What is the common oxidation state of manganese metal?

2 Answers
Oct 17, 2016

Answer:

Good question. How do you determine the most stable oxidation state?

Explanation:

Manganese metal has a very large redox manifold, and can form compounds with metal oxidation states from #0# to #VII+#. Subvalent oxidation states of #-II# and #-I# are known. Manganese has 7 valence electrons, and thus many possible oxidation states.

In water, in common with most of the transition metals, manganese commonly forms #Mn^(2+)# ions. So #Mn(II+)# compounds and complexes are common. This has a #d^5# ground state, and as a consequence, #Mn(II+)# are VERY palely coloured, i.e. almost colourless.

Oct 17, 2016

You can determine the most stable oxidation state by identifying the ground-state electron configuration.

Since an oxidation state is defined as the hypothetical charge of a pure ion, the ground-state configuration for the corresponding #"Mn"# ion should define the most stable oxidation state.

You can write the valence configuration as (#Z = 25#)#bb(""^"[*]")#:

#ul(" "" ")#
#" 4s"# (#-"7.84 eV"#)

#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))#
#underbrace(" "" "" "" "" "" "" "" "" "" "" "" "" "" ")#
#" "" "" "" "" ""3d orbitals"# (#-"11.4 eV"#)

This is said to be most stable because

  • as many electrons are unpaired as possible (coulombic repulsions from paired electrons are minimized), being distributed in accordance with Hund's rule.
  • they all occupy the non-highest-energy valence orbitals.

(We don't worry about the core orbitals because they are already low in energy and fully-occupied, thus not participating in bonding.)

In this state, manganese has lost its two valence #4s# electrons, going from an electron configuration of #[Ar] 3d^5 4s^2# for #stackrel(color(blue)(0))"Mn"# to #[Ar] 3d^5# for #stackrel(color(blue)(+2))"Mn"#.

So, the #+2# state is most stable.

#bb(""^"[*]")#: http://media.pearsoncmg.com/bc/bc_0media_chem/adv_chem/pdf/11054_appB_ts.pdf