Question

Among the species given, the total number of diamagnetic species is_____.
$H$ atom,$N{O_2}$ monomer, ${O_2}^ - $, dimeric sulphur in vapour phase, $M{n_3}{O_4},{\left( {N{H_4}} \right)_2}\left[ {FeC{l_4}} \right],{\left( {N{H_4}} \right)_2}\left[ {NiC{l_4}} \right],{K_2}Mn{O_4},{K_2}Cr{O_4}$

Answer 1

Hint:To solve this question, you must recall the electronic configurations of the central atoms in these molecules and the molecular orbital diagrams. If the species has unpaired electrons present, it is known as diamagnetic. If all electrons are paired, the species is said to be diamagnetic.

Complete step by step answer:
A hydrogen atom has only one electron and thus is paramagnetic. $N{O_2}$ monomer has one odd electron present which makes it paramagnetic. It is due to the presence of this electron that nitrogen dioxide generally exists as a dimer.
${O_2}^ - $ (superoxide) is a paramagnetic species due to the presence of one unpaired electron in its ${\pi ^*}$molecular orbital.
Dimeric sulphur has two unpaired electrons in its ${\pi ^*}$molecular orbital as is paramagnetic.
$M{n_3}{O_4}$is paramagnetic because it exists as $2MnO.Mn{O_2}$ of which both the compounds are paramagnetic.
${\left( {N{H_4}} \right)_2}\left[ {FeC{l_4}} \right]$: iron is present in $ + 2$ oxidation state and has 4 unpaired electrons. Thus, it is paramagnetic
${\left( {N{H_4}} \right)_2}\left[ {NiC{l_4}} \right]$: nickel is present in $ + 2$ oxidation state and has 2 unpaired electrons. Thus, it is paramagnetic.
${K_2}Mn{O_4}$: manganese is present in $ + 6$ oxidation state and has 1 unpaired electron. Thus, it is paramagnetic.
${K_2}Cr{O_4}$: chromium is present in $ + 6$ oxidation state. It has no unpaired electrons present. Thus, it is a diamagnetic compound.

Thus, the total number of diamagnetic species among the given species is 1.

Note:
Molecular orbital theory (MOT) is a method of depicting the electronic structures of molecules using quantum mechanics. In this theory, electrons in a molecule are not conventionally assigned to individual chemical bonds between atoms, but are treated as moving under the influence of the atomic nuclei in the whole molecule.