Astatine (symbol At, atomic number 85) is the rarest naturally occurring element on Earth, studied for cancer therapy. It is classified as a halogen and sits in group 17, period 6 of the periodic table.
Overview
Astatine is the chemical element with atomic number 85 and the symbol At. With a standard atomic weight of [210], it is a halogen. In the periodic table it occupies group 17 and period 6, and under standard conditions it is normally a solid. Astatine is the rarest naturally occurring element on Earth, studied for cancer therapy.
Atomic structure
An atom of Astatine has 85 protons in its nucleus and, when neutral, 85 electrons arranged in the configuration [Xe] 4f14 5d10 6s2 6p5. Astatine has no stable isotope; the value [210] refers to the mass number of its most stable or most commonly produced isotope.
Discovery and place in the table
Astatine was discovered in 1940 by Dale Corson, Kenneth MacKenzie, Emilio Segrè. It follows Polonium (Po) and precedes Radon (Rn) in order of atomic number.
| Atomic number | 85 |
|---|---|
| Symbol | At |
| Atomic mass | [210] |
| Category | Halogen |
| Group | 17 |
| Period | 6 |
| Electron configuration | [Xe] 4f14 5d10 6s2 6p5 |
| Phase at STP | Solid |
| Discovered | 1940 (Dale Corson, Kenneth MacKenzie, Emilio Segrè) |