Question

Stability order of group IIIA (boron family) element is:
A) ${\text{G}}{{\text{a}}^ + } < {\text{I}}{{\text{n}}^ + } < {\text{T}}{{\text{l}}^ + }$
B) ${\text{G}}{{\text{a}}^{3 + }} > {\text{G}}{{\text{a}}^ + }$
C) Both (A) and (B)
D) None of the above

Answer 1

We know that ${\text{Ga}}$, ${\text{In}}$ and ${\text{Tl}}$ are the elements of group 13 of the periodic table. To solve this we must know the stability of $+ 3$ and $+ 1$ oxidation state of the elements of the group 13 of the periodic table. The stability of oxidation states is affected by the inert pair effect.

Complete step by step answer:
We know that ${\text{Ga}}$, ${\text{In}}$ and ${\text{Tl}}$ are the elements of group 13 of the periodic table. The electronic configuration of group 13 is $n{s^2}n{p^1}$.
The elements of group 13 in the order are boron $\left( {\text{B}} \right)$, aluminium $\left( {{\text{Al}}} \right)$, gallium $\left( {{\text{Ga}}} \right)$, indium $\left( {{\text{In}}} \right)$ and thallium $\left( {{\text{Tl}}} \right)$.
We know that oxidation state is the charge acquired by the species may be positive, negative or zero by gain or loss of electrons.
The maximum number of electrons the p-orbital can occupy are 6. From the electronic configuration, we can say that the most common oxidation state exhibited by the elements of group 13 must be $+ 3$.
In group 13 as we move down the group the $+ 1$ oxidation state becomes more and more common. On moving down the group, the $+ 3$ oxidation state becomes less stable.
The $+ 3$ oxidation state becomes less stable due to the inert pair effect. The tendency of the two electrons of the valence atomic orbital to remain unshared in compounds is known as inert pair effect.
The elements ${\text{Ga}}$, ${\text{In}}$ and ${\text{Tl}}$ show both $+ 1$ and $+ 3$ oxidation state. But the stability of $+ 1$ oxidation state increases down the group. Thus,
${\text{G}}{{\text{a}}^ + } < {\text{I}}{{\text{n}}^ + } < {\text{T}}{{\text{l}}^ + }$
The ${\text{G}}{{\text{a}}^{3 + }}$ is more stable than ${\text{G}}{{\text{a}}^ + }$. Thus,
${\text{G}}{{\text{a}}^{3 + }} > {\text{G}}{{\text{a}}^ + }$
Thus, stability order of group IIIA (boron family) element is ${\text{G}}{{\text{a}}^ + } < {\text{I}}{{\text{n}}^ + } < {\text{T}}{{\text{l}}^ + }$ and ${\text{G}}{{\text{a}}^{3 + }} > {\text{G}}{{\text{a}}^ + }$.

Thus, the correct option is (C) both (A) and (B).

Note: The tendency of the two electrons of the valence atomic orbital to remain unshared in compounds is known as inert pair effect. As a result, the inert pair of the ns electrons remains more tightly held by the nucleus. Thus, the inert pair of the ns electrons participates less in the formation of bond.