Noble gas compound
Consistent with this classification, Kr, Xe, and Rn form compounds that can be isolated in bulk at or near standard temperature and pressure, whereas He, Ne, Ar have been observed to form true chemical bonds using spectroscopic techniques, but only when frozen into a noble gas matrix at temperatures of 40 K (−233 °C; −388 °F) or lower, in supersonic jets of noble gas, or under extremely high pressures with metals.
With the development of atomic theory in the early twentieth century, their inertness was ascribed to a full valence shell of electrons which render them very chemically stable and nonreactive.
All noble gases have full s and p outer electron shells (except helium, which has no p sublevel), and so do not form chemical compounds easily.
In 1933, Linus Pauling predicted that the heavier noble gases would be able to form compounds with fluorine and oxygen.
[11] In this section, the non-radioactive noble gases are considered in decreasing order of atomic weight, which generally reflects the priority of their discovery, and the breadth of available information for these compounds.
The radioactive elements radon and oganesson are harder to study and are considered at the end of the section.
; the range of compounds is impressive, similar to that seen with the neighbouring element iodine, running into the thousands and involving bonds between xenon and oxygen, nitrogen, carbon, boron and even gold, as well as perxenic acid, several halides, and complex ions.
[23] There is some empirical and theoretical evidence for a few metastable helium compounds which may exist at very low temperatures or extreme pressures.
Radon is not chemically inert, but its short half-life (3.8 days for 222Rn) and the high energy of its radioactivity make it difficult to investigate its only fluoride (RnF2), its reported oxide (RnO3), and their reaction products.
It has a face-centered cubic structure where krypton octahedra are surrounded by randomly oriented hydrogen molecules.
[citation needed] Hydrates are formed by compressing noble gases in water, where it is believed that the water molecule, a strong dipole, induces a weak dipole in the noble gas atoms, resulting in dipole-dipole interaction.
[37] Under these conditions, only about one out of every 650,000 C60 cages was doped with a helium atom; with higher pressures (3000 bar), it is possible to achieve a yield of up to 0.1%.
Xenic acid is a valuable oxidising agent because it has no potential for introducing impurities—xenon is simply liberated as a gas—and so is rivalled only by ozone in this regard.
[citation needed] Xenon-based oxidants have also been used for synthesizing carbocations stable at room temperature, in SO2ClF solution.
[39][non-primary source needed] Stable salts of xenon containing very high proportions of fluorine by weight (such as tetrafluoroammonium heptafluoroxenate(VI), [NF4][XeF7], and the related tetrafluoroammonium octafluoroxenate(VI) [NF4]2[XeF8]), have been developed as highly energetic oxidisers for use as propellants in rocketry.
[citation needed] (For instance, radioactive isotopes of krypton and xenon are difficult to store and dispose, and compounds of these elements may be more easily handled than the gaseous forms.
[4]) In addition, clathrates of radioisotopes may provide suitable formulations for experiments requiring sources of particular types of radiation; hence.
