Particulate Nature of Matter
Class 08 ScienceA constituent particle is the basic unit that makes up a larger piece of a substance or material. The spaces between the particles are known as interparticle spaces.
Different States of Matter
The constituent particles of matter are held together through forces which are attractive in nature. These forces are called interparticle attractions. The strength of these attractions depends on the nature of the substance and the interparticle distance. Even a slight increase in the distance decreases the interparticle forces drastically. The strength of these forces ultimately decides the physical state of the substances.
1. Solid State
Solids have a definite shape and volume. This is due to the fact that in solids, the particles are tightly packed and the interparticle attractions are very strong. These strong forces of attraction hold the particles in fixed positions, preventing them from moving freely. The particles can only move to and fro about their positions (vibrate or oscillate) but cannot move past each other.
When solids are heated, their particles vibrate more vigorously. A stage is reached when these vibrations become so vigorous that the particles start leaving their position. The interparticle forces of attraction get weakened and the solid gets converted into the liquid state. The temperature at which this happens is the melting point of the solid.
The minimum temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
Some solids have weak interparticle forces of attraction, so their melting points are low. While others have strong attractive forces and have high melting points.
2. Liquid State
The liquids do not have a fixed shape and take the shape of the container they are kept in. This happens because the particles of liquids are free to move. Liquids have no fixed shape but have a fixed volume.
In liquids, the interparticle attractions are slightly weaker than in solids, but still strong enough to keep the particles close together.
When a liquid is heated, a stage comes when it starts boiling. The temperature at which a liquid boils and turns into vapour at atmospheric pressure is called its boiling point. The movement of particles becomes so vigorous that they move apart from each other, resulting in a decrease in the interparticle forces of attraction. Eventually, the constituent particles can escape from the liquid state. The liquid is converted into vapour or the gaseous state.
3. Gaseous State
The particles in gases move freely in all directions and the interparticle attractions are negligible. As a result, gases do not have a fixed shape or volume.