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Name , symbol , atomic number Thulium, Tm, 69
Element category Lanthanoids
Group , period , block La , 6 , f
Appearance silvery gray
CAS number 7440-30-4
EC number 231-140-2
ECHA InfoCard 100.028.309
Mass fraction of the earth's envelope 0.19 ppm
Atomic mass 168,93422 (2) and
Atomic radius (calculated) 175 (222) pm
Covalent radius 190 pm
Electron configuration [ Xe ] 4 f 13 6 s 2
1. Ionization energy 6th.18431 (6) eV596.7 kJ / mol
2. Ionization energy 12.065 (20) eV1 164.1 kJ / mol
3. Ionization energy 23.66 (3) eV2 280 kJ / mol
4. Ionization energy 42.41 (4) eV4 090 kJ / mol
5. Ionization energy 65.4 (3) eV6 310 kJ / mol
Physical state firmly
Crystal structure hexagonal
density 9.318 g / cm 3 (25 ° C )
magnetism paramagnetic ( Χ m = 0.017)
Melting point 1818 K (1545 ° C)
boiling point 2223 K (1950 ° C)
Molar volume 19.1 · 10 −6 m 3 · mol −1
Heat of evaporation 247 kJ / mol
Heat of fusion 16.8 kJ mol −1
Electric conductivity 1.477 · 10 6 A · V −1 · m −1
Thermal conductivity 16.8 W m −1 K −1
Oxidation states 2, 3 , 4
Normal potential −2.32 V (Tm 3+ + 3 e - → Tm)
Electronegativity 1.25 ( Pauling scale )
isotope NH t 1/2 ZA ZE (M eV ) ZP
167 Tm {syn.} 9.25 d ε 0.748 167 he
168 Tm {syn.} 93.1 d ε 0.257 168 he
169 Tm 100  % Stable
170 Tm {syn.} 128.6 d β - 0.314 170 yb
171 Tm {syn.} 63.6 h β - 1,880 171 Yb
For other isotopes see list of isotopes
safety instructions
GHS labeling of hazardous substances


02 - Highly / extremely flammable 07 - Warning


H and P phrases H: 228-319-335
P: 210-261-305 + 351 + 338
As far as possible and customary, SI units are used.
Unless otherwise noted, the data given apply to standard conditions .

Thulium is a chemical element with the element symbol Tm and the atomic number 69. In the periodic table it is in the group of lanthanoids and is therefore one of the rare earth metals .


Thulium was discovered in the course of more detailed investigations into gadolinite and the elements that can be isolated from it. Carl Gustav Mosander and others initially succeeded in separating gadolinite into erbine earth ( erbium oxide ), terbine earth ( terbium oxide ) and yttrium earth ( yttrium oxide ). The hereditary earth soon turned out to be a mixture as well, when the ytterbium was separated first by Jean Charles Galissard de Marignac , then the scandium by Lars Fredrik Nilson .

In 1879, Per Teodor Cleve, by comparing the absorption spectra of different samples that were created when separating erbium and ytterbium, found that these contained certain absorption bands of different strengths, i.e. that additional elements must be included. He identified two elements that he named holmium and thulium. The characteristic absorption band of thulium was 684 nm. The name thulium was chosen after an old name from Scandinavia . Although had Jacques-Louis Soret , discovered the absorption bands for thulium and holmium before Cleve, however (called "X") only one new element that matched the Holmium identified.

After his discovery of thulium, Cleve tried to obtain pure thulium oxide in 1880, but he could not completely separate it from ytterbium and therefore only determine an approximate atomic mass. Charles James presented pure thulium oxide for the first time in 1911 through 15,000-fold fractional crystallization and separation of the bromates from erbium, thulium and ytterbium.

Elemental thulium was first received in 1936 by Wilhelm Klemm and Heinrich Bommer . They obtained the metal by reducing thulium (III) chloride with potassium at 250 ° C. They also determined the crystal structure and the magnetic properties of the metal.


Thulium is a rare element on earth, its abundance in the continental crust is about 0.52  ppm . Apart from the unstable promethium, it is the rarest lanthanoid. However, thulium is more common than elements like iodine or silver .

The element occurs exclusively as a minor component of various rare earth minerals, especially ytter earths of the heavy lanthanoids. Depending on the occurrence , monazite contains 0.01–0.51% thulium, xenotime up to 0.9% of the element. Minerals with the main component thulium or natural elemental thulium are not known.

Thulium is very complex and expensive to manufacture, but it is only used in very small quantities. Therefore the supply of thulium is not considered critical.

