Problem 203 - A Complete Resource Book in Chemistry for JEE Main

Question

In which of the following ionization processes, the bond order has increased and the magnetic behaviour has changed? (a) \(\mathrm{NO} \rightarrow \mathrm{NO}^{+}\) (b) \(\mathrm{O}_{2} \rightarrow \mathrm{O}_{2}^{+}\) (c) \(\mathrm{N}_{2} \rightarrow \mathrm{N}_{2}{\underline{\phantom{xx}}}^{+}\) (d) \(\mathrm{C}_{2} \rightarrow \mathrm{C}_{2}^{+}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{NO} \rightarrow \mathrm{NO}^{+}\) with increased bond order and changed magnetic behavior.

Step 1: Understand Bond Order and Magnetic Behavior

Bond order is determined by the formula \( \frac{1}{2}(\text{number of bonding electrons} - \text{number of antibonding electrons}) \). Magnetic behavior can change from diamagnetic to paramagnetic or vice versa. Identify bond order and magnetic property change when the ionization occurs.

Step 2: Analyze \(\text{NO} \rightarrow \text{NO}^+\)

NO has 15 electrons, making it paramagnetic. NO\(^+\) has 14 electrons and is diamagnetic. Calculate: In NO, bond order = \(\frac{1}{2}(10 - 5) = 2.5\). In NO\(^+\), bond order = \(\frac{1}{2}(10 - 4) = 3\). Bond order increases and magnetic behavior changes.

Step 3: Analyze \(\text{O}_2 \rightarrow \text{O}_2^+\)

O\(_2\) is paramagnetic with 16 electrons. O\(_2^+\) is also paramagnetic with 15 electrons. Bond order in O\(_2\) is \(\frac{1}{2}(10 - 6) = 2\) and in O\(_2^+\) is \(\frac{1}{2}(10 - 5) = 2.5\). Bond order increases, but the magnetic behavior does not change.

Step 4: Analyze \(\text{N}_2 \rightarrow \text{N}_2^+\)

N\(_2\) is diamagnetic with 14 electrons, while N\(_2^+\) is paramagnetic with 13 electrons. Bond order in N\(_2\) is \(\frac{1}{2}(10 - 4) = 3\), and in N\(_2^+\) is \(\frac{1}{2}(9 - 4) = 2.5\). Bond order decreases, and magnetic behavior changes, but not according to the question.

Step 5: Analyze \(\text{C}_2 \rightarrow \text{C}_2^+\)

C\(_2\) is diamagnetic with 12 electrons. C\(_2^+\) is paramagnetic with 11 electrons. Bond order in C\(_2\) is \(\frac{1}{2}(8 - 4) = 2\) and in C\(_2^+\) is \(\frac{1}{2}(7 - 4) = 1.5\). Bond order decreases, and magnetic behavior changes, but not according to the question.

Key Concepts

Ionization Process

The ionization process involves removing an electron from a molecule, which can lead to changes in its chemical and physical properties.
Ionization affects the electronic configuration, which in turn can modify molecular features like bond order and magnetic behavior.
To understand the changes during ionization:

• Identify the electron being removed. This often affects bonding and antibonding orbitals.
• Recalculate bond order using the formula: \( \text{Bond Order} = \frac{1}{2}(\text{number of bonding electrons} - \text{number of antibonding electrons}) \)
• Check for changes in magnetic properties by analyzing changes in electron spin alignment.

Magnetic Behavior

Magnetic behavior of a molecule is shaped by the presence and alignment of unpaired electrons.
If electrons are paired, the molecule is typically diamagnetic and weakly repelled by a magnetic field. Conversely, unpaired electrons result in paramagnetism, making the molecule attracted to a magnetic field.
During the ionization process, removing an electron can:

• Turn a previously paired system into one with unpaired electrons, leading to paramagnetism.
• Remove unpaired electrons, thus making the molecule diamagnetic.

Ensuring an understanding of electron spins will help predict magnetic changes after ionization.

Molecular Orbitals

Molecular orbitals form when atomic orbitals overlap, creating bonding and antibonding interactions that define a molecule's stability and properties.
In the context of ionization, understanding the molecular orbital configuration sheds light on how removing electrons affects the molecule:

• Bonding orbitals (usually lower energy) contribute to stability and increase bond order.
• Antibonding orbitals (higher energy) counteract bonding effects, reducing bond strength.

By identifying which orbitals electrons are removed from, predictions about changes in bond order and magnetic behavior can be made accurately.

Paramagnetism vs Diamagnetism

Whether a molecule is paramagnetic or diamagnetic relies on its electron configuration, particularly the presence of unpaired electrons.
This distinction becomes crucial for understanding changes during ionization:

• Paramagnetic molecules with unpaired electrons exhibit magnetic attraction.
• Diamagnetic molecules, with all electrons paired, exhibit magnetic repulsion.

Analyzing the electron configuration before and after ionization helps determine changes. For example, if ionization leads to pairing or unpairing of electrons, it will shift the molecule from one type of magnetic behavior to the other. Regularly employing molecular orbital theory aids in predicting these changes effectively.