Name Thulium
Symbol Tm
Atomic Number 69
Atomic Mass 168.934 atomic mass unit
Number of Protons 69
Number of Neutrons 100
Number of Electrons 69
Melting Point 1545.0 C
Boiling Point 1727.0 C
Density 9.321 grams per cubic centimeter
Normal Phase Solid
Family Rare Earth Metals
Period 6
Cost $40 to $50 per gram



Origin of Name From Thule, the ancient name of Scandinavia
Date and Place of Discovery In 1879 in Sweden
Discovered by Per Teodor Cleve
Common Compounds
Interesting facts
  • It is the least abundant of the rare earth metals.
  • It is easy to work with and can be cut with a knife.
  • It is somewhat resistant to corrosion in dry air.
  • Its stable isotope, Tm-169, is the only form that occurs naturally.
Common Uses
  • Lasers
  • Nuclear reactors
  • Portable X-ray power supplies
  • Possible energy source in the future
  • Microwave equipment


Photo Courtesy of
Chemical Elements
Jefferson Lab
Los Alamos National Labs
Web Elements

Thulium Atomic Structure Elements by Name Elements by Number Home