Editing Astatine (section)

== Characteristics ==
Astatine is an extremely radioactive element; all its isotopes have [[half-lives]] of 8.1 hours or less, decaying into other astatine isotopes, [[bismuth]], [[polonium]], or [[radon]]. Most of its isotopes are very unstable, with half-lives of seconds or less. Of the first 101 elements in the periodic table, only [[francium]] is less stable, and all the astatine isotopes more stable than the longest-lived francium isotopes (<sup>205–211</sup>At) are in any case synthetic and do not occur in nature.<ref name="Audi2003">{{NUBASE 2003|mode=cs1}}</ref>

The bulk properties of astatine are not known with any certainty.{{sfn|Greenwood|Earnshaw|2002|p=795}} Research is limited by its short half-life, which prevents the creation of weighable quantities.<ref name="MoreAtIC">{{cite book|title=Holleman-Wiberg: Inorganic Chemistry|publisher=Academic Press|page=423|editor-first1=N.|editor-last1=Wiberg|year=2001|isbn=978-0-12-352651-9|others=Translation of 101st German edition by M. Eagleson and W. D. Brewer, English language editor B. J. Aylett|url=https://books.google.com/books?id=Mtth5g59dEIC}}</ref> A visible piece of astatine would immediately vaporize itself because of the heat generated by its intense radioactivity.<ref name="Emsley" /> It remains to be seen if, with sufficient cooling, a macroscopic quantity of astatine could be deposited as a thin film.<ref name="Hermann" /> Astatine is usually classified as either a [[nonmetal]] or a [[metalloid]];<ref>{{cite book|title=Chemistry & Chemical Reactivity|year=2011|edition=8th|page=65|publisher=Cengage Learning|isbn=978-0-8400-4828-8|last1=Kotz|first1=J. C.|last2=Treichel|first2=P. M.|last3=Townsend|first3=J.}}</ref><ref name="Jahn2010">{{cite book|title=MIPS and Their Role in the Exchange of Metalloids|year=2010|last=Jahn|first=T. P.|page=41|volume=679|publisher=Springer|isbn=978-1-4419-6314-7|url=https://books.google.com/books?id=ayGhnf3A-L0C}}</ref> metal formation has also been predicted.<ref name="Hermann" /><ref>{{cite book|title=Concise Chemistry of the Elements|year=2002|pages=65, 122|publisher=Horwood|isbn=978-1-898563-71-6|last1=Siekierski|first1=S.|last2=Burgess|first2 =J.|url=https://books.google.com/books?id=1I8sByjBONoC&pg=PA3}}</ref>

