Editing Electronegativity (section)

===Mulliken electronegativity===
{{Anchor|Mulliken electronegativity}}

[[Image:Pauling and Mullikan electronegativities.png|thumb|upright=1.35|The correlation between Mulliken electronegativities (''x''-axis, in kJ/mol) and Pauling electronegativities (''y''-axis).]]
[[Robert S. Mulliken]] proposed that the [[arithmetic mean]] of the first [[ionization energy]] (E<sub>i</sub>) and the [[electron affinity]] (E<sub>ea</sub>) should be a measure of the tendency of an atom to attract electrons:<ref>{{cite journal |author = Mulliken, R. S.|year =1934 |journal = [[Journal of Chemical Physics]] |volume = 2 |title = A New Electroaffinity Scale; Together with Data on Valence States and on Valence Ionization Potentials and Electron Affinities |doi = 10.1063/1.1749394 |pages = 782–793 |issue = 11|bibcode = 1934JChPh...2..782M }}</ref><ref>{{cite journal |author= Mulliken, R. S. |year=1935 |title = Electronic Structures of Molecules XI. Electroaffinity, Molecular Orbitals and Dipole Moments |journal = [[Journal of Chemical Physics|J. Chem. Phys.]] |volume = 3 |doi = 10.1063/1.1749731 |pages = 573–585
|issue = 9|bibcode = 1935JChPh...3..573M }}</ref>
<math display="block">\chi = \frac{E_{\rm i} + E_{\rm ea}} 2 </math>

As this definition is not dependent on an arbitrary relative scale, it has also been termed '''absolute electronegativity''',<ref>{{cite journal |author=Pearson, R. G. |year=1985 |title=Absolute electronegativity and absolute hardness of Lewis acids and bases |journal=[[Journal of the American Chemical Society|J. Am. Chem. Soc.]] |volume=107 |issue=24 |pages=6801–6806 |doi=10.1021/ja00310a009}}</ref> with the units of [[Joule per mole|kilojoules per mole]] or [[electronvolt]]s. However, it is more usual to use a linear transformation to transform these absolute values into values that resemble the more familiar Pauling values. For ionization energies and electron affinities in electronvolts,<ref>{{cite book |last1=Huheey |first1=J.E. |last2=Keiter |first2=E.A. |last3=Keiter |first3=R.L. |date=December 1, 2008 |orig-year=1978 |chapter=17 |editor1-last=Kauffman |editor1-first=G.B. |title=Inorganic Chemistry: Principles of Structure and Reactivity |url=https://www.pdfdrive.com/inorganic-chemistry-principles-of-structure-and-reactivity-e175855674.html |type=digitalized |language=en |edition=3rd |location=New York |publication-date=1900 |page=167 |doi=10.1021/ed050pA379.1 |isbn=9780060429874 |oclc=770736023 |id= inorganicchemist00huhe_0 |archive-url=https://web.archive.org/web/20190908204147/https://www.pdfdrive.com/inorganic-chemistry-principles-of-structure-and-reactivity-e175855674.html |archive-date=September 8, 2019 |access-date=December 15, 2020 |via=Oxford University Press}} [https://archive.org/details/inorganicchemist00huhe_0 Alt URL]</ref>
<math display="block">\chi = 0.187(E_{\rm i} + E_{\rm ea}) + 0.17 \,</math>
and for energies in kilojoules per mole,<ref>This second relation has been recalculated using the best values of the first ionization energies and electron affinities available in 2006.</ref>
<math display="block">\chi = (1.97\times 10^{-3})(E_{\rm i} + E_{\rm ea}) + 0.19.</math>

The Mulliken electronegativity can only be calculated for an element whose electron affinity is known. [[Electron affinity (data page)|Measured values are available]] for 72 elements, while approximate values have been [[Electron affinity (data page)|estimated or calculated]] for the remaining elements.

The Mulliken electronegativity of an atom is sometimes said to be the negative of the [[chemical potential]].<ref>{{cite journal |last1=Franco-Pérez |first1=Marco |last2=Gázquez |first2=José L. |title=Electronegativities of Pauling and Mulliken in Density Functional Theory |journal=Journal of Physical Chemistry A |date=31 October 2019 |volume=123 |issue=46 |pages=10065–10071 |doi=10.1021/acs.jpca.9b07468 |pmid=31670960 |bibcode=2019JPCA..12310065F |s2cid=207814569 }}</ref>  By inserting the energetic definitions of the ionization potential and electron affinity into the Mulliken electronegativity, it is possible to show that the Mulliken chemical potential is a finite difference approximation of the electronic energy with respect to the number of electrons., i.e.,
<math display="block">\mu(\rm Mulliken) = -\chi(\rm Mulliken) = {}-\frac{E_{\rm i} + E_{\rm ea}} 2 </math>