53Iodine

Iodine is a halogen in group 17, period 5. At 25 °C it is a solid.

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

Symbol: I
Atomic number: 53 protons in the nucleus
Standard atomic weight: 126.90 ± 0.01
Electron configuration: [Kr] 4d¹⁰ 5s² 5p⁵
Electrons in each shell: 2, 8, 18, 18, 7
Group, period, block: 17, 5, p
Family: Halogens
State at 25 °C: solid
Electronegativity: 2.66 (Pauling scale)
First ionisation energy: 1008.4 kJ/mol (10.451236 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.