The Element Thulium
Atomic Number: 69
Atomic Weight: 168.93422
Melting Point: 1818 K (1545°C or 2813°F)
Boiling Point: 2223 K (1950°C or 3542°F)
Density: 9.32 grams per cubic centimeter
Phase at Room Temperature: Solid
Element Classification: Metal
Period Number: 6
Group Number: none
Group Name: Lanthanide
What's in a name? From the earliest name for Scandinavia, Thule.
Say what? Thulium is pronounced as THOO-lee-em.
History and Uses:
Thulium was discovered by Per Theodor Cleve, a Swedish chemist, in 1879. Cleve used the same method Carl Gustaf Mosander used to discover lanthanum, erbium and terbium, he looked for impurities in the oxides of other rare earth elements. He started with erbia, the oxide of erbium (Er2O3), and removed all of the known contaminants. After further processing, he obtained two new materials, one brown and the other green. Cleve named the brown material holmia and the green material thulia. Holmia is the oxide of the element holmium and thulia is the oxide of the element thulium. Today, thulium is primarily obtained through an ion exchange process from monazite sand ((Ce, La, Th, Nd, Y)PO4), a material rich in rare earth elements that can contain as much as 0.007% thulium.
Thulium is the least abundant of the naturally occurring rare earth elements. Metallic thulium is relatively expensive and has only recently become available. 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.
Thulium forms no commercially important compounds. Some of thulium's compounds include: thulium oxide (Tm2O3), thulium fluoride (TmF3) and thulium iodide (TmI3).
Estimated Crustal Abundance: 5.2×10-1 milligrams per kilogram
Estimated Oceanic Abundance: 1.7×10-7 milligrams per liter
Number of Stable Isotopes: 1 (View all isotope data)
Ionization Energy: 6.184 eV
Oxidation States: +3
3s2 3p6 3d10
4s2 4p6 4d10 4f13