Question

What is the total number of electrons in a superoxide ion, $O_2^ -$?

Answer 1

Electronic configuration of oxygen,$O$ atom is
$O$-$1{s^2}2{s^2}2{p^4}$
Therefore, total number of electrons in an oxygen atom is $2 + 2 + 4 = 8$
Superoxide ion is a free radical that exhibits paramagnetism due to the presence of an unpaired electron.
Superoxides are compounds in which the oxidation number of oxygen is $- \dfrac{1}{2}$.

Complete answer:
Total number of electrons in an oxygen atom= $8$
Total number of electrons in $2$ oxygen atoms = $2 \times 8 = 16$
We know, $1$ negative charge is equal to $1$ electrons.
Superoxide ion contains $1$ negative charge on its molecule.
Total number of electrons on superoxide ion,$O_2^ -$=( number of electrons in $2$ oxygen atoms + number of electron in negative charge)
$\;Total{\text{ }}number{\text{ }}of{\text{ }}electrons{\text{ }}on{\text{ }}superoxide{\text{ }}ion,O_2^ - = 16 + 1 = 17$
Hence, total number of electrons on superoxide ion, $O_2^ -$= $17$

Note:
Superoxide ion contains $2$ oxygen atoms linked together by a single bond and one of the oxygen atoms having an extra electron thus forming $O_2^ -$. In case of peroxide ion, it contains $2$ extra electrons, $1$ on each oxygen atom which results in $O_2^{2 - }$. In case of oxide ion, it contains only $1$ oxygen atom and carries $2$extra electrons and hence is present as $O_{}^{2 - }$.