Peroxide Ion Magnetic Nature

The magnetic property of an ion depends on the presence of unpaired electrons. We need to determine the electronic configuration of the peroxide ion ($O_2^{2-}$) using Molecular Orbital (MO) theory.

Electronic Configuration of Peroxide Ion

The peroxide ion has the formula $O_2^{2-}$. Each oxygen atom has 8 electrons. Therefore, the total number of electrons in the peroxide ion is:

Total electrons = (2 $\times$ 8) + 2 = 18 electrons.

The molecular orbital configuration for a molecule or ion with 18 electrons (like $O_2^{2-}$) is typically:

$(\sigma_{1s})^2 (\sigma_{1s}^*)^2 (\sigma_{2s})^2 (\sigma_{2s}^*)^2 (\sigma_{2p})^2 (\pi_{2p})^4 (\pi_{2p}^*)^4$

Let's check the total electrons filled:

• $2 (\sigma_{1s}) + 2 (\sigma_{1s}^*) = 4$ electrons
• $2 (\sigma_{2s}) + 2 (\sigma_{2s}^*) = 8$ electrons
• $2 (\sigma_{2p}) + 4 (\pi_{2p}) = 14$ electrons
• $4 (\pi_{2p}^*) = 18$ electrons

All 18 electrons are accommodated in the molecular orbitals, and importantly, all orbitals are completely filled, meaning all electrons are paired.

Determining Magnetic Property

• Diamagnetic: A substance is diamagnetic if all its electrons are paired. Diamagnetic substances are weakly repelled by a magnetic field.
• Paramagnetic: A substance is paramagnetic if it has one or more unpaired electrons. Paramagnetic substances are weakly attracted by a magnetic field.
• Ferromagnetic/Antiferromagnetic: These relate to specific ordered magnetic structures in solids and are generally not the primary classification for simple ions based solely on electron pairing.

Since the peroxide ion ($O_2^{2-}$) has all its electrons paired according to its MO configuration, it exhibits diamagnetic behavior.