• There are?five d orbitals?in an?isolated?transition element atom or ion
  • An isolated transition element is one that is not bonded to anything else
• These d orbitals are all at the same energy level (they are equal in energy) and are therefore said to be?degenerate orbitals
• When ligands are attached, the transition element ion is?not?isolated anymore
• The dative bonding from the ligands causes the five d orbitals to split into two sets
• These two sets are?not?equal in energy and are described as being?non-degenerate orbitals

Upon binding to ligands, the d orbitals of the transition element ion split into two non-degenerate sets of orbitals

• An isolated transition element has five?degenerate?3d orbitals
• Upon dative covalently bonding to a ligand, these d orbitals are split into two sets of non-degenerate orbitals

Splitting in octahedral complexes

• In?octahedral?complexes, there are six ligands arranged around the?central metal ion
• The lone pairs of the ligands repel the electrons in the x²-y²?and z²?orbitals of the metal ion?more than?they repel the electrons in the 3d_yz, 3d_xz,?and 3d_xy?orbitals
• This is because the 3d_x2-y2?and 3d_z2?orbitals line up with the dative bonds in the complex’s octahedral shape
• This is because the ligands are attached to or approaching the central metal ion along the x, y and z axes, and the 3d_x2-y2?and 3d_z2?orbitals have lobes along these axes
• The electrons in these two orbitals are closer to the bonding electrons, so there is more?repulsion
• This means that when the d orbitals split, the 3d_x2-y2?and 3d_z2?orbitals are at a slightly higher energy level than the other three
• The difference in energy between the?non-degenerate?d orbitals is labelled as?ΔE

Splitting of 3d orbitals in an octahedral complex

Splitting in tetrahedral complexes

• In?tetrahedral?complexes, there are four ligands arranged around the central metal ion
• The bonding pair of electrons from the four ligands now line up with the 3d_yz, 3d_xz,?and 3d_xy?orbitals of the central metal ion
• Now, the 3d_x2-y2?and 3d_z2?orbitals lie between the metal-ligand bonds
• Therefore, there is less repulsion with the 3d_x2-y2?and 3d_z2?orbitals
• When the d orbitals split this time, the 3d_x2-y2?and 3d_z2?orbitals are at?lower?and?more?stable?energy level than the other three

Splitting of 3d orbitals in a tetrahedral complex