Question

Explain lanthanide contraction clearly and give reason why many compounds of transition elements remain coloured.

Hint:

Lanthanide contraction affects the properties of elements, including ionic radii and electronegativity.

Answer 1

Lanthanide Contraction: A gradual decrease in atomic and ionic radii across the lanthanide series due to poor shielding by 4f electrons. 

Reason for Colour: Transition elements have partially filled d-orbitals. When light falls on them, d-d transitions occur, absorbing certain wavelengths and reflecting others, giving them color.