Problem 46 - A Complete Resource Book in Chemistry for JEE Main

Question

What is the number of sigma and pi bonds present in a molecule of sulphuric acid? (a) \(6 \sigma, 2 \pi\) (b) \(6 \sigma, 0 \pi\) (c) \(2 \sigma, 4 \pi\) (d) \(2 \sigma, 2 \pi\)

Step-by-Step Solution

Answer

The correct answer is (a) 6 σ, 2 π.

Step 1: Understand the Structure of Sulphuric Acid

Sulphuric acid has the chemical formula \( H_2SO_4 \). It comprises two hydroxyl (OH) groups and two oxygen atoms double-bonded to the sulfur atom.

Step 2: Identify Sigma Bonds

In a molecule, a sigma bond \( (\sigma) \) is the single bond connecting two atoms. In sulphuric acid, we have:- One sigma bond between each of the two hydrogens and two oxygens, totaling 2 sigma bonds.- One sigma bond between each of the two oxygen atoms in the hydroxyl groups and the sulfur atom, totaling 2 sigma bonds.- One sigma bond between each of the double-bonded oxygens and sulfur, totaling 2 sigma bonds.This results in a total of 6 sigma bonds.

Step 3: Identify Pi Bonds

A pi bond \( (\pi) \) is the second bond in a double bond. In sulphuric acid, the S=O double bonds each contain one sigma and one pi bond. As there are two S=O double bonds, there are 2 pi bonds in total.

Step 4: Count and Compare

From the above analysis, sulphuric acid has 6 sigma bonds and 2 pi bonds. Compare these results with the given options.

Key Concepts

Sigma Bonds

Sigma bonds, represented by \( \sigma \), are the primary type of bond that occurs between atoms. These bonds are formed when two orbitals overlap head-to-head, allowing electrons to be shared along the internuclear axis. They are strong, and typically located in all single bonds in a molecule. In the context of sulphuric acid \( H_2SO_4 \), sigma bonds are the backbone of its structure. For instance:

• Each hydrogen atom forms a sigma bond with the oxygen atoms in the hydroxyl groups (OH).
• The sulfur atom forms sigma bonds with two oxygen atoms directly double-bonded to it.
• Each oxygen in the OH group also forms a sigma bond with the sulfur atom.

With this understanding, sulphuric acid contains a total of 6 sigma bonds, ensuring a strong and stable configuration.

Pi Bonds

Pi bonds, symbolized as \( \pi \), are essential for understanding the nature of double and triple bonds in molecules. They are formed when the side-by-side overlap of orbitals takes place, above and below the plane of the nuclei. Pi bonds provide additional bonding that cannot be achieved through sigma bonds alone. They are weaker than sigma bonds but are crucial for creating the rigidity and multiple bonding characteristics in molecules like sulphuric acid.

• In sulfuric acid, each sulfur-to-oxygen double bond consists of one sigma and one pi bond.
• The pi bonds contribute to double bonds, adding stability and influencing the molecule's reactive properties.
Recognizing the presence of 2 pi bonds in sulphuric acid gives insight into its molecular shape and behavior.

Sulphuric Acid Structure

The chemical structure of sulphuric acid \( H_2SO_4 \) consists of multiple layers of bonding interactions that define its properties and reactivity. At the center of the molecule is a sulfur atom bonded to four oxygen atoms, two of which form double bonds, while the others are part of hydroxyl groups.

• The sulfur atom is the heart of the molecule, holding together various oxygen atoms through sigma and pi interactions.
• Two oxygen atoms are connected directly via sigma and pi bonds, forming S=O double bonds.
• The remaining oxygen atoms are part of hydroxyl groups and are bonded via single sigma bonds to both sulfur and hydrogen atoms.

This configuration not only defines the bonding but also influences the molecule's acidity, making sulphuric acid a powerful and highly corrosive agent in chemical reactions.