Why binding energy (Mettalic bond ) of Mn is less than Cr??

1 Answer
Truong-Son N.
Jan 7, 2018

If you mean nuclear binding energy, then that's not true.

http://hyperphysics.phy-astr.gsu.edu/

From this graph, with mass numbers of #52# for #""_(24)^(52) "Cr"# (#83.79%# abundant) and #55# for #""_(25)^(55) "Mn"# (#~~# #100%# abundant), #"Mn"# has the higher nuclear binding energy, experimentally.

When I hear binding energy, I think of the photoelectric effect, i.e. the energy input required to remove an electron from the metal, or the work function, or the threshold energy #phi = hnu_0#.

https://chemdemos.uoregon.edu/

In that case, #"Mn"# has an electron configuration of #[Ar] 3d^5 4s^2#, while #"Cr"# has an electron configuration of #[Ar] 3d^5 4s^1#.

Since the binding energy is less for #"Mn"#, it makes sense because the #bb(4s)# electron would be removed, but it is paired in #"Mn"# and not in #"Cr"#.

#underbrace(ul(uarr color(white)(darr)))_(Cr)# #" "" "# #underbrace(ul(uarr darr))_(Mn)#

Hence, there is electron repulsion among the #4s# electrons that decreases the binding energy, or ionization energy, of #"Mn"# relative to #"Cr"#.

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