DIFFERENT STATES OF MATTER
It is a well known fact that matter can be classified into three categories depending upon its physical state, namely: solid, liquid and gaseous states.
(a) Solid state. The matter in solid state possesses a definite volume, a definite shape and a definite mass. Some common examples are: table, chair, common salt, silver, etc.
(b) Liquid state. The matter in liquid state possesses a definite volume, a definite mass, but no definite shape. In fact, it acquires the shape of the container. Some common examples are: milk, water, alcohol, etc.
(c) Gaseous state. The matter in gaseous state neither has definite volume nor definite shape but it has definite mass. It acquires the shape and volume of the container. Some common examples are: air, oxygen, hydrogen, sulphur dioxide, etc.
The intensive investigation by the scientists over the years, led to the development of a model regarding the constitution of matter. This model is known as dynamic particle model or kinetic model. Some of its assumptions are:
All matter is made of tiny particles. However; the state of aggregation of particles is different in the three states of matter.
The particles are separated by empty spaces called voids.
The particles exert attractive forces on one another. However, the magnitudes of these interparticle forces differ in three states of matter.
The particles are not stationary, but they have tendency to acquire motion.
The basic difference between the three states of matter can be explained on the basis of kinetic particle model.
EVIDENCE FOR MOLECULAR MOTION IN MATTER
Tiny particles of matter are not visible even with the help of powerful microscope. However, their existence and movement particularly in liquids/gases can be indirectly noticed by Brownian movement. Brownian movement refers to random movement of a specks of a solid in a liquid/or gas.
It occurs because the particles of a liquid/or gas are in constant motion and they constantly bombard any particle of solid the surface of the liquid. Due to continuous bombardment, the particle of solid itself also acquires rapid zig-zag motion.
This observation was first made by a Scottish botanist, Robert Brown, (1827). He made this discovery when he was looking at some pollen grains on the surface of a liquid (water) through a microscope.