How are white phosphorus, red phosphorus, and black phosphorus different?

Phosphorus exists in several allotropic forms, with white, red, and black phosphorus being the three primary modifications. These forms differ significantly in their molecular structure, stability, and reactivity.1

White Phosphorus

White phosphorus consists of tetrahedral $P_4$ molecules held together by weak van der Waals forces. Because the bond angles within these tetrahedra are strained at 60°, this form is metastable and highly reactive. It is toxic, volatile, and inflames spontaneously in air at 35 °C, requiring storage under water. It is soluble in solvents like carbon disulfide and has been used in military incendiary applications.1

Red Phosphorus

Red phosphorus is a polymeric form created when white phosphorus is heated. It is amorphous or crystalline and significantly more stable than the white modification. It is insoluble in most solvents and relatively inert, though commercial forms can still ignite in air. It is commonly used in the manufacturing of safety matches.1

Black Phosphorus

Black phosphorus is a flaky, crystalline solid that resembles graphite. It is considered the most stable allotrope. Unlike the other forms, it is capable of conducting electricity and is chemically inert.1