Properties and Overview of Astatine

Overview:

Astatine (At) is a rare and highly radioactive element with the chemical symbol "At" and atomic number 85 on the periodic table. It is the heaviest halogen, located below iodine, and shares some chemical similarities with the other halogens, such as chlorine and bromine. Discovered in 1940 by scientists Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè, Astatine derives its name from the Greek word "astatos," meaning unstable, which reflects its extreme rarity and short half-life. Astatine's physical properties are not well-known due to its scarcity and radioactivity, which make it challenging to study. It is predicted to be a dark, metallic-looking solid at room temperature, possibly exhibiting a sheen similar to iodine. Astatine's melting point is estimated to be around 300°C, and its boiling point is approximately 335°C. The element is thought to have a density between 6.2 and 6.5 g/cm³, but these values are difficult to confirm experimentally due to the small quantities available.
Astatine exhibits chemical properties typical of halogens but with unique characteristics due to its heavy atomic mass and radioactivity. Astatine tends to form compounds with metals and non-metals. One of the few well-characterized compounds is astatine hydride (HAt), analogous to hydrogen chloride (HCl) and hydrogen iodide (HI). Astatine is also expected to form weak acids in aqueous solutions, similar to other halogen acids. However, due to its extreme radioactivity, astatine's chemical behavior is heavily influenced by radiolysis, the decomposition of molecules due to radiation, complicating its study.
Astatine is highly radioactive, making it extremely hazardous to handle. Its radiation primarily consists of alpha particles, which can cause significant damage if inhaled, ingested, or absorbed through the skin. Due to its short half-life, astatine is rarely encountered outside of specialized laboratories, and stringent safety protocols are required to protect researchers and the environment from its radiation. Handling astatine typically involves using remote manipulation tools, shielded containers, and proper ventilation systems to avoid contamination. As with other radioactive materials, exposure to astatine can increase the risk of cancer and other radiation-related illnesses.

Production:

Astatine is not found naturally in significant amounts due to its short half-life, which ranges from microseconds to a few hours, depending on the isotope. The most stable isotope, astatine-210, has a half-life of just over 8 hours. As a result, astatine is produced artificially, usually in a nuclear reactor or particle accelerator. It is typically generated by bombarding bismuth-209 with alpha particles (helium nuclei), which forms astatine-211, a relatively long-lived isotope used in research. The production of astatine requires careful handling and precise control, as only minuscule amounts are produced in each batch, and it decays quickly, making storage and transportation challenging.

Applications:

Despite its rarity and radioactivity, astatine has found limited but significant applications, primarily in the field of medical research. The isotope astatine-211, in particular, has sparked interest in targeted alpha-particle cancer therapy (TAT). In this treatment, astatine-211 is used to deliver highly localized radiation to cancer cells, thereby minimizing damage to surrounding healthy tissues. This approach, though still largely experimental, shows promise for treating certain types of cancers.
Astatine's potential applications in nuclear medicine are intriguing, but its short half-life and the difficulties associated with its production and handling have limited its widespread use. Nevertheless, research continues into optimizing its production and exploring new medical uses, underscoring the ongoing interest in astatine's potential in targeted cancer therapies.

Summary:

Astatine is an elusive and enigmatic element, known more for its scientific curiosity than for practical applications. Its extreme rarity, short half-life, and high radioactivity make it a challenging research subject, but its potential in targeted cancer therapies could offer significant medical benefits. Astatine's chemical behavior is somewhat predictable as a member of the halogen family, yet it remains uncharted mainly due to the practical difficulties of studying it. As technology advances, new methods may emerge to harness astatine's unique properties in ways that could transform its role in science and medicine.

See a comprehensive list of atomic, electrical, mechanical, physical and thermal properties for astatine below: