Which one of the following molecules is expected to exhibit diamagnetic behaviour?

Wait a moment while we are looking for your question.

.

Engineering

Chemistry

Molecular Orbital Theory or MOT

Colour and Magnetism

Dipole moment of Organic Compounds

Question

Which one of the following molecules is expected to exhibit diamagnetic behaviour?

A

O₂

B

P₂

C

S₂

D

N₂

N₂ = $σ$ (1s)² < $σ$ * (1s)² < $σ$ (2s)² < $σ$ * (2s)²< $π$ (2p_x)² = $π$ (2p_y)² < $σ$ (2p_z)²

Number of unpaired electron in N₂ and C₂ = 0 , so both are diamagnetic in nature

Number of unpaired electron in O₂ and S₂ = two, so both are paramagnetic in nature

To determine which molecule exhibits diamagnetic behavior, we need to understand the concept of paramagnetism and diamagnetism:

Paramagnetic substances are attracted to a magnetic field. This occurs when molecules have unpaired electrons.
Diamagnetic substances are repelled by a magnetic field. This occurs when all electrons in the molecule are paired.

We analyze the molecular orbital (MO) configuration for each diatomic molecule to check for unpaired electrons.

Step 1: Write Molecular Orbital Configurations

The general order for MO energy levels in diatomic molecules (for B₂, C₂, N₂ and similar) is:

σ 1s * < σ 1s < σ 2s * < σ 2s < π 2p < σ 2p < π 2p * < σ 2p *

For O₂, F₂, and beyond, the order changes slightly:

σ 1s * < σ 1s < σ 2s * < σ 2s < σ 2p < π 2p < π 2p * < σ 2p *

Step 2: Analyze Each Molecule

O₂ (16 electrons):

MO configuration: $(σ 1s) {(σ 1s *)}^{2} (σ 2s) {(σ 2s *)}^{2} (σ 2p) {(π 2p)}^{4} (π 2p *) {(π 2p *)}^{1}$

Two unpaired electrons in $π 2p *$ orbitals. Paramagnetic.

P₂ (30 electrons):

Similar to N₂ but with more electrons. Filled MOs up to $σ 2p$ . All electrons paired. Diamagnetic.

S₂ (32 electrons):

Similar to O₂. MO configuration has two unpaired electrons. Paramagnetic.

N₂ (14 electrons):

MO configuration: $(σ 1s) {(σ 1s *)}^{2} (σ 2s) {(σ 2s *)}^{2} (π 2p) {(π 2p)}^{4} (σ 2p) {(σ 2p)}^{2}$

All electrons are paired. Diamagnetic.

Step 3: Compare and Conclude

Both P₂ and N₂ are diamagnetic. However, P₂ is less common and often not considered in basic questions. N₂ is a standard example of a diamagnetic diatomic molecule.

Final Answer: N₂ and P₂ are diamagnetic, but typically N₂ is the expected answer.

Related Topics and Formulae

Molecular Orbital Theory (MOT): Explains bonding in molecules using molecular orbitals formed by the combination of atomic orbitals. Key points:

Bond order = (Number of bonding electrons - Number of antibonding electrons)/2
Paramagnetism indicates unpaired electrons; diamagnetism indicates all paired electrons.

Key Formulae:

Bond Order = $\frac{N_{b} - N_{a}}{2}$

Where $N_{b}$ = number of bonding electrons, $N_{a}$ = number of antibonding electrons.