On the table of electronegativies, why are there no electronegativity values for noble gases?

Question

a. Noble gases do not generally form negatively charged anions.

b. Noble gases do not generally participate in covalent bonding.

c. Noble gases do not generally participate in ionic bonding.

d. Noble gases do not have negatively charged electrons.

Answer 1

Hi Anna B.,

Interesting choices. You can eliminate (d) immediately; all electrons are negatively charged at all times. (a), (b) and (c) are all true. (a) is the best reason, I suppose, since electronegativity formally relates to energy release when an additional electron is added to a neutral atom of an element. Noble gases don't want to do that, so although the "value" would be zero (or even negative!), the process doesn't take place, hence (a). I don't recall the specifics of the bonding when Xe, for example, combines with O. I suspect it's covalent, since an ionic lattice would have to be stable to form at all, and XeO3, though explosion-prone, is stable until it does explode. But it's only a very weak bond, the Xe donates a little e-, the O accepts what it gets. Now, normally, you'd rate a strong covalent bond as one where the two atoms have way different electronegativities, so that it makes energetic sense for one to give an electron partially to the other. Hence, a weak covalent bond would imply that the two elements have comparable electronegativities (and no empty orbital filling). But oxygen is very electronegative, and xenon, zero! The problem here stems from the generalization of "electronegativity", the physicists' term for pure acceptance energy release, to the chemists' usage, which includes "wants to attract more and also keep the electrons it has" when forming a bond. Only in the case of the noble gases do these two usages really knock heads, so to speak.

-- Cheers, --Mr. d.