Symbol

Tm

Atomic Number

69

Atomic Mass

168.9342

Family

Lanthanide (Rare Earth Metal) Pronunciation

THU-lee-um

Overview

Thulium was given its name in honor of the earliest name for Scandanavia, Thule. The element was discovered and named by Swedish chemist Per Teodor Cleve (1840-1905) in 1879. Cleve made his discovery while studying the mineral erbia. Erbia was one of the many new elements found in a black rock discovered outside the town of Ytterby, Sweden, in 1787. The complete analysis of that rock took more than 100 years. In the process, nine new elements, including thulium, were discovered.

The chemical family to which thulium belongs is sometimes called the rare earth elements. That name is misleading. These elements are not really very rare. But they usually occur together in the earth, and they are very difficult to separate from each other. The more common chemical name for the group of rare earth elements is...