Astatine (At)
Metalloid · Radioactive
Astatine is the rarest naturally occurring element: less than 30 grams exists in the entire Earth's crust at any moment. Every isotope is intensely radioactive, and its bulk properties remain educated guesses.
Position on the periodic table
Atomic properties
| Atomic number | 85 |
|---|---|
| Atomic mass | 210 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5 |
| Noble gas shorthand | [Xe] 4f14 5d10 6s2 6p5 |
| Electrons per shell | 2, 8, 18, 32, 18, 7 |
| Valence electrons (outer shell) | 7 |
| Common oxidation states | -1, +1 |
| Electronegativity (Pauling) | 2.2 |
| Covalent radius (approx.) | 150 pm |
| First ionization energy | 899 kJ/mol |
| Electron affinity | 233 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 6.35 g/cm³ |
| Melting point | 301.85 °C (575 K) |
| Boiling point | 336.85 °C (610 K) |
| Appearance | unknown, probably metallic |
| Radioactive | Yes |
| Origin | Occurs naturally |
Electron configuration of astatine
Astatine's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5, usually shortened to [Xe] 4f14 5d10 6s2 6p5. Its electrons occupy 6 shells (2, 8, 18, 32, 18, 7), placing it in period 6 of the p-block. The 7 outer-shell electrons drive its bonding behaviour. Explore it interactively in the electron configuration calculator.
Uses of astatine
- Targeted alpha-particle cancer therapy research (At-211)
Biological role: None; it concentrates in the thyroid like iodine.
Occurrence: Fleeting traces from uranium decay chains — the rarest natural element.
History and discovery
Discovered: 1940 — Dale R. Corson. Name origin: From Greek astatos, meaning unstable.
Corson, MacKenzie and Segrè synthesised astatine at Berkeley in 1940 by bombarding bismuth with alpha particles.
Safety notes
Intensely radioactive; handled only in specialised research facilities.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Astatine
1. What is the chemical symbol of Astatine?
2. What is the atomic number of Astatine?
3. Which category does Astatine belong to?
4. What is the state of Astatine at room temperature?
5. Which period of the periodic table is Astatine in?
Astatine FAQs
What is the atomic number of astatine?
Astatine's atomic number is 85 — every astatine atom has 85 protons in its nucleus.
What is the symbol for astatine?
At. From Greek astatos, meaning unstable.
Is astatine a metal, nonmetal, or metalloid?
Astatine is classified as a metalloid — an element with properties between metals and nonmetals.
What state is astatine at room temperature?
At about 25 °C, astatine is a solid. It melts at 301.85 °C.
How many valence electrons does astatine have?
Astatine has 7 electrons in its outer shell (shell pattern: 2, 8, 18, 32, 18, 7).
What is astatine used for?
Key uses include: targeted alpha-particle cancer therapy research (at-211).
Related elements
Keep working with this element
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