Problem 22 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The correct statement(s) about \(\mathrm{O}_{3}\) is(are)(a) \(\mathrm{O}-\mathrm{O}\) bond lengths are equal (b) Thermal decomposition of \(\mathrm{O}_{3}\) is endothermic(c) \(\mathrm{O}_{3}\) is diamagnetic in nature (d) \(\mathrm{O}_{3}\) has a bent structure

Step-by-Step Solution

Answer

(a), (b), (c), and (d) are all correct statements about \( \mathrm{O}_3 \).

Step 1: Understanding Ozone Structure

Ozone, or \( \mathrm{O}_3 \), has three oxygen atoms where one atom forms a single bond and another forms a double bond with the central atom. Resonance structures cause both \( \mathrm{O}-\mathrm{O} \) bonds to have an equal bond length due to bond delocalization.

Step 2: Determining Thermal Decomposition Nature

Thermal decomposition breaks down \( \mathrm{O}_3 \) into \( \mathrm{O}_2 \) and individual oxygen atoms. This process absorbs heat from the surroundings, making it an endothermic reaction.

Step 3: Magnetic Properties

\( \mathrm{O}_3 \) has all its electrons paired, therefore it is diamagnetic in nature, meaning it does not have unpaired electrons to react to magnetic fields.

Step 4: Analyzing Molecular Geometry

Ozone has a bent molecular shape due to the presence of lone pairs which repel the bonded electron pairs, resulting in a bond angle of about 117°.

Key Concepts

Molecular Geometry

The molecular geometry of ozone (\( \mathrm{O}_3 \)) plays a significant role in its chemical behavior and physical properties. In ozone, the central oxygen atom is bonded to two other oxygen atoms. It features a bent structure with a bond angle of approximately 117°. This is due to the lone pairs of electrons on the central atom which repel the bonded pairs, leading to a distortion from the linear arrangement.

The VSEPR (Valence Shell Electron Pair Repulsion) theory explains this geometry by stating that electron pairs will arrange themselves around a central atom to minimize repulsion. In ozone, this results in a non-linear, or bent, shape.

• The central oxygen is bonded through one single and one double bond.
• An existence of resonance changes the perception of these bonds but keeps the basic geometry the same."

The peculiar shape of ozone enhances its ability to absorb UV radiation, which is crucial for protecting Earth from harmful sun rays.

Resonance Structures

Resonance is a key concept to understand when examining ozone (\( \mathrm{O}_3 \)). This molecule can be represented by multiple Lewis structures, known as resonance structures. In these structures, while one oxygen atom is shown forming a double bond with the central oxygen, the other is forming a single bond. Resonance causes the electron delocalization in the bonds, leading to properties shared by both bonds equally.

Specifically in ozone, this delocalization means that both \( \mathrm{O}-\mathrm{O} \) bonds are equivalent in length and strength, despite appearing differently in individual resonance structures.

• Ozone has only two main resonance structures.
• These structures contribute equally to the final and more stable form of ozone.

This concept of resonance clarifies why the bonds have equal length even though classical depictions show a single and a double bond.

Magnetic Properties

Understanding the magnetic properties of ozone helps in defining its chemical behavior. Ozone is diamagnetic, which means it does not have unpaired electrons and therefore does not exhibit magnetism under normal circumstances. Each electron in ozone is paired with another in its molecular orbital, resulting in no net magnetic moment.

Diamagnetism is a characteristic of molecules where:

• All electrons are paired in orbitals.
• As a result, it weakly repels magnetic fields.

This property contrasts with paramagnetic substances, which have unpaired electrons that cause strong interactions with magnetic fields.

Thermal Decomposition

The process of thermal decomposition refers to the breakdown of a compound into simpler substances when heated. For ozone (\( \mathrm{O}_3 \)), thermal decomposition occurs when it is heated, resulting in the production of molecular oxygen (\( \mathrm{O}_2 \)) and a single oxygen atom (\( \mathrm{O} \)).

This reaction is endothermic, meaning it absorbs heat from its surroundings. This absorption occurs because breaking the chemical bonds in \( \mathrm{O}_3 \) requires energy input.

• Endothermic reactions, like ozone decomposition, increase the potential energy of the products as compared to the reactants.
• Such reactions are typically accompanied by a temperature decrease in their immediate environment.

The endothermic nature of ozone decomposition is crucial for atmospheric chemistry, affecting ozone stability and concentration.