Hydrogen astatide

Hydrogen astatide

Identifiers
3D model (Jmol)	Interactive image
ChEBI	CHEBI:30418
ChemSpider	22432
Gmelin Reference	532398
PubChem	23996
InChI InChI=1S/AtH/h1H Key: PGLQOBBPBPTBQS-UHFFFAOYSA-N InChI=1/AtH/h1H Key: PGLQOBBPBPTBQS-UHFFFAOYAG
SMILES [AtH]
Properties
Chemical formula	AtH
Molar mass	211.01 g·mol^−1
Related compounds
Other anions	Hydrogen bromide Hydrogen chloride Hydrogen fluoride Hydrogen iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Hydrogen astatide, also known as astatine hydride, astatane, or astidohydrogen, is a chemical compound with the chemical formula HAt, consisting of an astatine atom covalently bonded to a hydrogen atom.^[1] It thus is a hydrogen halide.

This chemical compound can dissolve in water to form hydroastatic acid, which exhibits properties very similar to the other four binary acids, and is in fact the strongest among them. However, it is limited in use due to its ready decomposition into elemental hydrogen and astatine,^[2] as well as the short half-life of the various isotopes of astatine. Because the atoms have a nearly equal electronegativity, and as the At⁺ ion has been observed,^[3] dissociation could easily result in the hydrogen carrying the negative charge. Thus, a hydrogen astatide sample can undergo the following reaction:

2 HAt → H⁺ + At⁻ + H⁻ + At⁺ → H₂ + At₂

This results in elemental hydrogen gas and astatine precipitate. Further, a trend for hydrogen halides, or HX, is that enthalpy of formation lowers as the period increases for the halide. Whereas hydroiodic acid solutions are stable, the hydronium-astatide solution is clearly less stable than the water-hydrogen-astatine system. Finally, radiolysis from astatine nuclei could sever the H-At bonds.

Additionally, astatine has no stable isotopes. The most stable is astatine-210, which has a half-life of approximately 8.1 hours, making its chemical compounds especially difficult to work with,^[4] as the astatine will quickly decay into other elements.

References

1. PubChem, "astatane - Compound Summary", accessed July 3, 2009.
2. Fairbrother, Peter, "Re: Is hydroastatic acid possible?", accessed July 3, 2009.
3. Advances in Inorganic Chemistry, Volume 6 by Emeleus, p.219, Academic Press, 1964 ISBN 0-12-023606-0
4. Gagnon, Steve, "It's Elemental", accessed July 3, 2009.