Answer
See work below for details.
Work Step by Step
White phosphorus consists of $P_{4}$ molecules in a tetrahedral shape, with the phosphorus atoms at the corners of the tetrahedron. The bond angles between the three P atoms on any one face of the tetrahedron is small ($60^{\circ}C$) and strained, making the $P_{4}$ molecule unstable and reactive.
When heated to about $300^{\circ} C$ in the absence of air, white phosphorus slightly changes its structure to a different allotrope called red phosphorus, which is amorphous.
The general structure of red phosphorus is similar to that of white phosphorus, except that one of the bonds between two phosphorus atoms in the tetrahedron is broken. The two phosphorus atoms then link to other phosphorus atoms, making chains that vary in structure. Red phosphorus is neither as reactive nor as toxic as white phosphorus, and even though it is also flammable, it can be stored in air.
