Calcium monophosphide is the inorganic compound with the formula CaP. It is sometimes also known as "calcium phosphide", which also describes a different compound with composition Ca<sub>3</sub>P<sub>2</sub>. Calcium monophosphide is a black solid.
The structures of CaP and sodium peroxide (Na<sub>2</sub>O<sub>2</sub>) are very similar. The solid is described as a salt: (Ca<sup>2+</sup>)<sub>2</sub>P<sub>2</sub><sup>4âÂÂ</sup>, or Ca<sub>2</sub>P<sub>2</sub>. Since the bonding is ionic, the diphosphide centers carry negative charge and are easily protonated. Upon hydrolysis this material releases diphosphine (P<sub>2</sub>H<sub>4</sub>):
The hydrolyses of CaP and calcium carbide (CaC<sub>2</sub>) are similar, except that diphosphine spontaneously ignites in air. Thus, CaP must be protected from air.
CaP decomposes to Ca<sub>3</sub>P<sub>2</sub> at about 600 ðC.