What is the oxidation number and how is it calculated? The complete definition and explanation of the oxidation state of a molecule with a practical example.The oxidation number in chemistry is nothing more than the oxidation state of an atom in a substance, that is, the difference between the number of valence electrons and those remaining once all the bonding electrons have been assigned to the more electronegative atom of each pair. 

 Oxidation number: calculation

To find out if the oxidation number of an atom is positive, it is necessary to understand if electrons are given up, while if they are gained it is negative. Simple substances such as hydrogen or oxygen have an oxidation number equal to 0 because the two atoms of the pair have the same electronegativity and therefore the electrons of a bond are divided between them in equal parts.

Oxidation number: example

Let’s consider a water molecule H2O : here hydrogen forms two bonds with an oxygen atom. Hydrogen has a positive charge of +1, therefore +2. Hydrogen gives up a valence electron, oxygen acquires two electrons with a negative charge of -2. The sum of the charges (+2 and -2) therefore gives the value 0.