Question

Explain why [cu(nh3)4]2+ ion is colured but[cut(cn)4]3- ion is colurless

Answer 1

In Cu(NH3)4+ the ion is Cu+1 which has electronic configuration as 4s0 3d10. Therefore these 10 electrons in the d orbital completely fills eg and t2g orbitals (note: 10electrons in d orbital will form colourless compound)…hence the compound formed by Cu+1 is colourless.

Whereas the Cu+2 ion in Cu(NH3)+2 has electronic configuration as 4s0 3d9. Therefore these 9 electrons in the d orbital fills the t2g orbital completely but partially fills the eg orbital. Hence the compound formed by Cu+2 is coloured compound