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Periodic table / Lanthanoids

69Thulium

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

Tm
Shells: 2, 8, 18, 31, 8, 2. A simple picture: electrons do not move in circles.
Symbol
Tm
Atomic number
69 protons in the nucleus
Standard atomic weight
168.93 ± 0.01
Electron configuration
[Xe] 4f13 6s2
Electrons in each shell
2, 8, 18, 31, 8, 2
Group, period, block
–, 6, f
Family
Lanthanoids
State at 25 °C
solid
Electronegativity
1.25 (Pauling scale)
First ionisation energy
596.7 kJ/mol (6.184402 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.