Solids are those substances which are rigid, hard, have definite shape and definite volume. The atoms, ions, and molecules that make up a solid are closely packed. They are held together by strong cohesive forces. The constituent atoms, ions or molecules of solids cannot move at random. There exists a well ordered arrangement in solids.
Types of Solids
Solids can be classified on the basis of the regular arrangements of constituent atoms, ions, or molecules. There are two types of solids in this respect.
1. Crystalline Solids
Those solids in which atoms, ions, or molecules are arranged in a definite three dimensional pattern are called crystalline solids. This recurring regular geometrical pattern of structure extends three dimensionally.
2. Amorphous Solids
All solids are not crystalline. The word amorphous means shapeless. Amorphous substances are those whose constituent atoms, ions, or molecules do not possess a regular orderly arrangement. The best examples are glass, plastic, rubber, glue, etc. These substances have solid state properties and virtually complete maintenance of shape and volume. But they do not have an ordered crystalline state
Many crystalline solids can be changed into amorphous solids by melting them and then cooling the molten mass rapidly. In this way the constituent paricles do not find time to arranges themselves.