What are the different states of matter?

          Anything that occupies space and possesses mass or inertia is known as matter in one form or another. Iron, gold, silver, water, oxygen etc. all are matter. Of these, metals ordinarily exist in solid, water in liquid and oxygen in gaseous state. But all these materials can exist in any of the three states, namely: solid, liquid or gaseous. Matter is composed of basic units called molecules which themselves are made of smaller units called atoms.

          In solid state the molecules of a substance are very close to each other. The force of attraction between them is very strong. That is why the shape, size and volume of solids are fixed and do not compress easily. In the liquid state, the molecules of matter are not so close to each other and as such the force of attraction between them is comparatively less. As a result, the liquid acquires the shape of the container in which it is kept, but its volume remains constant. In the gaseous state, the molecules remain far apart from each other and there is only a very small force of attraction between them. The result is that neither its shape nor its volume remains constant – it acquires the shape and volume of the-container in which it is kept and can be easily compressed.

          All the substances of the universe can exist in any of the three aforesaid states – solid, liquid or gaseous. For example, water, which is normally in a liquid state, becomes solid on being frozen to ice and comes to gaseous state when it is converted into vapours. Similarly under normal conditions, oxygen is a gas, but by cooling it can be converted into a liquid or solid state.

          In addition to these three states of matter, there is a fourth one called the plasma state. The atoms and molecules of matter are ionized in this state. There are both positive and negative ions present in this condition. The shining material in the fluorescent tubes is the plasma state. And same is the case with ionosphere which reflects the radiowaves. Generally, lowering of temperature brings a substance to solid state and the increase in the temperature to a higher degree brings it to the gaseous state and finally to the plasma state.