Astatine is the rarest naturally occurring element in the Earth’s crust. It can only be produced synthetically, usually by bombarding bistuth-209 with alpha particles. The bulk properties ofastatine are not known with certainty, but it is likely to have a dark or lustrous appearance.
About Astatine in brief
Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth’s crust, occurring only as the decay product of various heavier elements. Astatine is an extremely radioactive element; all its isotopes have half-lives of 8. 1 hours or less, decaying into other astatine isotopes, bismuth, polonium, or radon. A sample of the pure element has never been assembled, because any macroscopic specimen would be immediately vaporized by the heat of its own radioactivity. The bulk properties ofastatine are not known with certainty, but it is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal. It also shows some metallic behavior, including being able to form a stable monatomic cation in aqueous solution. The structure of the solid is unknown, but some sources assert it does not exist, or at least that its existence has been observed, while other sources assert its existence is inconclusive and inconclusive. Evidence for the existence of diatomicAstatine has been inconclusive, while many other sources have asserted its existence, while others have never observed it or imply its existence. The absorption spectrum of astatin in the middle ultraviolet region has lines at 401 and 225, suggestive of 6p to 7s transitions. As an analogue of iodine it may have orthorhombic crystalline structure, and be a monatomic face-centered cubic structure; in this structure it may well be a superconductor, like the high-pressure phase of iodine.
It may also have a high melting point, like that of iodine, and a high boiling point, as well as being a metalloid or semiconductor. It has a low vapor pressure, having a lower vapor pressure than iodine, but half of a given quantity of ast atine will vaporize in approximately an hour if put on a clean glass surface at room temperature. It can only be produced synthetically, usually by bombarding bistuth-209 with alpha particles. Neither the most stable isotope astatina-210, nor the medically useful astatINE-211, occur naturally; they canonly be produced by bombarded bismutium-209. Less than one gram is present at any given time in the planet’s crust. Most of the physical properties of astAtine have been estimated, using theoretically or empirically derived methods. For example, halogens get darker with increasing atomic weight – fluorine is nearly colorless, chlorine is yellow-green, bromine is red-brown, and iodine is dark grayviolet. The melting and boiling points are also expected to follow the trend seen in the halogen series, increasing with atomic number. On this basis they are estimated to be 575 and 610 K, respectively. Some experimental evidence suggests astatined may have lower melting points than those implied by the Halogen trend.
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