Astat

Tecken	At
Atomnummer	85
Grupp	17 (Halogener)
Period	6
Block	p
Ämnesklass	Halvmetall

Utseende	Unknown, probably metallic
Färg	Silver

Antal protoner	85 p+
Antal neutroner	125 n0
Antal elektroner	85 e-

Från Wikipedia, den fria encyklopedinAstat är ett halvmetalliskt radioaktivt grundämne som tillhör gruppen halogener. Astats enda naturligt förekommande isotop är radioaktiv, med kort halveringstid på 8,3 timmar. Den totala massan av all astat som finns på jorden uppskattas till mellan några hundra milligram och 30 gram. Detta gör astat till det mest sällsynta grundämnet som förekommer på jorden, möjligtvis tillsammans med det likaledes mycket sällsynta grundämnet francium. Namnet astat kommer ifrån det grekiska ordet αστατος (astatos, som betyder "instabil").

Fas vid STP	Fast
Densitet	6.35 g/cm3
Relativ atommassa	210 u

Smältpunkt	575 K 301.85 °C 575.33 °F
Kokpunkt	610 K 336.85 °C 638.33 °F
Ångbildningsvärme	30 kJ/mol

Elektronegativitet (Paulingskalan)	2.2
Elektronaffinitet	233 kJ/mol
Oxidationstal	−1, +1, +3, +5, +7 ()
Jonisationspotential	899.003 kJ/mol

Elektronkonfiguration Kortfattad konfiguration	[Xe] 4f14 5d10 6s2 6p5
Elektronkonfiguration Full konfiguration	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5
Elektronkonfigurationsdiagram	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5
Elektroner per skal	2, 8, 18, 32, 18, 7
Valenselektroner	7
Valency-elektroner	1
Bohrs atommodell	Figur: Skaldiagram över Astat (At) atom.
Orbitaldiagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 6s 6p

Upptäckt

Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)

Upptäckten av astat Later in 1940, Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè isolated the element at the University of California, Berkeley. Instead of searching for the element in nature, the scientists created it by bombarding bismuth-209 with alpha particles in a cyclotron (particle accelerator) to produce, after emission of two neutrons, astatine-211. The discoverers, however, did not immediately suggest a name for the element. The reason for this was that at the time, an element created synthetically in "invisible quantities" that had not yet been discovered in nature was not seen as a completely valid one; in addition, chemists were reluctant to recognize radioactive isotopes as legitimately as stable ones. In 1943, astatine was found as a product of two naturally occurring decay chains by Berta Karlik and Traude Bernert, first in the so-called uranium series, and then in the actinium series. (Since then, astatine was also found in a third decay chain, the neptunium series.) Friedrich Paneth in 1946 called to finally recognize synthetic elements, quoting, among other reasons, recent confirmation of their natural occurrence, and proposed that the discoverers of the newly discovered unnamed elements name these elements. In early 1947, Nature published the discoverers' suggestions; a letter from Corson, MacKenzie, and Segrè suggested the name "astatine" coming from the Greek astatos (αστατος) meaning "unstable", because of its propensity for radioactive decay, with the ending "-ine", found in the names of the four previously discovered halogens. The name was also chosen to continue the tradition of the four stable halogens, where the name referred to a property of the element.

Original word	astatos
Language of origin	Greek
Name source	Egenskaper
Meaning	“Unstable”
Naming The name is derived from the Greek 'astatos', meaning unstable, because astatine has no stable isotopes and is the rarest naturally occurring element.

CAS Number	7440-68-8
ChemSpider ID	4573995
EC number	-
PubChem CID Number	5460480