=== 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}}

=== Chemical ===
The chemistry of astatine is "clouded by the extremely low concentrations at which astatine experiments have been conducted, and the possibility of reactions with impurities, walls and filters, or radioactivity by-products, and other unwanted nano-scale interactions".<ref name="Vernon">{{cite journal|last1=Vernon|first1=R.|year=2013|title=Which Elements are Metalloids?|journal=Journal of Chemical Education|volume=90|issue=12|pages=1703–1707 (1704)|bibcode=2013JChEd..90.1703V|doi=10.1021/ed3008457}}</ref> Many of its apparent chemical properties have been observed using [[radioactive tracer|tracer]] studies on extremely dilute astatine solutions,<ref name="Housecroft" /><ref>{{cite book | title = College chemistry | year = 1960 | page = 457 | publisher = Appleton-Century-Crofts | last1 = Smith | first1 = A. | last2 = Ehret | first2 = W. F.}}</ref> typically less than 10<sup>−10</sup> mol·L<sup>−1</sup>.<ref name="Champion">{{cite journal|last1=Champion|first1=J.|last2=Seydou|first2=M.|last3=Sabatié-Gogova|first3=A.|last4=Renault|first4=E.|last5=Montavon|first5=G.|last6=Galland|first6=N.|year=2011|title=Assessment of an Effective Quasirelativistic Methodology Designed to Study Astatine Chemistry in Aqueous Solution|journal=[[Physical Chemistry Chemical Physics]]|volume=13|issue=33|pages=14984–14992 (14984)|bibcode=2011PCCP...1314984C|doi=10.1039/C1CP20512A|pmid=21769335|url=https://pubs.rsc.org/en/content/articlelanding/2011/CP/c1cp20512a|url-access=subscription}}</ref> Some properties, such as anion formation, align with other halogens.<ref name="MoreAtIC" /> Astatine has some metallic characteristics as well, such as [[electroplating|plating]] onto a [[cathode]],{{efn|It is also possible that this is [[sorption]] on a cathode.<ref>{{cite journal|doi=10.1007/BF02037143|journal=Journal of Radioanalytical and Nuclear Chemistry|volume=83|pages=291–299|title=Chemical Properties of Positive Singly Charged Astatine Ion in Aqueous Solution|year=1984|first1=M.|last1=Milanov|first2=V.|last2=Doberenz|first3=V. A.|last3=Khalkin|first4=A.|last4=Marinov|issue=2|bibcode=1984JRNC...83..291M |s2cid=97361684}}</ref>}} and [[Coprecipitation|coprecipitating]] with metal sulfides in [[hydrochloric acid]].{{sfn|Lavrukhina|Pozdnyakov|1970|p=234}} It forms complexes with [[EDTA]], a metal [[chelating agent]],<ref>{{cite journal |last1=Milesz|first1=S. |last2=Jovchev|first2=M. |last3=Schumann|first3=D. |last4=Khalkin|first4=V. A. |year=1988|title=The EDTA Complexes of Astatine |journal=Journal of Radioanalytical and Nuclear Chemistry |volume=127 |issue=3 |pages=193–198 |doi=10.1007/BF02164864|bibcode=1988JRNC..127..193M |s2cid=93032218 }}</ref> and is capable of acting as a metal in [[antibody]] [[radiolabeling]]; in some respects, astatine in the +1 state is akin to silver in the same state. Most of the organic chemistry of astatine is, however, analogous to that of iodine.<ref name="Guerard">{{cite journal |first1=F.|last1=Guérard|first2=J.-F.|last2=Gestin|first3=M. W.|last3=Brechbiel |year=2013 |title=Production of [<sup>211</sup>At]-Astatinated Radiopharmaceuticals and Applications in Targeted α-Particle Therapy |journal=Cancer Biotherapy and Radiopharmaceuticals |volume=28 |issue=1|pages=1–20 |doi=10.1089/cbr.2012.1292|pmc=3545490 |pmid=23075373}}</ref> It has been suggested that astatine can form a stable [[monatomic cation]] in aqueous solution.{{sfn|Lavrukhina|Pozdnyakov|1970|p=234}}<ref>{{cite journal |last1= Champion |first1= J.|last2=Alliot |first2=C. |last3=Renault |first3=E. |last4=Mokili |first4=B. M. |last5=Chérel |first5=M.| last6=Galland |first6=N. |last7=Montavon |first7=G. | year=2010 |title=Astatine Standard Redox Potentials and Speciation in Acidic Medium |journal=The Journal of Physical Chemistry A |volume=114 |issue=1 |pages=576–582 (581) |doi=10.1021/jp9077008|pmid= 20014840|url=http://hal.in2p3.fr/in2p3-00450771 |bibcode=2010JPCA..114..576C |s2cid= 15738065}}</ref>

