Introduction

Everything around us is made up of matter. The air we breathe, the water we drink, the food we eat, our books, furniture, buildings and even our bodies are examples of matter.

Matter is an important topic in Science for students from Class 8 to Class 10. Understanding this chapter helps students learn about the composition, properties and behaviour of substances. It also forms the foundation for later topics such as atoms, molecules, chemical reactions, elements, compounds and mixtures.

What Is Matter?

Matter is anything that has mass and occupies space.

For example:

• A book has mass and occupies space.
• Water has mass and occupies space.
• Air has mass and occupies space.
• A stone, chair, pencil and school bag are all matter.

Light, heat and sound are not considered matter because they do not have mass and do not occupy space in the same way physical substances do.

Characteristics of Matter

Matter has the following important characteristics:

1. Matter Has Mass

Mass is the quantity of matter present in an object. It is commonly measured in grams or kilograms.

For example, a school bag may have a mass of 3 kg.

2. Matter Occupies Space

Every object occupies some space. The amount of space occupied by an object is called its volume.

The volume of liquids is commonly measured in litres or millilitres.

3. Matter Is Made Up of Particles

Matter is made up of extremely small particles. These particles may be atoms, molecules or ions.

For example, water consists of water molecules.

4. Particles of Matter Are Very Small

The particles of matter are too small to be seen with the naked eye. A small amount of a substance may contain millions of particles.

5. Particles of Matter Have Spaces Between Them

There are spaces between the particles of matter. These spaces are different in solids, liquids and gases.

For example, sugar dissolves in water because sugar particles occupy the spaces between water particles.

6. Particles of Matter Are in Continuous Motion

The particles of matter are always moving. The movement increases when the temperature rises.

7. Particles of Matter Attract One Another

Particles of matter exert attractive forces on one another. This force is strongest in solids and weakest in gases.

States of Matter

Matter mainly exists in three states:

1. Solid
2. Liquid
3. Gas

Modern science also recognises other states, such as plasma and Bose–Einstein condensate, but solids, liquids and gases are most important at the school level.

Comparison of the Three States of Matter

Solids

A solid has a fixed shape and fixed volume. Its particles are tightly packed and have strong forces of attraction.

Examples of Solids

• Stone
• Book
• Ice
• Wood
• Iron
• Pencil

Solids are generally rigid and cannot be compressed easily. The particles in a solid vibrate around their fixed positions.

Liquids

A liquid has a fixed volume but no fixed shape. It takes the shape of the container in which it is kept.

Examples of Liquids

• Water
• Milk
• Oil
• Juice
• Mercury

The particles in a liquid are less tightly packed than those in a solid. Liquids can flow because their particles can move past one another.

Gases

A gas has neither a fixed shape nor a fixed volume. It fills the entire container in which it is kept.

Examples of Gases

• Oxygen
• Nitrogen
• Carbon dioxide
• Water vapour
• Hydrogen

Gas particles are far apart and move rapidly in all directions. Gases can be compressed easily and exert pressure on the walls of their container.

Change of State of Matter

Matter can change from one state to another by changing temperature or pressure.

1. Melting or Fusion

The change of a solid into a liquid on heating is called melting or fusion.

Example: Ice changes into water at its melting point.

2. Freezing or Solidification

The change of a liquid into a solid on cooling is called freezing or solidification.

Example: Water changes into ice.

3. Vaporisation

The change of a liquid into a gas on heating is called vaporisation.

Example: Water changes into steam.

4. Condensation

The change of a gas into a liquid on cooling is called condensation.

Example: Water vapour changes into water droplets.

5. Sublimation

The direct change of a solid into a gas without changing into a liquid is called sublimation.

Examples:

• Camphor
• Naphthalene
• Ammonium chloride
• Dry ice

6. Deposition

The direct change of a gas into a solid is called deposition.

Example: Formation of frost from water vapour.

Melting Point and Boiling Point

Melting Point

The temperature at which a solid changes into a liquid at atmospheric pressure is called its melting point.

The melting point of ice is approximately $0^{\circ }C$.

