Thulium is the least abundant of all the lanthanide metals. It is used to create lasers that surgeons use to cut damaged body tissue. The most stable isotope is 169Tm, but it also has a radioactive form that can be used as an X-ray source. Thus, portable X-ray machines use radioactive isotopes of thulium.

Summary of properties (Tm)

Atomic weight168.934218(6)
Discoverer (year)Cleve, Per Teodor (1879)
Natural formmetallic solid (hexagonal)
Electron configuration[Xe] 413 6s2
Melting point (ºC)1545
Boiling point (ºC)1727
Abundance in earth's crust (ppm)0.52
Isotope (abundance)169Tm (100)
Density g/cm39.32
Van der Waals radius (pm)227
Covalent radius (pm)177
Electronegativity (Pauling)1.25
Vaporization enthalpy (kJ/mol)247.00
Enthalpy of fusion (kJ/mol)16.84
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.16
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.170
Oxidation state+3
Electron affinity (eV)1.03
1st Ionization potential (eV)6.1843

Back to the Periodic Table of the Elements.