CBSE Class 12 · 2005 · Delhi · Coordination CompoundsShort Answer

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Draw a sketch to show the splitting of d-orbitals in an octahedral crystal field. State, for a d⁶ ion, how the actual configuration of the split d-orbitals in an octahedral crystal field is decided by the relative values of Δ

_{0}

and P.

Solution

In an octahedral field the five degenerate d-orbitals split: the three t

_{2 g}

orbitals (d

_{x y}

, d

_{y z}

, d

_{z x}

, pointing between ligands) drop by 0.4Δ

_{0}

, while the two e

_{g}

orbitals (d

_{x^{2} - y^{2}}

, d

_{z^{2}}

, pointing at ligands) rise by 0.6Δ

_{0}

— energy gap Δ

_{0}

.
Sketch: two levels — t

_{2 g}

(lower, 3 orbitals) and e

_{g}

(upper, 2 orbitals), separated by Δ

_{0}

.
For a d

^{6}

ion the fourth-to-sixth electrons face a choice between pairing (cost P) and occupying e

_{g}

(cost Δ

_{0}

):
Δ

_{0}

> P (strong field): electrons pair in t

_{2 g}

→ \textbf{t

_{2 g}^{6}

_{g}^{0}

} (low-spin).
Δ

_{0}

< P (weak field): electrons enter e

_{g}

→ \textbf{t

_{2 g}^{4}

_{g}^{2}

} (high-spin).

CBSE Class 12 Board · 2005 · Delhi · Subjective

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CBSE Class 12 · 2005 · Delhi · Coordination CompoundsShort Answer

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