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ceriumpraseodymiumneodymium
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Pr

Pa
Appearance
grayish white
General properties
Name, symbol, number praseodymium, Pr, 59
Element category lanthanide
Group, period, block n/a6, f
Standard atomic weight 140.90765g·mol−1
Electron configuration [Xe] 4f3 6s2
Electrons per shell 2, 8, 18, 21, 8, 2 (Image)
Physical properties
Phase solid
Density (near r.t.) 6.77 g·cm−3
Liquid density at m.p. 6.50 g·cm−3
Melting point 1208 K, 935 °C, 1715 °F
Boiling point 3793 K, 3520 °C, 6368 °F
Heat of fusion 6.89 kJ·mol−1
Heat of vaporization 331 kJ·mol−1
Specific heat capacity (25 °C) 27.20 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1771 1973 (2227) (2571) (3054) (3779)
Atomic properties
Oxidation states 4, 3, 2 (mildly basic oxide)
Electronegativity 1.13 (Pauling scale)
Ionization energies 1st: 527 kJ·mol−1
2nd: 1020 kJ·mol−1
3rd: 2086 kJ·mol−1
Atomic radius 182 pm
Covalent radius 203±7 pm
Miscellanea
Crystal structure hexagonal
Magnetic ordering paramagnetic [1]
Electrical resistivity (r.t.) (α, poly)
0.700 µΩ·m
Thermal conductivity (300 K) 12.5 W·m−1·K−1
Thermal expansion (r.t.) (α, poly) 6.7 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2280 m/s
Young's modulus (α form) 37.3 GPa
Shear modulus (α form) 14.8 GPa
Bulk modulus (α form) 28.8 GPa
Poisson ratio (α form) 0.281
Vickers hardness 400 MPa
Brinell hardness 481 MPa
CAS registry number 7440-10-0
Most stable isotopes
Main article: Isotopes of praseodymium
iso NA half-life DM DE (MeV) DP
141Pr 100% 141Pr is stable with 82 neutrons
142Pr syn 19.12 h β 2.162 142Nd
ε 0.745 142Ce
143Pr syn 13.57 d β 0.934 143Nd

Praseodymium (pronounced /ˌpreɪzi.ɵˈdɪmiəm/ PRAY-zee-o- DIM-ee-əm or /ˌpreɪsi.ɵˈdɪmiəm/ PRAY-see-o- DIM-ee-əm) is a chemical element that has the symbol Pr and atomic number 59.

Contents

Characteristics

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Physical

Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanoid group. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air, exposing more metal to oxidation — a centimeter-sized sample of Pr completely oxidizes within a year.[2] For this reason, praseodymium is usually stored under a light mineral oil or sealed in glass.

Contrary to other rare-earth metals, which show antiferromagnetic or/and ferromagnetic ordering at low temperatures, Pr is paramagnetic at any temperatures above 1 K.[1]

Chemical

Praseodymium metal tarnishes slowly in air and burns readily at 150 °C to form praseodymium(III,IV) oxide:

12 Pr + 11 O2 → 2 Pr6O11

Praseodymium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form praseodymium hydroxide:

2 Pr (s) + 6 H2O (l) → 2 Pr(OH)3 (aq) + 3 H2 (g)

Praseodymium metal reacts with all the halogens:

2 Pr (s) + 3 F2 (g) → 2 PrF3 (s) [green]
2 Pr (s) + 3 Cl2 (g) → 2 PrCl3 (s) [green]
2 Pr (s) + 3 Br2 (g) → 2 PrBr3 (s) [green]
2 Pr (s) + 3 I2 (g) → 2 PrI3 (s)

Praseodymium dissolves readily in dilute sulfuric acid to form solutions containing green Pr(III) ions, which exist as a [Pr(OH2)9]3+ complexes:[3]

2 Pr (s) + 3 H2SO4 (aq) → 2 Pr3+(aq) + 3 SO 2−4 (aq) + 3 H2 (g)

Compounds

In its compounds, praseodymium occurs in oxidation states +2, +3 and/or +4. Praseodymium(IV) is a strong oxidant, instantly oxidizing water to elemental oxygen (O2), or hydrochloric acid to elemental chlorine. Thus, in aqueous solution, only the +3 oxidation state is encountered. Praseodymium(III) salts are yellow-green and, in solution, present a fairly simple absorption spectrum in the visible region, with a band in the yellow-orange at 589-590 nm (which coincides with the sodium emission doublet), and three bands in the blue/violet region, at 444, 468, and 482 nm, approximately. These positions vary slightly with the counter-ion. Praseodymium oxide, as obtained by the ignition of salts such as the oxalate or carbonate in air, is essentially black in color (with a hint of brown or green) and contains +3 and +4 praseodymium in a somewhat variable ratio, depending upon the conditions of formation. Its formula is conventionally rendered as Pr6O11.

Other praseodymium compounds include:

Isotopes

Naturally occurring praseodymium is composed of one stable isotope, 141Pr. Thirty-eight radioisotopes have been characterized with the most stable being 143Pr with a half-life of 13.57 days and 142Pr with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours and the majority of these have half-lives that are less than 33 seconds. This element also has six meta states with the most stable being 138mPr (t½ 2.12 hours), 142mPr (t½ 14.6 minutes) and 134mPr (t½ 11 minutes).

