Astatine
. Astatine (Greek astatos, “unstable”), symbol At, radioactive element that is the heaviest of the halogens . The atomic number of astatine is 85. Originally called alabamine because of early research with the element at Alabama Polytechnic Institute, it was prepared in 1940 by bombarding bismuth with high-energy alpha particles . The first isotope synthesized had an atomic weight of 211 and a half-life of 7.2 hours. Subsequently, astatine-210 was produced and found to have a half-life of about 8.3 hours. Isotopes of astatine with mass numbers from 200 to 219 have been cataloged, some with half-lives measured in fractions of a second (see Radioactivity ). Astatine is the halogen that behaves most like a metal and that has only radioactive isotopes. It is highly carcinogenic: Mammary and pituitary tumors have been induced in laboratory animals by a single injection. See also Periodic Law .