Astatine has an [[electronegativity]] of 2.2 on the revised [[Pauling scale]]&nbsp;– lower than that of iodine (2.66) and the same as hydrogen. In [[hydrogen astatide]] (HAt), the negative charge is predicted to be on the hydrogen atom, implying that this compound could be referred to as astatine hydride according to certain nomenclatures.<ref>{{cite journal|last1=Dolg|first1=M.|last2=Kuchle|first2=W.|last3=Stoll|first3=H.|last4=Preuss|first4=H.|last5=Schwerdtfeger|first5=P.|title=''Ab Initio'' Pseudopotentials for Hg to Rn: II. Molecular Calculations on the Hydrides of Hg to At and the Fluorides of Rn|journal=Molecular Physics|volume=74|issue=6|pages=1265–1285 (1265, 1270, 1282)|year=1991|doi=10.1080/00268979100102951|bibcode=1991MolPh..74.1265D}}</ref><ref>{{cite journal|last1=Saue|first1=T.|last2=Faegri|first2=K.|last3=Gropen|first3=O.|title=Relativistic Effects on the Bonding of Heavy and Superheavy Hydrogen Halides|journal=Chemical Physics Letters|volume=263|pages=360–366 (361–362)|year=1996|doi=10.1016/S0009-2614(96)01250-X|issue=3–4|bibcode=1996CPL...263..360S}}</ref><ref name="H-">{{cite book|title=Relativistic Methods for Chemists|first=M.|last=Barysz|page=79|publisher=Springer|year=2010 | isbn = 978-1-4020-9974-8 | url=https://books.google.com/books?id=QbDEC3oL7uAC}}</ref><ref>{{cite journal|last=Thayer|first=J. S.|title=Relativistic Effects and the Chemistry of the Heaviest Main-group elements|journal=Journal of Chemical Education|volume=82|issue=11|pages=1721–1727 (1725)|year=2005|doi=10.1021/ed082p1721|bibcode=2005JChEd..82.1721T}}</ref> That would be consistent with the electronegativity of astatine on the [[Allred–Rochow scale]] (1.9) being less than that of hydrogen (2.2).<ref>{{cite book | title =Inorganic Chemistry| year = 2000 | page = 37 | publisher = University Science Books | isbn = 978-1-891389-01-6 | last1= Wulfsberg | first1=G. }}</ref>{{efn|The algorithm used to generate the Allred-Rochow scale fails in the case of hydrogen, providing a value that is close to that of oxygen (3.5). Hydrogen is instead assigned a value of 2.2. Despite this shortcoming, the Allred-Rochow scale has achieved a relatively high degree of acceptance.<ref>{{cite book | title = Inorganic Substances: A Prelude to the Study of Descriptive Inorganic Chemistry | year = 1990 | page = [https://archive.org/details/inorganicsubstan0000smit/page/135 135] | publisher = Cambridge University Press | last = Smith | first = D. W.| isbn = 978-0-521-33738-0 | url = https://archive.org/details/inorganicsubstan0000smit| url-access = registration }}</ref>}} However, official IUPAC stoichiometric nomenclature is based on an idealized convention of determining the relative electronegativities of the elements by the mere virtue of their position within the periodic table. According to this convention, astatine is handled as though it is more electronegative than hydrogen, irrespective of its true electronegativity. The [[electron affinity]] of astatine, at 233 kJ mol<sup>−1</sup>, is 21% less than that of iodine.<ref>{{cite journal|last1=Leimbach |first1=D.|last2=Sundberg |first2=J.|last3=Yangyang|first3=G.|display-authors=etal|date=February 2020|title=The electron affinity of astatine|journal=Nature Communications|volume=11|issue=1|page=3824|doi=10.1038/s41467-020-17599-2|pmid=32733029|pmc=7393155|arxiv=2002.11418|bibcode=2020NatCo..11.3824L}}</ref> In comparison, the value of Cl (349) is 6.4% higher than F (328); Br (325) is 6.9% less than Cl; and I (295) is 9.2% less than Br. The marked reduction for At was predicted as being due to [[spin–orbit interaction]]s.<ref name="Champion" /> The first [[ionization energy]] of astatine is about 899&nbsp;kJ mol<sup>−1</sup>, which continues the trend of decreasing first ionization energies down the halogen group (fluorine, 1681; chlorine, 1251; bromine, 1140; iodine, 1008).<ref name="1IP" />