Formation of Coloured Ions
The formation of coloured ions in transition metals is primarily due to the excitation of electrons from lower-energy d orbitals to higher-energy d orbitals. This process occurs when light is absorbed, with the energy of the absorbed light corresponding to a specific frequency, typically within the visible spectrum.
The observed colour of a transition metal solution corresponds to the complementary colour of the light absorbed. For instance, if a particular ion absorbs light in the red region of the spectrum, it will appear green to the observer, as green is the complementary colour of red.
In aqueous solutions, where water serves as a ligand, various transition metal ions exhibit distinct colours. The nature of the ligand plays a crucial role in determining the specific energy levels of the d orbitals and thus affects the energy (and frequency) of light absorbed. This interaction leads to a variety of colours for different metal ions and their complexes. For instance, ions like
- (Table of colours included in the original text)
Understanding the formation of coloured ions has significant implications in both analytical chemistry, where the colours can indicate concentrations, and in other fields like art, where they are used in pigments.