Question

According to the molecular orbital theory, which of the following molecules should exhibit paramagnetism?

• A. \( {O}_2 \)
• B. \( {N}_2 \)
• C. \( {F}_2 \)
• D. \( {C}_2 \)

Hint:

Paramagnetism occurs in molecules with unpaired electrons. In molecular orbital theory, this is determined by looking at the electron configurations and checking for unpaired electrons in the molecular orbitals.

Answer 1

The Correct Option is A

Step 1: Understanding Molecular Orbital Theory.
According to Molecular Orbital (MO) theory, paramagnetism occurs when a molecule has one or more unpaired electrons in its molecular orbitals. These unpaired electrons create a magnetic field, making the molecule attracted to a magnetic field (paramagnetic behavior). Diamagnetic molecules, on the other hand, have all their electrons paired and do not exhibit such attraction.
Step 2: Molecular Orbitals for Diatomic Molecules.
Let’s apply the molecular orbital theory to the given molecules to check for unpaired electrons.
1. Oxygen ({ O }₂):
The electronic configuration for { O }₂ (in the molecular orbital theory) is:

   ( σ₁s², σ^{₁s}², σ₂s², σ^{₂s}², π₂p̀x;², π₂p̀y;², π^{₂p̀x;}¹, π^{₂p̀y;}¹ )
   

Here, the two π-antibonding orbitals each have one unpaired electron, making { O }₂ paramagnetic.
2. Nitrogen ({ N }₂):
The electronic configuration for { N }₂ is:

   ( σ₁s², σ^{₁s}², σ₂s², σ^{₂s}², π₂p̀x;², π₂p̀y;² )
   

All electrons in { N }₂ are paired, so it is diamagnetic and does not exhibit paramagnetism.
3. Fluorine ({ F }₂):
The electronic configuration for { F }₂ is:

   ( σ₁s², σ^{₁s}², σ₂s², σ^{₂s}², π₂p̀x;², π₂p̀y;², π^{₂p̀x;}², π^{₂p̀y;}² )
   

All electrons are paired in { F }₂, so it is diamagnetic and does not exhibit paramagnetism.
4. Carbon ({ C }₂):
The electronic configuration for { C }₂ is:

   ( σ₁s², σ^{₁s}², σ₂s², σ^{₂s}², π₂p̀x;², π₂p̀y;² )
   

All electrons are paired in { C }₂, so it is diamagnetic and does not exhibit paramagnetism.
Step 3: Conclusion.
Based on the molecular orbital theory, { O }₂ has unpaired electrons and exhibits paramagnetism. The correct answer is (1) { O }₂.