9.4 What is meant by unidentate, didentate and ambidentate ligands? Give two examples for each.

A ligand may contain one or more unshared pairs of electrons which are called the donor sites of ligands. Now, depending on the number of these donor sites, ligands can be classified as follows:

(a) Unidentate ligands: Ligands with only one donor sites are called unidentate ligands. For e.g.,  NH3 , CI- etc. 
(b) Didentate ligands: Ligands that have two donor sites are called didentate ligands.
For e.g.,
(a) Ethane-1,2-diamine
(b) Oxalate ion
(c) Ambidentate ligands:
A ligand that may have more than one kind of donor sites but at a time only one kind of donor site is utilized for donation is called as ambidentate ligand. 

For example:
(The donor atom is N)
(The donor atom is oxygen)
(The donor atom is S)
(The donor atom is N)