Class 9 Science

States of Matter

Table of Contents

There are three states of matter – solid, liquid and gas.


Matters which have fixed volume and shape are called solids. For example - stone, wood, brick, ice, sugar, salt, coal, etc. All metals are solid except mercury and gallium.

Properties of solids


Matters which have fixed volume but indefinite shape are called liquids. For example - milk, water, petrol, kerosene, alcohol, oil, etc. Since liquid can flow, it is also called fluid.

Properties of liquid


Matters which have indefinite shape and volume are called gases. For example - air, oxygen, hydrogen, nitrogen, carbon-dioxide, etc.

Properties of gas

Cause of different physical states of matters

The physical states of matter depend upon three main factors:


Because of great force of attraction particles of solids are closely packed together. This makes the space between particles of solids almost negligible. The lowest kinetic energy of particles does not able to move the particles of solids.

Hence, the great force of attraction and least space between particles of solids and lowest kinetic energy of particles keep the particles at fixed places. Because of the combination of these characters matter exists in solid state.


Strong force of attraction keeps the particles of liquids packed together. But the force of attraction between particles of solids is less strong than that of solid. Because of this particles of liquids are loosely packed compared to solid. The kinetic energy of particles of liquids is greater than that of solids.

Because of more space between particles and more kinetic energy than solids the particles of liquids slide over one another. These characters make a matter to exist in liquid state. Liquid can flow because its particles can slide over one another.


Because of negligible force of attraction the particles of gases are loosely packed consequently there are lots of spaces between their particles. Because of greatest kinetic energy the particles of gas move with high speed.

Because of negligible force of attraction between particles and greatest kinetic energy the particles of gas have always tendency to escape out. Because of these characters a matter exists in gaseous state.

Other states of matter

Plasma and BEC (Bose-Einstein Condensate) are considered as states of matter other than solid, liquid and gas. These are known as fourth and fifth states of matter.


It is considered as the fourth state of matter. Plasma is similar to the gas. Particles of plasma are made of free electrons and ions.

Plasma does not have a definite shape or a definite volume unless enclosed in a container.

Plasma may be defined as an electrically neutral medium of positive and negative particles.

Plasma is one of the most commonly occurring states of matter in universe. Plasma occurs naturally in the stars. All stars are made of plasma. Because of the presence of plasma stars glow. Plasma is formed because of nuclear fusion in stars. Our sun glows because of presence of plasma.

Plasma TV got its name because of presence of plasma in it. Plasma is also found in fluorescent light or neon sign. Plasma is formed when electricity is passed in a fluorescent tube or neon sign, which makes them glow.

Bose-Einstein Condensate (BEC)

It may be considered as fifth state of matter. Satyendra Nath Bose and Albert Einstein were predicted about this state of matters, that’s why it got its name as Bose-Einstein Condensate (BEC).

Plasma and BEC are has opposite characters. Plasma is a super hot and super excited atom while Condensate has super cool and super unexcited atoms.

BEC has been obtained by cooling the vapor of rubidium-87 at super low temperature by Eric Cornell and Carl Wieman on June 5 1995. After sometimes Wolfgang Ketterle also obtained BEC from sodium-23 at MIT, USA. Cornell, Wieman and Ketterle got Nobel Prize in Physics for this achievement in 2001.