Question

Give reasons:

The transition metal ions such as Cu⁺, Ag⁺ and Sc³⁺ are colourless.

Answer 1

1. These ions either have completely empty or fully filled d-orbitals.
2. Cu⁺ and Ag⁺ have fully filled d-orbitals (like 3d¹⁰ for Cu⁺), so no d-d electronic transitions are possible.
3. Sc³⁺ has empty d-orbitals (3d⁰), so there is no electron available to be excited by visible light.
4. Colour in transition metal ions arises from d-d transitions between split d-orbitals by visible light absorption.
5. Without unpaired electrons and available vacant d-orbitals, no absorption of visible light occurs, making these ions colourless.

Thus, Cu⁺, Ag⁺ (d¹⁰), and Sc³⁺ (d⁰) ions remain colourless due to the absence of d-d transitions.