Astatine: Radioactive Element and Discovery History

• Astatine is a radioactive element with the symbol At and atomic number 85.
• All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.
• Astatine is a member of the halogens and falls roughly along the dividing line between metals and nonmetals.
• Astatine is extremely radioactive, with all its isotopes having half-lives of 8.1 hours or less.
• Astatine is less stable than francium and all the astatine isotopes more stable than francium.
• Astatine sublimes less readily than does iodine.
• Even so, half of a given quantity of astatine will vaporize in approximately an hour if put on a clean glass surface at room temperature.
• The absorption spectrum of astatine in the middle ultraviolet region has lines at 224.401 and 216.225 nm, suggestive of 6p to 7s transitions.
• Astatine is an element on the Periodic Table and is not as reactive as iodine.
• Some chemical properties of astatine align with other halogens.
• Astatine has some metallic characteristics, such as plating onto a cathode.
• Astatine forms complexes with EDTA and is capable of acting as a metal in antibody radiolabeling.
• Astatine has an electronegativity of 2.2 on the revised Pauling scale and is lower than that of iodine.
• The electron affinity of astatine, at 233 kJ mol−1, is 21% less than that of iodine.
• Astatine is a radioactive element that has six known isotopes.
• Astatine is a metal halide that has an odd number of oxidation states.
• Astatine is known to bind to other elements, including boron, carbon, and nitrogen.
• Astatine forms cations in salts with oxyanions.
• Astatine reacts with its lighter homologs iodine and bromine.
• Astatine is a potentially hazardous element.
• Dmitri Mendeleev's 1869 table of the elements included a space for the fifth halogen, which was later called "eka-iodine."
• Scientists tried to find eka-iodine in nature before its officially recognized discovery, but failed.
• The first claimed discovery of eka-iodine was made by Fred Allison and his associates at the Alabama Polytechnic Institute (now Auburn University) in 1931.
• H. G. MacPherson of University of California, Berkeley disproved Allison's method and the validity of his discovery.
• There was another claim in 1937, by the chemist Rajendralal De. Working in Dacca in British India (now Dhaka in Bangladesh), he chose the name "dakin" for element 85, which he claimed to have isolated as the thorium series equivalent of radium F (polonium-210) in the radium series.
• The properties he reported for dakin do not correspond to those of astatine, and astatine's radioactivity would have prevented him from handling it in the quantities he claimed.
• In 1936, the team of Romanian physicist Horia Hulubei and French physicist Yvette Cauchois claimed to have discovered element 85 by observing its X-ray emission lines.
• In 1939, they published another paper which supported and extended previous data.
• In 1944, Hulubei published a summary of data he had obtained up to that time, claiming it was supported by the work of other researchers.
• He chose the name "dor", presumably from the Romanian for "longing" [for peace], as World War II had started five years earlier.

Test your knowledge about astatine, a radioactive element with characteristics of both metals and nonmetals. Learn about its isotopes, properties, and its disputed historical discovery.