ChemistryCode 9701
Colour of complexes
What this topic asks you to be able to do
- define the terms degenerate and non-degenerate d orbitals, and apply both terms correctly
- outline how degenerate d orbitals split into two sets of non-degenerate d orbitals at higher energy, and apply ΔE to: (a) octahedral complexes, where there are two higher-energy d orbitals and three lower-energy ones (b) tetrahedral complexes, where three d orbitals lie higher and two lie lower
- explain why transition elements form coloured compounds, linking this to the frequency of the light absorbed when an electron is promoted from one non-degenerate d orbital to another
- describe qualitatively how changing the ligand alters ΔE, and so the frequency of light absorbed and the complementary colour seen
- use the complexes that copper(II) and cobalt(II) ions form with water and ammonia molecules and with hydroxide and chloride ions to illustrate how ligand exchange changes the observed colour