Page 76 - Viva ICSE Science 4 : E-book

7

Air

We have already learnt in the previous class that KEY CONCEPTS
anything that has mass and occupies space is

called matter. Everything around us is matter and • Composition of air
it exists in three diff erent states—solids, liquids • Properties of air
and gases. • Process of breathing

On the basis of properties of a substance, it • Air pollution
is categorised as solid, liquid or gas. These
properties, in turn, depend on the arrangement

of tiny particles which constitute all matter.
Let’s see how the arrangement of tiny particles infl uence the properties of substances.

Solids: In solids, the particles are packed very close to each
other. Therefore, they have a fi xed shape and size. Solids

diff er greatly in their nature. Some solids like stones and
diamond are very hard while solids like cloth and paper are
very soft. molecules of paper

Liquids: The particles in liquids are not so closely packed as in
solids, and are free to move about. This is why liquids do not
have a fi xed shape. When poured, they fl ow easily and take the
shape of the container.
molecules of water
inside the beaker
Gases: They do not have a fi xed shape. They fi ll all the available
space because their particles are very loosely packed.
molecules of gas
inside the balloon

Air is a mixture of gases. We all are familiar that air is present everywhere around us. We
cannot see, smell, or touch air but we can feel it. We can feel the presence of air when
it moves, for example, when leaves of trees rustle and when the clothes hanging on a
clothesline sway.

Let’s read more about air in this chapter.

62