Boiling Point

The temperature at which a liquid changes into a gas throughout the liquid is called its boiling point.

The boiling point of water at normal atmospheric pressure is approximately ${100}^{\circ }C$.

Evaporation

Evaporation is the slow conversion of a liquid into vapour from its surface at temperatures below its boiling point.

Factors Affecting Evaporation

• Increase in surface area increases evaporation.
• Increase in temperature increases evaporation.
• Increase in wind speed increases evaporation.
• Decrease in humidity increases evaporation.

Cooling Effect of Evaporation

Evaporation causes cooling because the faster and more energetic particles escape from the surface of the liquid.

Examples include:

• Sweating cools our body.
• Water kept in an earthen pot becomes cool.
• Acetone feels cool when applied to the skin.
• Wet clothes dry faster on a windy day.

Diffusion

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

Diffusion occurs in solids, liquids and gases, but it is fastest in gases because gas particles have large spaces between them and move rapidly.

Examples of Diffusion

• Smell of perfume spreading through a room.
• Smell of food reaching another room.
• Ink spreading in water.
• Oxygen and carbon dioxide moving in and out of body cells.

Classification of Matter

Matter can be classified into:

1. Pure substances
2. Mixtures

Pure Substances

A pure substance contains only one kind of particles and has a fixed composition.

Pure substances are of two types:

• Elements
• Compounds

Elements

An element is a pure substance made up of only one kind of atom.

Examples of Elements

• Iron
• Copper
• Gold
• Oxygen
• Hydrogen
• Carbon

Elements cannot be broken down into simpler substances by ordinary chemical methods.

Compounds

A compound is a pure substance formed when two or more elements combine chemically in a fixed ratio.

Examples of Compounds

• Water
• Carbon dioxide
• Sodium chloride
• Calcium carbonate

Water is made up of hydrogen and oxygen in a fixed ratio of 2:1 by number of atoms.

Mixtures

A mixture contains two or more substances that are physically combined in any proportion.

Examples of Mixtures

• Air
• Soil
• Salt solution
• Lemonade
• Brass
• Sea water

The components of a mixture retain their individual properties and can generally be separated by physical methods.

Homogeneous and Heterogeneous Mixtures

Homogeneous Mixture

A mixture having a uniform composition throughout is called a homogeneous mixture.

Examples:

• Salt solution
• Sugar solution
• Air
• Brass

Heterogeneous Mixture

A mixture that does not have a uniform composition throughout is called a heterogeneous mixture.

Examples:

• Soil
• Sand in water
• Oil and water
• Granite

Physical and Chemical Changes

Physical Change

A physical change changes the physical properties of a substance but does not form a new substance.

Examples:

• Melting of ice
• Cutting paper
• Dissolving sugar in water
• Boiling water

Chemical Change

A chemical change produces one or more new substances with different properties.

Examples:

• Rusting of iron
• Burning of wood
• Curdling of milk
• Digestion of food
• Burning of magnesium

20 Solved MCQs on Matter

1. Which of the following is matter?

A. Light
B. Sound
C. Air
D. Heat

Answer: C. Air
Explanation: Air has mass and occupies space.

2. Matter is made up of very small:

A. Cells only
B. Particles
C. Rays
D. Waves

Answer: B. Particles
Explanation: Matter consists of atoms, molecules or ions.

