You can determine the splittings of the orbitals from the symmetry of the complex. This is beyond A level I'm afraid, but you can think of it simply like this:
The easiest example is an octahedral complex. Let the z-axis run vertically (through two of the ligands). The dz2 orbital will point towards these ligands. This creates a favourable overlap, lowering the energy of this orbital. Similarly, the dxy and dx2−y2 orbitals will point towards the 4 ligands in the x-y plane, lowering the energy of these orbitals. This gives us three orbitals with low energy. The dxz and dyz orbitals do not point towards the ligands and are thus higher in energy.
You can determine the splittings of the orbitals from the symmetry of the complex. This is beyond A level I'm afraid, but you can think of it simply like this:
The easiest example is an octahedral complex. Let the z-axis run vertically (through two of the ligands). The dz2 orbital will point towards these ligands. This creates a favourable overlap, lowering the energy of this orbital. Similarly, the dxy and dx2−y2 orbitals will point towards the 4 ligands in the x-y plane, lowering the energy of these orbitals. This gives us three orbitals with low energy. The dxz and dyz orbitals do not point towards the ligands and are thus higher in energy.
I was under the impression that in an octahedral complex the ligands orient to be between the axes in order to minimise repulsions from the dxy, dxz and dyz orbitals.
This lowers their energy in comparison to the d(x2-y2) and dz2, which (lying along the axes as they do) are relatively higher in energy due to repulsion effects.
You can determine the splittings of the orbitals from the symmetry of the complex. This is beyond A level I'm afraid, but you can think of it simply like this:
The easiest example is an octahedral complex. Let the z-axis run vertically (through two of the ligands). The dz2 orbital will point towards these ligands. This creates a favourable overlap, lowering the energy of this orbital. Similarly, the dxy and dx2−y2 orbitals will point towards the 4 ligands in the x-y plane, lowering the energy of these orbitals. This gives us three orbitals with low energy. The dxz and dyz orbitals do not point towards the ligands and are thus higher in energy.
Haven't you got that a little bit wrong?
The d orbitals are all raised in energy as the interaction between the ligand orbitals and the d orbitals is a destabilising one.
In an octahedral complex, the z^2 and x^2-y^2 (eg set) are both raised in energy more than the others (xy, xz and yz - the t2g set). This is because if you consider the ligands to lie on each of the 3 axes, the eg set point straight at the ligands and are hence raised in energy, and the t2g set point between the ligands and are not raised in energy as much. You can also tell that the orbitals are split in this fashion by looking at the symmetry tables for the Oh point group. The way you described it doesn't give you the orbital degeneracies in the right way.
The d orbitals are all raised in energy as the interaction between the ligand orbitals and the d orbitals is a destabilising one.
In an octahedral complex, the z^2 and x^2-y^2 (eg set) are both raised in energy more than the others (xy, xz and yz - the t2g set). This is because if you consider the ligands to lie on each of the 3 axes, the eg set point straight at the ligands and are hence raised in energy, and the t2g set point between the ligands and are not raised in energy as much. You can also tell that the orbitals are split in this fashion by looking at the symmetry tables for the Oh point group. The way you described it doesn't give you the orbital degeneracies in the right way.
You're right... As far as I understand things.
Yep silly me, I tried to do this without resorting to the character tables and it shows how much you can confuse your self!