Question

Discuss the pattern of variation in the oxidation states of
$BtoTl$

$CtoPb$

Answer 1

The electric configuration of group 13 elements is $n{s}^{2}n{p}^1$ . Therefore, the most common oxidation state exhibited by them should be +3. However, it is only boron and aluminium which practically show the +3 oxidation state. The remaining elements, i.e., Ga, In, Tl, show both the +1 and +3 oxidation states. On moving down the group, the +1 state becomes more stable. For example, Tl (+1) is more stable than Tl (+3). This is because of the inert pair effect. The two electrons present in the s-shell are strongly attracted by the nucleus and do not participate in bonding. This inert pair effect becomes more and more prominent on moving down the group. Hence, Ga (+1) is unstable, In (+1) is fairly stable, and Tl (+1) is very stable.
$\begin{array}{cc}Group13element& Oxidationstate\\ B& +3\\ Al& +3\\ Ga,In,Tl& +1,+3\end{array}$
The stability of the +3 oxidation state decreases on moving down the group.

The electronic configuration of group 14 elements is $n{s}^{2}n{p}^2$ . Therefore, the most common oxidation state exhibited by them should be +4. However, the +2 oxidation state becomes more and more common on moving down the group. C and Si mostly show the +4 state. On moving down the group, the higher oxidation state becomes less stable. This is because of the inert pair effect. Thus, although Ge, Sn, and Pb show both the +2 and + 4 states, the stability of the lower oxidation state increases and that of the higher oxidation state decreases on moving down the group.
$\begin{array}{cc}Group14element& Oxidationstate\\ c& +4\\ Si& +4\\ Ge,Sn,Pb& +2,+4\end{array}$

$\stackrel{stabilityof+2stateincreases}{\to }$
C Si Ge Sn Pb
$\underset{stabilityof+4statedecreases}{\overset{}{\to }}$