Question

How can iron have two oxidation numbers?

Answer 1

First of all we have to know about the oxidation state and oxidation state of any atom will define as the number of electrons gained or lost by that atom with another species from its outermost shell.

Complete answer:
Oxidation number are present in two types and they are:
-Positive oxidation number which shows by the atom when they lose electrons from the outermost shell.
-And negative oxidation number which shows by the atom when they accept electrons on the outermost shell from the surrounding.
Iron have two oxidations state because of the below reason:
-As we know that atomic number of iron is 26 & its electronic configuration is written as $\left[ {{\text{Ar}}} \right]{\text{3}}{{\text{d}}^{\text{6}}}{\text{4}}{{\text{s}}^{\text{2}}}$, so iron will show $+ 2$ as well as $+ 3$ oxidation state to gain stability.
-When two electrons from the ${\text{4s}}$orbital of iron atom lose then iron will show $+ 2$ oxidation state.
-And sometime to get more stability iron will remove one electron from ${\text{3d}}$ orbital in addition with the two electrons of ${\text{4s}}$ orbital of iron atom to get more stability because in the half filled condition d-orbital shows great stability, and due to this iron will show $+ 3$ oxidation state.

Note:
Here some of you may think that iron may also show $- 4$ oxidation to fulfill the d-orbital and attain highest stability, but this assumption is not correct because energy required to gain four electrons is high as compared to removing two or three electrons.