Why is the election affinity of beryllium negative?

1 Answer
Truong-Son N.
Aug 12, 2017

Well, beryllium has a POSITIVE electron affinity, because it gets less stable when we try to fill the next orbitals, the #2p# orbitals... but I suppose even atoms can dislike certain electoral processes...

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The electron affinity is the change in energy due to adding a new electron to an atom or molecule. The to-scale electronic structure of beryllium is:

#underbrace(ul(color(white)(uarr darr))" "ul(color(white)(uarr darr))" "ul(color(white)(uarr darr)))#
#" "" "" "color(white)(.)2p#
#" "#
#" "#
#" "#
#" "#
#ul(uarr darr)#
#color(white)(.)2s#

#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#
#" "#

#ul(uarr darr)#
#color(white)(.)1s#

And so, it takes energy input in order to place a new electron into a #2p# orbital. Thus, #"EA"("Be") > 0#.

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