Relative atomic mass: 168.93421 +- 0.00002

English: Thulium
French: Thulium
Croatian: Tulij
German: Thulium
Italian: Tulio
Spanish: Tulio

Atomic number: 69
Group numbers: 3
Period: 6
Standard state (20 oC): solid

Discovery: 1879 Per Theodor Cleve (SE)
Thulium was discovered by Per Theodore Cleve (SE) in 1879. Named after Thule, an ancient name for Scandinavia. It is a soft, malleable, ductile, silvery metal that tarnishes in air and reacts with water. Thulium dust is flammable. Thulium is found with other rare earths in the minerals gadolinite, euxenite, xenotime and monazite. Radioactive thulium is used to power portable x-ray machines, eliminating the need for electrical equipment. The price of 99.9 % pure thulium pieces is 291.00 for 5 g.
Electronic configuration: [Xe] 4f13 6s2
Formal oxidation number: +3
Atomic radius: 172.4 pm

Electronegativities: 1.25
Thermal conductivity: 16.8 W/(m K)
Electrical resistivity (20 oC): 79 microOhm cm

Melting point: 1545 oC
Boiling point: 1950 oC

Heat of fusion: 18.4 kJ/mol
Heat of vaporization: 247 kJ/mol
Heat of atomization: 233.43 kJ/mol

68Er <= 69Tm => 70Yb

ASCII Periodic Table of the Elements
6 Jan. 2020
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