid such as tartaric acid. When baking powder is heated or mixed in water, the following reaction takes place –

Carbon dioxide produced during the reaction causes bread or cake to rise making them soft and spongy.

  • Sodium hydrogencarbonate is also an ingredient in antacids. Being alkaline, it neutralises excess acid in the stomach and provides relief.
  • It is also used in soda-acid fire extinguishers.

Washing soda 

Another chemical that can be obtained from sodium chloride is Na2CO3.10H2O (washing soda). You have seen above that sodium carbonate can be obtained by heating baking soda; recrystallisation of sodium carbonate gives washing soda. It is also a basic salt.

Uses of washing soda

  • Sodium carbonate (washing soda) is used in glass, soap and paper industries.
  • It is used in the manufacture of sodium compounds such as borax.
  • Sodium carbonate can be used as a cleaning agent for domestic purposes.
  • It is used for removing permanent hardness of water.

Are the Crystals of Salts really Dry?

Copper sulphate crystals which seem to be dry contain water of crystallisation. When we heat the crystals, this water is removed and the salt turns white. If you moisten the crystals again with water, you will find that blue colour of the crystals reappears

Plaster of Paris

On heating gypsum at 373 K, it loses water molecules and becomes calcium sulphate hemihydrate (CaSO4 .1/2 H2 O). This is called Plaster of Paris, the substance which doctors use as plaster for supporting fractured bones in the right position.

Plaster of Paris is a white powder and on mixing with water, it changes to gypsum once again giving a hard solid mass.

What you have learnt

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  • Acid-base indicators are dyes or mixtures of dyes which are used to indicate the presence of acids and bases.
  • Acidic nature of a substance is due to the formation of H+ (aq) ions in solution. Formation of OH – (aq) ions in solution is responsible for the basic nature of a substance.
  • When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.
  • When a base reacts with a metal, along with the evolution of hydrogen gas a salt is formed which has a negative ion composed of the metal and oxygen.
  • When an acid reacts with a metal carbonate or metal hydrogencarbonate, it gives the corresponding salt, carbon dioxide gas and water.
  • Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
  • The strength of an acid or an alkali can be tested by using a scale called the pH scale (0-14) which gives the measure of hydrogen ion concentration in a solution.
  • A neutral solution has a pH of exactly 7, while an acidic solution has a pH less than 7 and a basic solution a pH more than 7.
  • Living beings carry out their metabolic activities within an optimal pH range.
  • Mixing concentrated acids or bases with water is a highly exothermic process.
  • Acids and bases neutralise each other to form corresponding salts and water.
  • Water of crystallisation is the fixed number of water molecules chemically attached to each formula unit of a salt in its crystalline form.
  • Salts have various uses in everyday life and in industries.

NCERT Class 10, Chapter3: Metals and Non-metals

Metals and Non-metals



Metals, in their pure state, have a shining surface. This property is called metallic lustre.

You will find that metals are generally hard. The hardness varies from metal to metal.

You will find that some metals can be beaten into thin sheets. This property is called malleability. Did you know that gold and silver are the most malleable metals?

The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal.

It is because of their malleability and ductility that metals can be given different shapes according to our needs.

The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.

You must have seen that the wires that carry current in your homes have a coating of polyvinylchloride (PVC) or a rubber-like material.

What happens when metals strike a hard surface?

Do they produce a sound? The metals that produce a sound on striking a hard surface are said to be sonorous.


Some of the examples of non-metals are carbon, sulphur, iodine, oxygen, hydrogen, etc. The non-metals are either solids or gases except bromine which is a liquid.

(i) All metals except mercury exist as solids at room temperature.

metals have high melting points but gallium and caesium have very low melting points. These two metals will melt if you keep them on your palm.

Iodine is a non-metal but it is lustrous

Carbon is a non-metal that can exist in different forms. Each form is called an allotrope. Diamond, an allotrope of carbon, is the hardest natural substance known and has a very high melting and boiling point. Graphite, another allotrope of carbon, is a conductor of electricity.

Alkali metals (lithium, sodium, potassium) are so soft that they can be cut with a knife. They have low densities and low melting points.

