85Astatine

Astatine is a halogen in group 17, period 6. At 25 °C it is a solid.

Shells: 2, 8, 18, 32, 18, 7. A simple picture: electrons do not move in circles.

Symbol: At
Atomic number: 85 protons in the nucleus
Standard atomic weight: None. Astatine has no stable isotopes, so the mass of a sample depends on which isotopes it holds.
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
Electrons in each shell: 2, 8, 18, 32, 18, 7
Group, period, block: 17, 6, p
Family: Halogens
State at 25 °C: solid
Electronegativity: 2.2 (Pauling scale)
First ionisation energy: 899 kJ/mol (9.31751 eV)

Where these numbers come from

Atomic weight: IUPAC CIAAW, abridged standard atomic weights 2024. Electron configuration and ionisation energy: NIST Atomic Spectra Database. Family, state and electronegativity: PubChem. See Sources. Melting points, boiling points and densities are left out for now: published values differ between sources, and we will add them once each has been checked.