View source for Astatine

{{Elementbox_header | number=85 | symbol=At | name=astatine | left=[[polonium]] | right=[[radon]] | above=[[iodine|I]] | below=([[Uus]]) | color1=#ffff99 | color2=purple }}
{{Elementbox_series | [[halogen]]s }}
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{{Elementbox_boilingpoint | k=? 610 | c=? 337 | f=? 639}}
{{Elementbox_heatvaporiz_kjpmol | ca. 40 }}
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{{Elementbox_oxistates | ±1, 3, 5, 7 }}
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{{Elementbox_cas_number | 7440-68-8 }}
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 | dm2=[[alpha decay|α]] | de2=5.631 | pn2=206 | ps2=[[bismuth|Bi]] }}
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'''Astatine''' ({{pronEng|ˈæstətiːn}}) is a [[radioactive]] [[chemical element]] with the symbol '''At''' and [[atomic number]] 85. It is the heaviest of the [[halogen]]s.

== Notable characteristics ==
This highly [[radioactive]] element has been confirmed by [[mass spectrometer]]s to behave chemically much like other [[halogen]]s, especially [[iodine]] (it would probably accumulate in the [[thyroid]] gland like iodine<ref>http://periodic.lanl.gov/elements/85.html</ref>), though astatine is thought to be more [[metal]]lic than iodine.  Researchers at the [[Brookhaven National Laboratory]] have performed experiments that have identified and measured elementary reactions that involve astatine; however, chemical research into astatine is limited by its extreme rarity, which is a consequence of its extremely short [[half-life]]. Its most stable isotope has a half-life of around 8.3 hours. The final product of the decay of astatine is an isotope of [[lead]].

== History ==
The existence of "eka-iodine" had been predicted by [[Mendeleev]]. Astatine (after [[Greek language|Greek]] αστατος ''astatos'', meaning "unstable") was first synthesized in 1940 by [[Dale R. Corson]], [[K. R. MacKenzie]], and [[Emilio Segrè]] at the [[University of California, Berkeley]] by barraging [[bismuth]] with [[alpha particle]]s. An earlier name for the element was ''alabamine'' (Ab).

== Occurrence ==
Astatine occurs naturally from [[uranium-235]] and [[uranium-238]] decay, but because of its short [[half-life]] is only found in minute amounts. 

Astatine is the rarest naturally-occurring element, with the total amount in Earth's crust estimated to be less than 1 [[ounce|oz]] (28 g) at any given time. This amounts to less than one teaspoon of the element. ''[[Guinness World Records]]'' has dubbed the element the rarest on Earth, stating: "Only around 0.9 oz (25 [[gram|g]]) of the element astatine (At) occurring naturally". [[Isaac Asimov]], in a [[Only a Trillion|1957 essay]] on [[large numbers]], [[scientific notation]], and the size of the atom, wrote that in "all of North and South America to a depth of ten miles", the number of astatine atoms at any time is "only a [[1000000000000 (number)|trillion]]".<ref>http://ia331335.us.archive.org/1/items/onlyatrillion017765mbp/onlyatrillion017765mbp_djvu.txt</ref>

Astatine is produced by bombarding [[bismuth]] with energetic [[alpha particles]] to obtain relatively long-lived <sup>209</sup>At - <sup>211</sup>At, which can then be [[distillation|distilled]] from the target by heating in the presence of air.

== Compounds ==
Multiple [[chemical compound|compounds]] of astatine have been synthesized in microscopic amounts and studied as intensively as possible before their inevitable radioactive disintegration. While these compounds are primarily of theoretical interest, they are being studied for potential use in [[nuclear medicine]].[http://www.medicalnewstoday.com/articles/80581.php]

== Isotopes ==
{{main|isotopes of astatine}}
Astatine has 33 known [[isotope]]s, all of which are [[radioactive]]; the range of their mass numbers is from 191 to 223. There exist also 23 [[metastable]] [[excited state]]s. The longest-lived isotope is <sup>210</sup>At, which has a [[half-life]] of 8.3 hours; the shortest-lived known isotope is <sup>213</sup>At, which has a half-life of 125 [[nanoseconds]].

== References ==
{{reflist|2}}
*[http://periodic.lanl.gov/elements/85.html Los Alamos National Laboratory - Astatine]

== External links ==
{{Commons|Astatine}}
{{wiktionary|astatine}}
*[http://www.webelements.com/webelements/elements/text/At/index.html WebElements.com - Astatine]


{{diatomicelements}}

[[Category:Chemical elements]]
[[Category:Halogens]]
[[Category:Astatine]]

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