Editing Electronegativity (section)

===Periodic trends===
[[File:Periodic variation of Pauling electronegativities.svg|thumb|upright=1.5|The variation of Pauling electronegativity (''y''-axis) as one descends the main groups of the periodic table from the second period to the sixth period]]
In general, electronegativity increases on passing from left to right along a period and decreases on descending a group. Hence, [[fluorine]] is the most electronegative of the elements (not counting [[noble gas]]es), whereas [[caesium]]<!-- not francium; please don't change unless you supply a citation for published experimental results --> is the least electronegative, at least of those elements for which substantial data is available.<ref name="Fr"/>

There are some exceptions to this general rule. [[Gallium]] and [[germanium]] have higher electronegativities than [[aluminium]] and [[silicon]], respectively, because of the [[d-block contraction]]. Elements of the [[Period 4 element|fourth period]] immediately after the first row of the transition metals have unusually small atomic radii because the 3d-electrons are not effective at shielding the increased nuclear charge, and smaller atomic size correlates with higher electronegativity (see [[#Allred–Rochow electronegativity|Allred-Rochow electronegativity]] and [[#Sanderson electronegativity equalization|Sanderson electronegativity]] above). The anomalously high electronegativity of [[lead]], in particular when compared to [[thallium]] and [[bismuth]], is an artifact of electronegativity varying with oxidation state: its electronegativity conforms better to trends if it is quoted for the +2 state with a Pauling value of 1.87 instead of the +4 state.