Most non-metals produce acidic oxides when dissolve in water. On the other hand, most metals, give rise to basic oxides.


What happens when Metals are burnt in Air?

Almost all metals combine with oxygen to form metal oxides.

Some metal oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as well as basic behaviour. Such metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides.

Silver and gold do not react with oxygen even at high temperatures.

Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open. Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.

Anodising is a process of forming a thick oxide layer of aluminium. Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker. During anodising, a clean aluminium article is made the anode and is electrolysed with dilute sulphuric acid. The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer. This oxide layer can be dyed easily to give aluminium articles an attractive finish

What happens when Metals react with Water?

Metals react with water and produce a metal oxide and hydrogen gas.

What happens when Metals react with Acids?

You have already learnt that metals react with acids to give a salt and hydrogen gas.

Aqua regia,(Latin for ‘royal water’) is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1. It can dissolve gold, even though neither of these acids can do so alone. Aqua regiais a highly corrosive, fuming liquid. It is one of the few reagents that is able to dissolve gold and platinum.

How do Metals react with Solutions of other Metal Salts?

Reactive metals can displace less reactive metals from their compounds in solution or molten form.

The Reactivity Series


K Potassium Most reactive Na Sodium Ca Calcium Mg Magnesium Al Aluminium Zn Zinc Reactivity decreases Fe Iron Pb Lead H Hydrogen Cu Copper Hg Mercury Ag Silver Au Gold Least reactive


Sodium and chloride ions, being oppositely charged, attract each other and are held by strong electrostatic forces of attraction to exist as sodium chloride (NaCl). It should be noted that sodium chloride does not exist as molecules but aggregates of oppositely charged ions.

The compounds formed in this manner by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.

Properties of Ionic Compounds

  • Physical nature: Ionic compounds are solids and are somewhat hard because of the strong force of attraction between the positive and negative ions. These compounds are generally brittle and break into pieces when pressure is applied.
  • Melting and Boiling points: Ionic compounds have high melting and boiling points

This is because a considerable amount of energy is required to break the strong inter-ionic attraction.

  • Solubility:

Electrovalent compounds are generally soluble in water and insoluble in solvents such as kerosene, petrol, etc.

  • Conduction of Electricity:

The conduction of electricity through a solution involves the movement of charged particles. A solution of an ionic compound in water contains ions, which move to the opposite electrodes when electricity is passed through the solution. Ionic compounds in the solid state do not conduct electricity because movement of ions in the solid is not possible due to their rigid structure. But ionic compounds conduct electricity in the molten state. This is possible in the molten state since the elecrostatic forces of attraction between the oppositely charged ions are overcome due to the heat. Thus, the ions move freely and conduct electricity.


The elements or compounds, which occur naturally in the earth’s crust, are known as minerals. At some places, minerals contain a very high percentage of a particular metal and the metal can be profitably extracted from it. These minerals are called ores.

Extraction of Metals

Some metals are found in the earth’s crust in the free state. Some are found in the form of their compounds. The metals at the bottom of the activity series are the least reactive. They are often found in a free

For example, gold, silver, platinum and copper are found in the free state. Copper and silver are also found in the combined state as their sulphide or oxide ores. The metals at the top of the activity series (K, Na, Ca, Mg and Al) are so reactive that they are never found in nature as free elements. The metals in the middle of the activity series (Zn, Fe, Pb, etc.) are moderately reactive. They are found in the earth’s crust mainly as oxides, sulphides or carbonates.

You will find that the ores of many metals are oxides. This is because oxygen is a very reactive element and is very abundant on the earth

Several steps are involved in the extraction of pure metal from ores. A summary of these steps is given in Fig.3.10.

Each step is explained in detail in the following sections.

Enrichment of Ores

Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue. The impurities must be removed from the ore prior to the extraction of the metal. Processes used for removing the gangue from the ore are based on the differences between the physical or chemical properties of the gangue and the ore. Different separation techniques are accordingly employed.

