# How to calculate denticity of ligands?

When looking at an ligand, how do I know its denticity? For instance, I know that though there are 2 lone pairs in $\ce{H2O}$, its denticity is only 1 due to geometrical reasons as the 2 of them can't be facing the metal ion at the same time. However, when I look at other ligands, especially unfamiliar ones, I cannot determine their denticity.

• You can never tell for sure. A ligand may have different denticity in different complexes. – Ivan Neretin Dec 31 '15 at 8:53
• I also want to point out that even if water used both lone pairs, it would still be monodentate because only one atom in the ligand is bonded to the metal. Denticity describes how many different atoms in the ligand are bonded. If one atom uses two lone pairs, then we have denticity 1 and bond order 2. See chemistry.stackexchange.com/questions/7366/… – Ben Norris Dec 31 '15 at 13:16