Classification of Solids

On the basis of nature of arrangements of the constituent particles the solids are classified into amorphous and crystalline solids.

In crystalline solids the constituent particles are arranged in a regular and periodic pattern and give a well defined shape to it. The regular pattern extends throughout the solid and such solids are said to have long range order. On the other hand, some solids have only a short range of order. This means that the particles are arranged regularly in only some regions of the solid and are relatively disordered in other regions. Such solids are called amorphous solids.

Sodium chloride and sucrose are common examples of crystalline solids while glass, fused silica, rubber and high molecular mass polymers are some examples of amorphous solids.

Difference Between Amorphous & Crystalline Solids

An important difference between the amorphous and crystalline solids is that while amorphous solids are isotropic in nature (these exhibit same value of some physical properties in all directions) the crystalline solids are anisotropic (the values of some physical properties are different in different directions). Refractive index and coefficient of thermal expansion are typical physical properties, which have different values when measured along different directions of a given crystal.

Another difference between amorphous and crystalline solids is that while crystalline solids have a sharp or definite melting point, whereas the amorphous solids do not have definite melting point, these melt over a range of temperature.