Electronegativity---what is the basis for the Pauling and others' ratings?

Question

OK.   Mostly we see the Pauling ratings for EN..but there are a few others...F is rated as highest and Cs is the lowest and it's all about propensity for giving vs. wanting electrons....but why the ranking scale from 0-4?  How was this arrived at and what are the latest guidelines determining ionic vs. polar covalent vs. non-polar covalent??  Thanks for any guidance in advance.

pisgahchemist · Accepted Answer

Electronegativity, depending on who is doing the calculating, can be computed from bond energies (Pauling), or from ionization energy and electron affinities (Mulliken), or from effective nuclear charge and covalent radius (Allred–Rochow).

Pauling did it first and the values came from a formula including bond energies in electron volts.  The other folks who made subsequent attempts at tweaking electronegativity using other factors, all made an attempt keep the values in the same ball park.

"Ionic" and "covalent" are simple arbitrary terms which are applied to a continuum.  I prefer to say that ALL bonds are covalent (since all bonding involves the sharing of electrons between different nuclei), but that some bonds are considerably more polar than others.  Specifying the percent ionic character is better than trying to say that a bond is either "ionic" or "covalent".

Percent ionic character = 100 [ 1 - e^(-DEN^2/4)] .... where DEN is the electronegativity difference

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Electronegativity---what is the basis for the Pauling and others' ratings?

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