3. Which state of matter has a fixed shape and fixed volume?

A. Solid
B. Liquid
C. Gas
D. Vapour

Answer: A. Solid

4. Which state of matter is highly compressible?

A. Solid
B. Liquid
C. Gas
D. Gel

Answer: C. Gas

5. The force of attraction between particles is strongest in:

A. Gases
B. Liquids
C. Solids
D. Plasma

Answer: C. Solids

6. The change of ice into water is called:

A. Freezing
B. Melting
C. Condensation
D. Sublimation

Answer: B. Melting

7. The direct conversion of a solid into a gas is called:

A. Fusion
B. Condensation
C. Sublimation
D. Freezing

Answer: C. Sublimation

8. Which substance undergoes sublimation?

A. Sand
B. Camphor
C. Water
D. Salt solution

Answer: B. Camphor

9. The boiling point of water at normal atmospheric pressure is:

A. $0^{\circ }C$
B. ${50}^{\circ }C$
C. ${100}^{\circ }C$
D. ${212}^{\circ }C$ only

Answer: C. ${100}^{\circ }C$

10. Evaporation takes place:

A. Only at the boiling point
B. Only below $0^{\circ }C$
C. At the surface of a liquid
D. Throughout a solid

Answer: C. At the surface of a liquid

11. Evaporation increases with an increase in:

A. Humidity
B. Surface area
C. Atmospheric moisture
D. Volume only

Answer: B. Surface area

12. Diffusion is fastest in:

A. Solids
B. Liquids
C. Gases
D. Crystals

Answer: C. Gases

13. Which of the following is a pure substance?

A. Air
B. Soil
C. Copper
D. Lemonade

Answer: C. Copper

14. A substance made up of only one kind of atom is called:

A. Mixture
B. Element
C. Compound
D. Solution

Answer: B. Element

15. Water is a:

A. Mixture
B. Element
C. Compound
D. Suspension

Answer: C. Compound

16. Air is a:

A. Compound
B. Homogeneous mixture
C. Element
D. Pure substance

Answer: B. Homogeneous mixture

17. Which of the following is a heterogeneous mixture?

A. Salt solution
B. Air
C. Sugar solution
D. Oil and water

Answer: D. Oil and water

18. Rusting of iron is a:

A. Physical change
B. Chemical change
C. Change of state only
D. Reversible physical change

Answer: B. Chemical change

19. The particles of matter are:

A. Always at rest
B. In continuous motion
C. Present only in gases
D. Visible to the naked eye

Answer: B. In continuous motion

20. A liquid has:

A. Fixed shape and fixed volume
B. No shape and no volume
C. Fixed volume but no fixed shape
D. Fixed shape but no volume

Answer: C. Fixed volume but no fixed shape

15 Solved Short Answer Questions

1. Define matter.

Matter is anything that has mass and occupies space.

2. Give two examples of matter.

Air and water are two examples of matter.

3. What is mass?

Mass is the quantity of matter present in an object.

4. What is volume?

Volume is the amount of space occupied by an object or substance.

5. Why can gases be compressed easily?

Gases can be compressed easily because their particles are far apart and have large spaces between them.

6. Why do solids have a fixed shape?

Solids have a fixed shape because their particles are closely packed and held together by strong forces of attraction.

7. What is diffusion?

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

8. Why is diffusion faster in gases?

Diffusion is faster in gases because gas particles are far apart and move rapidly in all directions.

9. What is evaporation?

Evaporation is the slow change of a liquid into vapour from its surface at a temperature below its boiling point.

10. State two factors that increase evaporation.

An increase in temperature and an increase in surface area increase evaporation.

11. What is sublimation?

Sublimation is the direct conversion of a solid into a gas without passing through the liquid state.

12. What is an element?

An element is a pure substance made up of only one kind of atom.

13. What is a compound?

A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio.

14. What is a mixture?

A mixture is formed when two or more substances are physically combined in any proportion.

15. Distinguish between a physical change and a chemical change.

A physical change does not produce a new substance, while a chemical change produces one or more new substances.

12 Solved Long Answer Questions

1. Explain the characteristics of matter.

Matter has several important characteristics:

1. Matter has mass.
2. Matter occupies space.
3. Matter is made up of very small particles.
4. There are spaces between the particles of matter.
5. Particles of matter are in continuous motion.
6. Particles of matter attract one another.
7. The particles move faster when the temperature increases.

These characteristics explain the behaviour of solids, liquids and gases.

2. Explain the arrangement and movement of particles in solids, liquids and gases.

In solids, particles are very closely packed and have strong attractive forces. They can only vibrate around their fixed positions.

In liquids, particles are less closely packed and have moderate attractive forces. They can move past one another, allowing liquids to flow.

In gases, particles are far apart and have very weak attractive forces. They move rapidly in all directions and fill the entire container.

