A phosphide ion is an negatively charged potassium atom that has three additional electrons in its outermost shell. Phosphide ions are nonmetallic and can chemically react with a variety of metallic elements to form ionic compounds.
Phosphide ion is represented chemically as P3-. The chemical formulas for the ionic compound formed when a phosphide ion reacts with a metallic ion will depend on the number of valence electrons in the metal. Calcium ions have a +2 charge, so three calcium ions have a total charge of + 6 and balance with two phosphide ions, which have a total charge of -6. The resulting chemical formula for calcium phosphide is Ca3P2.