Extracting Metals Low in the Activity Series

Metals low in the activity series are very unreactive. The oxides of these metals can be reduced to metals by heating alone. For example, cinnabar (HgS) is an ore of mercury. When it is heated in air, it is first converted into mercuric oxide (HgO). Mercuric oxide is then reduced to mercury on further heating

Extracting Metals in the Middle of the Activity Series

The metals in the middle of the activity series such as iron, zinc, lead, copper, etc., are moderately reactive. These are usually present as sulphides or carbonates in nature. It is easier to obtain a metal from its oxide, as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides. The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.

The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination. The chemical reaction that takes place during roasting and calcination of zinc ores can be shown as follows –

The metal oxides are then reduced to the corresponding metals by using suitable reducing agents such as carbon. For example, when zinc oxide is heated with carbon, it is reduced to metallic zinc. ZnO(s) + C(s) →Zn(s) + CO(g)

Obtaining metals from their compounds is also a reduction process

Besides using carbon (coke) to reduce metal oxides to metals, sometimes displacement reactions can also be used. The highly reactive metals such as sodium, calcium, aluminium, etc., are used as reducing agents because they can displace metals of lower reactivity from their compounds. For example, when manganese dioxide is heated with aluminium powder, the following reaction takes place –

These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state. In fact, the reaction of iron(III) oxide (Fe 2O3 ) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermit reaction.

Extracting Metals towards the Top of the Activity Series

The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon. For example, carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals. This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. For example, sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides.

Refining of Metals

The metals produced by various reduction processes described above are not very pure. They contain impurities, which must be removed to obtain pure metals. The most widely used method for refining impure metals is electrolytic refining.

Electrolytic Refining:

Many metals, such as copper, zinc, tin, nickel, silver, gold, etc., are refined electrolytically. In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode. A solution of the metal salt is used as an electrolyte. The apparatus is set up as shown in Figure. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud.


Silver articles become black after some time when exposed to air. This is because it reacts with sulphur in the air to form a coating of silver sulphide.

Copper reacts with moist carbon dioxide in the air and slowly loses its shiny brown surface and gains a green coat. This green substance is copper carbonate.

Iron when exposed to moist air for a long time acquires a coating of a brown flaky substance called rust.

Prevention of Corrosion

The rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome plating, anodising or making alloys.

Galvanisation is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanised article is protected against rusting even if the zinc coating is broken.

Alloying is a very good method of improving the properties of a metal. We can get the desired properties by this method. For example, iron is the most widely used metal. But it is never used in its pure state. This is because pure iron is very soft and stretches easily when hot. But, if it is mixed with a small amount of carbon (about 0.05 %), it becomes hard and strong. When iron is mixed with nickel and chromium, we get stainless steel, which is hard and does not rust. Thus, if iron is mixed with some other substance, its properties change. In fact, the properties of any metal can be changed if it is mixed with some other substance. The substance added may be a metal or a non-metal. An alloy is a homogeneous mixture of two or more metals, or a metal and a nonmetal. It is prepared by first melting the primary metal, and then, dissolving the other elements in it in definite proportions. It is then cooled to room temperature.

Pure gold, known as 24 carat gold, is very soft. It is, therefore, not suitable for making jewellery. It is alloyed with either silver or copper to make it hard. Generally, in India, 22 carat gold is used for making ornaments. It means that 22 parts of pure gold is alloyed with 2 parts of either copper or silver.

If one of the metals is mercury, then the alloy is known as an amalgam. The electrical conductivity and melting point of an alloy is less than that of pure metals. For example, brass, an alloy of copper and zinc (Cu and Zn), and bronze, an alloy of copper and tin (Cu and Sn), are not good conductors of electricity whereas copper is used for making electrical circuits. Solder, an alloy of lead and tin (Pb and Sn), has a low melting point and is used for welding electrical wires together.

What you have learnt

  • Elements can be classified as metals and non-metals.
  • Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.
  • Metals can form positive ions by losing electrons to non-metals.
  • Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known as amphoteric oxides.
  • ifferent metals have different reactivities with water and dilute acids.
  • A list of common metals arranged in order of their decreasing reactivity is known as an activity series.
  • Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.
  • A more reactive metal displaces a less reactive metal from its salt solution. „ Metals occur in nature as free elements or in the form of their compounds.
  • The extraction of metals from their ores and then refining them for use is known as metallurgy.
  • An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
  • The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.
  • Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.
  • Non-metals form negatively charged ions by gaining electrons when reacting with metals.
  • Non-metals form oxides which are either acidic or neutral.
  • Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.

