Chapter 20, Problem 20.12QE

Interpretation Introduction

Interpretation:

The reason has to be given for the high stability of Thallium than Aluminium in $\text{+1}$ oxidation state.

Inert pair effect:

  The valence electronic configuration of Group 3A (13) elements is ${\text{ns}}^{\text{2}}{\text{np}}^{\text{1}}$.  They generally form oxidation state of $\text{+3}$ compounds, but heavier members of the family, especially Thallium $\left(\text{Tl}\right)$, also form oxidation state of $\text{+1}$ compounds.  The trend for the heavier members of the group to use only the $p$ valence electron(s) in forming compounds is general and is observed in Groups 4A and 5A as well.  This tendency for the heavier members of Groups 3A to 5A elements not to use the pair of valence $s$ electrons for bonding is called the inert pair effect.