Solids can be classified on the basis of nature of order in the arrangement of constituent particles (atoms, ions or molecules) into two types as 1. Crystalline solids 2. Amorphous solids 1 . Crystalline solids (Topic for CSIR-NET Coaching in Chemistry) The substance whose constituent particles (atoms, ions or molecules) are arranged in a defined geometric pattern in three dimensional space are called crystalline solids. X-ray diffraction studies of these crystalline solids reveal that in these solids, the constituents (atoms, ions or molecules) are arranged in a definite orderly arrangement. The regular arrangement of the constituents extends throughout the three dimensional network of crystals. In other words, the crystalline substance are said to have Long range order. This means that in crystalline solids, there is a regular pattern or arrangement of particles which repeats itself periodically aver the entire crystal. In fact a crystalline solid consists of a l...