Allotropes of phosphorus
Phosphorus exists in at least six allotropic forms which are all solids at room temperature. Anyhow, we will mention only three:
- White phosphorus
- Red phosphorus
- Black phosphorus
- It is yellowish white substance.
- It is a waxy solid.
- It is a poisonous substance.
- It is volatile in nature.
- It is soluble in benzene and carbon disulphide.
- It is very reactive.
- It boils at 280°C and molecules of P4 are present in the vapours.
- When heated above 700°C, it dissociates to form P2molecules.
Structure of white phosphorus:
It has cubic structure in which P4 molecules occupy the corners of a tetrahedron. Each P4 molecules has a tetrahedral structure. Fig. (1.1)
It is prepared by heating white phosphorus in the pressure of little I2 or sulphur as a catalyst up to 250°C in vacuum.
- It is poisonous but less than that of white phosphorus.
- It is less reactive than white phosphorus.
Structure of red phosphorus:
Red phosphorus is a combination of tetrahedral P4 units to give macromolecules. Fig (1.2)
Black phosphorus is made by heating red phosphorus to high temperature and pressure. It is the most stable form of phosphorus under ordinary condition.