36Krypton

Krypton is a noble gase in group 18, period 4. At 25 °C it is a gas.

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

Symbol: Kr
Atomic number: 36 protons in the nucleus
Standard atomic weight: 83.798 ± 0.002
Electron configuration: [Ar] 3d¹⁰ 4s² 4p⁶
Electrons in each shell: 2, 8, 18, 8
Group, period, block: 18, 4, p
Family: Noble gases
State at 25 °C: gas
Electronegativity: 3 (Pauling scale)
First ionisation energy: 1350.8 kJ/mol (13.9996055 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.