Here we can say that the crystal field splitting energy or Δ of the octahedral complexes depends on the ligand. Now, depending on the type of ligand attached to our metal cation, it can influence the magnitude and size of our crystal field splitting energy. Here we're going to say that strong field ligands attached to metal cations result in large crystal field splitting energy. So if we take a look here, we'd see that the distance is between our lower orbitals to our higher level orbitals. There's a bigger gap. That's a larger Δ.
Next, we'd say that weak field ligands typically have result in a smaller or small crystal field splitting energy. Here our Δ is much smaller and we say in these cases we'd have orbitals that are more degenerate, similar or same energy. Now here when we're talking about strong field versus weak field ligands, we have these ones in particular, these are the ones that you need to commit to memory. So over here we have our large Δ. These are the largest Δ with cyanide being at the very end. And over here we have our smallest Δ with iodine.
Over here on this end. Now our strong field ligands, how do we memorize the order of them? Well, all you have to recall is this memory tool and it is that Larry cannot enter the neighborhood. So Larry Large can CN Cyanide, no deals with nitrate. Enter is ethylenediamine the neighborhood. So here we have ammonia. These represent our strong field ligands and then our weak field ligands we started with water and then you might notice that the rest of the ions are halogens.
If you look at group 7A on the periodic table, you'll see you have fluorine, chlorine, bromine and iodine. So this is listed as we go down group 7A, so fluoride, chloride, bromide and iodide. So just remember that Larry cannot enter the neighborhood. Then for the weak we have water and then look at group 7A flooring down to iodine. This gives us the order from strong field ligands to weak field ligands.
