Thulium is a rare earth element, one of the elements found in row 6 of the periodic table. It has an atomic number of 69, an atomic mass of 168.9342, and a chemical symbol of Tm.

Properties

Thulium is a silvery metal so soft it can be cut with a knife. It is both malleable and ductile and can be worked rather easily. Its melting point is 2,822°F (1,550°C), its boiling point is 3,141°F (1,727°C), and its density is 9.318 grams per cubic centimeter. Thulium is not a very active metal, although it does react slowly with water and more rapidly with most acids.

Occurrence and Extraction

Thulium is one of the rarest of the rare earth elements with an abundance in the Earth's crust of about 0.2-1 part per million. Its most common ores are monazite, euxenite, and gadolinite. The pure metal can be produced by treating thulium fluoride (TmF₃) with calcium metal: 2TmF₃ + 3Ca 3CaF₂ + 2Tm

Discovery and Naming

Thulium is one of the elements discovered in yttria, a mineral first found by a Swedish army officer named Carl Axel Arrhenius (1757-1824) in 1787 near the town of Ytterby, Sweden. Eventually, yttria was to yield nine new elements. Thulium was found by the Swedish chemist Per Teodor Cleve (1840-1905) in 1879. He named the element for the ancient name of Scandinavia, Thule.

Uses

Thulium is too expensive to have many commercial applications. It is sometimes used in special types of lasers that are used for photographic purposes on satellites circling the Earth.