Now, a ligand reaction kind of coincides with something we've seen before. Recall that the adduct equals the product of a Lewis base and acid reaction. So remember a ligand or ligand represents a Lewis base. It's donating a lone pair to a metal cation which represents our Lewis acid.

Now when we talk about adduct, we're adding them together. The overall charge of an adduct equals the sum of the metal cation plus ligand or ligand charge O. If we take a look here, we have our metal cation in the form of Cadmium ion. We have our ligands which is water here. This is a metal cation which can accept the lone pair, so it represents our Lewis acid, and we're going to say here that water can use one of its lone pairs and donate it to that metal cation. So this is our Lewis base.

Now it could be multiple waters attaching to this cadmium, not just necessarily one. Here we have our adduct, we have in fact 4 water molecules attaching themselves to 1 cadmium ion. So here because it's an ion, we put it in brackets and the charge is going to be on the outside. Cadmium has a 2 plus charge. The four water molecules that we're adding to it are all neutral. So their charge is 0.

So the overall charge would be the charge of the metal cation plus the charges of the ligands. So overall that's going to be two plus. So this would be the overall charge of our adduct product between our cadmium ion and four water molecules.