Question

Oxygen molecule is paramagnetic because (a) no of bonding electroos \(>\) no. of antibonding dectrons (b) no. of bonding electrons \(<\) no. of antibondimg eltctrons (c) Io. of bonding electrons = no. of antibonding clectrons (d) presence of unpaired electrons in molecular orbitals.

Short answer

Oxygen molecule is paramagnetic because of the presence of unpaired electrons in molecular orbitals, making (d) the correct answer.

Step-by-step solution

Understand Paramagnetism

Paramagnetism is a form of magnetism that occurs in materials with unpaired electrons, which align with a magnetic field. It is the unpaired electrons that allow a substance to be attracted to a magnetic field.

Analyze Molecular Orbital (MO) Theory for O2

According to MO theory, electrons fill the molecular orbitals starting from the lowest energy level. For O2, the molecular orbital configuration ends with two unpaired electrons in the antibonding \(\pi^*_2p_y\) and \(\pi^*_2p_z\) orbitals. This results in a paramagnetic molecule.

Compare Electron Placement Options

We need to evaluate the options given to determine which one correlates with the presence of unpaired electrons and hence paramagnetism. The number of bonding and antibonding electrons is a part of the molecular orbital theory but does not directly explain paramagnetism.

Identify the Correct Option

The correct option must explain the observed paramagnetism in an oxygen molecule. Since it is the unpaired electrons that cause paramagnetism, the presence of unpaired electrons in the molecular orbitals would be the correct answer.

Key concepts

Molecular Orbital Theory

Molecular Orbital Theory (MOT) is a fundamental concept in chemistry that helps explain the electronic structure of molecules. Under this theory, atomic orbitals of the constituent atoms combine to form new orbitals, known as molecular orbitals, when a molecule is formed.

These molecular orbitals are spread out over the entire molecule and can hold the electrons of the molecule in a delocalized way. Electrons in these orbitals are filled according to the same rules as atomic orbitals, following the Aufbau principle, Pauli's exclusion principle, and Hund's rule of maximum multiplicity.

Starting from the lowest energy level, electrons are placed in these molecular orbitals. In diatomic molecules like O2, there are both bonding molecular orbitals, which tend to hold electrons in a manner that favors bonding between the atoms, and antibonding molecular orbitals, which can detract from the bond strength if they contain electrons.

Unpaired Electrons

Unpaired electrons are those electrons in an atom or molecule that are alone in an orbital and therefore do not have a paired spin state. In chemistry, electron spin is a very important property, because two electrons occupying the same orbital must have opposite spins—a rule known as Pauli's exclusion principle.

The presence of unpaired electrons can significantly affect the magnetic properties of a substance. According to Hund's Rule, as an orbital is filled with electrons, it does so in a way that maximizes the number of unpaired spins, leading to a more stable electronic configuration. Unpaired electrons are especially relevant in the context of Molecular Orbital Theory as they are the key factor in determining whether a molecule will exhibit paramagnetic properties, which is the case with the oxygen molecule.

Paramagnetic Substances

Paramagnetic substances are materials that exhibit paramagnetism, which is a form of magnetism whereby the material is weakly attracted by an externally applied magnetic field. This property is due to the presence of at least one unpaired electron in the material's atoms or molecules.

When a paramagnetic material is placed in a magnetic field, the unpaired electrons' spins can align with the field, adding a magnetic moment in the direction of the field. This alignment is temporary and disappears once the external field is removed, as thermal motion randomizes the electron spin orientations.

Oxygen is a classic example of a paramagnetic substance due to the presence of two unpaired electrons in its antibonding molecular orbitals. When exposed to a magnetic field, these unpaired electrons cause the overall oxygen molecule to be attracted to the magnetic field, demonstrating its paramagnetic nature.