Astato . Chemical element with symbol At and atomic number 85. It is the heaviest element of the group of halogens , occupying the place below iodine in group VII of the periodic table.
Summary
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- 1 History
- 2 Features
- 3 Nomenclature
- 4 Obtaining
- 5 Applications
- 6 Isotopes
- 7 Health effects of astatine
- 8 Effects on the environment
- 9 Sources
History
Astate was first synthesized in 1940 by Dale R. Corson , KR MacKenzie, and Emilio Segrè at the University of Berkeley ( California ), bombarding bismuth with alpha particles . A first name for the element was alabamino (Ab).
Features
Astat is a very unstable element, existing only in short-lived radioactive forms. About 25 isotopes have been prepared by artificial transmutation nuclear reactions.
The isotope with the longest life span is 210 At , which decays in a half-life of only 8.3 h and isotopic framing is used. It is unlikely that a more stable, or longer-lived, form could be found in nature or artificially prepared.
Astate is found in nature as an integral part of uranium ores , but only in trace amounts of short-lived isotopes, continually supplied by the slow decay of uranium. The total amount of astatine in the earth’s crust is less than 28 g (1 ounce).
In aqueous solution, astate has properties similar to iodine except for differences attributable to the fact that astate solutions are, by necessity, highly dilute. Like halogen iodine, it is extracted with benzene when it is found as a free element in solution.
The element in solution is reduced by agents such as sulfur dioxide and is oxidized by bromine . It is the least electronegative of all halogens. It has oxidation states with coprecipitation characteristics similar to those of iodide ion , free iodine and iodate ion. Strong oxidizing agents produce the astate ion, but not the perastatate ion. It is easier to obtain and characterize in the free state due to its high volatility and ease of extraction with organic solvents.
The chemical behavior of this highly radioactive element is very similar to that of other halogens, especially iodine. Astatine is thought to be more metallic than iodine. Researchers at the Brookhaven National Laboratory have conducted experiments that have identified and measured elemental reactions involving astatine.
Astatine, followed by francium , is the rarest element in nature, with a total amount on the earth’s surface of less than 25 grams at the same instant of time; that is, less than a small spoonful
Nomenclature
The astatus (from the Greek αστατος, astatos, meaning unstable)
Obtaining
Astatine is obtained today in the same way as in its beginnings, bombarding bismuth with alpha particles, obtaining isotopes 209At and 210At, with a relatively high half-life.
Applications
It has no important applications, although the most important isotope, 211At, is used in isotopic labeling.
Isotopes
There are 41 known isotopes of astate, all radioactive . The longest-lived isotope, 210At, which has a half-life of 8.1 hours, and the least long-lived isotope 213At, with one of 125 nanoseconds.
Health effects of astatine
The total amount of astate in the earth’s crust is less than 30 grams and only a few micrograms have been artificially produced. This, together with its short life, leaves no reason to consider the effects of astate on human health.
Astate is studied in a few research laboratories where its high radioactivity requires special precautions and handling techniques. It is a halogen and possibly accumulates in the thyroid gland as iodine . From a chemical point of view, it can be speculated that its toxicity will be identical to that of iodine.
Effects on the environment
Asstate does not occur in significant quantities in the biosphere , so it usually never poses a risk
