Properties

Atomic Number	85
CAS Registry Number	7440-68-8
Chemical Symbol	At

History

The atomic number is 85 and the chemical symbol is At. The name derives from the Greek astatos for unstable since it is an unstable element. It was first thought to have been discovered in nature in 1931 and was named alabamine. When it was determined that there are no stable nuclides of this element in nature that claim was discarded. It was later shown that astatine had been synthesized by the physicists Dale R. Corson Kenneth R. Mackenzie and Emilio Segre at the University of California lab in Berkeley California in 1940 who bombarded bismuth with alpha particles in the reaction 209Bi( 4He 2n) 211At. Independently a claim about finding some x-ray lines of astatine was the basis for claiming discovery of an element helvetium which was made in Bern Switzerland. However the very short half-life precluded any chemical separation and identification. The longest half-life associated with this unstable element is 8.1 hour 210At.

Holden, Norman E., (2004). History of the origin of the chemical elements and their discoverers. National Nuclear Data Center. Retrieved from http://www.nndc.bnl.gov/content/elements.html