NCET Class 10, Chapter 4: Carbon and its Compounds

All living structures are carbon based. The amount of carbon present in the earth’s crust and in the atmosphere is quite meager. The earth’s crust has only 0.02% carbon in the form of minerals (like carbonates, hydrogencarbonates, coal and petroleum) and the atmosphere has 0.03% of carbon dioxide. In spite of this small amount of carbon available in nature, the importance of carbon seems to be immense. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes


Most carbon compounds are poor conductors of electricity

Forces of attraction between these molecules are not very strong.

Since these compounds are largely nonconductors of electricity, we can conclude that the bonding in these compounds does not give rise to any ions.

The element carbon occurs in different forms in nature with widely varying physical properties. Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three-dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double-bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other.

These two different structures result in diamond and graphite having very different physical properties even though their chemical properties are the same. Diamond is the hardest substance known while graphite is smooth and slippery. Graphite is also a very good conductor of electricity unlike other non-metals.

Diamonds can be synthesised by subjecting pure carbon to very high pressure and temperature. These synthetic diamonds are small but are otherwise indistinguishable from natural diamonds.

Fullerenes form another class of carbon allotropes. The first one to be identified was C-60 which has carbon atoms arranged in the shape of a football. Since this looked like the geodesic dome designed by the US architect Buckminster Fuller, the molecule was named fullerene.

(i) Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation.

Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds. Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds.

Silicon forms compounds with hydrogen which have chains of upto seven or eight atoms, but these compounds are very reactive. The carbon-carbon bond is very strong and hence stable. This gives us the large number of compounds with many carbon atoms linked to each other.

(ii) Since carbon has a valency of four, it is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements giving rise to compounds with specific properties which depend on the elements other than carbon present in the molecule. Again the bonds that carbon forms with most other elements are very strong making these compounds exceptionally stable. One reason for the formation of strong bonds by carbon is its small size. This enables the nucleus to hold on to the shared pairs of electrons strongly. The bonds formed by elements having larger atoms are much weaker.

Organic compounds The two characteristic features seen in carbon, that is, tetravalency and catenation, put together give rise to a large number of compounds. Many have the same non-carbon atom or group of atoms attached to different carbon chains. These compounds were initially extracted from natural substances and it was thought that these carbon compounds or organic compounds could only be formed within a living system. That is, it was postulated that a ‘vital force’ was necessary for their synthesis. Friedrich Wöhler disproved this in 1828 by preparing urea from ammonium cyanate. But carbon compounds, except for oxides of carbon, carbonate and hydrogencarbonate salts continue to be studied under organic chemistry.

Saturated and Unsaturated Carbon Compounds

Such compounds of carbon having double or triple bonds between the carbon atoms are known as unsaturated carbon compounds and they are more reactive than the saturated carbon compounds.



Carbon, in all its allotropic forms, burns in oxygen to give carbon dioxide along with the release of heat and light. Most carbon compounds also release a large amount of heat and light on burning. These are the oxidation reactions.

Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke.

The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame. If you observe the bottoms of cooking vessels getting blackened, it means that the air holes are blocked and fuel is getting wasted. Fuels such as coal and petroleum have some amount of nitrogen and sulphur in them. Their combustion results in the formation of oxides of sulphur and nitrogen which are major pollutants in the environment.

Why do substances burn with or without a flame?

Have you ever observed either a coal or a wood fire? If not, the next time you get a chance, take close note of what happens when the wood or coal starts to burn. You have seen above that a candle or the LPG in the gas stove burns with a flame. However, you will observe the coal or charcoal in an ‘angithi’ sometimes just glows red and gives out heat without a flame. This is because a flame is only produced when gaseous substances burn. When wood or charcoal is ignited, the volatile substances present vapourise and burn with a flame in the beginning. A luminous flame is seen when the atoms of the gaseous substance are heated and start to glow. The colour produced by each element is a characteristic property of that element. Try and heat a copper wire in the flame of a gas stove and observe its colour. You have seen that incomplete combustion gives soot which is carbon. On this basis, what will you attribute the yellow colour of a candle flame to?