The isotopes of praseodymium range in atomic weight from 120.955 u (121Pr) to 158.955 u (159Pr). The primary decay mode before the stable isotope, 141Pr, is electron capture and the primary mode after is beta minus decay. The primary decay products before 141Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes.

History

The name praseodymium comes from the Greek prasios (πράσιος), meaning green, and didymos (δίδυμος), twin. Praseodymium is frequently misspelled as praseodynium.

In 1841, Mosander extracted the rare earth didymium from lanthana. In 1874, Per Teodor Cleve concluded that didymium was in fact two elements, and in 1879, Lecoq de Boisbaudran isolated a new earth, samarium, from didymium obtained from the mineral samarskite. In 1885, the Austrian chemist baron Carl Auer von Welsbach separated didymium into two elements, praseodymium and neodymium, which gave salts of different colors.

Leo Moser (son of Ludwig Moser, founder of the Moser Glassworks in what is now Karlovy Vary, Bohemia, in the Czech Republic, not to be confused with Leo Moser, a mathematician) investigated the use of praseodymium in glass coloration in the late 1920s. The result was a yellow-green glass given the name "Prasemit". However, a similar color could be achieved with colorants costing only a minute fraction of what praseodymium cost in the late 1920s, such that the color was not popular, few pieces were made, and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in German), which was more widely accepted. The first enduring commercial use of purified praseodymium, which continues today, is in the form of a yellow-orange stain for ceramics, "Praseodymium Yellow", which is a solid-solution of praseodymium in the zirconium silicate (zircon) lattice. This stain has no hint of green in it. By contrast, at sufficiently high loadings, praseodymium glass is distinctly green, rather than pure yellow.

Using classical separation methods, praseodymium was always difficult to purify. Much less abundant than the lanthanum and neodymium from which it was being separated (cerium having long since been removed by redox chemistry), praseodymium ended up being dispersed among a large number of fractions, and the resulting yields of purified material were low. Praseodymium has historically been a rare earth whose supply has exceeded demand. This has occasionally led to its being offered more cheaply than the far more abundant neodymium. Unwanted as such, much praseodymium has been marketed as a mixture with lanthanum and cerium, or "LCP" for the first letters of each of the constituents, for use in replacing the traditional lanthanide mixtures that were inexpensively made from monazite or bastnäsite. LCP is what remains of such mixtures, after the desirable neodymium, and all the heavier, rarer and more valuable lanthanides have been removed, by solvent extraction. However, as technology progresses, praseodymium has been found possible to incorporate into neodymium-iron-boron magnets, thereby extending the supply of the much in demand neodymium. So LC is starting to replace LCP as a result.

Occurrence

Monazite

Praseodymium is available in small quantities in Earth’s crust (9.5 ppm). It is found in the rare earth minerals monazite and bastnäsite, typically comprising about 5% of the lanthanides contained therein, and can be recovered from these minerals by an ion exchange process, or by counter-current solvent extraction. Misch metal, used in making cigarette lighters, contains about 5% praseodymium metal.[4]

Applications

Uses of praseodymium:

Precautions

Like all rare earths, praseodymium is of low to moderate toxicity. Praseodymium has no known biological role.

References

  1. ^ a b M. Jackson "Magnetism of Rare Earth" The IRM quarterly col. 10, No. 3, p. 1, 2000
  2. ^ "Rare-Earth Metal Long Term Air Exposure Test". http://www.elementsales.com/re_exp/index.htm. Retrieved 2009-08-08.  
  3. ^ "Chemical reactions of Praseodymium". Webelements. https://www.webelements.com/praseodymium/chemistry.html. Retrieved 2009-06-06.  
  4. ^ Gschneidner, K.A., and Eyring, L., Handbook on the Physics and Chemistry of Rare Earths, North Holland Publishing Co., Amsterdam, 1978.
  5. ^ L. L. Rokhlin (2003). Magnesium alloys containing rare earth metals: structure and properties. CRC Press. ISBN 0415284147.  
  6. ^ a b c C. R. Hammond (2000). The Elements, in Handbook of Chemistry and Physics 81th edition. CRC press. ISBN 0849304814.  
  7. ^ "ANU team stops light in quantum leap". http://info.anu.edu.au/ovc/Media/Media_Releases/2005/August/290805_stop_light. Retrieved 18 May 2009.  
  8. ^ Emsley, John (2001). Nature's building blocks. Oxford University Press. pp. 342. ISBN 0-1985-0341-5.  
  9. ^ Jha, A; Naftaly, M; Jordery, S; Samson, B N; Taylor, E R; Hewak, D; Payne, D N; Poulain, M; Zhang, G (1995). Pure and Applied Optics: Journal of the European Optical Society Part A 4: 417. doi:10.1088/0963-9659/4/4/019.  
  10. ^ Borchert, Y.; Sonstrom, P.; Wilhelm, M.; Borchert, H.; Baumer, M. (2008). "Nanostructured Praseodymium Oxide: Preparation, Structure, and Catalytic Properties". Journal of Physical Chemistry C 112: 3054. doi:10.1021/jp0768524.  

Books

  • R.J. Callow, "The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium", Pergamon Press, 1967.

External links


Simple English

Praseodymium is a chemical element that has the symbol Pr on the periodic table. It has the atomic number 59 which means it has 59 protons in an atom. It is a soft silvery metal that can be used to make yellow-green salts. It is also mixed with magnesium to produce strong metal used in aircraft engines. It was first isolated (separated from other elements) in 1885 by the Austrian chemist Carl Auer von Welsbach.


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