Divalent/BIVALENT functional groups:these group has a valence of two. Valency is the number of chemical bonds formed, which may be covalent, polar covalent, or ionic.

Example: Compounds include the imino (=NH) and carbonyl (=O)

For Monovalent you can follow this link for Valance in Chemistry where you will get introduced to more valant groups.

One more example: