Now we can say that coordination complexes form predictable geometries based on either their coordination number or their electron configuration and we're going to say with a coordination number of four. That's when you must determine the metal cations electron geometry. So if you don't have a coordination number of four then it's pretty straightforward.

If we take a look here, remember our coordination numbers that are possible are two, four and six at least in terms of this level of Gen. Cam. When we have a coordination of two, that means we have two ligands or ligands attached to my metal cation. Here we have an example of a complex ion that's formed. Its geometry would be linear, and a memory tool to help us remember is 2 points in a straight line. 2 ligands or ligands help to make a linear align.

In terms of geometry, if you have a coordination number of six, that means you have 6 ligands or ligands attached to your metal cation. This would be octahedral. When you think about octahedral you can think of octopus. But an octopus has eight tentacles, not 6:00. So we just say 8 tentacles here -2 eyes equals 6 for coordination number.

Now here we finally get to coordination numbers of four with coordination numbers of four. Just say that if we have for the metal cation an electron configuration that ends with D10 then we are tetrahedral and if it end with D8 then you are square planar. If we come back U here tetrahedral we have a zinc here with four hydroxides. Tetrahedral is drawn in this configuration.

Remember we said if the metal cation has an electron configuration of ending with D10 then it is tetrahedral. So D10 10 is TENTE tetrahedral. They match together. If your metal cation ends with D8 then it is square planar or square planar. One way to remember this is square has four sides, a plane has two wings. 4 * 2 gives US8D8 right? So just use these little memory tools to help you remember when you have a coordination of two, four and six to figure out the correct geometry for your particular complex ion.