ICSE Class 8 Physics Chapter 01 Matter

Matter

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Theme

Building on previous learning in classes VI and VII. In this class, the theme aims at introducing children, the kinetic theory that will help them in understanding the difference in the three states of matter. The theory states that all matter is made of tiny particles that in an object are always in motion that may move slow or fast. In solids, the particles have less energy hence, do not move around freely. In liquids, they have relatively more energy and move freely within the container. The particles of gases have much more energy and move freely at high speeds. The increase or decrease in the movement or energy is the result of heating or cooling of an object. Heating an object increases the energy of particles whereas cooling decreases the energy of particles of an object.

In This Chapter You Will Learn To

Distinguish the three states of matter in terms of movement of particles

Relate the three states of matter with energy of movement of particles in them

Describe the changes of state using kinetic theory:

Boiling

Vaporization

Melting

Fusion

Evaporation

Condensation

Sublimation

Deposition

Freezing

Identify appropriate observable parameters in experiments

Present the results in the form of tables

Consider results using scientific knowledge and communicate these

Learning Objectives

Revising previous concepts learnt by children.

Building on children's previous learning.

Demonstrating matter in three states.

Demonstrating change of state, solid to liquid, liquid to gas etc.

Demonstrating the phenomenon of melting and boiling.

Engaging children to undertake activities related to melting and boiling, condensation and freezing and make observations followed by discussion.

Engaging children (individually/in groups) to observe change of state; solid to liquid, liquid to gas and record what is observed.

Explaining the different terms like boiling, melting, freezing, condensation, sublimation etc. with examples from daily life.

Observations of above mentioned phenomena in possible classroom situations (using different samples).

Children observing solids and liquids (compare and contrast the physical characteristics).

Encouraging children to prepare a comparison table of different states based on shape, texture and volume.

Asking children to describe the interconversion of states using examples like water, naphthalene balls etc. and additional examples of all types of change of state.

Engaging children in pairs or small groups in investigation of the related change of state due to addition of energy (heating or cooling) due to a substance.

Engaging children (individually/in groups/in pairs) in the design of activities to show that melting or boiling occurs at a fixed temperature for a substance.

Knowing Concepts

Kinetic theory of matter.

Three states of matter in terms of movement of particles.

Energy contents in the three states of matter.

Change of state in matter using the kinetic theory:

Boiling

Vaporization

Melting

Fusion

Evaporation

Condensation

Sublimation

Deposition

Freezing

Change of state diagrams (using the terms mentioned above).

Matter

We have read in class VI, that matter is something which occupies space, has mass and can be perceived by our senses. For example, air, water, iron, hydrogen, oxygen, milk, oil, sugar, salt etc. all are matter. Actually, matter means all the living and non-living things of the universe.

Composition

In the past, Indian philosophers considered that matter was made up of five tatvas (or constituents) namely akash, vayu, tejas (or agni), jal and prithvi. Later on, Maharishi Kanada considered matter to be made up of tiny particles which he called anu. Now, it is established that matter is composed of tiny particles called molecules. A molecule can exist free in nature and it has all the properties of that substance.

Do You Know?

A molecule composed of atoms can exist independently and freely in nature.

A molecule composed of one atom is called monoatomic molecule (such as helium, neon, argon, etc.).

A molecule composed of two atoms is called a diatomic molecule (e.g. hydrogen molecule, oxygen molecule, nitrogen molecule, etc.) and a molecule composed of more than two atoms is called polyatomic molecule (e.g. water, ammonia, carbon dioxide etc.).

Activity 1

To demonstrate that matter is composed of tiny particles.

Take a 100 mL beaker. Fill it half with water. Mark the level of water in the beaker (Fig. 1.1 (a)). Now, add some sugar in the water of the beaker. Stir it with a glass rod so that sugar gets dissolved in water

[Fig. 1.1 (b)]. Note the level of water with sugar. You will notice that there is no change in the level of water with sugar. This shows that each substance (water and sugar) is composed of tiny particles. The particles of sugar mix with the particles of water. They simply occupy the spaces between the particles of water.

Characteristics Of Molecules

The molecules of matter have the following characteristics:

1. They Are Very Small In Size

A molecule is of size nearly 10-10 metre. It is too small that it cannot be seen even with the help of a microscope.

Activity 2

Dissolve a crystal of potassium permanganate in 100 mL of water taken in a beaker (Fig. 1.2). You will see that the colour of water is pink.

Now, take about 10 mL of the above solution in another beaker. Mix 90 mL of water in it. Again you will see that the colour of solution is pink. Repeat the above process several times. Each time you dilute the solution, the colour remains pink.

This shows that the size of a particle of potassium permanganate is so small that it makes the water pink.

2. The Molecules Of Matter Have Spaces Between Them

The spacing between the molecules of matter is called inter-molecular space. It is less in solids, more in liquids and still more in gases. In other words molecules are more closely packed in solids, less in liquids and still less in gases.

Activity 3

Take 100 mL of water in a measuring cylinder. Add gently 20 grams of salt in water and stir it well so as to dissolve the salt evenly in water. It is noticed that the level of water does not change (Fig. 1.3). It shows that the molecules of salt occupy the spaces between the molecules of water.

3. The Molecules Are In Constant Motion

The molecules of matter are not at rest, but they are constantly in motion. In solids, the molecules vibrate about their mean positions without leaving their positions. In liquids, the molecules are free to move well within the boundary of the liquid. In gases, the molecules can move in a random manner everywhere in space available to them.

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