Astatine (At)

Astatine is a chemical element with symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements.

Atomic Number

85

Atomic Mass

210 u

Category

halogen

Phase

solid

Density

7 g/cm³

Electron Shells

2, 8, 18, 32, 18, 7

Atomic Structure

Protons: 85 • Electrons: 85 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁵

Discovery

1940 • Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè