Praseodymium

properties
[ Xe ] 4 f 3 6 s 2 59 Pr Periodic table
General
Name , symbol , atomic number	Praseodymium, Pr, 59
Element category	Lanthanoids
Group , period , block	La , 6 , f
Appearance	silvery white, yellowish hue
CAS number	7440-10-0
EC number	231-120-3
ECHA InfoCard	100.028.291
Mass fraction of the earth's envelope	5.2 ppm
Atomic
Atomic mass	140.90766 (2) and
Atomic radius (calculated)	185 (247) pm
Covalent radius	203 pm
Electron configuration	[ Xe ] 4 f 3 6 s 2
1. Ionization energy	5.4702 (4) eV ≈ 527.79 kJ / mol
2. Ionization energy	10.631 (20) eV ≈ 1 025.7 kJ / mol
3. Ionization energy	21st.6237 (25) eV ≈ 2 086.37 kJ / mol
4. Ionization energy	38.981 (25) eV ≈ 3 761.1 kJ / mol
5. Ionization energy	57.53 (5) eV ≈ 5 550 kJ / mol
Physically
Physical state	firmly
Crystal structure	hexagonal
density	6.475 g / cm 3 (25 ° C )
magnetism	paramagnetic ( Χ m = 2.9 · 10 −3 )
Melting point	1208 K (935 ° C)
boiling point	3403 K (3130 ° C)
Molar volume	20.80 · 10 −6 m 3 · mol −1
Heat of evaporation	331 kJ / mol
Heat of fusion	6.9 kJ mol −1
Speed ​​of sound	2280 m s −1 at 293.15 K.
Electric conductivity	1.43 · 10 6 A · V −1 · m −1
Thermal conductivity	13 W m −1 K −1
Chemically
Oxidation states	3 , 4, 2
Normal potential	−2.35 V (Pr 3+ + 3 e - → Pr)
Electronegativity	1.13 ( Pauling scale )
Isotopes
isotope NH t 1/2 ZA ZE (M eV ) ZP 137 Pr {syn.} 1.28 h ε 2.702 137 Ce 138 Pr {syn.} 1.45 min ε 4,437 138 Ce 139 pr {syn.} 4.41 h ε 2.129 139 Ce 140 pr {syn.} 3.39 min ε 3.388 140 Ce 141 Pr 100  % Stable 142 pr {syn.} 19.12 h β - 2.162 142 Nd ε 0.745 142 Ce 143 Pr {syn.} 13.57 d β - 0.934 143 Nd 144 pr {syn.} 17.28 min β - 2.997 144 Nd 145 Pr {syn.} 5.984 h β - 1.805 145 Nd
For other isotopes see list of isotopes
NMR properties
Spin quantum number I γ in rad · T −1 · s −1 E r  ( 1 H) f L at B = 4.7 T in MHz 141 Pr 5/2 8.1397 · 10 7 30,062
safety instructions
GHS labeling of hazardous substances powder danger H and P phrases H: 250 P: 222-231-422
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Praseodymium is a chemical element with the element symbol Pr and the atomic number 59. In the periodic table it is in the group of lanthanoids and is therefore also one of the rare earth metals . The name comes from the green color of its connections : the Greek word πράσινος prásinos means “green”, δίδυμος didymos “double” or “twin”.

history

Praseodymium

In 1841 Carl Gustav Mosander extracted the rare earth didymium from lanthanum oxide . In 1874 Per Teodor Cleve noticed that Didym actually consisted of two elements. In 1879 Lecoq de Boisbaudran isolated samarium from Didym, which he extracted from the mineral samarskite . In 1885 Carl Auer von Welsbach succeeded in separating didymium into praseodymium and neodymium , which both form salts with different colors.

Occurrence

Praseodymium occurs naturally only in chemical compounds associated with other lanthanoids , mainly in the minerals

Cerite Monazite Bastnesite Misch metal contains 3–5% praseodymium

in front.

The global reserves are estimated at 4 million tons.

Extraction and manufacture

As with all lanthanides , the ores are first enriched by flotation , then the metals are converted into corresponding halides and separated by fractional crystallization , ion exchange or extraction .

The metal is obtained by fused-salt electrolysis or reduction with calcium .

${\displaystyle \mathrm {2\ PrF_{3}\ +\ 3\ Ca\ \longrightarrow \ 2\ Pr\ +\ 3\ CaF_{2}} }$

properties

Crystal structure of praseodymium

Physical Properties

Praseodymium is a soft, silver-white paramagnetic metal, which belongs to the lanthanides and rare earth metals . At 798 ° C, the hexagonal α-Pr converts to the body-centered cubic β-Pr.

Chemical properties

At high temperatures, praseodymium burns to sesquioxide Pr ₂ O ₃ . It is somewhat more corrosion-resistant in air than europium , lanthanum or cerium , but easily forms a green oxide layer that flakes off in air. It reacts with water to form praseodymium hydroxide  (Pr (OH) ₃ ) , forming hydrogen . Praseodymium is trivalent and tetravalent in its compounds, the trivalent oxidation number being the more common. Pr (III) ions are yellow-green, Pr (IV) ions are yellow. Bivalent praseodymium can also be produced under special reductive conditions, e.g. B. in praseodymium (II, III) iodide  (Pr ₂ I ₅ ).

