Question

Diamagnetic species among the following is:
(A) $ H_{2}^{+} $
(B) $ NO $
(C) $ O_{2}^{-} $
(D) $ N_{2}^{2+} $

Answer 1

Hint: We know that elements are distinguished by their atomic properties. An atom contains a core of protons and neutrons and the electrons revolve around the core in different orbitals. We also know that different capacities. The electrons revolving in the orbitals have quantum numbers assigned. Diamagnetic and paramagnetic properties of an element in its state are determined by the quantum numbers assigned.

Complete step by step solution:
We should understand that diamagnetism is a quantum mechanical effect that occurs in all materials. When this effect contributes to magnetism, the material is called diamagnetic. Diamagnetic materials are repelled by magnetic force in the two directions. In chemistry, the thumb rule is used to determine whether the particle atom, ion or molecule is paramagnetic or diamagnetic. If all the electrons in the atom or molecule are paired then the substance is diamagnetic. If the atom or molecule has unpaired electrons then the substance is paramagnetic. If we look at the oxygen molecule, the two atoms of oxygen form a molecule.
We know that one oxygen atom has 8 electrons hence; a molecule will have 16 electrons. Using molecular orbital theory, we can write the electronic configuration is given as: $ 1{{s}^{2}}2{{s}^{2}}2{{p}^{4}} $ .
The neutral oxygen is paramagnetic according to MO theory because it ends up with two unpaired electrons in two degenerate pi antibonding molecular orbitals. The other two are paramagnetic because they have an odd number of electrons so it doesn’t matter what kind of bonding they are involved in, the electrons cannot be all paired up.
Therefore, $ O_{2}^{-} $ is Diamagnetic species, i.e. option C.

Note:
Remember that we need to know that in case of paramagnetic and ferromagnetic materials, they too have diamagnetic properties but the diamagnetic forces are overruled by the paramagnetic forces. In orbital molecular theory, the magnetic forces are distinguished by the electrons in the orbitals. If there are unpaired electrons in the orbitals, then the substance is paramagnetic. If all the electrons are paired then the substance is diamagnetic.