Element 85 · Halogen
Astatine (At) — Element 85
Greek astatos — unstable
Astatine (At) is a halogen in Period 6, Group 17 of the periodic table with atomic number 85, standard atomic weight [210] u, and ground-state electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵. At standard temperature and pressure it is classified as a solid with 7 valence electrons and common oxidation states -1, +1, +5.
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What are the atomic properties and physical constants of Astatine?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 85
- Standard atomic mass
- [210] u
- Chemical family
- Halogen
- Ground-state configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
- Electrons per shell
- 2, 8, 18, 32, 18, 7
- Valence electrons
- 7
- Common ion charges / oxidation states
- -1, +1, +5
- Phase at STP
- Solid
- Pauling electronegativity
- 2.20 Pauling
- First ionization energy
- 920 kJ/mol
- Atomic radius
- 127 pm
- Melting point
- 302 °C
- Boiling point
- 337 °C
- Discovery year
- 1940
- Table coordinate
- Period 6, Group 17
- Radioactivity
- Radioactive (no stable isotopes)
How are electrons arranged across Astatine’s shells?
A neutral Astatine atom contains 85 electrons distributed across 6 occupied principal energy shells ([Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵). The table below compares Astatine’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in At | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 32 e⁻ | 32 e⁻ |
| n = 5 | O | 18 e⁻ | 50 e⁻ |
| n = 6 | P | 7 e⁻ | 72 e⁻ |
Frequently Asked Questions about Astatine (At)
What is the atomic mass and atomic number of Astatine (At)?
Astatine (At) has atomic number Z = 85 (85 protons in its nucleus) and an IUPAC standard atomic weight of [210] u. It sits in Period 6, Group 17 and is classified as a halogen.
What is the ground-state electron configuration of Astatine?
The neutral ground-state electron configuration of Astatine (Z = 85) is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵. Across its 6 occupied principal shells (n = 1 to n = 6), the electrons per shell are 2, 8, 18, 32, 18, 7, with 7 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Astatine?
Astatine commonly forms -1, +1, +5 oxidation states or ion charges in compounds. Its Pauling electronegativity is 2.20 and its first ionization energy is 920 kJ/mol.
When was Astatine discovered and what is it used for?
Astatine was discovered in 1940 (Greek astatos — unstable). Targeted cancer therapy research
How does Astatine compare to neighboring elements?
Other halogen elements: