Question

Which of the following shapes of $S{F_4}$ is more stable and why?

(A) (i) Lone pair at axial position is stable
(B) (ii) Lone pair at equatorial position is stable
(C) Both are equally stable due to lp-lp repulsion
(D) Both are unstable since $S{F_4}$ has tetrahedral shape

Answer 1

Repulsive forces between bond pairs and lone pairs have influence on the shapes of the molecules. Lone pair-lone pair repulsions are the most strong repulsions of these types of repulsions.

Complete step by step solution:
In both the shapes of $S{F_4}$, we can say that the only difference is that lone pair is at axial position and in another shape, the lone pair of sulphur atoms is in equatorial position. So, let’s compare them two and their stability.
- In (i), lone pair is at axial position and hence, it has three fluorine atoms in the vicinity that give lone pair-bond pair repulsion. While in case of (ii), the lone pair of sulphur is having only two fluorine atoms in the vicinity and hence it will have two lone pair-bond pair repulsions with fluorine atoms.
- The rest of the repulsive factors are almost the same in both the molecules.
- So, based on this discussion, we can conclude that structure (ii) will be more stable because there is less repulsion for sulphur lone pair in comparison with structure (i).

Thus correct answer is (B) (ii) Lone pair at equatorial position is stable

Additional Information:
- If the atoms that are situated at a position that is in the plane that involves most number of atoms in that molecule, then the positions are called equatorial positions and axial positions are perpendicular to the equatorial ones.

Note: Do not consider that $S{F_4}$ has a tetrahedral shape because it has 4 atoms binded with it, also take the lone pair of the central atom into consideration which also has higher repulsion towards other bond pairs. Do not consider that the amount of repulsion will be the same for all the compounds that have the same atoms; the arrangement of these atoms in space decides the repulsive factors.