Crystalline and Amorphous Solids

Depending on the nature of order in the arrangement of the constituent particles (atom, molecules or ions), there may be two types of solids—crystalline solids and Amorphous solids.

(i) Crystalline Solids : Here the constituent particles have long range order which means there is a regular pattern of arrangement of particles which repeats itself over long distances. They possess sharp melting point and undergo clean cleavage (cut). They show anisotropic behaviour.

Examples : NaCl, quartz, most of the metallic and non-metallic elements and their compounds.

(ii) Amorphous Solids : (Greek word amorphos = shapeless) Here, the constituent particles do not possess long range order of arrangement but a short range arrangement and therefore they undergo irregular cut. They are pseudo solids and do not possess sharp melting points. They soften over a range of temperature and can be moulded and blown into various shapes. On heating they become crystalline at some temperature. They show isotropic behaviour.

Examples : Glass. Rubber and plastics. Glass is an example of supercooled liquid.

Amorphous solids are very useful materials. Glass, rubber and plastics find many applications in our everyday lives. Amorphous silicon being one of the best photovoltaic material used for conversion for sunlight into electricity.