Divalent

In chemistry, a divalent (sometimes bivalent^[1]) 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.

Examples:

• 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).

Water Hardness

The divalent cations Ca²⁺ and Mg²⁺ contribute to the properties of water that cause it to be hard, such as the formation of limescale.^[2]

See also

• Valency (chemistry)
• Valence electron

References

1. Explanation on numerical prefixes
2. World Health Organization Hardness in Drinking-Water, 2003