About

Astatine is the rarest naturally occurring element in the Earth's crust. It is a highly radioactive halogen, and its properties are inferred to be similar to iodine. All its isotopes are extremely short-lived, with the longest half-life being just over 8 hours, making it incredibly difficult to study. It is being researched for use in targeted alpha-particle therapy for cancer due to its potent radiation.

Atomic Properties

Atomic Number85

Atomic Weight209.987 u

Neutrons (common)125

Electron Configuration[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁵

Electrons per Shell2, 8, 18, 32, 18, 7

Electronegativity2.2

Electron Affinity270.1 kJ/mol

Oxidation States+7, +5, +3, +1, -1

Covalent Radius145 pm

Van der Waals Radius202 pm

Periodic Table Position

Group17

Period6

BlockP

Chemical SeriesHalogens

Physical Properties

State at STPsolid

Appearanceexpected to be a black or dark metallic solid

Thermal Properties

Melting Point575 K

Boiling Point610 K

Thermal Conductivity1.7 W/(m·K)

Heat of Fusion11.7 kJ/mol

Heat of Vaporization40 kJ/mol

Abundance

In Earth's Crust0 ppm

Discovery

Discovered byDale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè

Discovery Year1,940

Occurrencefrom_decay

CAS Number7440-68-8

Electron Configuration

Energy

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Isotopes of Astatine

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
²⁰⁹At	208.986169	—	5.42 h	Electron Capture, Alpha Decay
²¹⁰At	209.987140	—	8.1 h	Electron Capture, Alpha Decay
²¹¹At	210.987496	—	7.214 h	Electron Capture, Alpha Decay

Interactive Visualization

Explore the 3D Bohr model of Astatine in our interactive viewer.

View 3D Model of Astatine