Category: Metalloid
Atomic Number: 85
Period: 6 | Group: 17
Block: p-block
The rarest naturally occurring element on Earth — perhaps 25 grams exist in the entire crust at any moment.
| Property | Value |
|---|---|
| Phase at STP | Solid |
| Density | N/A |
| Melting Point | 575.00 K (301.85 °C) |
| Boiling Point | 610.00 K (336.85 °C) |
| Heat Capacity | N/A |
| Property | Value |
|---|---|
| Atomic Mass | 210.0000 u |
| Electronegativity (Pauling) | N/A |
| Oxidation States | -1, +1, +3, +5, +7 |
| Electron Configuration |
| Discovered By | Unknown |
|---|---|
| Discovery Year | 1940 |
| Named After | Greek astatos, "unstable" |
A missing halogen
Mendeleev's periodic table left a gap below iodine for an element he called eka-iodine. Several claims to have found it in nature, under names such as alabamine (1931) and helvetium (1940), could not be confirmed.
Made at Berkeley (1940)
In 1940 Dale R. Corson, Kenneth Ross MacKenzie and Emilio Segrè at the University of California, Berkeley, produced element 85 by bombarding bismuth-209 with alpha particles in a cyclotron, making astatine-211.
Found in nature (1943)
In 1943 Berta Karlik and Traude Bernert in Vienna detected astatine isotopes in the natural decay chains of uranium and thorium.
The name (1947)
The discoverers named the element astatine in 1947, from the Greek astatos, meaning unstable.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| At-207 | 122 | - | 1.81 hr | ε/β⁺ (91.4%), α (8.6%) |
| At-208 | 123 | - | 1.63 hr | ε/β⁺ |
| At-209 | 124 | - | 5.42 hr | ε/β⁺ (95.9%), α (4.1%) |
| At-210 | 125 | - | 8.1 hr | ε/β⁺ |
| At-211 | 126 | - | 7.214 hr | ε (58.2%), α (41.8%) |
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Cancer therapy research
Astatine is used only in research, mainly in nuclear medicine. Astatine-211 emits alpha particles that travel only a few cell widths, so when it is attached to antibodies or other molecules that seek out cancer cells, it can destroy them with little damage to nearby tissue. This targeted alpha therapy is being tested in clinical trials.
Chemistry research
Chemists study astatine using only billionths of a gram at a time, with tracer techniques. These experiments test how relativistic effects change the chemistry of heavy elements and show that astatine behaves partly like iodine and partly like a metal.
| Earth's Crust | N/A |
|---|---|
| Universe | N/A |