Astatine
The rarest naturally occurring element, a fleeting halogen.
Inside the Astatine atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Astatine atom step by step.
Electron configuration
[Xe] 4f14 5d10 6s2 6p5
A neutral Astatine atom has 85 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 575 K (302 °C)
- Boiling point
- 610 K (337 °C)
- Density
- —
- Electronegativity
- 2.2 Pauling
- Atomic radius
- 150 pm
- 1st ionization energy
- 899 kJ/mol
- Category
- Metalloids
Discovery & naming
- Discovered
- 1940
- Discovered by
- Corson, MacKenzie, and Segrè
- Origin of name
- Greek 'astatos', meaning unstable.
Notable uses
Targeted cancer-therapy research (extremely rare).
Where Astatine comes from
Neutron star mergers
Occurs on Earth only as a fleeting decay product of uranium and thorium, so it inherits their r-process origin.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 85
- Atomic mass
- [210]
- Category
- Metalloids
- Group · Period
- 17 · 6
- Block
- p-block
- Shells
- 2 · 8 · 18 · 32 · 18 · 7