Question

The paramagnetism of \(\mathrm{O}_{2}\) molecule is believed to be due to the presence of two electrons in (1) bonding \(\pi\) -orbitals with parallel spin (2) antibonding \(\pi\) -orbitals with parallcl spin (3) antibonding \(\pi\) -orbitals with opposite spin (4) antibonding o-orbitals with parallel spin

Short answer

Option 2: Antibonding \( \pi \)-orbitals with parallel spin.

Step-by-step solution

- Understand Paramagnetism

Paramagnetism is a form of magnetism that occurs in materials with unpaired electrons. These unpaired electrons have aligned spins, which contribute to a net magnetic moment.

- Identify Molecular Orbitals in \(\mathrm{O}_{2} \)

\( \mathrm{O}_{2} \) molecule has molecular orbitals, which include bonding and antibonding orbitals. We know the electronic configuration for \( \mathrm{O}_{2} \) molecule to be: \( \sigma_{1s}^{2} \sigma^{*}_{1s}^{2} \sigma_{2s}^{2} \sigma_{2s}^{*2} \sigma_{2p_z}^{2} \pi_{2p_x}^{2} \pi_{2p_y}^{2} \pi_{2p_x}^{*1} \pi_{2p_y}^{*1} \).

- Analyze the Unpaired Electrons

From the configuration, the unpaired electrons are present in the \( \pi^{*} \) (antibonding \( \pi \)-orbitals) orbitals.

- Spin Orientation

Given that there are two unpaired electrons in the antibonding \( \pi \)-orbitals and paramagnetism is due to parallel spins, the unpaired electrons must have parallel spins for the molecule to exhibit paramagnetism.

- Determine the Correct Answer

The paramagnetism of \(\mathrm{O}_{2}\) is due to the presence of two electrons in antibonding \(\pi\)-orbitals with parallel spin.

Key concepts

Paramagnetism in the O2 Molecule

Paramagnetism occurs in materials where there are unpaired electrons. When these electrons have aligned spins, they contribute to a net magnetic moment, making the material attracted to a magnetic field.
In simpler terms, atoms or molecules with unpaired electrons can be drawn to a magnet, because of their magnetic properties. For instance, in the case of the \( \mathrm{O}_{2} \) molecule, the paramagnetic nature is directly related to its electronic structure and the presence of certain types of molecular orbitals.

Molecular Orbitals in \( \mathrm{O}_{2} \) Molecule

In \( \mathrm{O}_{2} \), electrons occupy molecular orbitals, which are formed from the atomic orbitals of oxygen atoms combining together:
* Bonding orbitals - They help hold the atoms together.
* Antibonding orbitals - These tend to push the atoms apart if occupied by electrons.
When we consider the electronic configuration for the \( \mathrm{O}_{2} \) molecule, it looks like this: \[ \sigma_{1s}^{2} \sigma^{*}_{1s}^{2} \sigma_{2s}^{2} \sigma_{2s}^{*2} \sigma_{2p_z}^{2} \pi_{2p_x}^{2} \pi_{2p_y}^{2} \pi_{2p_x}^{*1} \pi_{2p_y}^{*1} \]
These configurations show which molecular orbitals are filled with electrons. Notice the antibonding \( \pi_{2p_x}^{*1} \) and \( \pi_{2p_y}^{*1} \)

Electron Spin Configuration

Each electron in a molecular orbital has a property called spin, which can either be 'up' or 'down'.
When we observe the \( \mathrm{O}_{2} \) molecule, it has two unpaired electrons in the antibonding \( \pi \)-orbitals.
These unpaired electrons must have the same spin orientation (parallel spins) to make the molecule exhibit paramagnetism. In this case, the electrons are essentially spinning in the same direction, one in \( \pi_{2p_x}^{*} \) and one in \( \pi_{2p_y}^{*} \). This parallel spin results in a net magnetic moment.

Bonding and Antibonding Orbitals

Bonding orbitals are where electrons reside to help bind the atoms together, leading to a stable molecule.
Antibonding orbitals, on the other hand, work to destabilize the molecule when occupied.
In the electronic configuration for \( \mathrm{O}_{2} \), we see that the last two electrons occupy these antibonding \( \pi \)-orbitals: \( \pi_{2p_x}^{*1} \) and \( \pi_{2p_y}^{*1} \). Their presence here and their parallel spins are what gives \( \mathrm{O}_{2} \) its characteristic paramagnetic property.
This is an important feature because it helps distinguish between different types of molecular behaviors and their interactions with magnetic fields.
To sum up, the paramagnetic nature stems from having unpaired electrons in these specific antibonding orbitals with aligned or parallel spins.