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General Info
Atomic Symbol Atomic symbol::Tm
Atomic Number Atomic number::69
Atomic Weight Atomic weight::168.9342 g/mol
Chemical series Lanthanide
Appearance Silvery metal with a bright luster
Group, Period, Block n/a,6,f-block
Electron configuration [Xe] 6s2 4f 13,
Electrons per shell 2, 8, 18, 31, 8, 2
Electron shell thulium.png
CAS number CAS number::
Physical properties
Phase solid
Density Density::9.321 grams per cubic centimeter g/ml
Melting point Melting point::1545 °C
Boiling point Boiling point::1950 °C
Isotopes of Thulium
iso NA half-life DT DE (MeV) DP
167Tm syn 9.25 d ε 0.748 167Er
168Tm syn 93.1 d ε 1.679 168Er
169Tm 100% 168Tm is stable with 100 neutrons.
170Tm syn 128.6 d β− 0.968 170Yb
171Tm syn 1.92 y β− 0.096 171Yb
All properties are for STP unless otherwise stated.

Thulium is a chemical element classified in the Lanthanide series. This rare earth metal is classified in the Lanthanide series due to its resemblance to lanthanum. Often times, Lanthanides can used in the production of petroleum and similar synthetic products. Although some, such as Thulium, are so rare that they cannot possibly be developed in abundance, its high price and unique characteristics make this an element highly valued by many. Thulium's atomic number is 69 and its atomic weight 168.9342.[1] Its use in medical and military procedures proves the importance of this small, but crucial element.


Thulium has many distinct physical and chemical properties. First, it appears very silvery and shiny to the eye. It is also very soft and can therefore be cut very easily. So easily in fact, that it can be cut with a knife.[2] The element is both malleable and ductile making it an easy one to work with. The malleability allows the Thulium to be hammered and pressed into shin sheets used for commercial means, and the ductility allows for stretching that results in thin wires. It should be protected from moisture in the air which can cause permanent damage to its structure. It is ferromagnetic below 32 K, anti-ferromagnetic between 32 and 56 K, and paramagnetic above 56 K.[3]

Thulium's distinct chemical properties include reacting slowly with water and more quickly with acids. However, it is somewhat stable in the air, therefore, it does not react easily with oxygen and other elements in the air. [4]



Thulium is an element which does not ever occur in pure form in nature, yet it is found in smaller amounts in minerals and earth metals. After ion exchanges, scientists are actually able to remove Thulium from Monazite ores, which are ores consisting of .007% Thulium. Euxenite and gadolinite are also rare earth metals containing small amounts of thulium.[5] These ores are often found in river sands.New method developed in recent times have led to much easier ways of separating rare earth metals. These ion exchanges and solvent extractions have actually significantly lowered the production costs of Thulium.[6]Today, a majority of Thulium is found in ion adsorption clays of Southern China.[7] Thulium, being the rarest element in the Lanthanide series, is estimated to take up .2 to 1 part per million in the Earth's crust. Yet this tiny amount still makes the element more abundant than silver, gold, platinum, and mercury.


Due to its scarcity, Thulium does not have many commercial uses. One important use benefiting society is the use of Thulium in lasers. The use of this element causes the laser to work well at higher temperatures and require less cooling. This comes in handy to scientists and astronauts who use the lasers in satellites that take pictures of Earth's surface.The Holium-chromium-thulium triple doped was developed with high efficiency. It makes use of thulium to create a laser that effectively and accurately does its job. The laser projects at 2097 nm and is specifically used by the military, as well as certain medical fields. The lasers actually prove very effective for laser based surgeries. The specific wavelength of the Thulium laser allows for superficial ablation of tissues.[8] Those who do use Thulium do so by first treating its fluorine with calcium. This process, called extraction, is used with many of the Lanthanide elements and creates the purest form of thulium. As a result of its scarcity, Thulium sells for about $50 a gram or $23,000 a pound.[9] Thulium is also used in medical x-ray machines. This is possible because the element can be obtained from monazite, which contains an x-ray emitting isotope.[10]


Thulium, from the Scandinavian word Thule, was first discovered in 1879 by Per Theodor Cleave. Cleave, a Swedish chemist, utilized the same method as Carl Gustaf when he discovered Lanthanum, Erbium, and Terbium. The method started by using the oxide of rare earth elements and removing all impurities. Cleave used erbia, the oxide of erbia, to find two new metals; one brown and the other green. He named the brown element holmia, now the oxide of holmium, and the other thulia serves as the oxide of thulium.[11] Initially, scientists and workers were unable to view thulium in its purest form. They spectroscopically viewed erbium being removed until the element formed Thulium. Charles James, in 1911, became the first researcher to view Thulium in its almost purest form. He was a British expatriate working at New Hampshire College in Durham. He made the discovery using his patented method of bromate fractional crystallization. His discovery paved the way for the use of Thulium in modern times. In the late 1950's high-purity Thulium oxide first became available for commercial use. Its price has increased since then, but it still comes in second to lutetium. [12]


  1. [1] Thulium, Unknown Author, Wikipedia, 12/2/10
  2. [2] Unknown author, Thulium, 12/2/10
  3. [3] Thulium, Unknown Author, Wikipedia 12/2/10
  4. [4] J Rank, Chemistry Explained, 11/30/10
  5. [5] Chemistry Explained, Author unknown, 12/2/10
  6. [6]Unknown author, Thulium, 12/2/10
  7. [7] Thulium, Unknown Author, 12/2/10
  8. [8] Thulium, Unknown Author, 12/2/10
  9. [9] Chemistry Explained, Author unknown, 12/2/10
  10. [10] Facts About Thulium, Author unknown, 12/2/10
  11. [11]Author Unknown, Jefferson Lab, Accessed 11/22/10
  12. [12] Thulium, Unknown Author, Wikipedia 12/2/10