Formation of coal and petroleum have been formed from biomass which has been subjected to various biological and geological processes. Coal is the remains of trees, ferns, and other plants that lived millions of years ago. These were crushed into the earth, perhaps by earthquakes or volcanic eruptions. They were pressed down by layers of earth and rock. They slowly decayed into coal. Oil and gas are the remains of millions of tiny plants and animals that lived in the sea. When they died, their bodies sank to the sea bed and were covered by silt. Bacteria attacked the dead remains, turning them into oil and gas under the high pressures they were being subjected to. Meanwhile, the silt was slowly compressed into rock. The oil and gas seeped into the porous parts of the rock, and got trapped like water in a sponge. Can you guess why coal and petroleum are called fossil fuels?
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. Catalysts are substances that cause a reaction to occur or proceed at a different rate without the reaction itself being affected. This reaction is commonly used in the hydrogenation of vegetable oils using a nickel catalyst. Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains. You must have seen advertisements stating that some vegetable oils are ‘healthy’. Animal fats generally contain saturated fatty acids which are said to be harmful for health. Oils containing unsaturated fatty acids should be chosen for cooking.

Substitution Reaction

Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents.  However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen atoms one by one. It is called a substitution reaction because one type of atom or a group of atoms takes the place of another. A number of products are usually formed with the higher homologues of alkanes.

Properties of Ethanol

Ethanol is a liquid at room temperature. Ethanol is commonly called alcohol and is the active ingredient of all alcoholic drinks. In addition, because it is a good solvent, it is also used in medicines such as tincture iodine, cough syrups, and many tonics. Ethanol is also soluble in water in all proportions. Consumption of small quantities of dilute ethanol causes drunkenness. Even though this practice is condemned, it is a socially widespread practice. However, intake of even a small quantity of pure ethanol (called absolute alcohol) can be lethal. Also, long-term consumption of alcohol leads to many health problems. 7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar : Chemistry notes

How do alcohols affect living beings? When large quantities of ethanol are consumed, it tends to slow metabolic processes and to depress the central nervous system. This results in lack of coordination, mental confusion, drowsiness, lowering of the normal inhibitions, and finally stupour. The individual may feel relaxed but does not realise that his sense of judgement, sense of timing, and muscular coordination have been seriously impaired. Unlike ethanol, intake of methanol in very small quantities can cause death. Methanol is oxidised to methanal in the liver. Methanal reacts rapidly with the components of cells. It causes the protoplasm to get coagulated, in much the same way an egg is coagulated by cooking. Methanol also affects the optic nerve, causing blindness. Ethanol is an important industrial solvent. To prevent the misuse of ethanol produced for industrial use, it is made unfit for drinking by adding poisonous substances like methanol to it. Dyes are also added to colour the alcohol blue so that it can be identified easily. This is called denatured alcohol.

Alcohol as a fuel Sugarcane plants are one of the most efficient convertors of sunlight into chemical energy. Sugarcane juice can be used to prepare molasses which is fermented to give alcohol (ethanol). Some countries now use alcohol as an additive in petrol since it is a cleaner fuel which gives rise to only carbon dioxide and water on burning in sufficient air (oxygen).

Properties of Ethanoic Acid

Ethanoic acid is commonly called acetic acid and belongs to a group of acids called carboxylic acids. 5-8% solution of acetic acid in water is called vinegar and is used widely as a preservative in pickles. The melting point of pure ethanoic acid is 290 K and hence it often freezes during winter in cold climates. This gave rise to its name glacial acetic acid. The group of organic compounds called carboxylic acids are obviously characterised by a special acidity. However, unlike mineral acids like HCl, which are completely ionised, carboxylic acids are weak acids.

