Illustrated Glossary of Organic Chemistry

Divalent: An atom having two covalent bonds.

In this molecule the hydrogen atom and chlorine atoms are monovalent, the oxygen atom is divalent, the nitrogen atom is trivalent, and the carbon atom is tetravalent.

Acetic acid contains two divalent oxygen atoms. The oxygen atom of the hydroxyl group has two single bonds, and the oxygen atom of the carbonyl group has one double bond.