Question

How can iron have two oxidation numbers?

Answer 1

It's important to note that many elements have multiple oxidation states. In chem class - you typically just learn the most common ones.

For example, calcium normally forms +2 ions, but it is possibly (but rare) that calcium can form compounds when the calcium has a +1 oxidation state.

So why can iron form both a +2 or a +3 oxidation state? Both will give better stability then the ground state electron configuration for iron.

Ground state: [Ar] `4s^2` `3d^6`
+2 ion: [Ar] `3d^6`
+3 ion: [Ar] `3d^5`

What is your take home message? Ions form because they give ** better ** stability than ground state atoms, but not necessarily perfect stability.

The two ions of iron both give better stability to the particle.

Noel P.