Crystal field splitting energy is the energy difference between two sets of d-orbitals of a transition metal ion when ligands approach and form a coordination complex.

Simple class 12 definition

For Class 12 (NCERT level), you can write:

  • In a free transition metal ion, all five d-orbitals have the same energy (they are degenerate).
  • When ligands come close and create an electrostatic field (crystal field), these d-orbitals no longer remain equal in energy and split into two groups of different energies.
  • The energy gap between the higher-energy set and the lower-energy set of d-orbitals is called crystal field splitting energy , denoted by Δ (Δ₀ for octahedral, Δₜ for tetrahedral).

A Class 12–style exam sentence:

Crystal field splitting energy (Δ) is the energy difference between the higher and lower sets of d-orbitals of a transition metal ion when its degenerate d-orbitals split under the influence of surrounding ligands in a coordination complex.

Key points to remember

  • Symbol:
    • Octahedral complexes: Δ₀ or 10Dq.
* Tetrahedral complexes: Δₜ.
  • Origin:
    • Due to repulsion between electrons in ligands and electrons in metal d-orbitals → different orientations of d-orbitals feel different repulsions → energy levels split.
  • Importance (often asked in exams):
    • Decides color of complex: visible light absorbed corresponds to Δ (Δ = hν).
* Decides **magnetic behaviour** : high spin vs low spin depends on size of Δ compared to pairing energy.

* Helps compare **weak-field** and **strong-field** ligands (spectrochemical series idea).

Octahedral vs tetrahedral (quick view)

[1] [1] [7][9][1] [5][1] [5][1] [5][1] [1][5] [5][1]
Type of complex Lower- energy set Higher-energy set Symbol for splitting Relative size of Δ
Octahedral t₂g (dxy, dxz, dyz) eg (dz², dx²−y²) Δ₀ or 10Dq Larger; reference value
Tetrahedral e (dz², dx²−y²) t₂ (dxy, dxz, dyz) Δₜ Smaller; roughly about 2/3 or less of Δ₀

How to phrase in 1–line for exams

  • “Crystal field splitting energy is the energy difference (Δ) between the sets of d-orbitals of a transition metal ion produced when ligands cause the degenerate d-orbitals to split in a coordination complex.”

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