Colour of Ions and Compounds of d-Block Elements

Most of the compounds of d-block elements are coloured or they give coloured solution when dissolved in water. This property of transition elements is in marked contrast to that of the s- and p-block elements, which often yield white compounds. In transition metal compounds colour is generally associated with incomplete (n-1)d subshell of the transition metal.

When white light, which has colored constituents, interacts with a substance, a part of it is absorbed by the substance. For example, if red portion of white light is absorbed by a substance, it would appear blue (the complementary colour of red). This is observed in case of copper sulphate solution. Since most compounds of transition elements are coloured, there must be energy transition, which can absorb some of the energy of the visible light. The colour of transition metal ions containing unpaired electrons is attributed to electronic transitions from one energy level to another in the d-subshell.

• Ti³⁺: Violet
• V³⁺: Blue
• V²⁺: Violet
• Cr³⁺: Green
• Mn³⁺: Violet
• Fe³⁺: Yellow/colorless
• Mn²⁺: Yellow/colorless
• Fe²⁺: Pale green
• Co²⁺: Pink
• Ni²⁺: Green
• Cu²⁺: Blue