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In chemistry, a divalent (sometimes bivalent) element, ion, functional group or molecule has a valence of two. Valency is the number of chemical bonds formed, which may be covalent, polar covalent or ionic.
- Divalent elements include calcium and sulfur. While the bonds formed by calcium are ionic, sulfur can form covalent bonds as in H2S or ionic bonds as in Na2S.
- Divalent anions have a charge of −2, for example S2− and SO42−.
- Divalent cations have a charge of +2, for example Fe2+, Ca2+ and Hg22+.
- Divalent functional groups include the imino (=NH) and carbonyl (=O).
Main article: Water hardness