Why is there an exception in the ionization energy trend in the second-row p-block elements?
1 Answer
I think you are wondering why nitrogen has an ionization energy that locally peaks in the ionization energy chart:
(search for the atom one left of
#"O"# , nitrogen, which is atomic number#7# .)
Nitrogen's atomic electron configuration is:
#[He]2s^2 2p^3# ,
or more explicitly:
#ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))#
#underbrace(" "" "" "" "" "" "" "" ")#
#" "" "" "2p#
#ul(uarr darr)#
#2s#
All the electrons are unpaired, so that's not the exception here.
The exception arises with
This is due to the atomic electron configuration for
#[He]2s^2 2p^4#
or more explicitly:
#ul(uarr darr)" "ul(uarr color(white)(darr))" "ul(uarr color(white)(darr))#
#underbrace(" "" "" "" "" "" "" "" ")#
#" "" "" "2p#
#ul(uarr darr)#
#2s#
One of the
That is enough to lower the first ionization energy of oxygen atom to be below that of nitrogen atom by about