Question

What are the allotropes of phosphorus?

Answer 1

Phosphorus exists in a variety of allotropic forms, the most important of which are white, red, and black.

White phosphorus

• White phosphorus is a waxy, transparent white substance.
• It is poisonous, water-insoluble, but soluble in carbon disulfide, and glows in the dark(chemiluminescence).
• The structure of white phosphorus is as follows:-

Red phosphorus

• Red phosphorus is formed by heating white phosphorus for several days at $573\text{K}$ in an inert environment.
• Red phosphorus has an iron-grey luster. It has no odor, is nonpoisonous, and is insoluble in both water and carbon disulfide.
• It does not light up in the dark.
• The diagram of red phosphorus is as follows:-

Black phosphorus

• There are two types of black phosphorus:$\text{α}$ -black phosphorus and $\text{β}$-black phosphorus.
• When red phosphorus is heated in a sealed tube at $803\hspace{0.17em}\text{K}$, the formation of $\text{α}$-black phosphorus takes place.
• In the air, $\text{α}$ -black phosphorus does not oxidize.
• $\text{β}$-black phosphorus is made by heating white phosphorus under high pressure at $473\text{K}$.