Advantages of crystal field theory over valence bond theory
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The Crystal field theory considers ionic bond arising purely from electrostatic interaction between metal atom (positively charged) and ligands ( negatively charged). The transition metal ion is considered to be positive charge equal to its oxidation state. The central metal atom is surrounded by negatively charged ligands. The ligands were considered as point charges.
The energy of d orbitals remains degenerate (same energy) in the free transition metal ion . When ligand approach the metal ion, there arises attraction between the nucleus of the metal ion and the ligands. In the same time, there will be repulsion between the electrons present in the metal atom and the negative ends of the ligands. Due to this repulsion, the energy of the metal ion will no longer be degenerate. Consequently, the degeneracy is split.
The energy of egset greater than t2g set
The eg set consists of the dx2-y2 and dz2orbitals. The lobes of these orbitals point along the axes x, y and z.The lobes of t2g orbitals (dxy, dyz, dyz) point in between the axes. The energy of the eg orbital is high because the orbitals dx2-y2 and dz2 falls directly along the path of the incoming ligand . Therefore they experience great force of repulsion and have higher energy than t2g.
The energy of d orbitals remains degenerate (same energy) in the free transition metal ion . When ligand approach the metal ion, there arises attraction between the nucleus of the metal ion and the ligands. In the same time, there will be repulsion between the electrons present in the metal atom and the negative ends of the ligands. Due to this repulsion, the energy of the metal ion will no longer be degenerate. Consequently, the degeneracy is split.
The energy of egset greater than t2g set
The eg set consists of the dx2-y2 and dz2orbitals. The lobes of these orbitals point along the axes x, y and z.The lobes of t2g orbitals (dxy, dyz, dyz) point in between the axes. The energy of the eg orbital is high because the orbitals dx2-y2 and dz2 falls directly along the path of the incoming ligand . Therefore they experience great force of repulsion and have higher energy than t2g.
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