Question

In some of the reactions thallium resembles aluminium, whereas in others it resembles with the group I metals. Support this statement by giving some evidence.

Answer 1

Inert pair effect is the non - participation of the s -orbital electron due to which they remain unshared. Inert pair effect is also responsible for the oxidation state $\text{+1}$ of the heavy element of group 13, Alkali metals show an oxidation state of +1.

Complete answer:
-Thallium belongs to group 13 which can show both oxidation states i.e. +3 and +1.
-Also, aluminium has the oxidation state of +3 because according to the electronic configuration of aluminium i.e. $\text{1}{{\text{s}}^{2}}\text{ 2}{{\text{s}}^{2}}\text{ 2}{{\text{p}}^{6}}\text{ 3}{{\text{s}}^{2}}\text{ 3}{{\text{p}}^{1}}$ there are a total of 3 valence electron.
-That’s why thallium resembles aluminium. For example, in $\text{T}{{\text{l}}_{2}}{{\text{O}}_{3}},\text{ TlC}{{\text{l}}_{3}}$, etc thallium shows the oxidation state of
-Moreover, it also forms octahedral complexes just like aluminium.
-Thallium also shows the oxidation state of +1 some compounds just like metals.
For example, $\text{T}{{\text{l}}_{2}}\text{O},\text{ TlCl}$these compounds show a +1 oxidation state.
-+1 oxidation state occurs due to the inert pair effect.
-+1 oxidation state is stable than the +3 oxidation state due to the inert pair effect.
-Because according to the electronic configuration of thallium i.e. $\text{Xe 4}{{\text{f}}^{14}}\text{ 5}{{\text{d}}^{10}}\text{ 6}{{\text{s}}^{2}}\text{ 6}{{\text{p}}^{1}}$, the 2 electron that is present in the 6s-orbital do not participate in the bond formation because they are tightly held with each other due to more effective nuclear charge.
Therefore, thallium resembles both aluminium and group I metals.

Note: Thallium has a variety of oxidation which differs in compounds such as -5, -2, -1, +1, +2 and +3. Among them, the +1 oxidation state is the most stable. There are two allotropes of thallium i.e. α-thallium and β - thallium.