85 At
Halogen
Astatine
Rarest natural element.
Properties of Astatine
- Atomic number (Z)
- 85
- Symbol
- At
- Atomic mass
- 210 g/mol
- Category
- Halogen
- Group
- 17
- Period
- 6
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
- Electronegativity (Pauling)
- 2.2
- Atomic radius
- 127 pm
- First ionization energy
- 899 kJ/mol
- Melting point
- 575 K (301.9 °C)
- Boiling point
- 610 K (336.9 °C)
- Density
- 6.35 g/cm³
- Phase at 25 °C
- Solid
- Discovered
- Discovered in 1940