Praseodym, Pr, Atomic number 59

General

Praseodymium is a chemical element with the element symbol Pr and atomic number 59. In the periodic table it is in the group of lanthanides and is thus also one of the rare earth metals. From the green color of its compounds is also the name: The Greek word means prásinos "leek green", didymos "double" or "twin".
1841 CG extracted the rare earth didymium from Mosander lanthanum. 1874 Per Teodor Cleve noticed, that it is actually in didymium were two elements. In 1879 isolierte Lecoq de Boisbaudran Samarium aus Didym, which he won from the mineral samarskite. 1885 succeeded Carl Auer von Welsbach,, To separate didymium in praseodymium and neodymium, the two salts with different colors form.
Praseodymium is a companion to the typical rare-earth minerals Cerit, Monazite and bastnaesite ago. The world's reserves are at 4 Million tons estimated.

Extraction

As with all lanthanides are first enriched ores by flotation, thereafter, the metals are converted into corresponding halides and by fractional crystallization, Ion exchange or extraction separated. The metal is obtained by electrolysis or reduction with calcium.

Special features

Praseodymium is a soft, silvery-white metal paramagnetic, which is one of the lanthanides and rare earth metals. It is in air somewhat more corrosion resistant than europium, Lanthan oder Cer, is but slightly from a green oxide, the peel of air. At 798 ° C, converts the hexagonal α-Pr into the body centered cubic β-Pr. Natural praseodymium consists only of the stable isotope 141Pr. 38 other radioactive isotopes are known, wherein 143Pr and 142Pr with a half-life of 13,57 Days or 19,12 Hours are the longest. All other isotopes have half-lives of less than 5,985 Hours, most of even less than 33 Seconds. There are also 6 metastable states, where 138mPr (t½ 2,12 Hours), 142MPR (t½ 14,6 Minutes) and 134mPr (t½ 11 Minutes) are the most stable.
The isotope is an atom moving mass range of 120,955 (121Pr) to 158,955 (159Pr). Because of its sensitivity to air praseodymium should be kept sealed in gasoline or in plastic or glass.
A biological significance is not known, Praseodymverbindungen but should have a slightly hepatotoxic. However, there are no toxicity values.
Praseodymium occurs in its compounds three- and quadrivalent at, the trivalent oxidation state is the more common. Pr(III)-Ions are yellow-green, Pr(IV)-Ion colorless. Under special conditions, reductive divalent praseodymium also be realized, of. B. im Pr2I5.
Are known by all levels of several halides, for example PrF3, PrF4, PrCl3, PrBr3, PrI3, Pr2I5. The trivalent halides form various hydrates.
There are also several connections with chalcogens: the normal brown-black praseodymium(III,IV)-oxid Pr6O11, The almost black Pro2, the green Pr2O3, Pr2S3, Pr2Te3 and other binary compounds such as PrN, PrP. In addition, praseodymium salts in various, dem know hygroskopischem Praseodymnitrat Pr(NO3)3 · x H2O, the beautifully crystallized Praseodymsulfat Pr2(SO4)2 · 8 H2O and the other represented.
It also forms several Fluoridokomplexe as z. B. the K2[PrF6] with tetravalent Pr.

Use

Praseodymium is used in alloys with magnesium for the production of high-strength metal for aircraft engines.
Alloys with cobalt and iron are strong permanent magnets.
Praseodymverbindungen be used for coloring glass and enamels (For example, in green colored headlight glass in lighting technology).
The compounds also improve the UV absorption and are used for eye protection glasses during welding.

General
Name, Symbol

Atomic number

Praseodym, Pr, 59
Series Lanthanides
group, Period, Block The, 6, f
Appearance silvery white, yellowish
CAS-Nummer 7440-10-0
Mass fraction of element 5,2 ppm
Atomic
Atomic mass 140,90765 you
Atomradius 185 pm
Kovalenter Radius 203 pm
Elektronenkonf. [Car] 4f(3) 6s2
1. Ionization 527,0 KJ / mol
2. Ionization 1020 KJ / mol
3. Ionization 2086 KJ / mol
Physically
Physical State fixed
Crystal structure hexagonal
Density 6,475 g/cm3 (25 ° C)
Magnetism paramagnetisch (χm = 2,9 * 10(-3))
Melting point 1208 K (935 C)
Boiling point 3563 K (3290 C)
Molar Volume 20,80 * 10(-6)m(3)/mol
Heat of vaporization 330 KJ / mol
Schmelzwärme 6,9 KJ / mol
Electrical conductivity 1,43*10(6) A/(V * m)
Thermal conductivity 13 W /(m*K)
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