What is the primary difference in the magnetic properties of dioxygen and ozone?

The primary difference lies in their magnetic behavior. Dioxygen ($O_2$) is paramagnetic, meaning it is weakly attracted to a magnetic field. This property arises from the presence of two unpaired electrons in its antibonding $pi^*$ molecular orbitals, as predicted by Molecular Orbital Theory. In contrast, ozone ($O_3$) is diamagnetic, meaning it is weakly repelled by a magnetic field. All electrons in ozone are paired, which is consistent with its resonance structures and $sp^2$ hybridization of the central oxygen atom.

Why is a 'silent electric discharge' used for the preparation of ozone?

Ozone formation from dioxygen is an endothermic process ($ \Delta H = +142, ext{kJ/mol}$). This means it requires energy input. However, ozone is thermodynamically unstable and readily decomposes back into dioxygen. If a high-temperature electric discharge were used, the heat generated would cause the newly formed ozone to decompose immediately. A silent electric discharge provides the necessary energy for ozone formation without generating excessive heat, thus preventing its decomposition and allowing for a reasonable yield.

How does ozone act as a bleaching agent and disinfectant?

Ozone's effectiveness as a bleaching agent and disinfectant stems from its powerful oxidizing nature. When ozone decomposes, it releases nascent oxygen ($O_3 \rightarrow O_2 + O$). This nascent oxygen is extremely reactive and can oxidize colored substances, breaking down their chromophores (color-imparting groups) and rendering them colorless, thus bleaching them. Similarly, this nascent oxygen can oxidize and destroy the cell walls and vital enzymes of bacteria, viruses, and other microorganisms, effectively disinfecting water or air without leaving harmful residues like chlorine.

Explain the role of the ozone layer in the stratosphere.

The ozone layer, located in the Earth's stratosphere (10-50 km above the surface), plays a critical role in protecting life on Earth. It absorbs a significant portion of the Sun's harmful ultraviolet (UV) radiation, particularly UV-B and UV-C rays. These high-energy radiations can cause DNA damage, skin cancer, cataracts, and suppress the immune system in humans, and harm plant life and marine ecosystems. By absorbing these radiations, the ozone layer acts as a natural shield, making the Earth's surface habitable. This absorption process also contributes to heating the stratosphere.

What is 'tailing of mercury' and how is it related to ozone?

Tailing of mercury refers to the phenomenon where mercury, which normally forms a convex meniscus and does not stick to glass, loses its characteristic meniscus and starts to stick to the glass surface, leaving a 'tail.' This occurs when mercury comes into contact with ozone. Ozone oxidizes mercury to mercurous oxide ($Hg_2O$), which is a solid. The formation of this oxide film on the surface of the mercury causes it to lose its metallic luster and cohesive properties, leading to the 'tailing' effect. The reaction is $2Hg(l) + O_3(g) \rightarrow Hg_2O(s) + O_2(g)$.

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Dioxygen and Ozone

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Version 1Updated 22 Mar 2026

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Dioxygen ( $O_2$ ) and ozone ( $O_3$ ) are the two primary allotropic forms of the element oxygen, a member of Group 16 in the periodic table. Dioxygen, the most common and stable allotrope, is a diatomic molecule essential for respiration and combustion, characterized by its paramagnetic nature due to two unpaired electrons in its antibonding molecular orbitals. Ozone, a triatomic molecule, is a less…

Quick Summary

Dioxygen ( $O_2$ ) and ozone ( $O_3$ ) are the two main allotropes of oxygen. Dioxygen is a colorless, odorless, and tasteless gas, making up about 21% of the atmosphere. It is crucial for respiration and combustion.

A key property is its paramagnetism, due to two unpaired electrons. Industrially, it's obtained from liquid air, and in labs, from decomposing oxygen-rich compounds like $KClO_3$ or $H_2O_2$ . Dioxygen is reactive, forming oxides with most elements, and typically exhibits a $-2$ oxidation state, with exceptions like peroxides ( $-1$ ) and superoxides ( $-1/2$ ).

Ozone ( $O_3$ ) is a pale blue gas with a pungent smell, formed by passing a silent electric discharge through dry oxygen. It has a bent structure with identical $O-O$ bond lengths due to resonance and is diamagnetic.

Ozone is a powerful oxidizing agent, stronger than dioxygen, due to its instability and tendency to release nascent oxygen. It's used as a germicide, disinfectant, and bleaching agent. In the stratosphere, it forms a protective layer against UV radiation, but at ground level, it's a harmful pollutant.

Understanding their distinct properties, preparation, and reactions is vital for NEET.

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Key Concepts

Paramagnetism of Dioxygen (

O_2

)

The paramagnetism of dioxygen is a classic example demonstrating the power of Molecular Orbital Theory (MOT)…

Structure and Resonance of Ozone (

O_3

)

Ozone ( $O_3$ ) has a bent molecular geometry, not linear. The central oxygen atom is $sp^2$ hybridized. It…

Oxidizing Power of Ozone

Ozone is a significantly stronger oxidizing agent than dioxygen. This enhanced oxidizing power stems from its…

Dioxygen ($O_2$) — Colorless, odorless, tasteless. Paramagnetic. Linear structure. Essential for respiration/combustion. Lab prep:

2KClO_3 \xrightarrow{MnO_2} 2KCl + 3O_2

;

2H_2O_2 \xrightarrow{MnO_2} 2H_2O + O_2

. Industrial prep: Fractional distillation of liquid air.

Ozone ($O_3$) — Pale blue gas, pungent smell. Diamagnetic. Bent structure (

116.8^circ

), resonance, identical

O-O

bond lengths (

128,\text{pm}

). Strong oxidizing agent (

O_3 \rightarrow O_2 + O

). Lab prep:

3O_2 \xrightarrow{\text{silent electric discharge}} 2O_3

. Thermodynamically unstable.

Key Reactions of $O_3$ —

2KI + H_2O + O_3 \rightarrow 2KOH + I_2 + O_2

;

PbS + 4O_3 \rightarrow PbSO_4 + 4O_2

;

2Hg + O_3 \rightarrow Hg_2O + O_2

Environmental — Stratospheric

O_3

(UV shield), Tropospheric

O_3

(pollutant).

OZONE's Properties: Pungent smell, Pale blue, Powerful oxidizer, Prepped by silent discharge. Bent structure, Bond lengths equal, But Bad at ground level. Diamagnetic, Decomposes easily.

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