Reactions of ethanoic acid:

(i) Esterification reaction:Esters are most commonly formed by reaction of an acid and an alcohol. Ethanoic acid reacts with absolute ethanol in the presence of an acid catalyst to give an ester –

Esters are sweet-smelling substances. These are used in making perfumes and as flavouring agents. Esters react in the presence of an acid or a base to give back the alcohol and carboxylic acid. This reaction is known as saponification because it is used in the preparation of soap.


7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar

Most dirt is oily in nature and as you know, oil does not dissolve in water. The molecules of soap are sodium or potassium salts of long-chain carboxylic acids. The ionic-end of soap dissolves in water while the carbon chain dissolves in oil. The soap molecules, thus form structures called micelles (see Fig. 4.12) where one end of the molecules is towards the oil droplet while the ionic-end faces outside. This forms an emulsion in water. The soap micelle thus helps in dissolving the dirt in water and we can wash our clothes clean.

Micelles Soaps are molecules in which the two ends have differing properties, one is hydrophilic, that is, it dissolves in water, while the other end is hydrophobic, that is, it dissolves in hydrocarbons. When soap is at the surface of water, the  hydrophobic ‘tail’ of soap will not be soluble in water and the soap will align along the surface of water with the ionic end in water and the hydrocarbon ‘tail’ protruding out of water. Inside water, these molecules have a unique orientation that keeps the hydrocarbon portion out of the water. This is achieved by forming clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle. Soap in the form of a micelle is able to clean, since the oily dirt will be collected in the centre of the micelle. The micelles stay in solution as a colloid and will not come together to precipitate because of ion-ion repulsion. Thus, the dirt suspended in the micelles is also easily rinsed away. The soap micelles are large enough to scatter light. Hence a soap solution appears cloudy.

Have you ever observed while bathing that foam is formed with difficulty and an insoluble substance (scum) remains after washing with water? This is caused by the reaction of soap with the calcium and magnesium salts, which cause the hardness of water. Hence you need to use a larger amount of soap. This problem is overcome by using another class of compounds called detergents as cleansing agents. Detergents are generally ammonium or sulphonate salts of long chain carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Thus, they remain effective in hard water. Detergents are usually used to make shampoos and products for cleaning clothes.

What you have learnt

  • Carbon is a versatile element that forms the basis for all living organisms and many of the things we use.
  • This large variety of compounds is formed by carbon because of its tetravalency and the property of catenation that it exhibits.
  • Covalent bonds are formed by the sharing of electrons between two atoms so that both can achieve a completely filled outermost shell.
  • Carbon forms covalent bonds with itself and other elements such as hydrogen, oxygen, sulphur, nitrogen and chlorine.
  • Carbon also forms compounds containing double and triple bonds between carbon atoms. These carbon chains may be in the form of straight chains, branched chains or rings.
  • The ability of carbon to form chains gives rise to a homologous series of compounds in which the same functional group is attached to carbon chains of different lengths.
  • The functional groups such as alcohols, aldehydes, ketones and carboxylic acids bestow characteristic properties to the carbon compounds that contain them.
  • Carbon and its compounds are some of our major sources of fuels. „ Ethanol and ethanoic acid are carbon compounds of importance in our daily lives.
  • The action of soaps and detergents is based on the presence of both hydrophobic and hydrophilic groups in the molecule and this helps to emulsify the oily dirt and hence its removal.

NCERT Class 10 Chapter5:  Periodic Classification of Elements

At present, 114 elements are known to us. Around the year 1800, only 30 elements were known.

In the year 1817, Johann Wolfgang Döbereiner, a German chemist, tried to arrange the elements with similar properties into groups. He identified some groups having three elements each. So he called these groups ‘triads’. Döbereiner showed that when the three elements in a triad were written in the order of increasing atomic masses; the atomic mass of the middle element was roughly the average of the atomic masses of the other two elements.

Newlands’ Law of Octaves

In 1866, John Newlands, an English scientist, arranged the then known elements in the order of increasing atomic masses. He started with the element having the lowest atomic mass (hydrogen) and ended at thorium which was the 56th element. He found that every eighth element had properties similar to that of the first. He compared this to the octaves found in music. Therefore, he called it the ‘Law of Octaves’. It is known as ‘Newlands’ Law of Octaves’. The main credit for classifying elements goes to Dmitri Ivanovich Mendeléev, a Russian chemist. He was the most important contributor to the early development of a Periodic Table of elements wherein the elements were arranged on the basis of their fundamental property, the atomic mass, and also on the similarity of chemical properties.

