|Name, Symbol, Number||thulium, Tm, 69|
|Group, Period, Block||n/a, 6, f|
|Atomic mass||168.93421(2) g/mol|
|Electron configuration||[Xe] 4f13 6s2|
|Electrons per shell||2, 8, 18, 31, 8, 2|
|Density (near r.t.)||9.32 g/cm³|
|Liquid density at m.p.||8.56 g/cm³|
|Melting point||1818 K
(1545 °C, 2813 °F)
|Boiling point||2223 K
(1950 °C, 3542 °F)
|Heat of fusion||16.84 kJ/mol|
|Heat of vaporization||247 kJ/mol|
|Heat capacity||(25 °C) 27.03 J/(mol·K)|
|Electronegativity||1.25 (Pauling scale)|
|1st: 596.7 kJ/mol|
|2nd: 1160 kJ/mol|
|3rd: 2285 kJ/mol|
|Atomic radius||175 pm|
|Atomic radius (calc.)||222 pm|
|Magnetic ordering||no data|
|Electrical resistivity||(r.t.) (poly) 676 nΩ·m|
|Thermal conductivity||(300 K) 16.9 W/(m·K)|
|Thermal expansion||(r.t.) (poly)
|Speed of sound (thin rod)||(r.t.) 74.0 m/s|
|Shear modulus||30.5 GPa|
|Bulk modulus||44.5 GPa|
|Vickers hardness||520 MPa|
|Brinell hardness||471 MPa|
|CAS registry number||7440-30-4|
The element is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths. It is principally extracted from monazite (~0.007 percent thulium) ores found in river sands through ion-exchange. Newer ion-exchange and solvent extraction techniques have led to easier separation of the rare earths, which has yielded much lower costs for thulium production. The metal can be isolated through reduction of its oxide with lanthanum metal or by calcium reduction in a closed container. None of thulium's compounds are commercially important.
Thulium was discovered by Swedish chemist Per Teodor Cleve in 1879 by looking for impurities in the oxides of other rare earth elements (this was the same method Carl Gustaf Mosander earlier used to discover some other rare earth elements). Cleve started by removing all of the known contaminants of erbia (Er2O3) and upon additional processing, obtained two new substances; one brown and one green. The brown substance turned out to be the oxide of the element holmium and was named holmia by Cleve and the green substance was the oxide of an unknown element. Cleve named the oxide thulia and its element thulium after Thule, Scandinavia.
Thulium is an inner transition metal (or lanthanide) that lies in period six of the periodic table, between erbium and ytterbium. It is easy to work and can be cut by a knife. It is ductile and is somewhat resistant to corrosion in dry air.
Naturally occurring thulium is composed of a single stable isotope, Tm-169 (100 percent natural abundance). 31 radioisotopes have been characterized, with the most stable being Tm-171 with a half-life of 1.92 years, Tm-170 with a half-life of 128.6 days, Tm-168 with a half-life of 93.1 days, and Tm-167 with a half-life of 9.25 days. All of the remaining radioactive isotopes have half-lives that are less than 64 hours, and the majority of these have half lives that are less than two minutes. This element also has 14 meta states, with the most stable being Tm-164m (t½ 5.1 minutes), Tm-160m (t½ 74.5 seconds), and Tm-155m (t½ 45 seconds).
The isotopes of thulium range in atomic weight from 145.966 u (Tm-146) to 176.949 u (Tm-177). The primary decay mode before the most abundant stable isotope, Tm-169, is electron capture, and the primary mode after is beta emission. The primary decay products before Tm-169 are element 68 (erbium) isotopes, and the primary products after are element 70 (ytterbium) isotopes.
Thulium has been used to create lasers, but high production costs have prevented other commercial uses from being developed. Other applications, real and potential, include:
Thulium has a low-to-moderate acute toxic rating and should be handled with care. Metallic thulium in dust form presents a fire and explosion hazard.
All links retrieved December 7, 2015.
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