Extraction and presentation

After an elaborate separation of the other thulium companions, the oxide is reduced with lanthanum to the metallic thulium. The thulium is then sublimed off.


Thulium, sublimates dendritic

Physical Properties

The silver-gray metal of the rare earths is very soft, ductile and malleable.

Chemical properties

Thulium is quite stable in dry air, but turns gray in moist air. At higher temperatures it burns to sesquioxide .

It reacts with water to form the hydroxide, producing hydrogen . It dissolves in mineral acids with the formation of hydrogen.

In its compounds it is in the +3 oxidation state, the Tm 3+ cations form pastel-bluish-green solutions in water.


Thulium is the rarest rare earth metal, but is still more abundant in the earth's crust than gold or platinum . In addition to minimal use in televisions (to activate the phosphors on the screen surface ), there are only a few commercial applications:

  • 170 Tm extracted from nuclear reactors serves as an X-ray source ( gamma emitter in materials testing)
  • Thuliumdotiertes yttrium or lanthanum (LaOBr) serves as a scintillator in X-ray intensifying screens or fluorescent screens in the X-ray technology
  • Thulium-doped calcium sulfate is used as a detector in personal dosimeters for measuring low radiation doses
  • Thulium crystals can be used as an active medium in diode-pumped solid-state lasers (wavelength 2 µm) with a total efficiency of up to 10% at a maximum of 60 W light output.
  • Thulium-doped silica glass as an active medium in fiber lasers (wavelength 2 µm) was operated with a differential efficiency of 53.2% at a power> 1000 W.
  • It is also used in laser devices that serve as surgical scalpels

safety instructions

Thulium and thulium compounds are slightly toxic. Thulium dusts are flammable and explosive.


Web links

Commons : Thulium  - collection of images, videos and audio files
Wiktionary: Thulium  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
  2. The values ​​for the properties (info box) are taken from (Thulium) , unless otherwise stated .
  3. ^ IUPAC, Standard Atomic Weights Revised v2 ( Memento of March 3, 2016 in the Internet Archive ).
  4. CIAAW, Standard Atomic Weights Revised 2013 .
  5. a b c d e Entry on thulium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( ). Retrieved June 13, 2020.
  6. a b c d e entry on thulium at WebElements, , accessed on June 13, 2020.
  7. ^ NN Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. VCH, Weinheim 1988, ISBN 3-527-26169-9 , p. 1579.
  8. Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values ​​there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
  9. a b Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values ​​for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337, doi: 10.1021 / je1011086 .
  10. a b Data sheet Thulium, powder from Sigma-Aldrich , accessed on April 26, 2017 ( PDF ).
  11. ^ Per Teodor Cleve: Sur deux nouveaux elements dans l'erbine. In: Comptes rendus. 89, 1879, pp. 478-481 ( digitized on Gallica ).
  12. Per Teodor Cleve: Sur l'erbine. In: Comptes rendus. 89, 1879, pp. 708-709 ( digitized on Gallica ).
  13. ^ Per Teodor Cleve: Sur le thulium. In: Comptes rendus. 91, 1880, pp. 328-329 ( digitized on Gallica ).
  14. C. James: thulium I. In: Journal of the American Chemical Society. 33, 1911, pp. 1332-1344, doi: 10.1021 / ja02221a007 .
  15. W. Klemm, H. Bommer: To the knowledge of the metals of the rare earths. In: Journal of Inorganic and General Chemistry. 231, 1937, pp. 138-171, doi: 10.1002 / zaac.19372310115 .
  16. David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Geophysics, Astronomy, and Acoustics; Abundance of Elements in the Earth's Crust and in the Sea, pp. 14-18.
  17. ^ Ian McGill: Rear Earth Elements. In: Ullmann's Encyclopedia of Industrial Chemistry . Wiley-VCH, Weinheim 2005, doi: 10.1002 / 14356007.a22_607 .
  18. Harald Elsner: Critical supply situation with heavy rare earths - development of “green technologies” endangered? In: Commodity Top News. No. 36, 2011. (pdf)
  19. Thomas Ehrenreich, Ryan Leveille, Imtiaz Majid, Kanishka Tankala, Glen Rines, Peter Moulton: 1-kW, All-Glass Tm: fiber laser. SPIE Photonics West 2010: LASE Fiber Lasers VII: Technology, Systems, and Applications, Conference 7580, Session 16: Late-Breaking News, January 28, 2010.
  20. Hintermaier-Erhard, Gerd: Everything is chemistry! : the chemical elements and how we use them . Munich 2017, ISBN 978-3-8310-3339-3 .