Astatine
Atomic Data
| Atomic Number | 85 |
| Symbol | At |
| Atomic Weight | 210 u |
| Density (STP) | N/A |
| Melting Point | 301.85 °C (575 K) |
| Boiling Point | 336.85 °C (610 K) |
| Electronegativity | 2.2 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p5 |
| Oxidation States | −1, +1, +3, +5, +7 |
| Phase at STP | Solid |
| Category | Halogen |
| Period / Group | 6 / 17 |
| CAS Number | 7440-68-8 |
Electron Configuration
[Xe] 4f14 5d10 6s2 6p5
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 2 | 80 |
| P | 6 | 6p | 5 | 85 |
| Total | 85 | 85 | ||
Isotopes of Astatine
Astatine has two naturally occurring stable isotopes. The most abundant is ²¹⁰At, comprising None% of all naturally occurring Astatine.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Astatine-210 | ²¹⁰At | 85 | 125 | trace | Stable |
| Astatine-211 | ²¹¹At | 85 | 126 | trace | Stable |
Abundance & Occurrence
Astatine is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Radioactivity: no stable isotopes: All astatine isotopes are radioactive; the longest-lived, At-210 (t½ = 8.1 h), is an alpha emitter; the extreme rarity of astatine means macroscopic handling is not a practical concern outside specialised nuclear medicine facilities.
- Alpha-emitter hazard: Astatine-211 (t½ = 7.2 h), used in targeted alpha therapy research, delivers high localised radiation doses; all handling must occur in appropriate radioactive containment with alpha monitoring and radiation worker training.
- Chemical hazard: halogen: As a halogen, astatine is expected to form corrosive compounds analogous to iodine; its chemical and biological behaviour is extrapolated from lighter halogens but has not been fully characterised due to its extreme scarcity.
- Regulatory controls: Astatine is produced only in cyclotron facilities; production and use are subject to national nuclear regulatory authority licensing.
Astatine in the Real World
Real-World Uses
- Targeted alpha therapy (clinical research): Astatine-211 (t½ = 7.2 h) emits alpha particles with a range of only a few cell diameters; it is covalently attached to tumour-targeting molecules (antibodies, peptides) to deliver a lethal dose to individual cancer cells while sparing surrounding tissue.
- Thyroid cancer treatment (research): Because astatine is chemically analogous to iodine, At-211-labelled compounds concentrate in the thyroid, making it a candidate radiopharmaceutical for treating thyroid cancer by analogy with iodine-131, with the advantage of alpha rather than beta emission.
- Scientific study of heavy halogen chemistry: Astatine is the heaviest stable-like halogen; short-lived experiments on microgram quantities probe its chemistry, oxidation states, and biological behaviour, informing models of relativistic effects on chemical bonding at high atomic numbers.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
How rare is astatine?
Astatine is the rarest naturally occurring element on Earth. At any given moment, the total amount of astatine in Earth's crust is estimated at less than 30 grams: it exists only as a fleeting product of uranium and thorium radioactive decay chains, and its longest-lived natural isotope (At-210) has a half-life of only 8.1 hours. Any astatine produced decays away almost immediately.
Has astatine ever been used for anything?
Astatine-211 is used in targeted alpha therapy for cancer treatment. At-211 has a 7.2-hour half-life and decays by emitting high-energy alpha particles, which are very damaging to cells over a short range. When attached to tumour-seeking molecules, At-211 can deliver destructive alpha radiation directly to cancer cells with minimal damage to surrounding normal tissue. Clinical trials for thyroid cancer and brain tumours are ongoing.
How was astatine discovered?
Astatine was synthesised in 1940 at the University of California, Berkeley, by Dale Corson, Kenneth Ross MacKenzie, and Emilio Segrè. They produced it by bombarding bismuth-209 with alpha particles in a cyclotron. The name comes from the Greek 'astatos', meaning unstable: a fitting description given that all its isotopes are radioactive with short half-lives.
What are the chemical properties of astatine?
Astatine is the heaviest stable halogen (below iodine in Group 17), and its chemistry is largely inferred from studies with tiny quantities and from relativistic quantum calculations. It is more metallic in character than iodine: it may partly exist as At+ ions in solution rather than purely as At-. Its chemistry with organic molecules is similar enough to iodine that astatinated radiopharmaceuticals can be made by adapting iodination chemistry, which is why it is used in targeted radionuclide therapy.