Anything which has mass and occupies space is called matter. The important characteristics of the particles of matter(atoms or molecules) are following:

(i) The particles of matter have spaces between them. Particles of one type of matter are able to get into the spaces of the particles of other. For example, when we dissolve salt or sugar in water, the particles of sugar or salt get evenly distributed in water. Particles of different types of matter are also able to intermix on their own with each other. This happens because of the presence of spaces between the particles. This intermixing of particles of two different types of matter on their own is called diffusion. Diffusion becomes faster on heating.

(ii) The particles of matter are constantly moving and they possess kinetic energy. With the increase in temperature, particles move faster. As a result, the kinetic energy of the particles also increases.

(iii) The particles of matter attract each other. They have force of attraction acting between them. This force helps to keep the particles of matter together. The strength of this force of attraction depends on the nature of matter.