Question

What are monodentate ligands ? Write one example .

Answer 1

The donor atoms , molecules or ions which donate a pair of electrons to the metal atom or ion and form a coordinate bond with it are called ligands and the metal atom or ion to which these ligands are attached is called central metal atom or ion .

Complete step by step answer:
There are various kinds of ligands as they are classified on the basis of the number of donor atoms , they may contain one or more than one donor atom .
If only one donor atom is present in the molecule ( or atom or ion ) which can coordinate , then it is called as unidentate or monodentate ligand .
OR
Monodentate ligand is a ligand that has only one atom that coordinates directly to the central atom in a complex .
For example , monodentate ligands may be simple ions such as $C{l^ - }$ or small molecules such as ${H_2}O$ or $N{H_3}$ .
${H_2}O$ may seem like a bidentate ligand since oxygen contains two lone pairs of electrons ${H_2}\ddot O:$ but it is not because the condition for a ligand to be bidentate is that it should have two donor atoms . Hence water is a monodentate ligand only .
As we know that ligands contain lone pairs of electrons therefore they are also called Lewis bases .

Note:
Unidentate ligands containing more than one coordinating atoms are called ambidentate ligands .
For example , $N{O_2}^ -$ can coordinate through either nitrogen or oxygen . Also , $C{N^ - }$ can coordinate through either carbon or nitrogen . Hence they are ambidentate ligands .