Why Fe 3+ is more common than Fe 2+

I heard that $\ce{Fe}(\mathrm{III})$ is more common than $\ce{Fe}(\mathrm{II})$ but I've not heard a very clear explanation. Could someone please explain this incorporating electron configurations in their answer?




I think the best answer is not to try to describe this in terms of electron orbitals. The main factor is that Fe(II) is fairly easily oxidized by atmospheric oxygen to give Fe(III). Because we spend most of our time living in an oxygen atmosphere, Fe(III) is more common in our ordinary experience than Fe(II).


In environments with less oxygen, Fe(II) is very common. The mantle is full of Fe(II) minerals like olivine and ferropericlase. I don't know which species is actually the majority on earth, but I would bet on Fe(II).


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The electron configuration of $\ce{Fe(II)}$ is $1s^22s^22p^6 3s^23p^6 3d^6$.


The electron configuration of $\ce{Fe(III)}$ is $1s^22s^22p^6 3s^23p^6 3d^5$.


The half filled orbital $3d$ is more stable than the same orbital filled with 6 electrons. So, $\ce{Fe(III)} $ ion is more common than $\ce{Fe(II)}$.


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