# What is "oxidation number"?

Jun 8, 2017

Oxidation number is the charge left on the central atom.......Typically iron displays $0$, $+ I I$, and $+ I I I$ oxidation states.

#### Explanation:

.....when all the bonding pairs of electrons are removed, with the charge assigned to central atom:

$1.$ $\text{The oxidation number of a free element is always 0.}$

$2.$ $\text{The oxidation number of a mono-atomic ion is equal}$ $\text{to the charge of the ion.}$

$3.$ $\text{For a given bond, X-Y, the bond is split to give } {X}^{+}$ $\text{and}$ ${Y}^{-}$, $\text{where Y is more electronegative than X.}$

$4.$ $\text{The oxidation number of H is +I, but it is -I in when}$ $\text{combined with less electronegative elements.}$

$5.$ $\text{The oxidation number of O in its}$ compounds $\text{is usually -II, but it is -I in peroxides.}$

$6.$ $\text{The oxidation number of a Group 1 element}$ $\text{in a compound is +I.}$

$7.$ $\text{The oxidation number of a Group 2 element in a}$ $\text{compound is +II.}$

$8.$ $\text{The oxidation number of a Group 17 element}$ $\text{in a binary compound is -I.}$

$9.$ $\text{The sum of the oxidation numbers of all of the atoms}$ $\text{in a neutral compound is 0.}$

$10.$ $\text{The sum of the oxidation numbers in a polyatomic}$ $\text{ion is equal to the charge of the ion.}$

The given rules are a formalism. When we take an iron salt, or an iron complex, i.e. $F e S {O}_{4}$, or $F e C {l}_{2}$, or $F e {\left(O {H}_{2}\right)}_{6}^{2 +}$, the charge on the IRON ATOM is formally $I I +$; i.e. it is a $\text{ferrous ion}$. In $F {e}_{2} {\left(S {O}_{4}\right)}_{3}$, or $F e C {l}_{3}$, or $F e {\left(O {H}_{2}\right)}_{6}^{3 +}$, we has $F {e}^{3 +}$, $\text{the ferric ion}$, $F e \left(I I I +\right)$. Iron complexes with different oxidation states are more rare.