7.1 Kinetic Molecular Theory of Matter
According to this theory, matter is composed of very small particles called molecules which are always in motion. Their motion may be vibrational, rotational, or linear. There exists a mutual force of attraction between the molecules known as intermolecular force. This force depends upon the distance between the molecules. It decreases with increasing distance between them.
The molecules possess kinetic energy due to motion and potential energy due to the force of attraction. When a substance is heated, its temperature rises and its molecular motion becomes more vigorous, which increases the kinetic energy of the molecules. Thus, the temperature of a substance depends upon the average kinetic energy of its molecules.
In general, matter exists in three states: solids, liquids, and gases.