Hydrogen astatide

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Hydrogen astatide
Skeletal formula of hydrogen astatide with the explicit hydrogen and a measurement added
Ball-and-stick model of hydrogen astatide
Spacefill model of hydrogen astatide
ChEBI CHEBI:30418 YesY
ChemSpider 22432 YesY
Jmol-3D images Image
PubChem 23996
Molar mass 211.00 g·mol−1
Related compounds
Other anions
Hydrogen bromide

Hydrogen chloride
Hydrogen fluoride
Hydrogen iodide

Except where noted otherwise, data is 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]

This chemical compound exhibits properties very similar to the other four hydrogen halides, and is in fact the strongest acid 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; of which 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.


  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.