Chemistry – The Periodic Table - Transition elements | e-Consult

Transition metal compounds often exhibit vibrant colours due to the presence of d-d electronic transitions. In a transition metal complex, the metal ion has unpaired electrons in its d orbitals. These unpaired electrons can absorb light of specific wavelengths when an electron transitions between different d orbitals. The wavelengths of light absorbed correspond to the colour we observe. The colour of a compound depends on the energy difference between the d orbitals and the nature of the ligands surrounding the metal ion. Different ligands cause different energy differences, leading to different colours.

Examples:

• [Fe(CN)₆]^3-: This complex is deep purple in colour. The d-d transition involves the movement of electrons between the d orbitals, which absorb light in the yellow-green region of the visible spectrum, resulting in the absorption of the complementary colour, purple.
• Cupric chloride (CuCl₂): This compound is typically blue. The blue colour arises from the d-d transition involving the d orbitals of the Cu²⁺ ion.