Number of sites a ligand binds

[Izzy Ick 4B]

For polydentate ligands, how are you supposed to determine how many binding sites it has? Do you have to draw the lewis structure?

[JasmineAlberto4J]

If a ligand is monodentate, It has one binding site, bidentate 2 sites, tridendate 3 etc.

[Bryan Nguyen 1A]

If an atom in a molecule has 1 lone pair of electrons, then that atom is considered to be one binding site. If there are two lone pairs on an atom in a molecule, that atom would still be considered to be one binding site, not two.

To determine how many binding sites a ligand has, count how many atoms in the ligand have at least one lone pair. Ethylenediamine (en) is a bidentate because it has 2 atoms that have at least one lone pair (both N has a lone pair). There's also the shape of the molecule. For example, oxalate (ox) looks like a tetradentate, but it's actually a bidentate because only two of the O atoms can attach to a metal due to it's shape. The other two O atoms can't attach to the metal. If there is an atom between the C atoms of ox (would be a different molecule though), then it would be considered a tetradentate. So basically count the number of atoms with lone pair(s) and think about "how many atoms with lone pair(s) can attach to this metal?"

You don't have to draw the Lewis structure unless the question asks you to, but it would help determine the number of binding sites if you need to visually see what the ligand looks like.