Helium compounds

l viaxs. Modeling Marvels, DOI 10.1007/978-1-4020-6973-4-5, Springer Science+Business Media B.V. 2008 

This would mean that there are 10 electrons in the valence shell of the Ng atom in xenon difluoride or krypton difluoride and 12 or 14 electrons for xenon tetrafluoride or hexafluoride, and even more for the octafluoroxenate ion, [XeFs] . Since one s and three p orbitals can accommodate only eight electrons, this would require the participation of d orbitals. In fact, the currently favored model uses only s and p atomic orbitals [16]. For example, XeF2 can be constmcted with a three-center-two-electron (3c-2e) bond, like NF5 (Chapter 4, Fig. 4.5) without using d orbitals (Fig. 5.1). Perhaps one should not worry much about which orbitals are involved, because as has been pointed out, bonding is not an observable quantity only bonding distancies and electron density are amenable to observation although 

2 electrons In a non bonding MO delocalized ever the two axial fluorines 

Neon and argon have so far revealed a far sparser chemistry than xenon and even krypton. This is in accord with their lEs (eV) Ne, 21.6 15.8 Kr, 14.0, Xe, 

Li et al. presented computational evidence that the anions FHeO , FArO, and FKrO are local minima (stable toward dissociation), and that the neutrals LiFArO (a trapezium-like stmcture) and LiFKrO (linear) can exist [29]. The former was calculated to lie 720kJmor below LL and FArO , and 84kJmol below LiF and ArO the latter was calculated to lie 649kJmor below LL and FKrO, and 46 kJ mor below LiF and KrO. 

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Up to the year of 2000, no compound of helium, neon, or argon was known. However, that did not discourage theoretical chemists from nominating candidate compounds to the synthetic community. In a conference in London in August 2000, there were two poster papers with the following intriguing titles Prediction of a stable helium compound HHeF by M. W. Wong and Will... 

In the course of their systematic theoretical investigation of positively charged helium compounds, Frenking, Cremer, and coworkers found [4, 7, 11,... 

For the honor of being a representative of neutral covalent helium compounds, there seem to be in the hterature otdy two serious (HeLiH may be very slightly - ca. 0.4kJmol - bound) candidates HHeF which, as briefly mentioned above, has been examined computationally, and HeBeO. Despite doubts [31], the evidence, on the whole, is that HHeF can exist [30], at least under pressure in sohd helium [32, 33] (conditions which, it must be conceded, wonld require somewhat specialized experimental equipment). Let us examine theoretical rationales for the possible existence of HHeF. In the simplest electronic pictnre, helium would use ls-2p... 

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