Astatine, symbolized by At and holding the atomic number 85, is an element shrouded in mystery due to its extreme rarity and radioactivity.
Synthesized for the first time in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè at the University of California, Berkeley, astatine was produced by bombarding bismuth-209 with alpha particles in a cyclotron, resulting in the creation of astatine-211.
The name “astatine” originates from the Greek word ‘astatos,’ meaning unstable, aptly reflecting the element’s radioactive nature and propensity for decay.
Chemical and Physical Properties
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: Estimated to be around 7 g/cc (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: Predicted to be about 150 pm
Astatine is a member of the halogen group, which also includes fluorine, chlorine, bromine, and iodine. As the heaviest halogen, astatine exhibits some common chemical properties of the group, such as forming salts with metals. However, its properties are somewhat metallic, making it a metalloid. Due to its scarcity and high radioactivity, the chemistry of astatine is less understood compared to other halogens. All its isotopes are radioactive, with the most stable isotope, astatine-210, having a half-life of only 8.1 hours.
Relation to Other Elements
Astatine’s position in the periodic table places it at the boundary between metals and nonmetals, providing a unique set of characteristics. As a halogen, it shares similarities with iodine, forming salts and other compounds. Yet, its metallic properties set it apart, making it a metalloid. The element’s high atomic weight and radioactivity significantly influence its chemical behavior, presenting challenges for researchers aiming to understand its full range of properties.
Natural Occurrence
Astatine is one of the rarest naturally occurring elements on Earth. It is produced in minute quantities from the decay of uranium and thorium ores through a 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 of Astatine
Given its rarity and radioactivity, practical applications of astatine are limited. However, there are notable potential uses:
Radiotherapy
The most promising application of astatine lies 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. Alpha particles can selectively kill cancer cells while minimizing damage to surrounding healthy tissues, offering a focused approach to radiotherapy.
Historical Context and Significance
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. This discovery not only completed the halogen group but also opened new avenues for research into the behavior of heavy elements. Despite its limited applications, research into astatine’s potential in medical treatments highlights the ongoing interest in understanding and utilizing even the rarest elements.
Production and Synthesis
The synthesis of astatine involves complex procedures due to its high radioactivity and short half-life. The most common method is the bombardment of bismuth-209 with alpha particles using a cyclotron. This process results in the creation of astatine-211, which can then be isolated for research purposes. The production of astatine requires advanced facilities and stringent safety measures due to the element’s radioactive nature.
Challenges in Research
Studying astatine presents several challenges:
- Scarcity: The extreme rarity of astatine makes it difficult to obtain in significant quantities for research.
- Radioactivity: The high radioactivity of all astatine isotopes necessitates special handling and containment measures to protect researchers and the environment.
- Short Half-Life: The short half-life of astatine isotopes limits the time available for conducting experiments, requiring efficient and rapid research techniques.
Despite these challenges, advancements in technology and research methods continue to shed light on the unique properties and potential applications of astatine.
Conclusion
Astatine remains one of the most elusive and fascinating elements in the periodic table. Its discovery in 1940 marked a significant milestone in the field of chemistry, completing the halogen group and expanding our understanding of the behavior of heavy elements. While its practical applications are currently limited due to its rarity and radioactivity, the potential for astatine in targeted alpha-particle radiotherapy represents a promising area of research. As technology advances, the study of astatine will continue to unveil the mysteries of this rare element, contributing to both scientific knowledge and potential medical breakthroughs.