Matter in our Surroundings and Physical nature of matter
Anything which occupies space and has mass is called matter. Air and water, sugar and sand, hydrogen and oxygen etc.
Ancient Indian philosophers said that all the matter, living or non-living was made up of five basic elements (panch tatva): air, earth, fire, sky and water.
Modern day scientists classify matter in two ways: on the basis of its physical properties and on the basis of its chemical properties.
On the basis of physical properties, matter is classified as solids, liquids and gases.
On the basis of chemical properties, matter is classified as elements, compounds and mixtures.
Physical nature of matter
Matter is made up of particles.
Everything around us is made up of tiny pieces or particles. The particles of matter are constantly moving (they are in motion).
The particles which make up matter are atoms and molecules.
Evidence of particles in matter:
The evidence for the existence of particles in matter and their motion comes from the experiments on diffusion and Brownian motion.
Dissolving a solid in a liquid:
When a crystal of potassium permanganate is placed in a beaker of water, the water slowly turns purple on its own, even without stirring.
Both potassium permanganate crystal and water are made up of tiny particles.
When the potassium permanganate crystal is put in water, its particles separate from one another.
These purpled colored particles of potassium permanganate spread throughout water making the whole water look purple.
Actually, on dissolving, the particles of potassium permanganate get into the spaces between the particles of water.
So it is concluded that the particles are moving or they are in motion.
Mixing of two gases:
Air is a colorless gas. Bromine vapor is red-brown in color, and it is heavier than air.
A gas jar containing air is placed upside down on a gas jar of bromine vapor.
We will see that the red brown vapors of bromine from the lower gas jar spread up into air in the upper gas jar. And after some time, the gas jar containing air also becomes completely red-brown in color.
Both air and bromine vapors are made of tiny moving particles. The moving particles of bromine collide with each other and bounce about in all directions, due to which they get mixed uniformly. This is another example of diffusion.
The process if diffusion gives us two conclusions about the nature of matter.
The matter is made up of tiny particles.
The particles of matter are constantly moving.
Movement of pollen grains in water:
The best evidence for the existence and movement of particles in liquids was given by Robert Brown in 1827. Robert Brown suspended extremely small pollen grains in water.
It was found that the pollen grains were moving rapidly throughout water in a very irregular way.
Water is made up of tiny particles which are moving very fast. The pollen grains move on the surface of water because they are constantly being hit by the fast moving particles of water.
The zigzag movement of the small particles suspended in a liquid (or gas) is called Brownian motion.
The existence of Brownian motion gives us two conclusions about the nature of matter.