Thullium

General properties
Name, symbol, number	thulium, Tm, 69
Element category	lanthanide
Group, period, block	n/a, 6, f
Standard atomic weight	168.93421
Electron configuration	[Xe] 4f13 6s2 2, 8, 18, 31, 8, 2
History
Discovery	Per Teodor Cleve (1879)
First isolation	Per Teodor Cleve (1879)

Thullium is a chemical element that has the symbol Tm and atomic number 69. Thulium is the second least abundant of the lanthanides(promethium is only found in trace quantities on Earth). It is an easily workable metal with a bright silvery-gray luster. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices and in solid-state lasers.

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