Why is it easier to oxidise Fe^(2+) to Fe^(3+) than it is to oxidise Mn^(2+) to Mn^(3+)?

1 Answer
Nov 13, 2017

Well, consider the NEUTRAL electron configurations:

"Fe": [Ar] 3d^6 4s^2
"Mn": [Ar] 3d^5 4s^2

The 4s orbital is higher in energy in these atoms, so it is ionized first:

"Fe"^(2+): [Ar] 3d^6
"Mn"^(2+): [Ar] 3d^5

Drawn out:

"Fe"^(2+): ul(uarr darr)" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))

"Mn"^(2+): ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))

A single oxidation is the act of singly ionizing:

"M"^(2+) -> "M"^(3+) + e^(-)

The electron to be removed from Fe^(2+) is paired, having charge repulsions (making it easier to remove, i.e. the ionization energy is smaller).

Therefore, it is easier to ionize "Fe"^(2+) than "Mn"^(2+).