Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where astatine sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 150 pm — that is 0.15 nm, so about 3333 million of them side by side would span a millimetre.
Thermal range
Astatine is liquid over a 35 K window, from 575 K to 610 K.
The story
The rarest naturally occurring element on Earth — perhaps 25 grams exist in the entire crust at any moment.
Astatine was discovered in 1940 by Dale Corson, Kenneth MacKenzie, and Emilio Segrè at the University of California, Berkeley, making it the last naturally occurring element to be discovered. The team created astatine artificially by bombarding bismuth-209 with alpha particles in the 60-inch cyclotron, producing astatine-211. This discovery filled the final gap in the periodic table of naturally occurring elements.
Before its discovery, element 85 was known to exist based on Mendeleevs periodic law, but it had eluded detection for decades. Many false claims had been made, with proposed names like "alabamine" (1931) and "dor" (1936). The Berkeley team initially called their discovery "alabamine" but later changed it to "astatine" from the Greek word "astatos," meaning "unstable," perfectly describing its radioactive nature.
The discovery required incredibly sophisticated techniques for 1940. The team had to distinguish astatine from other radioactive products by studying decay patterns, half-lives, and chemical behavior. They proved astatines existence by showing it behaved chemically like a halogen, could be extracted with organic solvents, and had the predicted radioactive properties for element 85.
While first created artificially, scientists later confirmed astatines natural existence in 1943 by identifying it in uranium decay chains. This made astatine unique as an element that was artificially created before being found in nature, highlighting both human ingenuity and the elements extreme rarity in natural systems.
Applications
Astatine-211 represents one of the most promising targeted alpha therapy (TAT) radioisotopes in modern nuclear medicine. Its 7.2-hour half-life provides the perfect therapeutic window - long enough for complex radiopharmaceutical preparation and patient treatment, yet short enough to minimize long-term radiation exposure. Research institutions worldwide are investigating At-211 conjugated to monoclonal antibodies for treating various cancers including glioblastoma, ovarian cancer, and hematological malignancies.
Despite its extreme rarity (less than 30 grams exist on Earth at any time), astatine serves as a crucial tracer in nuclear physics experiments. Researchers use microscopic amounts to study halogen chemistry behavior, helping understand how other halogens might behave in extreme conditions. Its unique position as the heaviest naturally occurring halogen makes it invaluable for testing periodic table predictions and quantum mechanical models.
Astatine isotopes help scientists understand radioactive decay pathways and nuclear stability. At-210 through At-219 provide insights into alpha decay processes and help calibrate detection equipment for other radioactive materials. These studies are essential for nuclear waste management, radiological security, and advancing our understanding of superheavy element synthesis.
While actual astatine samples are impossibly rare and dangerous, computer simulations and theoretical models of astatine behavior help train nuclear chemists and health physicists. Understanding astatine chemistry principles prepares researchers for working with other unstable, heavy elements and helps develop safety protocols for superheavy element research.
Astatine-211 is being intensively studied as a next-generation cancer treatment. Unlike beta emitters used in conventional radiotherapy, At-211 emits high-energy alpha particles that can destroy cancer cells with pinpoint precision while causing minimal damage to surrounding healthy tissue. Clinical trials are ongoing at major cancer centers, though the extreme difficulty of producing At-211 limits its availability to only the most specialized research facilities.
Researchers use femtogram quantities (10^-15 grams) of astatine isotopes to study chemical behavior and test theoretical predictions about halogen properties. These studies help validate computer models used to predict the behavior of other rare elements and contribute to our understanding of chemical bonding in heavy atoms.
Known quantities of astatine isotopes serve as reference standards for calibrating sensitive radiation detection equipment. This application is crucial for nuclear security, environmental monitoring, and ensuring the accuracy of medical radiation therapy equipment.
Due to its extreme rarity and radioactivity, astatine has no commercial applications. All uses are limited to highly specialized academic and medical research conducted in facilities with the advanced radiation safety protocols. Most astatine research is theoretical, using computer models rather than actual samples.
