Question

Compounds of ${\mathbf{Sc}}^{\mathbf{3}\mathbf{+}}$are not colored, but those of ${\mathbf{Ti}}^{\mathbf{3}\mathbf{+}}$and role="math" localid="1664042982323" ${\mathbf{V}}^{\mathbf{3}\mathbf{+}}$are. Why?

Short answer

${\mathrm{Sc}}^{3+}$is colourless. But ${\mathrm{Ti}}^{3+}$and ${\mathrm{V}}^{3+}$are coloured.

Step-by-step solution

Step:1

The transition metal ions which have completely filled d orbital (d¹⁰) are colourless and those which have completely empty d orbital (d⁰) are colourless since d-d transitions can’t take place in such ions.

${\mathrm{Sc}}^{3+}$has 3d⁰ electronic configuration so it is colourless.

Step:2

But ${\mathrm{Ti}}^{3+}$has the electronic configuration 3d¹, so it is purple colour and ${\mathrm{V}}^{3+}$has 3d² electronic configuration, so it is green colour.