Astati

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 was first synthesized in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley. The name "astatine" is derived from the Greek word "astatos," meaning "unstable," reflecting the element's high radioactivity.

Astatine is a highly radioactive element, with no stable isotopes. Its most stable isotope, astatine-210, has a half-life of about 8.1 hours. Due to its rarity and radioactivity, astatine has limited practical applications. However, it has been used in medical research for targeted alpha therapy, a treatment that uses radioactive isotopes to kill cancer cells. Astatine's chemistry is similar to that of iodine and astatine halides have been synthesized in the laboratory.

Astatine is a member of the halogen group on the periodic table, which includes fluorine, chlorine, bromine, iodine, and tennessine. Like other halogens, astatine is a nonmetal and forms salts with metals. However, due to its rarity and radioactivity, astatine is not commonly used in industrial or commercial applications. The study of astatine's properties and behavior continues to be an active area of research in the field of nuclear chemistry.