Where it comes from
0 mg/kg of Earth's crust · more abundant than 0% of elements
Astatine holds the distinction of being the rarest naturally occurring element on Earth, with an estimated total abundance of less than 30 grams in the entire Earths crust at any given moment. This extraordinary scarcity results from its position in multiple radioactive decay chains and its extremely short half-life, making it more rare than many artificially created elements.
Natural astatine occurs exclusively as intermediate products in three major radioactive decay series: the uranium-235 series (producing At-215 and At-219), the uranium-238 series (producing At-218), and the thorium-232 series (producing At-216). These isotopes form when heavier radioactive elements like francium, radium, and polonium undergo alpha or beta decay, but they quickly decay further, typically within seconds to hours.
Because astatine forms through radioactive decay rather than geological processes, it has no concentrated deposits or specific geographic distribution. Trace amounts exist wherever uranium and thorium ores are found, including locations like the Athabasca Basin in Canada, Olympic Dam in Australia, and various sites in Kazakhstan, Namibia, and the western United States. However, the concentrations are so infinitesimally small that extraction is impossible.
The longest-lived natural astatine isotope, At-219, has a half-life of only 56 seconds, while At-215 lasts just 0.1 milliseconds. This means that astatine atoms are continuously being created and destroyed in uranium-bearing rocks. The element exists in a state of dynamic equilibrium - new atoms form from radioactive decay at roughly the same rate that existing atoms decay into other elements.
Handling
Astatine is radioactive. It has no stable isotope — every nucleus decays. Handling requires appropriate shielding and licensing.
Astatine is one of the most dangerous radioactive elements known. All isotopes emit high-energy alpha particles, and some also emit beta particles and gamma rays. Even microscopic amounts can deliver lethal radiation doses. At-211, the most studied isotope, emits 5.9 MeV alpha particles that can cause severe cellular damage and DNA destruction.
Astatine research requires the highest level radiation containment facilities (Biosafety Level 3+ equivalent). All work must be conducted in specialized hot cells with remote manipulation equipment. Personnel must wear full radiation protection suits with independent air supplies and undergo continuous radiation monitoring. Even the smallest spill could contaminate an entire laboratory permanently.
There is no safe level of astatine exposure. The elements tendency to concentrate in the thyroid gland (like iodine) makes it particularly dangerous, potentially causing thyroid cancer, radiation sickness, and death. The biological half-life in humans is unknown due to ethical constraints, but animal studies suggest rapid uptake and severe tissue damage.
Astatine is available only to licensed nuclear research facilities with appropriate containment capabilities. Transportation requires special Nuclear Regulatory Commission permits and armored vehicles designed for high-level radioactive materials. Emergency response protocols must be in place wherever astatine is present, including evacuation procedures and specialized medical treatment for radiation exposure.
Quick answers
Astatine (symbol At) is element 85 on the periodic table, a metalloid in period 6, group 17. The rarest naturally occurring element on Earth — perhaps 25 grams exist in the entire crust at any moment. At room temperature it is a solid, and it is radioactive.
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵, giving 6 occupied shells holding 2, 8, 18, 32, 18, 7 electrons respectively. Its outer shell holds 7 electrons, which is what sets its bonding behaviour.Astatine melts at 575 K (301.9 °C) and boils at 610 K (336.9 °C).
Astatine has no stable isotope, so it has no standard atomic weight. The figure quoted, 210, is the mass number of its longest-lived known isotope.
Astatine has a density of 7 g/cm³. Water is 1.0 g/cm³, so a block of astatine is about 7× heavier.
Astatine has a Pauling electronegativity of 2.2. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Astatine was discovered in 1940 by Corson, MacKenzie & Segre. It is named after greek astatos, "unstable".
Astatine does not occur naturally on Earth in any meaningful quantity — it is made in a reactor or an accelerator.
Yes. Astatine has no stable isotope — every one of its nuclei decays. Trace amounts occur naturally as decay products of heavier elements.