Editing Astatine (section)

=== Physical ===
Most of the physical properties of astatine have been estimated (by [[interpolation]] or [[extrapolation]]), using theoretically or empirically derived methods.<ref>{{cite book|title=Supplement to Mellor's Comprehensive Treatise on Inorganic and Theoretical Chemistry, Supplement II, Part 1, (F, Cl, Br, I, At)| pages=1064–1079|chapter=Astatine|year=1956|first=A. G.|last=Maddock |publisher = Longmans, Green & Co. (Ltd.)}}</ref> For example, halogens get darker with increasing atomic weight&nbsp;– [[fluorine]] is nearly colorless, [[chlorine]] is yellow-green, [[bromine]] is red-brown, and [[iodine]] is dark gray/violet. Astatine is sometimes described as probably being a black solid (assuming it follows this trend), or as having a metallic appearance (if it is a metalloid or a metal).<ref>{{cite book|url=https://books.google.com/books?id=NKUNAQAAIAAJ|title=Chemistry: A First Course in Modern Chemistry|year=1961|page=313|publisher=Ginn|last1=Garrett|first1=A. B.|last2=Richardson|first2=J. B.|last3=Kiefer|first3=A. S.}}</ref><ref>{{cite book|chapter-url=https://www.britannica.com/EBchecked/topic/603220/transuranium-element/81196/The-first-transactinoid-elements|chapter=Transuranium element|author-link=Glenn T. Seaborg|last=Seaborg|first=G. T.|title=Encyclopædia Britannica|year=2015|access-date=24 February 2015}}</ref><ref>{{cite book|title=Chemistry Expression: An Inquiry Approach|publisher=John Wiley and Sons|page=300|first=H. L.|last=Oon|year=2007|isbn=978-981-271-162-5|url=https://books.google.com/books?id=jd-BR-nfzIoC}}</ref>

Astatine sublimes less readily than iodine, having a lower [[vapor pressure]].<ref name="MoreAtIC" /> Even so, half of a given quantity of astatine will vaporize in approximately an hour if put on a clean glass surface at [[room temperature]].{{efn|This half-vaporization period grows to 16 hours if it is instead put on a gold or platinum surface; this may be caused by poorly understood interactions between astatine and these [[noble metal]]s.{{sfn|Lavrukhina|Pozdnyakov|1970|p=251}}}} The [[absorption spectrum]] of astatine in the [[middle ultraviolet]] region has lines at 224.401 and 216.225&nbsp;nm, suggestive of [[electron configuration|6p to 7s]] [[atomic electron transition|transitions]].<ref>{{cite journal |first1=R.|last1= McLaughlin |year=1964|title= Absorption Spectrum of Astatine |journal= Journal of the Optical Society of America
|volume=54 |issue=8|pages=965–967|doi=10.1364/JOSA.54.000965|url= http://www.escholarship.org/uc/item/3j83k4hx |bibcode= 1964JOSA...54..965M }}</ref>{{sfn|Lavrukhina|Pozdnyakov|1970|p=235}}

The structure of solid astatine is unknown.<ref>{{cite book | title = The Structures of the Elements | year = 1982 | page = 400 | publisher = Robert E. Krieger | isbn = 978-0-89874-230-5 | last = Donohue | first = J. | url=https://books.google.com/books?id=MshQAAAAYAAJ}}</ref> As an analog of iodine it may have an [[orthorhombic crystal system|orthorhombic crystalline structure]] composed of [[diatomic]] astatine molecules, and be a semiconductor (with a [[band gap]] of 0.7&nbsp;[[electronvolt|eV]]).<ref name="Vernon" /><ref>{{Cite journal |last=Batsanov |first=S. S. |date=1972 |title=Quantitative characteristics of bond metallicity in crystals |url= |journal=Journal of Structural Chemistry |language=en |volume=12 |issue=5 |pages=809–813 |doi=10.1007/BF00743349 |bibcode=1972JStCh..12..809B |s2cid=96816296 |issn=0022-4766}}</ref> Alternatively, if condensed astatine forms a metallic phase, as has been predicted, it may have a monatomic [[cubic close packed|face-centered cubic structure]]; in this structure, it may well be a [[superconductor]], like the similar high-pressure phase of iodine.<ref name="Hermann" /> Metallic astatine is expected to have a density of 8.91–8.95&nbsp;g/cm<sup>3</sup>.<ref name="Arblaster" />

