Chemistry

Chemistry

Problem

The crystal field-splitting order for Cr3+\text{Cr}^{3+} cation in an octahedral field for ligands CH3COO−\text{CH}_3\text{COO}^-, NH3\text{NH}_3, H2O\text{H}_2\text{O}, CN−\text{CN}^- is: a. CH3COO−<H2O<NH3<CN−\text{CH}_3\text{COO}^- < \text{H}_2\text{O} < \text{NH}_3 < \text{CN}^- b. CH3COO−<NH3<H2O<CN−\text{CH}_3\text{COO}^- < \text{NH}_3 < \text{H}_2\text{O} < \text{CN}^- c. H2O<CH3COO−<NH3<CN−\text{H}_2\text{O} < \text{CH}_3\text{COO}^- < \text{NH}_3 < \text{CN}^- d. NH3<CH3COO−<H2O<CN−\text{NH}_3 < \text{CH}_3\text{COO}^- < \text{H}_2\text{O} < \text{CN}^-
Intuitive explanation

Crystal field splitting depends on how strongly each ligand polarizes the d-orbitals—this is measured by the spectrochemical series, which ranks ligands by their ability to cause dd-orbital splitting. Strong-field ligands like CN−\text{CN}^- create large gaps between t2gt_{2g} and ege_g orbitals, while weak-field ligands like H2O\text{H}_2\text{O} create smaller gaps. The key is memorizing (or reasoning through) where common ligands fall: π\pi-acceptors like CN−\text{CN}^- rank highest, ammonia is moderate, water is weak, and carboxylate is among the weakest.

Intuitive explanation

Crystal field splitting depends on how strongly each ligand polarizes the d-orbitals—this is measured by the spectrochemical series, which ranks ligands by their ability to cause dd-orbital splitting. Strong-field ligands like CN−\text{CN}^- create large gaps between t2gt_{2g} and ege_g orbitals, while weak-field ligands like H2O\text{H}_2\text{O} create smaller gaps. The key is memorizing (or reasoning through) where common ligands fall: π\pi-acceptors like CN−\text{CN}^- rank highest, ammonia is moderate, water is weak, and carboxylate is among the weakest.

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