Editing Electronegativity (section)

{{Short description|Tendency of an atom to attract a shared pair of electrons}}
{{Redirect|Electronegative|the Nightfall EP|Electronegative (EP){{!}}''Electronegative'' (EP)}}
[[Image:Electrostatic Potential.jpg|thumb|alt=A water molecule is put into a see-through egg shape, which is color-coded by electrostatic potential. A concentration of red is near the top of the shape, where the oxygen atom is, and gradually shifts through yellow, green, and then to blue near the lower-right and lower-left corners of the shape where the hydrogen atoms are.|upright=1.5|right|Electrostatic potential map of a water molecule, where the oxygen atom has a more negative charge (red) than the positive (blue) hydrogen atoms]]
'''Electronegativity''', symbolized as <span class="nounderlines">''[[Chi (letter)|χ]]''</span>, is the tendency for an [[atom]] of a given [[chemical element]] to attract shared [[electron]]s (or [[electron density]]) when forming a [[chemical bond]].<ref name="definition">{{GoldBookRef|file=E01990|title=Electronegativity}}</ref> An atom's electronegativity is affected by both its [[atomic number]] and the distance at which its [[valence electrons]] reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons. Electronegativity serves as a simple way to quantitatively estimate the [[bond energy]], and the sign and magnitude of a bond's [[chemical polarity]], which characterizes a bond along the continuous scale from [[Covalent bonding|covalent]] to [[ionic bonding]]. The loosely defined term '''electropositivity''' is the opposite of electronegativity: it characterizes an element's tendency to donate valence electrons.

On the most basic level, electronegativity is determined by factors like the [[effective nuclear charge|nuclear charge]] (the more [[protons]] an atom has, the more "pull" it will have on electrons) and the number and location of other electrons in the [[Electron shell|atomic shells]] (the more electrons an atom has, the farther from the [[Atomic nucleus|nucleus]] the valence electrons will be, and as a result, the less positive charge they will experience—both because of their increased distance from the nucleus and because the other electrons in the lower energy core [[atomic orbital|orbitals]] will act to [[Shielding effect|shield]] the valence electrons from the positively charged nucleus).

The term "electronegativity" was introduced by [[Jöns Jacob Berzelius]] in 1811,<ref name="Jensen">{{cite journal |author= Jensen, W.B.
 |author-link=William B. Jensen
 |year= 1996
 |journal= [[Journal of Chemical Education]]
 |volume= 73
 |issue= 1
 |pages= 11–20
 |title= Electronegativity from Avogadro to Pauling: Part 1: Origins of the Electronegativity Concept
 |doi= 10.1021/ed073p11|bibcode = 1996JChEd..73...11J }}</ref>
though the concept was known before that and was studied by many chemists including [[Amadeo Avogadro|Avogadro]].<ref name="Jensen"/>
In spite of its long history, an accurate scale of electronegativity was not developed until 1932, when [[Linus Pauling]] proposed an electronegativity scale which depends on bond energies, as a development of [[valence bond theory]].<ref name="paulingJACS">{{cite journal |author= Pauling, L.
 |author-link=Linus Pauling
 |year= 1932
 |journal= [[Journal of the American Chemical Society]]
 |volume= 54
 |issue= 9
 |pages= 3570–3582
 |title= The Nature of the Chemical Bond. IV. The Energy of Single Bonds and the Relative Electronegativity of Atoms
 |doi= 10.1021/ja01348a011
 }}</ref> It has been shown to correlate with a number of other chemical properties. Electronegativity cannot be directly measured and must be calculated from other atomic or molecular properties. Several methods of calculation have been proposed, and although there may be small differences in the numerical values of the electronegativity, all methods show the same [[periodic trends]] between [[Chemical element|elements]].<ref>{{Cite journal |last=Sproul |first=Gordon D. |date=2020-05-26 |title=Evaluation of Electronegativity Scales |url=https://doi.org/10.1021/acsomega.0c00831 |journal=ACS Omega |volume=5 |issue=20 |pages=11585–11594 |doi=10.1021/acsomega.0c00831|pmid=32478249 |pmc=7254809 }}</ref>

The most commonly used method of calculation is that originally proposed by Linus Pauling. This gives a [[dimensionless quantity]], commonly referred to as the '''Pauling scale''' (''χ''<sub>r</sub>), on a relative scale running from 0.79 to 3.98 ([[hydrogen]]&nbsp;= 2.20). When other methods of calculation are used, it is conventional (although not obligatory) to quote the results on a scale that covers the same range of numerical values: this is known as an electronegativity in ''Pauling units''.

As it is usually calculated, electronegativity is not a property of an atom alone, but rather a property of an atom in a [[molecule]].<ref name="NOTCB">{{cite book|author=Pauling, Linus|year=1960|title=Nature of the Chemical Bond|url=https://archive.org/details/natureofchemical00paul|url-access=registration|publisher=Cornell University Press|pages=[https://archive.org/details/natureofchemical00paul/page/88 88–107]|isbn=978-0-8014-0333-0}}</ref> Even so, the electronegativity of an atom is strongly correlated with the [[Ionization energy|first ionization energy]]. The electronegativity is slightly negatively correlated (for smaller electronegativity values) and rather strongly positively correlated (for most and larger electronegativity values) with the [[electron affinity]].<ref>"[https://web.archive.org/web/20190621000348/https://pubchem.ncbi.nlm.nih.gov/periodic-table/#view=table&property=Electronegativity PubChem ElectroNegativity]," Downloaded, line-graphed, and correlated 'Electronegativity' with 'ElectronAffinity', showing a rather strong positive correlation of '0.712925965'. (Accessed linked site on 2023-09-16.)</ref> It is to be expected that the electronegativity of an element will vary with its chemical environment,<ref>{{cite book|author1=Greenwood, N. N. |author2=Earnshaw, A. |year=1984|title=Chemistry of the Elements|publisher=Pergamon|isbn=978-0-08-022057-4|page=30}}</ref> but it is usually considered to be a [[Transferability (chemistry)|transferable property]], that is to say that similar values will be valid in a variety of situations.

[[Caesium]] is the least electronegative element (0.79);<!--NOT FRANCIUM SEE BELOW--> [[fluorine]] is the most (3.98).