Formation of Coloured Ions
- An electron from a lower energy d orbital is excited to a higherenergy d orbital, the energy of excitation corresponds to the frequencyof light absorbed.
- This frequency generally lies in the visible
- The colour of the transition metal ions is due to the presence of unpaired or incomplete d-orbitals.
- The absorption of visible light and hence coloured nature of the transition metal cations is due to the promotion of one or more unpaired d-electron from a lower to a higher level within the same d-subshell. This promotion requires small amount of energy available in the visible light.
- Sc3+, Ti4+, Cu+ and Zn2+ have either entirely empty or entirely filled 3d-orbital, i.e. they do not have any unpaired d-electron, and hence appear colourless.