AskDefine | Define astatine

Dictionary Definition

astatine n : a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium [syn: At, atomic number 85]

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Pronunciation

  • , /ˈæstətiːn/, /"

Extensive Definition

Astatine () is a radioactive chemical element with the symbol At and atomic number 85. It is the heaviest of the halogens.

Notable characteristics

This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially iodine (it would probably accumulate in the thyroid gland like iodine), though astatine is thought to be more metallic 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. Following the color trend of the halogens, the elements get darker in color with increasing molecular weight and atomic number. Thus, following the trend, astatine would be expected to be a nearly black solid, which, when heated, sublimes into a dark, purplish vapor (darker than iodine). Astatine is expected to form ionic bonds with metals such as sodium, like the other halogens, but it can be displaced from the salts by lighter, more reactive halogens. Astatine can also react with hydrogen to form hydrogen astatide, which when dissolved in water, forms hydroastatic acid. Astatine is the least reactive of the halogens, being less reactive than iodine.

History

The existence of "eka-iodine" had been predicted by Mendeleev. Astatine (after 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 particles. An earlier name for the element was alabamine (Ab)http://www.time.com/time/magazine/article/0,9171,743159,00.html.
The name Dakin was proposed for this element in 1937 by chemist Rajendralal De working in Dhaka.

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 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 g) of the element astatine (At) occurring naturally". Isaac Asimov, in a 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 trillion".
Astatine is produced by bombarding bismuth with energetic alpha particles to obtain relatively long-lived 209At - 211At, which can then be distilled from the target by heating in the presence of air.

Compounds

Multiple 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 Astatine is expected to form ionic bonds with metals such as sodium, like the other halogens, but it can be displaced from the salts by lighter, more reactive halogens. Astatine can also react with hydrogen to form hydrogen astatide, which when dissolved in water, forms hydroastatic acid.

Isotopes

Astatine has 33 known isotopes, all of which are radioactive; the range of their mass numbers is from 191 to 223. There exist also 23 metastable excited states. The longest-lived isotope is 211At, which has a half-life of 8.1 hours; the shortest-lived known isotope is 213At, which has a half-life of 125 nanoseconds.

Applications

Because of the extremely short life span of astatine no practical applications exist other than scientific study. The isotope 211 of astatine is used for treating different types of tumors. Astatine 211 is an alpha emitter with a physical halflife of 7.2 h. These features have led to its use in radiation therapy.

Precautions

Since Astatine is radioactive, it should be handled with care. Because of its extreme rarity, it is not likely that the general public will be exposed.
Astatine is a halogen, and standard precautions apply. It is less reactive than iodine, but they share similar characteristics.
astatine in Arabic: أستاتين
astatine in Bengali: এস্টাটিন
astatine in Belarusian: Астат
astatine in Bosnian: Astat
astatine in Bulgarian: Астатий
astatine in Catalan: Àstat
astatine in Chuvash: Астат
astatine in Czech: Astat
astatine in Corsican: Astatu
astatine in Danish: Astat
astatine in German: Astat
astatine in Estonian: Astaat
astatine in Modern Greek (1453-): Άστατο
astatine in Spanish: Astato
astatine in Esperanto: Astato
astatine in Basque: Astato
astatine in Persian: استاتین
astatine in French: Astate
astatine in Friulian: Astat
astatine in Irish: Astaitín
astatine in Manx: Astatçheen
astatine in Galician: Astato
astatine in Korean: 아스타틴
astatine in Armenian: Աստատ
astatine in Croatian: Astat
astatine in Ido: Astatino
astatine in Indonesian: Astatin
astatine in Icelandic: Astat
astatine in Italian: Astato
astatine in Hebrew: אסטטין
astatine in Javanese: Astatin
astatine in Swahili (macrolanguage): Astatini
astatine in Latin: Astatinum
astatine in Latvian: Astats
astatine in Luxembourgish: Astat
astatine in Lithuanian: Astatis
astatine in Lojban: klirlxastati
astatine in Hungarian: Asztácium
astatine in Dutch: Astatium
astatine in Japanese: アスタチン
astatine in Norwegian: Astat
astatine in Norwegian Nynorsk: Astat
astatine in Occitan (post 1500): Astat
astatine in Polish: Astat
astatine in Portuguese: Astato
astatine in Romanian: Astatiniu
astatine in Russian: Астат
astatine in Sicilian: Astatu
astatine in Simple English: Astatine
astatine in Slovak: Astát
astatine in Slovenian: Astat
astatine in Serbian: Астат
astatine in Serbo-Croatian: Astat
astatine in Saterfriesisch: Astat
astatine in Finnish: Astatiini
astatine in Swedish: Astat
astatine in Thai: แอสทาทีน
astatine in Vietnamese: Astatin
astatine in Turkish: Astatin
astatine in Ukrainian: Астат
astatine in Chinese: 砹
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