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

Question

Which of the following is the wrong statement (a) ONCl and \(\mathrm{ONO}^{-}\)are not isoelectronic. (b) \(\mathrm{O}_{3}\) molecule is bent (c) Ozone is violet-black in solid state (d) Ozone is diamagnetic gas.

Step-by-Step Solution

Answer

All given statements are correct; none is wrong.

Step 1: Understanding 'Isoelectronic'

To determine if two species are isoelectronic, they must have the same number of total electrons. Let's calculate the total number of electrons in ONCl and \( \mathrm{ONO}^{-} \). **ONCl**: O (8 electrons) + N (7 electrons) + Cl (17 electrons) = 32 electrons. **\( \mathrm{ONO}^{-} \)**: O (8 electrons) + N (7 electrons) + O (8 electrons) + 1 (for the extra electron due to the \( - \) charge) = 24 electrons. Since 32 \( eq \)24, they are not isoelectronic. So, statement (a) is correct.

Step 2: Reviewing Shape and Structure of \( \mathrm{O}_3 \)

The \( \mathrm{O}_3 \) (ozone) molecule has a bent structure due to the presence of lone pairs on the central oxygen atom causing repulsion, which forces the molecule from a linear shape. Checking this confirms that statement (b) is correct.

Step 3: Analyzing Solid Ozone Color

In its solid state, ozone is violet-black in color. This statement is factual, hence statement (c) is correct.

Step 4: Checking Magnetic Properties of Ozone

Diamagnetic substances either have no unpaired electrons or all paired electrons. Ozone in its gaseous state has all electrons paired, making it a diamagnetic gas. This means statement (d) is correct.

Step 5: Final Decision on Incorrect Statement

All statements (a), (b), (c), and (d) are true according to the provided analysis, so none of them provide an incorrect choice. However, in practice, often one is a trick or misunderstood; recheck if the premise allows one.” Notable: statement (a) was often miscalculated historically hence it may highlight that for cross-verification, (a) remains a commonly reviewed choice.

Key Concepts

Isoelectronic Species

Inorganic chemistry often deals with the concept of isoelectronic species. Two species are considered isoelectronic if they have the same number of electrons. This similarity in electronic configuration can lead to similarities in chemical properties and behavior, despite differing atomic compositions or charges.
To see this in action, consider the molecules ONCl and \( \mathrm{ONO}^{-} \). By counting the electrons for each atom, ONCl has a total of 32 electrons, while \( \mathrm{ONO}^{-} \) has 24 electrons. Because these numbers differ, ONCl and \( \mathrm{ONO}^{-} \) are not isoelectronic. It’s crucial to accurately count all electrons, including additional ones from negative charges, to avoid errors. This concept assists in predicting molecular behavior in varied chemical environments.

Molecular Geometry

The shape of a molecule is critical in understanding its chemical and physical properties. For ozone \( \mathrm{O}_3 \), the structure is bent. This is due to lone pairs of electrons on the central oxygen atom. These lone pairs exert a repulsive force, causing the molecule to deviate from a linear shape.
The VSEPR theory (Valence Shell Electron Pair Repulsion) helps predict molecular shapes by considering electron pairs' repulsions. In ozone, these repulsions create a bent formation, with an internal bond angle that is less than \( 180^\circ \).

• Each oxygen in \( \mathrm{O}_3 \) shares electrons, forming covalent bonds.
• The lone pairs on the central oxygen push the bonded pairs closer, leading to a bent structure.

Recognizing the geometry of \( \mathrm{O}_3 \) allows for better understanding of its reactive nature and role in atmospheric chemistry.

Ozone Properties

Ozone is an allotrope of oxygen with distinct properties that differ from the diatomic \( \mathrm{O}_2 \). When in the solid state, ozone appears violet-black, displaying a striking color. This property is linked to the electronic transitions within the ozone molecules.
The color of ozone changes with its state:

• In solid state: violet-black.
• In liquid: dark blue.
• In gaseous form: pale blue.

These transitions are indicative of how closely the molecules are packed, affecting how light is absorbed and emitted, thereby changing its color. Such visual clues help in identifying the state of ozone without additional equipment, vital in several chemical applications.

Magnetic Properties

Ozone's magnetic properties are interesting because they reflect its electron configuration. Ozone, as a molecule, is classified as diamagnetic. This means that all of its electrons are paired, and it exhibits no net magnetic moment.
Diamagnetism occurs in substances with no unpaired electrons. Ozone's paired electrons contribute to its stability and weak response in magnetic fields.

• Paired electrons: indicative of diamagnetic behavior.
• Lack of unpaired electrons ensures no attraction to magnetic fields.

Understanding ozone's diamagnetic nature is crucial in fields like atmospheric chemistry, where its interactions with magnetic fields can influence environmental effects.