Solids can be broadly classified into two categories according to it’s crystal structure.
- Crystalline Solid
- Amorphous Solid
- In a crystalline solid the structural units (atoms molecules or ions) are arranged in a definite pattern.
- This definite pattern is repeated constantly throughout the solid. on account of the constant repetition of this definite pattern, a crystalline solid has a definite geometrical configuration which is characteristic of the nature of the substance.
- Crystalline solid possess sharp melting points and characteristic heat of fusion. If a molten crystalline solid is cooled, the original geometric configuration reappears again.
- These solids are incompressible.
- They possess planar surface and characteristics angles between the faces. A crystalline solids can be cleaved only a long definite planes and on cleavage gives a clean cut.
- The crystalline solid are anisotropic in nature, that is they may possess different magnitudes of physical properties in different direction.
- Crystalline solids are regarded as true solids
Examples – Table Salt (NaCl), sugar (sucrose), Diamond, Quartz, Silver iodide
- In an amorphous solid the structural units are not arranged in a definite pattern.
- In an amorphous solid there may be and orderly arrangement of its structural units, but this arrangement is not very regular and is extended only a few Angstroms.
- The amorphous solids are said to possess only short range order.
- The amorphous solid do not have sharp melting point.
- This solid do not possess characteristics of heats of fusion.
- This solid do not give a regular cut when cut with a knife.
- The amorphous solid can be compressed to some extent.
- The amorphous solids are isotropic in nature, that is they show the same value of an property in all direction.
- Amorphous solids are generally regarded as supercooled liquid, because the arrangement of structural units in them is almost similar to that in the liquid.
Examples – Glass, Wax, Rubber, Starch, Plastics
Difference between Crystalline & Amorphous Solid
|Properties||Crystalline Solids||Amorphous Solids|
|Arrangement of Structural Units||Very Regular||Not Regular|
|Geometrical Configuration||Definite||Not Definite|
|Melting Points||Very Sharp||Not Sharp|
|Heats of Fusion||Definite and characteristic||Neither definite nor characteristic|
|Cleavage with a knife||Regular clean cut||Irregular cut|
|Compressibility||Generally incompressible||Generally compressible to some extent|
|Anisotropy||Anisotropic in nature||Isotropic in nature|