Thulium

Symbol: Tm
Atomic number: 69
Category: lanthanides
Group: n/a
Period: 6
Block: f
Atomic weight: 168.93421 g/mol
Electrons per shell: 2, 8, 18, 31, 8, 2
CAS number: 7440-30-4
Phase: solid
Density: 9.32 kg/dm³ (near room temperature)
Melting point: 1818 K (1545 °C, 2813 °F)
Boiling point: 2223 K (1950 °C, 3542 °F)
Crystal structure: hexagonal
Oxidation states: 3
Electronegativity: 1.25 (Pauling scale)
Name's origin: Thule
Name's meaning: the name of Scandinavia in classical literature - the discoverer was Swedish
Facts:
- is the least abundant of the rare earths
- is an easily workable metal with a bright silvery-gray luster and can be cut by a knife
- has some corrosion resistance in dry air and good ductility
- naturally occurring thulium is made entirely of the stable isotope thulium-169
- as a rare and expensive, thulium does not have many practical applications
- has been used to create laser lights, but production costs have been too high for commercial use
- is never found in nature in pure form, but it is found in small quantities in minerals with other rare earths
- is used as interstellar money in the book Illegal Aliens, due to its rarity and lack of other uses
- has a low-to-moderate degree of acute toxicity and should be handled with care, and metallic thulium in dust form presents a fire and explosion hazard