Science Education Home Home Teachers Students Games Videos VA SOL Programs

It's Elemental

The Element Thulium

[Click for Isotope Data]


69 Tm Thulium 168.93422

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

Electron Shell Configuration:


2s2   2p6

3s2   3p6   3d10

4s2   4p6   4d10   4f13

5s2   5p6


Citation and linking information

For questions about this page, please contact Steve Gagnon.