Question

Explain why:
Transition elements form coloured compounds.

Answer 1

Transition metal ions generally possess one or more unpaired electrons. When visible light falls on a transition metal compound or ion, the unpaired electrons present in the lower energe d-orbital get promoted to high energy d-orbitals, called d-d transition, due to the absorption of visible light. Since, the energy involved in d-d transition is quantised, only a definite wavelength gets absorbed, remaining wavelengths present in the visible region got transmitted. Therefore, transmitted light shows some colour complementary to the absorbed colour.