What is Astatine?
Astatine is a chemical element with the symbol At and atomic number 85. It is the heaviest member of the halogen group, which also includes more familiar elements like fluorine, chlorine, bromine, and iodine. Unlike these common halogens, astatine is an extremely rare and highly radioactive element, existing only in very tiny quantities on Earth at any given moment. Its scarcity means that its properties are largely inferred from its position in the periodic table and from studying its radioactive decay.
Discovery of Astatine
The discovery of Astatine occurred in 1940 at the University of California, Berkeley, in the United States. Scientists Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè created the element by bombarding bismuth atoms with alpha particles in a cyclotron accelerator. This artificial synthesis allowed for the first observation and study of this elusive element.
The Meaning Behind the Name
The name “Astatine” originates from the Greek word “astatos,” which translates to “unstable.” This name was chosen due to the element’s inherent characteristic: all known isotopes of astatine are intensely radioactive and decay rapidly, highlighting its fundamental instability.
Quick Facts About Astatine
- Extreme Rarity: Astatine is considered the rarest naturally occurring element on Earth. Estimates suggest that the total amount of astatine present in Earth’s crust at any given time is less than one gram.
- Intense Radioactivity: Every isotope of astatine is radioactive. The longest-lived isotope, astatine-210, has a half-life of approximately 8.1 hours, meaning half of any given sample will decay away in just over eight hours.
- Halogen Properties: As a halogen, astatine is expected to exhibit chemical properties similar to iodine, though it is predicted to be more metallic in character due to its heavier atomic mass.
- Unseen Appearance: Due to its extreme rarity and rapid decay, no macroscopic sample of astatine has ever been observed. Its appearance is theorized to be a dark, metallic solid, but this has not been confirmed visually.
- Potential Medical Applications: Astatine-211 is being actively researched for its potential use in targeted alpha therapy for cancer treatment. Its emission of alpha particles over a short range makes it a candidate for destroying cancer cells while minimizing damage to surrounding healthy tissue, with research being conducted in various institutions worldwide, including in Japan and Europe.