Hydrogen astatide

"HAt" redirects here. For other uses, see Hat (disambiguation).

Hydrogen astatide, also known as astatine hydride, astatane, astatidohydrogen or hydroastatic acid, is a chemical compound with the chemical formula HAt, consisting of an astatine atom covalently bonded to a hydrogen atom.^[4] It thus is a hydrogen halide.

Hydrogen astatide

Ball-and-stick model of hydrogen astatide Spacefill model of hydrogen astatide
Names
IUPAC name Hydrogen astatide[1]
Systematic IUPAC name Astatane[2]
Identifiers
CAS Number	13464-71-6 Y
3D model (JSmol)	Interactive image
ChEBI	CHEBI:30418 Y
ChemSpider	22432 Y
Gmelin Reference	532398
PubChem CID	23996
CompTox Dashboard (EPA)	DTXSID10274755
InChI InChI=1S/AtH/h1H Y Key: PGLQOBBPBPTBQS-UHFFFAOYSA-N Y InChI=1/AtH/h1H Key: PGLQOBBPBPTBQS-UHFFFAOYAG
SMILES [AtH]
Properties
Chemical formula	HAt
Molar mass	211 g·mol−1
Boiling point	−3 °C (27 °F; 270 K) estimated[3]
Solubility in water	Soluble
Conjugate acid	Astatonium
Conjugate base	Astatide
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). Y verify (what is YN ?) Infobox references

This chemical compound can dissolve in water to form hydroastatic acid, which exhibits properties very similar to the other five 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,^[5] 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,^[6] 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. Furthermore, a trend for hydrogen halides, or HX, is that enthalpy of formation becomes less negative, i.e., decreases in magnitude but increases in absolute terms, as the halide becomes larger. 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,^[7] as the astatine will quickly decay into other elements.

Preparation

Hydrogen astatide can be produced by reacting astatine with hydrocarbons (such as ethane):^[8]

C₂H₆ + At₂ → C₂H₅At + HAt

This reaction also produces the corresponding alkyl astatide, in this case ethyl astatide (astatoethane).

References

1. "Hydrogen astatide (CHEBI:30418)".
2. Henri A. Favre; Warren H. Powell, eds. (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. Cambridge: The Royal Society of Chemistry. p. 131.
3. Analytical Chemistry of Technetium, Promethium, Astatine and Francium by Avgusta Konstantinovna. Lavrukhina, Aleksandr Aleksandrovich Pozdnyakov ISBN 0250399237
4. PubChem, "astatane - Compound Summary", accessed July 3, 2009.
5. Fairbrother, Peter, "Re: Is hydroastatic acid possible?" Archived 2011-02-02 at the Wayback Machine, accessed July 3, 2009.
6. Advances in Inorganic Chemistry, Volume 6 by Emeleus, p.219, Academic Press, 1964 ISBN 0-12-023606-0
7. Gagnon, Steve, "It's Elemental", accessed July 3, 2009.
8. Hagen, A. P. (1989). The formation of bonds to halogens. New York: VCH Publishers. ISBN 978-0-470-14538-8. OCLC 472256324.