Problem 114 - A Complete Resource Book in Chemistry for JEE Main

Question

Consider the following substances: 1\. \(\mathrm{OF}_{2}\) 2\. \(\mathrm{Cl}_{2} \mathrm{O}\) 3\. \(\mathrm{Br}_{2}^{2} \mathrm{O}\) The correct sequence of \(X-O-X\) bond angle is (a) \(3>2>1\) (b) \(1>2>3\) (c) \(2>1>3\) (d) \(1>3>2\)

Step-by-Step Solution

Answer

(b) 1 > 2 > 3

Step 1: Recognize the molecular shape

First, it is essential to recognize the geometries of the given molecules. - **OF9** and **Cl2O** have bent geometries due to the presence of two lone pairs on the central atom (Oxygen). - **Br2O** is an uncommon and possibly flawed example, as typically dibromine monoxide is represented as Br1O. The standard reasoning will assume it resembles Cl2O in terms of bond angle determination.

Step 2: Consider the electronegativity impact

- Electronegativity affects bond angle; higher electronegativity leads to larger bond angles due to stronger repulsion. - Fluorine (2OF) is more electronegative than Chlorine (2ClO) which is more electronegative than Bromine (2BrO). This implies that 2OF should have the largest bond angle due to the strongest lone pair-bond pair repulsion.

Step 3: Compare lone pair-bond pair repulsion

Evaluate the steric and electronic effects due to lone pairs and high electronegativity. Based on typical VSEPR theory results: - Lone pairs repel more strongly than shared pairs of electrons (bond pairs). - A more electronegative terminal atom increases this repulsion further. Hence, the bond angle order is determined by comparing these interactions across the substances.

Step 4: Determine the bond angle order

From the above evaluations, we can establish: - 2OF corresponds to the largest bond angle due to the strong lone pair-bond pair repulsion from highly electronegative fluorine. - 2ClO and 2BrO will have smaller bond angles but follow the sequence with chlorine giving a larger angle than bromine. Thus, the bond angle sequence is: 1 (2OF) > 2 (2ClO) > 3 (2BrO).

Key Concepts

Molecular Geometry

Understanding molecular geometry is essential when discussing chemical structures, as it explains how atoms in a molecule are placed and connected. Molecular geometry explores the three-dimensional arrangement of atoms which directly impacts the molecule's properties and reactivity.

Molecules like - **OF2** - **Cl extsubscript{2}O**
Their geometries can be classified as being "bent" because they have two lone pairs attached to the central atom, oxygen, pushing the bonds into a bent shape. This shape results from electron pairs striving to be as far apart as possible to minimize repulsion, as described by the VSEPR theory.

Recognizing molecular shapes is the first step in predicting molecule behavior, which plays a fundamental role in deciphering chemical reactivity and interactions between different molecules. This can, in turn, influence everything from boiling points to solubility.

Electronegativity

Electronegativity is an element's ability to attract electrons towards itself in a chemical bond. It serves as a crucial factor in determining bond angles and molecular geometry.

For molecules like - OF extsubscript{2} - Cl extsubscript{2}O - Br extsubscript{2}O
Electronegativity differences between central and terminal atoms can significantly affect their bonding characteristics. Elements with higher electronegativity, such as fluorine, increase the lone pair-bond pair repulsion. This results in larger bond angles as electrons are more tightly held towards the more electronegative atom, causing more significant push on the bond electron pairs.

Understanding electronegativity not only helps predict molecular shapes but also indicates molecule polarity, which ultimately determines the molecule's interactions and reactions within chemical mixtures.

Bond Angles

Bond angles between atoms in a molecule are determined by the repulsion between electron pairs, as influenced by the VSEPR theory. VSEPR stands for Valence Shell Electron Pair Repulsion theory, and it states that electron pairs will arrange themselves as far apart as possible to reduce repulsion.

When examining substances such as - OF extsubscript{2} - Cl extsubscript{2}O - Br extsubscript{2}O Each molecule's bond angles hinges on their central atom's electron pairs' interactions.

For instance, the presence of lone pairs can considerably increase repulsion, forcing bond angles to widen to accommodate this additional repulsion. This effect is compounded by a substance's terminal atoms' electronegativity. More electronegative atoms, like fluorine, create stronger lone pair-bond pair repulsions, resulting in the widest bond angles among the given substances.

Accurately predicting bond angles can provide chemists insight into molecule behavior in various environments, including reactions and under specific conditions."}]}]}