1.

Most of the transition metal compounds are coloured in solid & aqueous states. Why?

Answer»

This is due to the presence of unpaired electrons in (n-1)d orbitals i.e. d1 to d9 . In presence of ligands, the degeneracy of d orbitals is lost & it splits up into two sets of orbitals t2g& eg (according to CF theory). When electrons of lower energy state of d orbitals absorb energy of white light & jump to higher d orbitals, the remaining energy emitted is the colour of the compound. 

Example: If an ion of transition metal absorbs light of wavelength 4500Å(blue), the complementary colour emitted is yellow. [d1& d10 are colourless or white].



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