Animated Solution for Chemistry - s and p-Block Elements: The number of bonds between sulphur and oxygen atoms in ${\text{S}}_2{\text{O}}_8^{2-}$ and the number of bonds between sulphur and sulphur atoms in rhombic sulphur, respectively, are

Counting Bonds in $S_2{O}_8^{2-}$ and $S_8$

Chemical bonding is the language through which atoms communicate, and drawing Lewis structures is how we read that language. In this problem, we are tasked with a simple yet highly conceptual exercise: counting specific types of bonds in two fascinating sulphur-containing species.

Let's break down the structures of the peroxydisulphate ion ($S_2{O}_8^{2-}$) and rhombic sulphur ($S_8$) to find our answer.

The peroxydisulphate ion, often recognized as the anion of Marshall's acid ($H_2{S}_2{O}_8$), has a unique structural feature that often trips up students: a peroxide linkage ($-O-O-$).

If we draw the structure, we place the two sulphur atoms on either side of this peroxide bridge. Each sulphur atom is then bonded to three other oxygen atoms to complete its valency (expanding its octet to minimize formal charge). Specifically, each sulphur forms two double bonds ($S=O$) and one single bond ($S-O^{-}$) with terminal oxygen atoms, plus the single bond connecting it to the central peroxide oxygen.

When the question asks for the "number of bonds between sulphur and oxygen atoms," it is asking for the total number of $S-O$ linkages (regardless of whether they are single or double bonds).

Let's count them: - For the first Sulphur atom: $4$ linkages to Oxygen. - For the second Sulphur atom: $4$ linkages to Oxygen.

Total $S-O$ bonds = $4+4=8$.

Next, we turn our attention to elemental sulphur. At room temperature, the most stable allotrope of sulphur is rhombic sulphur, which exists as discrete $S_8$ molecules.

Due to the bond angles and lone pair repulsions, the $S_8$ molecule does not form a flat ring. Instead, it puckers into a highly symmetrical crown structure.

Imagine eight sulphur atoms holding hands in a circle. Every atom is bonded to exactly two neighbors. In any simple closed ring of $n$ atoms, there are exactly $n$ bonds connecting them.

Therefore, in the $S_8$ ring, the total number of $S-S$ bonds is simply $8$.

By carefully analyzing the structures, we have found our counts: - Number of $S-O$ bonds in $S_2{O}_8^{2-}$ = $8$ - Number of $S-S$ bonds in $S_8$ = $8$

This perfectly matches option (b).

Pro Tip: Whenever you encounter oxyacids of sulphur or phosphorus, always draw the structure first. Relying purely on molecular formulas can lead to silly mistakes, especially when peroxide linkages or direct metal-metal bonds are involved!