Question

Give an example of a colourless ion.

Answer 1

Ions:-

• Ions are chemically charged particles, which are formed either by losing electrons or by gaining electrons.
• Ions which are formed by losing electrons are called cations(+ve).
• Ions which are formed by gaining electrons are called anions(-ve)
• Examples of cations are: ${\mathrm{Sc}}^{3+},{\mathrm{Na}}^{+}$and Examples of Anions are: ${\mathrm{Cl}}^{-},{{\mathrm{NO}}_3}^{-}$.

Scandium ion$\left({\mathrm{Sc}}^{3+}\right)$is colourless:-

• The electronic configuration of scandium is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{1}4{\mathrm{s}}^2$.
• After losing 3 electrons, the electronic configuration of ${\mathrm{Sc}}^{3+}$is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^6$.
• Hence we can see that it has no unpaired electrons, and due $\mathrm{d}-\mathrm{d}$transition does not take place.
• As a result, ${\mathrm{Sc}}^{3+}$is colourless.

Therefore, an example of an ion which is colourless is ${\mathrm{Sc}}^{3+}$.