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 including crystalline solids and amorphous solids. Those solids or substances in which atoms, ions or molecules are arranged in a definite three dimensional pattern are called crystalline solids or substances. This recurring regular geometrical pattern of structure extends three dimensionally. The word amorphous means shapeless. Amorphous substances are those whose constituent atoms, ions or molecules do not posses a regular orderly arrangement.