65Terbium

Terbium is a lanthanoid in period 6, in the lanthanoid series. At 25 °C it is a solid.

Shells: 2, 8, 18, 27, 8, 2. A simple picture: electrons do not move in circles.

Symbol: Tb
Atomic number: 65 protons in the nucleus
Standard atomic weight: 158.93 ± 0.01
Electron configuration: [Xe] 4f⁹ 6s²
Electrons in each shell: 2, 8, 18, 27, 8, 2
Group, period, block: –, 6, f
Family: Lanthanoids
State at 25 °C: solid
Electronegativity: no value
First ionisation energy: 565.8 kJ/mol (5.8638 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.