term matter from your earlier classes. Anything which has mass and occupies space is called matter . Everything around us, for example, book, pen, pencil, water, air, all living beings, etc., are composed of matter. You know that they have mass and they occupy space.
Let us recall the characteristics of the states of matter, which you learnt in your previous classes. . . States of Matter You are aware that matter can exist in three physical states viz.
solid , liquid and gas . The constituent particles of matter in these three states can be represented as shown in Fig. . .
Particles are held very close to each other in solids in an orderly fashion and there is not much freedom of movement. In liquids , the particles are close to each other but they can move around. However, in gases , the particles are far apart as compared to those present in solid or liquid states and their movement is easy and fast. Because of such arrangement of particles, different states of matter exhibit the following characteristics: Solids have definite volume and definite shape .
Liquids have definite volume but do not have definite shape . They take the shape of the container in which they are placed. (iii) Gases have neither definite volume nor definite shape . They completely occupy the space in the container in which they are placed.
These three states of matter are interconvertible by changing the conditions of temperature and pressure. Solid liquid Gas On heating, a solid usually changes to a liquid, and the liquid on further heating changes to gas (or vapour). In the reverse process, a gas on cooling liquifies to the liquid and the liquid on further cooling freezes to the solid. .
. . Classification of Matter In Class IX (Chapter ), you have learnt that at the macroscopic or bulk level, matter can be classified as mixture or pure substance . These can be further sub-divided as shown in Fig.
. . When all constituent particles of a substance are same in chemical nature, it is said to be a