Thulium Information
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Thulium Element
Thulium is a chemical element
with the symbol Tm and atomic number 69. It is the thirteenth and third-last
element in the lanthanide series. Like the other lanthanides, the most common
oxidation state is +3, seen in its oxide, halides and other compounds; because
it occurs so late in the series, however, the +2 oxidation state is also
stabilized by the nearly full 4f shell that results. In aqueous solution, like
compounds of other late lanthanides, soluble thulium compounds form
coordination complexes with nine water molecules.
In 1879, the Swedish chemist
Per Teodor Cleve separated from the rare earth oxide erbia another two
previously unknown components, which he called holmia and thulia; these were
the oxides of holmium and thulium, respectively. A relatively pure sample of
thulium metal was first obtained in 1911.
Thulium is a moderately hard,
silvery white metal that is stable in air but can easily be dissolved in
diluted acids—except hydrofluoric acid (HF), in which an insoluble trifluoride
(TmF3) layer forms on the surface of the metal, impeding further chemical
reaction. Thulium is a strong paramagnet above 56 K (−217 °C, or −359 °F).
Between 56 and 32 K (−241 °C, or −402 °F) the metal is antiferromagnetic with a
sinusoidally modulated magnetic structure along the c-axis of its crystal
structure, and below 32 K thulium is ferrimagnetic.
Thulium was discovered in 1879,
along with holmium, by Per Teodor Cleve, who named the oxide thulia after an
ancient name for Scandinavia. It is found in small amounts in such rare-earth
minerals as laterite ionic clays, xenotime, and euxenite and in products of
nuclear fission. Thulium is one of the rarest of the rare-earth elements. Its
abundance in Earth’s crust is nearly the same as those of antimony and iodine.
Thulium is the second-least
abundant of the lanthanides, after radioactively unstable promethium which is
only found in trace quantities on Earth. It is an easily workable metal with a
bright silvery-gray luster. It is fairly soft and slowly tarnishes in air.
Despite its high price and rarity, thulium is used as the radiation source in
portable X-ray devices, and in some solid-state lasers. It has no significant
biological role and is not particularly toxic.
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