Core Reactions: Redox
Slide 12 of 42
Oxidation State assignments rules
1. The oxidation state of an uncombined atom (or atoms in a diatomic molecule) is zero.
Element Oxidation state of atom
–Eg. Na 0
– Cl2 0
– O2 0
– He 0
2. In monatomic ion the oxidation state of the element is the same as the charge on the ion.
Monatomic ion Oxidation state of atom
–Eg. Na+ 1+ (or +1)
– Cl- 1- (or -1)
– O2-  2-