Thulium

Symbol: Tm
Date of discovery: 1879
Name origin: Thule, Scandinavia
Appearance: silvery white
Discoverer: Per Teodor Cleve
Obtained from: monazite

Melting point: 1545 K
Boiling point: 1950 K
Density[kg/m³]: 9.32
Molar volume: 19.1 × 10^-6 m³/mol
Protons/Electrons: 69
Neutrons: 100
Shell structure: 2,8,18,31,8,2
Electron configuration: [Xe]4f136s2
Oxidation state: 3
Crystal structure: hexagonal

Thulium is a rare earth metal never found as a free element. It is found in small quantities with other rare earths in minerals, such as monazite. In its pure form, this metal has a bright, silvery lustre. Thulium is reasonably stable in air, but must be protected from moisture. The element is silvery-grey, soft, malleable, ductile, and can be cut with a knife. It currently has no commercial applications, although one of its isotopes, thulium-169, could be used as a radiation source for portable X-ray machines. First identified in Sweden by chemist Per Theodor Cleve, Thulium gets its name from the ancient name for Scandinavia, Thule.