Transition metals form colored compounds because of the d-electrons and their interaction with light. Here’s a explanation:
1. Cause of color
- In a free metal ion, the d-orbitals have the same energy.
- When ligands form a complex, the d-orbitals split into different energy levels (crystal field splitting).
- Electrons in lower-energy d-orbitals can jump to higher-energy d-orbitals by absorbing light.
2. Light absorption
- The energy absorbed corresponds to certain wavelengths of visible light.
- The remaining light that is reflected or transmitted is what we see as the color of the compound.
3. Factors affecting color
- Type of metal: Different metals have different d-orbital energies.
- Oxidation state: Higher or lower charge changes orbital energies.
- Type of ligand: Strong-field ligands increase splitting → change the color.
- Geometry of the complex: Octahedral, tetrahedral, or square planar arrangements affect splitting.
In short:
Transition metal compounds are colored because d-electrons absorb certain wavelengths of light to jump between split d-orbitals, and the remaining light gives the compound its visible color.