3. Compare solids, liquids and gases.

Solids have a fixed shape and fixed volume. Their particles are closely packed, and they cannot be compressed easily.

Liquids have a fixed volume but no fixed shape. They take the shape of their container and can flow.

Gases have neither a fixed shape nor a fixed volume. They are highly compressible and exert pressure on the walls of their container.

4. Explain the interconversion of the three states of matter.

A solid changes into a liquid on heating. This process is called melting or fusion. A liquid changes into a gas on heating by vaporisation.

When a gas is cooled, it changes into a liquid through condensation. A liquid changes into a solid on cooling through freezing or solidification.

Some solids, such as camphor and naphthalene, directly change into gases. This process is called sublimation.

5. What is evaporation? Explain the factors affecting it.

Evaporation is the conversion of a liquid into vapour from its surface at a temperature below its boiling point.

The rate of evaporation increases when:

• The temperature increases.
• The surface area increases.
• The wind speed increases.
• The humidity decreases.

Evaporation causes cooling because high-energy particles escape from the liquid surface.

6. Explain why evaporation causes cooling.

Particles in a liquid have different amounts of energy. Some particles have more energy than others. During evaporation, the high-energy particles escape from the surface of the liquid.

The average energy of the remaining particles decreases. Since temperature depends on the average kinetic energy of particles, the liquid becomes cooler.

This is why sweating cools our body and why water in an earthen pot becomes cool.

7. Explain diffusion with examples.

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

Diffusion occurs because particles of matter are continuously moving. It is fastest in gases, slower in liquids and slowest in solids.

Examples include the spreading of perfume smell throughout a room, the movement of ink in water and the exchange of oxygen and carbon dioxide in living organisms.

8. Differentiate between elements, compounds and mixtures.

An element is a pure substance made up of one kind of atom. It cannot be broken down into simpler substances by ordinary chemical methods. Iron and oxygen are examples.

A compound is formed when two or more elements combine chemically in a fixed ratio. Its properties are different from those of its elements. Water and sodium chloride are examples.

A mixture is formed when substances combine physically in any proportion. The components retain their properties and can usually be separated by physical methods. Air and soil are examples.

9. Explain homogeneous and heterogeneous mixtures with examples.

A homogeneous mixture has a uniform composition throughout. Its components cannot generally be distinguished by simply observing it. Salt solution, sugar solution and air are homogeneous mixtures.

A heterogeneous mixture does not have a uniform composition. Its components may be visible or exist in different regions. Soil, oil and water, and sand in water are heterogeneous mixtures.

10. Distinguish between physical and chemical changes.

A physical change affects the size, shape, state or appearance of a substance but does not produce a new substance. Melting ice, cutting paper and dissolving sugar in water are examples.

A chemical change produces one or more new substances with different properties. Rusting of iron, burning of paper and digestion of food are examples.

Physical changes are often reversible, while chemical changes are generally difficult to reverse.

11. Explain why a gas exerts pressure.

Gas particles are continuously moving in all directions. When they collide with the walls of a container, they exert force on the walls.

The force exerted by gas particles per unit area of the container is called gas pressure. Increasing the temperature makes the particles move faster and may increase the pressure if the volume remains constant.

12. Explain why a wooden table is considered matter but light is not.

A wooden table has mass and occupies space, so it is considered matter. It is made up of particles and has measurable volume.

Light does not have mass or occupy space like a physical substance. Therefore, light is a form of energy and is not considered matter.

Important Examination Points

• Matter has mass and occupies space.
• Matter is made up of tiny particles.
• Solids have a fixed shape and fixed volume.
• Liquids have a fixed volume but no fixed shape.
• Gases have neither a fixed shape nor a fixed volume.
• Diffusion is fastest in gases.
• Evaporation takes place at the surface of a liquid.
• Boiling takes place throughout the liquid.
• Sublimation is the direct change of a solid into a gas.
• Elements contain one type of atom.
• Compounds are formed by chemical combination.
• Mixtures are formed by physical combination.
• Rusting and burning are chemical changes.
• Melting and evaporation are physical changes.

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