85210AtAstatine
Astatine (At) — element 85halogen · group 17, period 6
Astatine is a chemical element with the symbol At and atomic number 85. It is a halogen in group 17, period 6 of the periodic table (the p-block), with a standard atomic mass of 210 u. At room temperature (25 °C) astatine is a solid.
💡 Known for: The rarest naturally occurring element — only a tiny amount exists in Earth's crust at any moment.
# Astatine properties
| Symbol | At |
|---|---|
| Atomic number | 85 |
| Atomic mass | 210 u |
| Category | halogen |
| Group | 17 |
| Period | 6 |
| Block | p-block |
| Electron configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁵ |
| Electrons per shell | 2, 8, 18, 32, 18, 7 |
| Protons / electrons | 85 / 85 |
| State at 25 °C | solid |
| Melting point | 575 K (301.9 °C, 575.3 °F) |
| Boiling point | 610 K (336.9 °C, 638.3 °F) |
| Density | 7 g/cm³ |
| Electronegativity (Pauling) | 2.2 |
| First ionization energy | 9.318 eV |
| Atomic radius | 127 pm |
| Discovered | 1940 |
# Electron configuration of astatine
The electron configuration of astatine is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵, written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁵. Its 85 electrons fill 6 shells as 2, 8, 18, 32, 18, 7, so the outermost shell holds 7 electrons. As a group 17 element, astatine has 7 valence electrons.
# Related elements
PoPoloniumprevious elementRnRadonnext elementFFluorinegroup 17ClChlorinegroup 17BrBrominegroup 17IIodinegroup 17TsTennessinegroup 17
# Astatine FAQ
What is the atomic number of astatine?
The atomic number of astatine is 85: every astatine atom has 85 protons in its nucleus. Its symbol is At.
What is the atomic mass of astatine?
The standard atomic mass of astatine is 210 u.
What is the electron configuration of astatine?
Astatine's electron configuration is [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁵), with 2, 8, 18, 32, 18, 7 electrons per shell.
Is astatine a metal?
No. Astatine is a halogen, a nonmetal.
What is the melting point of astatine?
Astatine melts at 575 K (301.9 °C, 575.3 °F) and boils at 610 K (336.9 °C, 638.3 °F).
What is astatine used for / known for?
The rarest naturally occurring element — only a tiny amount exists in Earth's crust at any moment.