Three states of matter are solid, liquid and gas. Amongst them liquid and gases are called fluids because of their ability to flow. But solid cannot flow. The reason for that is particles in solid are not free to move in available space. There is strong intermolecular force of attraction in between the particles in solid. The constituents particles in solid have fixed position and can only oscillate about their mean position.

In nature the particular state of matter is governed by two opposing forces at given set of temperature and pressure. These forces are intermolecular force of attraction and thermal energy. If intermolecular force of attraction is high as compared to thermal energy, particles remains in closest position and hence very less movement in particles is observed. In this case solid state is the preferred state of matter.

Let us revise the general characteristics of solid:

i) Fixed mass, volume and shape

ii) Strong intermolecular force of attraction

iii) Least intermolecular space

iv) Fixed position of constituent particles

v) Incompressible and rigid

Solids are classified on the basis of arrangement of their constituent particles. If the arrangement of constituent particles is same throughout the solid (long range order) it is called crystalline. If the arrangement of particles does not follow any regular pattern throughout the solid (short range order) it is called amorphous solid.