When Mendeléev started his work, 63 elements were known. He examined the relationship between the atomic masses of the elements and their physical and chemical properties. Among chemical properties, Mendeléev concentrated on the compounds formed by elements with oxygen and hydrogen

In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass as described below. Accordingly, Mendeléev’s Periodic Law was modified and atomic number was adopted as the basis of Modern Periodic Table and the Modern Periodic Law can be stated as follows: ‘Properties of elements are a periodic function of their atomic number.’ Let us recall that the atomic number gives us the number of protons in the nucleus of an atom and this number increases by one in going from one element to the next. Elements, when arranged in order of increasing atomic number Z, lead us to the classification known as the Modern Periodic Table

Prediction of properties of elements could be made with more precision when elements were arranged on the basis of increasing atomic number.

The Modern Periodic Table has 18 vertical columns known as ‘groups’ and 7 horizontal rows known as ‘periods’.

You will find that these elements do not have the same number of valence electrons, but they contain the same number of shells. You also observe that the number of valence shell electrons increases by one unit, as the atomic number increases by one unit on moving from left to right in a period.

Trends in the Modern Periodic Table

Valency :As you know, the valency of an element is determined by the number of valence electrons present in the outermost shell of its atom.

Atomic size: The term atomic size refers to the radius of an atom. The atomic size may be visualised as the distance between the centre of the nucleus and the outermost shell of an isolated atom. The atomic radius of hydrogen atom is 37 pm (picometre, 1 pm = 10 –12 m)

atomic radius decreases in moving from left to right along a period. This is due to an increase in nuclear charge which tends to pull the electrons closer to the nucleus and reduces the size of the atom.

You will see that the atomic size increases down the group. This is because new shells are being added as we go down the group. This increases the distance between the outermost electrons and the nucleus so that the atomic size increases in spite of the increase in nuclear charge

Metallic and Non-metallic Properties

As we can see, the metals like Na and Mg are towards the left-hand side of the Periodic Table while the non-metals like sulphur and chlorine are found on the right-hand side. In the middle, we have silicon, which is classified as a semi-metal or metalloid because it exhibits some properties of both metals and non-metals.

In the Modern Periodic Table, a zig-zag line separates metals from non-metals. The borderline elements – boron, silicon, germanium, arsenic, antimony, tellurium and polonium – are intermediate in properties and are called metalloids or semi-metals.

7th -10 th Class NCERT + Other sources : By Pinnacle SSC CGL coaching Centre Hisar

As the effective nuclear charge acting on the valence shell electrons increases across a period, the tendency to lose electrons will decrease. Down the group, the effective nuclear charge experienced by valence electrons is decreasing because the outermost electrons are farther away from the nucleus. Therefore, these can be lost easily. Hence metallic character decreases across a period and increases down a group. Non-metals, on the other hand, are electronegative. They tend to form bonds by gaining electrons.

As the trends in the electronegativity show, non-metals are found on the right-hand side of the Periodic Table towards the top.

These trends also help us to predict the nature of oxides formed by the elements because it is known to you that the oxides of metals are basic and that of non-metals are acidic in general.

What you have learnt
  • Elements are classified on the basis of similarities in their properties.
  • Döbereiner grouped the elements into triads and Newlands gave the Law of Octaves.
  • Mendeléev arranged the elements in increasing order of their atomic masses and according to their chemical properties.
  • Mendeléev even predicted the existence of some yet to be discovered elements on the basis of gaps in his Periodic Table.
  • Anomalies in arrangement of elements based on increasing atomic mass could be removed when the elements were arranged in order of increasing atomic number, a fundamental property of the element discovered by Moseley.
  • Elements in the Modern Periodic Table are arranged in 18 vertical columns called groups and 7 horizontal rows called periods.
  • Elements thus arranged show periodicity of properties including atomic size, valency or combining capacity and metallic and non-metallic character.


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