Editing Electronegativity (section)

===Allen electronegativity===
[[Image:Pauling and Allen electronegativities.png|thumb|upright=1.35|The correlation between Allen electronegativities (''x''-axis, in kJ/mol) and Pauling electronegativities (''y''-axis).]]
Perhaps the simplest definition of electronegativity is that of Leland C. Allen, who has proposed that it is related to the average energy of the [[valence electron]]s in a free atom,<ref>{{cite journal |doi=10.1021/ja00207a003 |title=Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms|year=1989|author=Allen, Leland C.|journal=Journal of the American Chemical Society |volume=111|pages=9003–9014 |issue=25}}</ref><ref>{{cite journal|doi=10.1021/ja992866e|title=Configuration Energies of the Main Group Elements|year=2000|author=Mann, Joseph B. |author2=Meek, Terry L. |author3=Allen, Leland C. |journal=Journal of the American Chemical Society |volume=122 |pages=2780–2783|issue=12}}</ref><ref>{{cite journal|doi=10.1021/ja9928677|title=Configuration energies of the d-block elements |year=2000|author=Mann, Joseph B. |author2=Meek, Terry L. |author3=Knight, Eugene T. |author4=Capitani, Joseph F. |author5=Allen, Leland C. |journal=Journal of the American Chemical Society|volume=122|pages=5132–5137|issue=21}}</ref>

<math display="block">\chi = {n_{\rm s}\varepsilon_{\rm s} + n_{\rm p}\varepsilon_{\rm p} \over n_{\rm s} + n_{\rm p}}</math>

where ''ε''<sub>s,p</sub> are the one-electron energies of s- and p-electrons in the free atom and ''n''<sub>s,p</sub> are the number of s- and p-electrons in the valence shell.

The one-electron energies can be determined directly from [[Spectroscopy|spectroscopic data]], and so electronegativities calculated by this method are sometimes referred to as '''spectroscopic electronegativities'''. The necessary data are available for almost all elements, and this method allows the estimation of electronegativities for elements that cannot be treated by the other methods, e.g. [[francium]], which has an Allen electronegativity of 0.67.<ref name="Fr">The widely quoted Pauling electronegativity of 0.7 for francium is an extrapolated value of uncertain provenance. The Allen electronegativity of caesium is 0.66.</ref> However, it is not clear what should be considered to be valence electrons for the d- and f-block elements, which leads to an ambiguity for their electronegativities calculated by the Allen method.

On this scale, [[neon]] has the highest electronegativity of all elements, followed by [[fluorine]], [[helium]], and [[oxygen]].

{{periodic table (electronegativity by Allen scale)}}