Periodic Table of Elements




Thulium was discovered by Per Theodor Cleve, a Swedish chemist, in 1879.

Name: Thulium
Symbol: Tm
Atomic number: 69
Atomic weight: 168.93
State: solid
Group, period, block: n/a, 6, f
Color: silvery gray
Classification: lanthanide
Electron configuration: 4f13 6s2

Physical properties

Density: 9.32 g/cm-3
Melting point: 1818 K,1545 C,2813 F
Boiling point: 2223 K,1950 C,3542 F

Atomic properties

Oxidation states: 2, 3, 4
Electronegativity: 1.25 (Pauling scale)
Ionization energies: 1st: 596.7 kJmol-1
Covalent radius: 19010 pm
Van der Waals radius: no data
  • Tm
  • Electron Configuration


There is one naturally occurring isotope of thulium exists, 169Tm.