Praseodymium Information
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Praseodymium Element
Praseodymium is a chemical
element with the symbol Pr and atomic number 59. It is the third member of the
lanthanide series and is traditionally considered to be one of the rare-earth
metals. Praseodymium is a soft, silvery, malleable and ductile metal, valued
for its magnetic, electrical, chemical, and optical properties. It is too
reactive to be found in native form, and pure praseodymium metal slowly
develops a green oxide coating when exposed to air.
Praseodymium always occurs
naturally together with the other rare-earth metals. It is the fourth most
common rare-earth element, making up 9.1 parts per million of the Earth's
crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl
Gustav Mosander extracted a rare-earth oxide residue he called didymium from a
residue he called "lanthana", in turn separated from cerium salts. In
1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into
two elements that gave salts of different colours, which he named praseodymium
and neodymium. The name praseodymium comes from the Greek prasinos (πράσινος),
meaning "green", and didymos (δίδυμος), "twin".
Praseodymium is a moderately
soft, ductile, and malleable silvery white metal. It rapidly displaces hydrogen
from water in diluted acids (except hydrofluoric acid [HF]) and slowly oxidizes
in air, developing a green-yellowish oxide coating with complex and varying
stoichiometry that can be expressed using a generic formula PrOx (1.5 ≤ x ≤ 2).
The metal is best stored sealed in a plastic covering either in vacuum or in an
inert atmosphere. Praseodymium is strongly paramagnetic, and an unstrained
single-crystal sample will order antiferromagnetically at 0.03 K (−273.12 °C,
or −459.62 °F). However, if praseodymium is strained, it may order at
temperatures as high as about 20 K (−253 °C, or −424 °F).
Praseodymium was discovered in
didymia, a mixture of several rare-earth oxides. From it, by repeated
fractional crystallization of ammonium didymium nitrate, Austrian chemist Carl
Auer von Welsbach in 1885 separated salts of the elements praseodymium (the
green fraction) and neodymium (the pink fraction). Praseodymium occurs in
minerals such as monazite and bastnasite and as one of the products of nuclear
fission.
Like most rare-earth elements,
praseodymium most readily forms the +3 oxidation state, which is the only
stable state in aqueous solution, although the +4 oxidation state is known in
some solid compounds and, uniquely among the lanthanides, the +5 oxidation
state is attainable in matrix-isolation conditions. Aqueous praseodymium ions
are yellowish-green, and similarly praseodymium results in various shades of
yellow-green when incorporated into glasses. Many of praseodymium's industrial
uses involve its ability to filter yellow light from light sources.
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