Astatine is chemical element which is the 85 th element of the periodic table with a symbol At and atomic 85 is atomic number. It is a radioactive element and is said to be the most heavier among the halogens. This element exhibits similar chemical properties that of the element iodine. The isotopes of astatine have a short life of about 8.1 hours, and some isotopes are said to be unstable. It has about seven isotopes.
This element appears as a black solid with a metallic look. It is considered as one of the rarest occurring natural element. About 2.36 × 1025 grams of the earth’s crust comprises of astatine which measures about lesser than 1 gram. At is mainly formed by the decay of thorium and uranium.
The first synthesis of the element was in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio G. Segrè at the University of California, Four isotopes of astatine were subsequently found to be naturally occurring, although much less than one gram is present at any given time in the Earth’s crust. Neither the most stable isotope astatine-210, nor the medically useful astatine-211, occur naturally; they can only be produced synthetically, usually by bombarding bismuth-209 with alpha particles.
Characteristics of Astatine
- It is an extremely radioactive element; all its isotopes have short half-lives of 8.1 hours or less, decaying into other astatine isotopes, bismuth, polonium or radon.
- Most of its isotopes are very unstable with half-lives of one second or less. Of the first 101 elements in the periodic table, only francium is less stable, and all the astatine isotopes more stable than francium are in any case synthetic and do not occur in nature.
- The bulk properties of At are not known with any certainty. Research is limited by its short half-life, which prevents the creation of weighable quantities.
- A visible piece of At would immediately vaporize itself because of the heat generated by its intense radioactivity.
- It remains to be seen if, with sufficient cooling, a macroscopic quantity of astatine could be deposited as a thin film. At is usually classified as either a nonmetal or a metalloid; metal formation has also been predicted.