Praseodymium is a chemical element,
symbol Pr and atomic number 59.
Praseodymium is a silver gray metal from the rare earth group. It is part of the
lanthanide family. At room temperature, it is ductile, malleable and oxidizes
slowly in air. It is stored in mineral oil because it reacts strongly with
water.
Its name comes from the Greek words prason (¦Ð¦Ñά¦Ò¦Ï¦Í - "leek") and didymos (¦Äί¦Ä¦Ô¦Ì¦Ïς
- "twin"), due to the green color of its nitrate.
Chemists have long believed that the mixture of praseodymium-neodymium oxide was
a single body until Carl Auer von Welsbach separated them in 1885.
Praseodymium is a soft, silvery, malleable and ductile metal from the lanthanide
group. It is a little more resistant to corrosion in air than europium,
lanthanum, cerium and neodymium but it produces a green layer of weakly adherent
oxide which bursts when exposed to air5. The metal is thus exposed again to
oxidation. In general, therefore, the praseodymium is stored under oil or in
sealed ampoules.
Unlike other rare earth metals which are shown to be antiferromagnetic and / or
ferromagnetic at low temperatures, Pr is paramagnetic at any temperature above 1
K.
In its compounds, praseodymium occurs in the +2, +3 and / or +4 states.
Praseodymium (IV) is a powerful oxidant, it instantly oxidizes water to oxygen
(O2) or hydrochloric acid to chlorine. Thus in aqueous solution, the oxidation
state +3 is the maximum.
The praseodymium salts are greenish yellow and, in solution, show a simple
absorption spectrum in the visible region with a band in orange-yellow at
589-590 nm and three bands in the blue / purple region at 444, 468 and 482 nm
approx. These positions vary slightly depending on the counterion. Praseodymium
oxide when obtained by calcination of salts such as oxalate or carbonate in air
is black in color (with brown-green reflections) and contains praseodymium +3
and +4 in a variable proportion depending on the reaction conditions. Its
formula is conventionally written: Pr6O11.
Molecular compounds of praseodymium is mainly found in the oxidation state + III
like any other lanthanide. Several examples contain a praseodymium (II) ion. 7
On the contrary, there is only one example of a molecular compound of Pr (IV).
Naturally, praseodymium is composed of a stable isotope, 141Pr; which makes it a
monoisotopic element. Thirty eight radioisotopes were characterized, the most
stable of which is 143Pr with a half-life of 13.57 days and 142Pr with a
half-life of 19.12 hours. All other radioactive isotopes have a half-life less
than 6 hours and the majority have a half-life less than 33 seconds. This
element also has six nuclear isomers, the most stable being 138mPr (t½ 2.12
hours), 142mPr (t½ 14.6 minutes) and 134mPr (t½ 11 minutes).
The range of atomic weights for isotopes is 120.955 u (121Pr) to 158.955 u
(159Pr). The first type of decay before the stable isotope, 141Pr, is electronic
capture and the first type after this isotope is beta radioactivity. The first
radioactivity product before 141Pr are the isotopes of element 58 (cerium) and
the primary products after 141Pr are the isotopes of element 60 (neodymium).
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rhenium germanium zirconium cadmium hafnium
barium lithium beryllium strontium calcium
Tantalum gadolinium samarium yttrium ytterbium
Lutetium praseodymium holmium erbium thulium dysprosium
terbium europium lanthanum cerium neodymium scandium
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