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Which transition metal ion forms a purple-coloured compound when combined with a ligand?

Option: 1

Iron (Fe)

Option: 2

Copper (Cu)

Option: 3

Chromium (Cr)

Option: 4

Cobalt (Co)

Answers (1)


When transition metal ions form complexes with ligands, the d-orbitals split into different energy levels due to the crystal field effect. The absorption of certain wavelengths of light by these complexes leads to the observation of colour. The splitting of d-orbitals determines the energy difference between them, which in turn determines the colour of the complex.

In the case of chromium, it forms coloured ions due to the presence of unpaired electrons in its d-orbitals. The energy difference between these orbitals corresponds to absorption in the visible light region, resulting in the observed colour. For example, when chromium forms a complex with a ligand, such as water, the hydrated chromium ion \left [ Cr\left ( H_{2}O \right )_{6} \right ]^{3+} exhibits a purple colour.


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