ASTATINE

Astatine 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 astatine 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 astatine 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.Astatine is usually classified as either a nonmetal or a metalloid. Most of the physical properties of astatine have been estimated (by interpolation or extrapolation), using theoretically or empirically derived methods. The structure of solid astatine is unknown.As an analogue of iodine it may have an orthorhombic crystalline structure composed of diatomic astatine molecules, and be a semiconductor.