Question

Why do the d-block elements form coloured compounds?

Answer 1

1. Compounds (or ions) of many d-block elements or transition metals are coloured. This is due to the presence of one or more unpaired electrons in (n - 1) d orbital. The transition metals have incompletely filled (n  - 1) d orbital.
2. The energy required to promote one or more electrons within the d orbitals involving d-d transitions is very low
3. Therefore transition metal ions absorb the radiation in the visible region and appear coloured.
4. Colour of ions of d block elements depends on the number of unpaired electrons in (n  - 1) d orbital. The ions having equal number of unpaired electrons have similar colour.