Animated Solution for Chemistry - s and p-Block Elements: The oxoacid of sulphur that does not contain bond between sulphur atoms is

When we dive into the chemistry of p-block elements, sulphur stands out because of its remarkable ability to form a wide variety of oxoacids. These molecules are not just random collections of atoms; their structures follow logical patterns based on oxidation states and bonding rules. In this problem, we are tasked with finding the oxoacid that lacks a direct bond between two sulphur atoms.

To solve this, we must visualize the chemical structures of the given options. Let's break them down one by one.

1. Thiosulphuric Acid ($H_2{S}_2{O}_3$) The prefix "thio-" in chemistry usually means that an oxygen atom has been replaced by a sulphur atom. If you take standard sulphuric acid ($H_{2}S{O}_4$) and replace one of the double-bonded terminal oxygen atoms with a sulphur atom, you get thiosulphuric acid. Because of this substitution, the central sulphur atom is double-bonded to another sulphur atom ($S=S$). Thus, it clearly contains a bond between sulphur atoms.

2. Dithionous Acid ($H_2{S}_2{O}_4$) Dithionous acid is a lower oxidation state oxoacid. In its structure, the two sulphur atoms are directly connected to each other via a single covalent bond ($S-S$). Each sulphur is also bonded to one hydroxyl group ($-OH$) and double-bonded to one oxygen atom. Therefore, this molecule also contains an $S-S$ bond.

3. Tetrathionic Acid ($H_2{S}_4{O}_6$) The name "tetra" gives us a massive hint—it contains four sulphur atoms! In tetrathionic acid, these four sulphur atoms form a continuous chain right in the center of the molecule ($S-S-S-S$). The terminal sulphur atoms are bonded to oxygen atoms. With a chain of four sulphur atoms, it definitely has multiple $S-S$ bonds.

Pyrosulphuric Acid

4. Pyrosulphuric Acid ($H_2{S}_2{O}_7$) Also known as oleum, pyrosulphuric acid is formed when sulphur trioxide ($S{O}_3$) is dissolved in concentrated sulphuric acid ($H_{2}S{O}_4$). The prefix "pyro-" often indicates that the molecule is formed by the condensation of two acid molecules with the loss of a water molecule ($H_{2}O$).

When two $H_{2}S{O}_4$ molecules condense, they share an oxygen atom, creating an oxygen bridge between the two central sulphur atoms. This forms an $S-O-S$ linkage. Because the oxygen atom sits right between them, there is no direct $S-S$ bond in pyrosulphuric acid.

By carefully drawing and analyzing the structures, we can confidently conclude that pyrosulphuric acid ($H_2{S}_2{O}_7$) is the only oxoacid among the choices that does not contain a direct bond between sulphur atoms. Understanding the nomenclature prefixes like "thio-" and "pyro-" can often help you deduce the structure without having to memorize every single molecule!