CIE A Level Chemistry

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6.2.7 Degenerate & non-Degenerate d Orbitals

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Define Degenerate & non-Degenerate d Orbitals

  • 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

Chemistry of Transition Elements - Degenerate and Non-Degenerate Orbitals, downloadable AS & A Level Chemistry revision notes

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

Degenerate d Orbital Splitting

  • 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 3dyz, 3dxz, and 3dxy orbitals
  • This is because the 3dx2-y2 and 3dz2 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 3dx2-y2 and 3dz2 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 3dx2-y2 and 3dz2 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

Chemistry of Transition Elements - Splitting in octahedral complex, downloadable AS & A Level Chemistry revision notes

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 3dyz, 3dxz, and 3dxy orbitals of the central metal ion
  • Now, the 3dx2-y2 and 3dz2 orbitals lie between the metal-ligand bonds
  • Therefore, there is less repulsion with the 3dx2-y2 and 3dz2 orbitals
  • When the d orbitals split this time, the 3dx2-y2 and 3dz2 orbitals are at lower and more stable energy level than the other three

Chemistry of Transition Elements - Splitting in tetrahedral complex, downloadable AS & A Level Chemistry revision notes

Splitting of 3d orbitals in a tetrahedral complex

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