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Name: Melissa F.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 11/24/2003


Question:
Why do some electronegative periodic charts have values for the noble gas Xenon at approximately 2.6?


Replies:
Historically Xe was thought to be non-reactive. In the past 20-40 years relatively stable compounds of both Xe and Kr with fluorine and/or oxygen have been made. Consequently, Xe can be assigned an electronegativity, its tendency to attract electrons, like other elements.

Vince Calder


Dear Melissa,

Xenon is now known to react with highly electronegative species. For example, xenon will react with fluorine to form XeF6. In 1962, N. Bartlett showed that Xe will react with PtF6 to form a red solid, which we now know is a xenoplatinum salt but he thought was XePtF6. At about the same time, R. Hoppe at al. carried out the same reaction, and also formed XeF2 by a different reaction. Xe has the ability hybridize its filled s and p orbitals with d orbitals to form hybrid orbitals which can bond to F, but of course it "violates" the Octet Rule. Of course, P and S also regularly violate this rule, so this is no big deal. It's a rule, not a law of nature...

As to the specific value you cited, I have not been able to dig that up. Pauling's scale was developed before Xe's chemistry was known and so Pauling electronegativity tables do not have an entry for Xe typically (although I guess it is possible that he proposed a value for Xe in the 70s or 80s. That would not be surprising to me at all). Kr is also now known to undergo some reactions.

There are several electronegativity scales in addition to Pauling's. The two best known are the Mullekin and Allred-Rochow scales, and there is a fourth one which is called the "spectroscopic electronegativity." The Allred-Rochow scale agrees pretty well trend-wise with the Pauling scale, and gives an electronegativity value of 2.4. This same scale also predicts electronegativity values for the other noble gases:

He=5.50, Ne=4.84, Ar=3.20, Kr=2.94, Xe=2.40.

I hope this did not muddy the waters too much. In the final analysis, the noble gases are fairly unreactive, but they are not all completely unreactive.

Best, Prof. Topper



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