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.
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