TABLE OF CONTENTS Solids are characterized by their definite shape and also their considerable mechanical strength and rigidity. The rigidity is due to the absence of the translatory motion of the structural units of the solid. These units remain fixed to a mean position about which they may vibrate. The forces of attraction between these units are quite large. In general, solids are classified as crystalline or amorphous:
Crystalline solids exist in well-defined crystalline forms, with their atoms, molecules, or ions arranged in a certain definite geometrical pattern, throughout the 3D network of the crystal. Thus, in crystalline solids, there is a long range order in their structures. Sulphur, sugar, sodium chloride, diamond, and so on are examples of crystalline solids.
Amorphous solids have completely random particle arrangement. Thus, they lack the regular arrangement of atoms or molecules, and they also lack a long range order in their structures. In fact, amorphous solids can be regarded as supercooled liquids with small structural units and a short range order. Examples of amorphous solids are glass, rubber, plastics, pitch, and so on. Table 7.1 shows the difference between crystalline and amorphous solids.
| Crystalline Solids | Amorphous Solids |
|---|---|
| A regular arrangement of particles in an orderly manner. | A completely random particle arrangement. |
| Sharp melting points. | Melt over a range of temperature and do not have sharp melting points. |
| Physical properties are different in different directions. Hence, crystals are anisotropic. | The same physical properties in all... |
