In chemistry, a divalent ion or molecule has a valence of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent.[1]
Divalent anions are atoms or radicals with two additional electrons when compared to their elemental state (that is, with 2 more electrons than protons). For instance, S2– is the sulfide anion.
A divalent cation is missing two electrons as compared with the neutral atom. For instance, iron(II) or Fe2+ is the divalent cationic form of iron. Divalent cations are present in abundance in hard water, for example, calcium (Ca2+) and magnesium (Mg2+). These ionic minerals in solution are what contribute to the properties of water which cause it to be hard, such as the formation of limescale.[2]