Periodic Table -> Astatine


Astatine Details

Astatine Symbol: At

Astatine Atomic Number: 85

Astatine Atomic Weight: (210)

What is Astatine?

Astatine (atomic number 85, symbol At) is a radioactive metal, first produced by Emilio Segre, Kenneth Ross MacKenzie, and Dale Corson in 1940. In nature, it is formed by radioactive decay and exists in small amounts because of its short half-life. This element is, in fact, the rarest one to occur naturally, with estimates that no more than thirty grams are found in the earth's crust. Astatine is the heaviest halogen, known to men. It is believed that the metal accumulates in the thyroid gland similar to iodine.

Astatine has 20 known isotopes and all of them are radioactive. Other sources point to between 7 and 33 isotopes. The most stable isotope of astatine is astatine-210. Through electron capture, it decays into polonium-210 and through alpha decay astatine-210 decays into bismuth-206. Its half-life is 8.1 or 8.3 hours. Astatine itself occurs as a result of decay of thorium or uranium. Isotopes of lead are the products of its decay. With increasing atomic number and molecular weight, the halogens get a darker coloration. Therefore, the element is a black solid which turns into a purplish, dark vapor when heated.

This metal is highly radioactive but the least reactive element from the group of halogens. It would be expected to react with sodium and other metals to form salts. Astatine also forms hydrogen astatide by reacting with hydrogen. The latter forms hydroastatic acid when dissolved in water. The structure of astatine is unknown. The Vanderwaals radius and ionic radius of astatine as well as its density are unknown. Its melting point is 302 °C while its boiling point is estimated at 337 °C. Astatine’s electronegativity according to Pauling is 2.2. The element has not been researched extensively due to the short half-lives of its isotopes.
Astatic compounds include carbon tetraastatide, magnesium astatide, and sodium astatide. A number of compounds have been successfully synthesized but in very small amounts. They were researched as thoroughly as possible before disintegration. Dilute solutions of astatine were used to test the reactions, mixed with iodine, which plays the role of a carrier. This ensures there would be enough material to use laboratory techniques like precipitation and filtration. Research has been carried out mainly at the theoretical level, but these compounds have been studied to be used in nuclear medicine. More reactive and lighter halogens can displace astatine from salts.

In terms of uses, astatine has been used in cancer treatment and as a radioactive tracer. The heavier isotopes of astatine have uses in medicine. The alpha emitter Astatine-211 is used in radiation therapy and has a half-life of 7.2 hours. Astatine-211–tellurium has been employed for treatment of mice and has not been found to cause undue toxicity. Phosphorus-32, which is beta-emitting, has no antineoplastic activity. Astatine does not pose risk to the environment because it is not present in the biosphere in significant amounts. The element is not hazardous to human health given that just a couple of micrograms have been produced artificially. Moreover, it has a short-half life. A few nuclear research laboratories have studied astatine but because of its radioactivity, it requires precautions and special handling. Astatine can be produced by using alpha particles to bombard bismuth. Relatively long-lived isotopes are produced as a result. When air is present, the distillation of 211At can take place by heating.

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