What do we understand by Oxidation number of oxygen is 1/2 in superoxides?

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jerichorayel eNotes educator| Certified Educator

Superoxide is a compound that contains a superoxide ion in it with a chemical formula `O_2^(-)` . The valence number of superoxides as a whole is 1 and the oxidation number is -1. So for each oxygen atoms the oxidation number is -1/2. To better understand this let us take an example and do the Lewis structure. 

For potassium superoxide (`KO_2` )

`K = +1`

`O = ?`

`1 + 2(x) = 0`

`2x = -1`

`x = -1/2` = oxidation of O in the superoxide molecule.

Consider the attached image. The red electron is signifies the negative charge of the ion. 

Superoxide ion can be formed when a dioxygen is singly reduced or an electron is added in an elemental dioxygen leaving a charged molecule which is considered a free radical. Superoxide exhibits paramagnetism.

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