Evidence for (or against) the existence of diatomic astatine (At<sub>2</sub>) is sparse and inconclusive.<ref>{{cite journal | language = fr| title = Etude de la formation en phase gazeuse de composés interhalogénés d'astate par thermochromatographie | trans-title = Study of the gas-phase formation of interhalogen compounds of astatine by [[wikt:thermochromatography|thermochromatography]] | last1= Merinis | first1 = J. | last2= Legoux | first2 = G. | last3 = Bouissières | first3 = G. | journal = Radiochemical and Radioanalytical Letters | volume = 11 | pages = 59–64 | year = 1972 | issue = 1 }}</ref><ref>{{cite journal | title = The Mechanism of the Reaction of Elementary Astatine with Organic Solvents | last1= Takahashi | first1 = N. | last2= Otozai | first2 = K. | journal = Journal of Radioanalytical and Nuclear Chemistry | volume = 103 | pages = 1–9 | year = 1986 | issue= 1 | doi =10.1007/BF02165358 | bibcode= 1986JRNC..103....1T | s2cid= 93572282 }}</ref><ref>{{cite conference | title = Chemical Behavior of Astatine Molecules | last1= Takahashi | first1 = N. | last2= Yano | first2 = D. | last3= Baba | first3 = H. | book-title = Proceedings of the International Conference on Evolution in Beam Applications, Takasaki, Japan, 5–8 November 1991 | pages = 536–539| year = 1992 }}</ref>{{sfn|Zuckerman|Hagen|1989|p=21}}{{sfn|Kugler|Keller|1985|pp=110, 116, 210–211, 224}} Some sources state that it does not exist, or at least has never been observed,<ref name="Meyers2002">{{cite encyclopedia | encyclopedia = Encyclopedia of Physical Science and Technology | edition=3rd| title = Halogen Chemistry| year = 2001 | last = Meyers | first = R. A. | pages = 197–222 (202) | isbn = 978-0-12-227410-7 | publisher = Academic Press}}</ref><ref name="Ullmann">{{cite book | last1= Keller | first1 = C.| title = Ullmann's Encyclopedia of Industrial Chemistry| last2= Wolf | first2 = W. | last3 = Shani | first3 = J.| volume = 31 | pages = 89–117 (96) | year = 2011 | doi =10.1002/14356007.o22_o15 | isbn = 978-3-527-30673-2 | chapter= Radionuclides, 2. Radioactive Elements and Artificial Radionuclides}}</ref> while other sources assert or imply its existence.<ref name="boiling_point_chromatography">{{cite journal | title = Estimation Chemical Form Boiling Point Elementary Astatine by Radio Gas Chromatography | last1= Otozai | first1 = K. | last2= Takahashi | first2 = N. | journal = Radiochimica Acta | volume = 31 | pages = 201–203 | year = 1982 |url = http://www.mendeley.com/research/estimation-chemical-form-boiling-point-elementary-astatine-radio-gas-chromatography/ | issue = 3–4 | doi=10.1524/ract.1982.31.34.201| s2cid= 100363889 }}</ref><ref>{{cite book | title = Chemistry | edition=8th | year = 2008 | page = 56 | publisher = Cengage Learning | isbn = 978-0-547-12532-9 | last1 = Zumdahl | first1 = S. S. | last2 = Zumdahl | first2 = S. A. | url = https://books.google.com/books?id=LLWkH82PNbYC}}</ref><ref name="Housecroft">{{cite book | title = Inorganic chemistry | edition=3rd| year = 2008 | page = 533 | publisher = Pearson Education | isbn = 978-0-13-175553-6 | last1 = Housecroft | first1 = C. E. | last2 = Sharpe | first2 = A. G.}}</ref> Despite this controversy, many properties of diatomic astatine have been predicted;{{sfn|Kugler|Keller|1985|p=116}} for example, its bond length would be {{val|300|10|u=[[picometer|pm]]}}, dissociation energy <{{val|50|u=kJ/mol}},<ref>{{cite journal | last1=Burgers | first1=Peter C. | last2=Zeneyedpour | first2=Lona | last3=Luider | first3=Theo M. | last4=Holmes | first4=John L. | title=Estimation of thermodynamic and physicochemical properties of the alkali astatides: On the bond strength of molecular astatine (At<sub>2</sub>) and the hydration enthalpy of astatide (At<sup>−</sup>) | journal=Journal of Mass Spectrometry | volume=59 | issue=4 | date=2024 | pages=e5010 | issn=1076-5174 | doi=10.1002/jms.5010| pmid=38488842 | doi-access=free }}</ref> and [[heat of vaporization]] (∆H<sub>vap</sub>) 54.39&nbsp;kJ/mol.<ref name="Glushko">{{cite book|first1=V. P.|last1=Glushko |first2=V. A.|last2=Medvedev|last3=Bergma|first3=G. A.|year=1966|title=Termicheskie Konstanty Veshchestv|language=ru|volume=1|publisher=Nakua|page=65}}</ref> Many values have been predicted for the [[melting point|melting]] and [[boiling point]]s of astatine, but only for At<sub>2</sub>.{{sfn|Kugler|Keller|1985|pp=116–117}}