Thulium Facts

Find out more about the chemical & physical properties of thulium

These are various forms of elemental thulium
Alchemist-hp, Creative Commons License

Thulium is one of the rarest of the rare earth metals. This silver-gray metals share many common properties with other lanthanides but also displays some unique characteristics. Here is a look at some interesting thulium facts:

  • Although the rare earth elements aren't all that rare, they are so-named because they are difficult to extract from their ores and purify. Thulium actually is the least abundant of the rare earths.
  • Thulium metal is soft enough that it can be cut with a knife. Like other rare earths, it is malleable and ductile.
  • Thulium has a silvery appearance. It is fairly stable in air. It reacts slowly in water and more quickly in acids.
  • Swedish chemist Per Teodor Cleve discovered thulium in 1879 from an analysis of the mineral erbia, a source of several rare earth elements.
  • Thulium is named for the early name for Scandinavia—Thule.
  • The principal source of thulium is the mineral monazite, which contains thulium at a concentration of about 20 parts per million.
  • Thulium is not toxic, although it has no known biological function.
  • Natural thulium consists of one stable isotope, Tm-169. 32 radioactive isotopes of thulium have been produced, with atomic masses ranging from 146 to 177.
  • The most common oxidation state of thulium is Tm3+. This trivalent ion most commonly forms green compounds. When excited, Tm3+ emits a strong blue fluorescence. One interesting fact is that this fluorescence, along with red from europium Eu3+ and green from terbium Tb3+, is used as security markers in Euro banknotes. The fluorescence appears when the notes are held under black or ultraviolet light.
  • Because of its rarity and expense, there are not many uses for thulium and its compounds. However, it is used to dope YAG (yttrium aluminum garnet) lasers, in ceramic magnetic materials, and as a radiation source (after bombardment in a reactor) for portable x-ray equipment.

Thulium Chemical and Physical Properties

Element Name: Thulium

Atomic Number: 69

Symbol: Tm

Atomic Weight: 168.93421

Discovery: Per Theodor Cleve 1879 (Sweden)

Electron Configuration: [Xe] 4f13 6s2

Element Classification: Rare Earth (Lanthanide)

Word Origin: Thule, the ancient name of Scandinavia.

Density (g/cc): 9.321

Melting Point (K): 1818

Boiling Point (K): 2220

Appearance: soft, malleable, ductile, silvery metal

Atomic Radius (pm): 177

Atomic Volume (cc/mol): 18.1

Covalent Radius (pm): 156

Ionic Radius: 87 (+3e)

Specific Heat (@20°C J/g mol): 0.160

Evaporation Heat (kJ/mol): 232

Pauling Negativity Number: 1.25

First Ionizing Energy (kJ/mol): 589

Oxidation States: 3, 2

Lattice Structure: Hexagonal

Lattice Constant (Å): 3.540

Lattice C/A Ratio: 1.570

References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)

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Your Citation
Helmenstine, Anne Marie, Ph.D. "Thulium Facts." ThoughtCo, Aug. 25, 2020, Helmenstine, Anne Marie, Ph.D. (2020, August 25). Thulium Facts. Retrieved from Helmenstine, Anne Marie, Ph.D. "Thulium Facts." ThoughtCo. (accessed June 8, 2023).