Question

Explain why:
(i) Transition elements form coloured compounds. 
(ii) Interhalogen compounds are more reactive than their constituent elements.
(iii) Cu⁺ is diamagnetic but Cu²⁺ is paramagnetic. (Z = 29)

Answer 1

(i) Transition metal ions generally possess one or more unpaired electrons. By absorbing a requisite amount of energy from visible light, the unpaired electrons present in the lower energy d-orbital get promoted to high energy d-orbitals. This is called a d-d transition. The energy involved in the d-d transition is very small and such radiations are present within the visible region of light. Transition metal ions absorb such radiations from visible light and remaining wavelengths present in the visible region get transmitted and this imparts colour.
(ii) Interhalogen compounds are more reactive than their constituent elements because X-Y bonds present between two different halogens in them are weaker than X-X or Y-Y bonds.
(iii) Cu⁺ is diamagnetic because it has no impaired electrons in its core.