Question

The correct statement(s) about $O_3$ is(are) (A) $O-O$ bond lengths are equal. (B) Thermal decomposition of $O_3$ is endothermic. (C) $O_3$ is diamagnetic in nature. (D) $O_3$ has a bent structure.

Short answer

All the given statements (A) O-O bond lengths are equal, (B) Thermal decomposition of O3 is endothermic, (C) O3 is diamagnetic in nature, and (D) O3 has a bent structure are correct.

Step-by-step solution

Analyze Bond Lengths in Ozone

Ozone, or $O_3$, consists of three oxygen atoms with a resonance structure, which means that the $O-O$ bonds are delocalized over the three atoms. Since the negative charge and the bonding are delocalized, the $O-O$ bond lengths in ozone are equal. This makes option (A) correct.

Evaluate the Thermal Decomposition of Ozone

The decomposition of ozone into oxygen molecules ($O_2$) absorbs heat from the surroundings, which is an indication of an endothermic reaction. $2O_3\to 3O_2$. Therefore, the thermal decomposition of $O_3$ is endothermic, making option (B) correct.

Identify Diamagnetic Nature of Ozone

Diamagnetism is a property of all materials and arises from the opposition to magnetic fields generated by the orbital motion of electrons. Since all electrons in ozone are paired, there are no unpaired electrons, which means that ozone is diamagnetic. Thus, option (C) is correct.

Determine the Molecular Structure of Ozone

Ozone has a bent (angular) molecular structure due to the presence of a lone pair of electrons on the central oxygen atom which influences the molecular geometry. This makes ozone non-linear, verifying that option (D) is correct.

Key concepts

Ozone Molecular Structure

Ozone, or $O_3$, is a fascinating molecule with significant environmental implications. It is composed of three oxygen atoms connected in a way that exhibits the elegance of chemical structures. The molecular structure of ozone has a 'V' shape or bent geometry, which is determined by the arrangement of its electron pairs.

Ozone's central oxygen atom has four electron domains: one lone pair and three bonding pairs that form two sigma bonds with the other two oxygen atoms, while the third bonding pair is part of a delocalized pi system that connects all three oxygen atoms. According to the VSEPR (Valence Shell Electron Pair Repulsion) theory, the optimal geometry for four electron domains is tetrahedral. However, due to the lone pair on the central oxygen, the molecule ends up adopting a bent structure as the lone pairs repel the bonding pairs more strongly, resulting in unequal bond angles. The resonance structure of ozone contributes to the equivalence of the $O-O$ bond lengths, as this delocalization allows the electrons to be more evenly distributed over the three atoms.

This equality in bond lengths is a direct consequence of the phenomenon of resonance and is critical to understanding why ozone has such unusual chemical and physical properties. In essence, rather than possessing fixed double and single bonds, the two $O-O$ bonds in an ozone molecule are identical and have a bond order of 1.5, which lies between that of a single and a double bond.

Thermal Decomposition of Ozone

Ozone plays a crucial role in absorbing ultraviolet radiation in the Earth's stratosphere, but it can also undergo thermal decomposition, a process relevant to understanding ozone's stability and reactivity. The decomposition of ozone ($O_3$) into diatomic oxygen ($O_2$) is an endothermic reaction, meaning it requires the absorption of heat from its surroundings to proceed.

The thermal decomposition of ozone can be represented by the following chemical equation: $$2O_3\to 3O_2\text{.}$$ This reaction entails a net absorption of energy, indicating a destabilization of the ozone molecule as it splits into a more stable form of oxygen. The endothermic nature of this reaction is of particular importance in atmospheric chemistry, where the presence of certain catalysts, such as nitrogen oxides or chlorofluorocarbons, can accelerate the decomposition of ozone, leading to environmental concerns such as ozone layer depletion.

Ozone decomposes more readily at higher temperatures. This is of environmental concern because natural or human-made sources of heat can trigger increased rates of ozone decomposition, altering the delicate balance of atmospheric ozone and potentially affecting the protective barrier it forms against harmful UV radiation.

Diamagnetism of Molecules

Diamagnetism is a subtle but universal property of matter, arising from the response of electrons in a material to an external magnetic field. A molecule is diamagnetic when all of its electrons are paired, resulting in no net magnetic field from the electrons. In the case of ozone ($O_3$), this molecule is indeed diamagnetic as all of its valence electrons are paired.

To further explore this concept, when a diamagnetic substance like ozone is placed in a magnetic field, it will induce a magnetic field in the opposite direction, causing a repulsive effect. However, this effect is usually very weak compared to the attractive force experienced by paramagnetic substances, which have unpaired electrons. Since ozone has no unpaired electrons in its molecular orbital configuration, its diamagnetic nature is consistent and contributes to understanding the behavior of ozone under various chemical and physical conditions.

The understanding of diamagnetism in molecules such as ozone not only illuminates fundamental aspects of molecular magnetism but also underscores the importance of electron pairing in the chemical stability and reactivity of substances. This property is essential for scientists and environmentalists who monitor and model the influence of ozone in the atmosphere and its interactions with man-made materials.