QUICK REFERENCE
- Symbol: At
- Atomic Number: 85
- Atomic Weight: [210]
- Element Classification: Halogen
- Discovered By: Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè
- Discovery Date: 1940
- Name Origin: Greek: ‘astatos’ (unstable)
- Density(g/cc): Estimated to be around 7 (predicted)
- Melting Point: 302°C (estimated)
- Boiling Point: 337°C (estimated)
- Appearance: Likely to be a solid under standard conditions, but its exact appearance is unknown due to its extreme rarity and radioactivity
- Atomic Radius(pm): Predicted to be about 150
Discovery
Astatine was synthesized for the first time in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley. They produced it by bombarding bismuth-209 with alpha particles in a cyclotron, leading to the creation of astatine-211. The name “astatine” is derived from the Greek word ‘astatos’, meaning unstable, reflecting the element’s radioactive nature and tendency to undergo decay.
Relation to Other Elements
Astatine is a member of the halogen group, which also includes fluorine, chlorine, bromine, and iodine. As the heaviest halogen, astatine exhibits some chemical properties common to the group, such as forming salts with metals. However, its properties are somewhat metallic, making it a metalloid. Astatine’s chemistry is less well understood compared to other halogens due to its scarcity and high radioactivity. All its isotopes are radioactive, with the most stable isotope, astatine-210, having a half-life of only 8.1 hours.
Natural Occurrence
Astatine is extremely rare in nature, produced in minute quantities from the decay of uranium and thorium ores through the series of alpha and beta decays, resulting in the formation of astatine isotopes. The total amount of astatine in the Earth’s crust is estimated to be less than 1 gram at any given time. Due to its short half-life and scarcity, most astatine used in research is synthetically produced in particle accelerators.
Uses
Given its rarity and radioactivity, practical applications of astatine are limited:
- Radiotherapy: The most promising use of astatine is in targeted alpha-particle radiotherapy, particularly using astatine-211. Its ability to emit alpha particles makes it a potential treatment for certain types of cancer, as it can selectively kill cancer cells while minimizing damage to surrounding healthy tissues.
The discovery of astatine filled the last spot in the halogen group, providing insights into the properties of elements at the boundary between metals and nonmetals. Despite its limited applications, research into astatine’s potential in medical treatments highlights the ongoing interest in understanding and utilizing even the rarest elements.