Isotopes

Natural praseodymium consists only of the stable isotope ¹⁴¹ Pr. 38 other radioactive isotopes are known, with ¹⁴³ Pr and ¹⁴² Pr being the longest-lived with a half-life of 13.57 days and 19.12 hours, respectively. All other isotopes have half-lives of less than 6 hours, most even less than 33 seconds. There are also 6 metastable states, with ^{138 m} Pr (t _½ 2.12 hours), ^{142 m} Pr (t _½ 14.6 minutes) and ^{134 m} Pr (t _½ 11 minutes) being the most stable.

The isotopes move in an atomic mass range from 120.955 ( ¹²¹ Pr) to 158.955 ( ¹⁵⁹ Pr).

use

• Praseodymium is used in alloys with magnesium to make high-strength metal for aircraft engines.
• Alloys with cobalt and iron are strong permanent magnets .
• Praseodymium become the dyeing of glass and enamel used (for example, in green colored headlight glass in lighting technology).
• Improve links the UV - absorption and are used for eye protection glasses during welding used.

links

Oxides

• green praseodymium (III) oxide (Pr ₂ O ₃ )
• brown-black praseodymium (III, IV) oxide (Pr ₆ O ₁₁ )
• almost black praseodymium (IV) oxide (PrO ₂ )

Halides

Several halides of all oxidation levels are known, for example praseodymium (III) fluoride  (PrF ₃ ), praseodymium (IV) fluoride  (PrF ₄ ), praseodymium (III) chloride  (PrCl ₃ ), praseodymium (III) bromide  (PrBr ₃ ), Praseodymium (III) iodide  (PrI ₃ ), praseodymium (II, III) iodide  (Pr ₂ I ₅ ). The trivalent halides form different hydrates .

It also forms several fluorido complexes such as B. the K ₂ [PrF ₆ ] with tetravalent Pr.

Other connections

Binary connections are e.g. B. Praseodymium (III) sulfide  (Pr ₂ S ₃ ), praseodymium  nitride (PrN), praseodymium phosphide  (PrP).

In addition, praseodymium is in various salts, such as the hygroscopic praseodymium (III) nitrate  (Pr (NO ₃ ) ₃  x H ₂ O), the nicely crystallizing praseodymium (III) sulfate  (Pr ₂ (SO ₄ ) ₃  8 H ₂ O) and others.

The category: Praseodymium compounds provides an overview of praseodymium compounds .

• 

  Praseodymium (III) sulfate octahydrate

• 

  Praseodymium (III) chloride heptahydrate

Web links

Commons : Praseodymium  - collection of images, videos and audio files

Wiktionary: Praseodymium  - explanations of meanings, word origins, synonyms, translations

• Entry on praseodymium. In: Römpp Online . Georg Thieme Verlag, accessed on January 3, 2015.
• Metallic praseodymium

Individual evidence

1. ^ Harry H. Binder: Lexicon of the chemical elements. S. Hirzel Verlag, Stuttgart 1999, ISBN 3-7776-0736-3 .
2. ↑ The values ​​for the properties (info box) are taken from www.webelements.com (praseodymium) , unless otherwise stated .
3. ^ IUPAC, Standard Atomic Weights Revised v2 ( Memento of March 3, 2016 in the Internet Archive ).
4. ↑ CIAAW, Standard Atomic Weights Revised 2013 .
5. ↑ ^{a b c d e} Entry on praseodymium in Kramida, A., Ralchenko, Yu., Reader, J. and NIST ASD Team (2019): NIST Atomic Spectra Database (ver. 5.7.1) . Ed .: NIST , Gaithersburg, MD. doi : 10.18434 / T4W30F ( https://physics.nist.gov/asd ). Retrieved June 11, 2020.
6. ↑ ^{a b c d e} Entry on praseodymium at WebElements, https://www.webelements.com , accessed on June 11, 2020.
7. ^ NN Greenwood, A. Earnshaw: Chemistry of the elements. 1st edition. VCH, Weinheim 1988, ISBN 3-527-26169-9 , p. 1579.
8. ↑ Robert C. Weast (Ed.): CRC Handbook of Chemistry and Physics . CRC (Chemical Rubber Publishing Company), Boca Raton 1990, ISBN 0-8493-0470-9 , pp. E-129 to E-145. Values ​​there are based on g / mol and given in cgs units. The value specified here is the SI value calculated from it, without a unit of measure.
9. ↑ ^{a b} Yiming Zhang, Julian RG Evans, Shoufeng Yang: Corrected Values ​​for Boiling Points and Enthalpies of Vaporization of Elements in Handbooks. In: Journal of Chemical & Engineering Data . 56, 2011, pp. 328-337; doi: 10.1021 / je1011086 .
10. ↑ ^{a b} Datasheet Praseodymium, powder from Sigma-Aldrich , accessed on April 26, 2017 ( PDF ).
11. ↑ Carl Auer v. Welsbach: The decomposition of the Didym into its elements. In: Monthly magazine for chemistry . 6 (1), 1885, pp. 477-491; doi: 10.1007 / BF01554643 .