Meanwhile, the hypervalency of Xe in XeF2 is explained by the 3c4e bond, where the p orbitals of the 3 atoms overlap to form a delocalized system of 3 MO's in which 4 electrons (two from the Xe p orbital and one each from the p orbitals of the F atoms). This leads to a bond order of 1/2 per Xe-F group.

Obviously, the lewis representation that can be found everywhere on the Internet cannot be correct:

enter image description here

That would indicate a bond order of 1 per F-Xe Group, not 1/2.

As far as I know, resonance drawings are used to indicate delocalized bonds, so they also represent bond orders of 1/2. Shouldn't XeF2 then be represented as a lewis diagram as follows:

enter image description here

And I also wonder what orbitals are those 3 lone pairs at Xe? s,p,p? Or 3 sp2 hybride orbitals (which would make more sense for the geometry but less sense because hybridisation just makes sense for bonds)?

  • 2
    $\begingroup$ Lewis structures are not intended to be accurate representations of the electronic structure of molecules. They follow conventional rules that make the drawings simple, but informative. According to those conventions, expanded octets are preferred in the drawing for elements larger than fluorine, whether or not they are truly hypervalent. $\endgroup$
    – Andrew
    Dec 2, 2022 at 13:34
  • $\begingroup$ @Andrew Thank you! Btw. what do you mean by "whether or not they are truly hypervalent"? Are there compounds that are/ aren't truly hypervalent? $\endgroup$
    – iwab
    Dec 2, 2022 at 22:41
  • $\begingroup$ @Andrew Or more precisely, are there really any that are truly hypervalent? ch.imperial.ac.uk/rzepa/blog/?p=2599 $\endgroup$
    – iwab
    Dec 2, 2022 at 22:52
  • $\begingroup$ @Andrew Maybe I should consider hypervalency as a synonym for hypercoordination? $\endgroup$
    – iwab
    Dec 2, 2022 at 23:03
  • $\begingroup$ sure, if that helps you understand it. $\endgroup$
    – Andrew
    Dec 3, 2022 at 14:13

1 Answer 1


Just after XeF2 was discovered, D. F. Smith published a short communication Xenon Difluoride J. Chem. Phys. 38, 270 (1963) mentioning the electronic structure of your second drawing.

Smith conducted infrared spectroscopy of XeF2 and wrote:

enter image description here

Then C. A. Coulson published The nature of the bonding in xenon fluorides and related molecules J. Chem. Soc., 1964, 1442-1454, which considered the validity of four models (plus some sub-models) of XeF2 bonding.

Coulson adds more resonance structures in addition to the two mentioned by Smith, including a purely ionic F- Xe2+ F- resonance structure.

For a more recent article on the topic, see The essential role of charge-shift bonding in hypervalent prototype XeF2 Nature Chemistry 5, 417–422 (2013). (official link)

Overall, ionic contributions do need to be considered.


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