Question

Which is most stable in +2 oxidation state Cr,Mn,Fe or Co and why?

Answer 1

Among the given ions, the ion with more (-)ve value of E0(red) will loose the electron more easily, thus is more stable in (+)2 oxidation state. Hence, Mn in (+)2 oxidation state is more stable species.

Answer 2

Mn shows a stable +2 oxidation state.

• The electronic configuration of $Cr^{+2}$ is as follows-
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {3d}^{4}$
• Thus the 3d orbital contains 4 electrons and is moderately stable.
• The electronic configuration of $Mn^{+2}$ is as follows-
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {3d}^{5}$
• Thus the 3d orbital contains 5 electrons and is highly stable due to half filled valance shell.
• The electronic configuration of $Fe^{+2}$ is as follows-
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {3d}^{6}$
• Thus the 3d orbital contains 6 electrons and is moderately stable.
• The electronic configuration of $Co^{+2}$ is as follows-
• ${1s}^{2} {2s}^{2} {2p}^{6} {3s}^{2} {3p}^{6} {3d}^{7}$
• Thus the 3d orbital contains 7 electrons and is moderately stable.