`[Ti (H_2O)_6]^(3+)` is coloured while `[Sc(H_2O)_6]^(3+)` is colourless. Explain.

Explanation

In `[Ti(H_2O)_6]^(3+), Ti(III)` is coloured because it has one unpaired 3d - electron. It absorbs energy at 5000Å from visible regions. This energy excites the electron from `t_(2g)` to `e_g` . Ti (III) absorbs green and yellow colour and emits blue and red colour. So that `[Ti(H_2O)_6]^(3+)` appears purple in colour.

On the other hand `[Sc(H_2O)_6]^(3+)` is coloureless, because it does have unpaired electron.