why iron shows variable valency?explain the chemistry behind!

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jerichorayel | College Teacher | (Level 2) Senior Educator

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Iron has variable valencies of Fe2+ and Fe3+

Being in the transition area, Iron has an incomplete subshell. It's outermost electrons are 4s^2 and 3d^6. Most of the metals in this area often lose the 4s electrons. 

So if Iron will lose firsts its 4s electrons, it will become Fe2+. Fe3+ happens when one of the electrons in the 4d orbitals will be lost together with the two 4s electrons. let me show you an illustration:


Fe  4s2 3d6           ll     ll   l     l    l    l 

                           4s          3d


when Fe2+ happens:

                            _    ll    l     l    l    l 

                           4s          3d

* 2 electrons in 4s are lost.


when Fe3+ happens:

                            _      l    l     l    l    l 

                           4s          3d

*another electron is lost from the 3d orbitals.


it happens because an element prefer to have half filled degeneracy. 



Hope this helps :)

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