Number of ambidentate ligands among the following is _________.
NO₂⁻, SCN⁻, C₂ O₄²⁻, NH₃, CN⁻, SO₄²⁻, H₂ O .

Solution

Chemistry ma’am · 3 steps

Ask one thing of each ligand: does it have two different atoms that can each bind, one at a time?

1. What ambidentate means. An ambidentate ligand has two different donor atoms but binds through only one of them at a time. Two donor atoms binding together makes a ligand bidentate, not ambidentate.

   Ligand	Can bind through	Ambidentate?
   NO₂⁻	N (nitro) or O (nitrito)	yes
   SCN⁻	S (thiocyanato) or N (isothiocyanato)	yes
   CN⁻	C (cyano) or N (isocyano)	yes
   C₂O₄²⁻	two O atoms together	no, bidentate
   NH₃	N only	no
   SO₄²⁻	O only	no
   H₂O	O only	no

2. The tricky one. Oxalate has two donor atoms, but both are oxygen and they bind at the same time to form a ring. That is bidentate. Sulfate also binds only through oxygen, so it does not count.
3. So. The ambidentate ligands are NO₂⁻, SCN⁻ and CN⁻, which makes 3.

The common slip: 4. Counting oxalate as ambidentate because it has two donor atoms gives 4. Its two donors are the same atom, oxygen, and they bind together, so oxalate is bidentate.

The idea to keep. Ambidentate means two different donor atoms, but only one binds at a time. Two atoms binding together, like oxalate's two oxygens, makes a ligand bidentate instead.

Answer from the NTA final answer key. Solution by PrepWiser.