I propose the Pauling Scale is not valid in all circumstances, and other scales of electronegativity would do better to predict the behavior of electron density in molecules: Electronegativity seems to be poorly defined for such a widely used chemical property: a 'tendency' of an atom or functional group to attract electrons. Although the Pauling Scale works well in most cases to describe the relative stability of ionic bonds, it does not always correctly predict which atom or functional group will 'more strongly' attract electrons. As an example: According to the Pauling Scale: Ru = 2.2 Si = 1.9 With these values in mind, we will compare the electron density in the compounds Ruthenium Dioxide and Silicon Dioxide: Since Oxygen is more electronegative (on any electronegativity scale, not just Pauling) than either Ru or Si it is safe to assume that there will be a transfer of electron density from the Ru or Si cations to the Oxygen anions. This much we are sure of. If we were chemists we might be satisfied with this as both Ru and Si will be in a 4+ oxidation state. But as a physicist we know that an exact charge transfer does not occur in either case. Instead the electron probability density will reside closer to Oxygen, but again the exact charge transfer does not occur, so how much charge transfer exactly? Using the Pauling Scale one might assume that the ruthenium will be relatively less likely to transfer its electron density to oxygen than silicon. Going along with this we will find that there will be a greater negative screening charge around the oxygen atoms in SiO2 than those in RuO2... But this is not the case. Experimental data has shown that the binding energy of the Oxygen 1s electrons in RuO2 is lower than that of that of the Oxygen 1s electrons in SiO2. This shows the ruthenium transferred more electron density to the oxygen atoms in RuO2 than silicon to oxygen in SiO2. (Please comment if you do not accept this, and I will point you in the direction of XPS evidence.) For those of you unfamiliar with the relation of core electron binding energies and the surrounding electron density: The more reduced (greater excess electron density) an atom is the lower the binding energy of core electrons. I find that these results agree with other electronegativity scales such as the Absolute (Mulliken) Scale and the Allen Scale, however the Pauling scale, horrendously fails in this situation. Would the readers please comment on why the Pauling Scale is still used over others (besides historical reasons) specifically if it has any advantages over the Allen or Mulliken Scales. Further, if the reader has any knowledge of the reason the Mulliken Scale is used over the Pauling Scale in XPS analysis, I would be grateful if you would show me why.