astatin

Astatine is a chemical element with the symbol At and atomic number 85. It is a synthetic radioactive element, meaning it is not found naturally in significant quantities. Astatine belongs to the halogen group of elements, located in Group 17 of the periodic table, alongside fluorine, chlorine, bromine, and iodine. However, its chemical properties are not as well-studied as those of the lighter halogens due to its extreme rarity and radioactivity.

The most stable isotope of astatine, astatine-210, has a half-life of about 8.1 hours. All isotopes of astatine decay relatively quickly, making it difficult to accumulate and study. Because of its short half-life and scarcity, astatine has very few practical applications. It is primarily used in scientific research, particularly in nuclear medicine for targeted radiation therapy. The alpha particles emitted during its decay can be used to damage cancerous cells.

Astatine was first synthesized in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley, by bombarding bismuth with alpha particles. Its name comes from the Greek word "astatos," meaning unstable. Due to its extreme radioactivity and rarity, astatine is considered one of the rarest naturally occurring elements, though it does exist in trace amounts from the decay of heavier radioactive elements. Its physical properties are largely inferred from its position in the periodic table and studies of its few known compounds. It is predicted to be a solid at room temperature, with a color ranging from dark red to black.