|Boiling Point: 610°K,
Melting Point: 575°K, 302°C, 576°F
Electrons Energy Level: 2, 8, 18, 32, 18, 7
Heat of Vaporization: unknown
Heat of Fusion: 114 kJ/mol
Specific Heat: unknown
Atomic Radius: 1.43Å
Ionic Radius: unknown
Electronegativity: 2.2 (Pauling); 1.96 (Allrod Rochow)
|Astatine is the
last of the known halogens. The existence of "eka-iodine" had been predicted by
Dimetri Mendeleev. Astatine (after Greek, astat, astatos, meaning
"unsteady") was first synthesized in 1940 by Dale R. Corson, K.R. MacKenzie, and
Emilio Segre at the University of California, Berkeley by bombarding targets made of
bismuth-209 with high energy alpha particles (helium nuclei). Astatine 211 is the
product and has a half-life of 7.2 hours. The most stable isotope of Astatine is 210
which has a half-life of 8.1 hours. An earlier name for the element was alabamine
Not much is known about the chemical properties of Astatine but it is expected to react like the other halogens, although much less vigorously, and it should be more metallic than Iodine. There should be tiny quantities of Astatine in the earth's crust as products of other radioactive decays, but their existence would be short-lived.
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).
1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p5
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 result of its extremely short half-life.
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. The Guinness Book of records has dubbed the element the rarest on Earth, stating: "Only around 0.9 oz (25 g) of the element Astatine (At) occurring naturally"; Issac Asimov wrote a 1955 essay on large numbers, scientific notation, and the size of the atom, in which he stated that the number of Astatine atoms on Earth at any time was "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.
Multiple compounds of Astatine have been synthesized in microscopic amounts and studied as intensively as possible before their inevitable radioactive disintegration. These compounds are primarily of theoretical interest; however, they are also being studied for potential use in nuclear medicine.
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 meta states. The longest-lived isotope is 210At, which has a half-life of 8.1 hours; the shortest-lived known isotope is 213At, which has a half-life of 125 nanoseconds.
Atomic Radius (Å): 1.43Å
Electrochemical Equivalents: 7.8346g/amp-hr
Atomic Mass Average: 209.9871
(Gr. astatos, unstable) Synthesized in 1940 by D.R. Corson, K.R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with alpha particles. The longest-lived isotopes, with naturally occurring Uranium and Thorium isotopes, and traces of At-217 are equilibrium with U-233 and Np-239 resulting from interaction of thorium and uranium with naturally produced neutrons. The total amount of Astatine present in the earth's crust, however, is less than 1 oz. Astatine can be produced by bombarding Bismuth with energetic alpha particles to obtain the relatively long-lived At-209-211, which can be distilled from the target by heating in air. The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly Iodine. Astatine is said to be more metallic than Iodine, and, like Iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving Astatine.
Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond