Praseodymium

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For other meanings of the abbreviation Pr, see PR.
59 ceriumpraseodymiumneodymium
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Pr

Pa
Pr-TableImage.png
General
Name, Symbol, Number praseodymium, Pr, 59
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance grayish white
Pr,59.jpg
Atomic mass 140.90765(2) g/mol
Electron configuration [Xe] 4f3 6s2
Electrons per shell 2, 8, 18, 21, 8, 2
Physical properties
Phase solid
Density (near r.t.) 6.77 g/cm³
Liquid density at m.p. 6.50 g/cm³
Melting point 1208 K
(935 °C, 1715 °F)
Boiling point 3793 K
(3520 °C, 6368 °F)
Heat of fusion 6.89 kJ/mol
Heat of vaporization 331 kJ/mol
Heat capacity (25 °C) 27.20 J/(mol·K)
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1771 1973 (2227) (2571) (3054) (3779)
Atomic properties
Crystal structure hexagonal
Oxidation states 3
(mildly basic oxide)
Electronegativity 1.13 (Pauling scale)
Ionization energies
(more)
1st: 527 kJ/mol
2nd: 1020 kJ/mol
3rd: 2086 kJ/mol
Atomic radius 185 pm
Atomic radius (calc.) 247 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (r.t.) (α, poly)
0.700 µΩ·m
Thermal conductivity (300 K) 12.5 W/(m·K)
Thermal expansion (r.t.) (α, poly)
6.7 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2280 m/s
Speed of sound (thin rod) (r.t.) (α form) 37.3 m/s
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
Notable isotopes
Main article: Isotopes of praseodymium
iso NA half-life DM DE (MeV) DP
141Pr 100% Pr 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[1] (chemical symbol Pr, atomic number 59) is a soft silvery metallic element that is a member of the lanthanide series of chemical elements. It is considered one of the "rare earth metals."[2]

Praseodymium and its alloys and compounds are useful in a variety of ways. For instance, praseodymium forms the core of carbon arc lights that are used by the motion picture industry for studio lighting. An alloy of praseodymium with magnesium is useful for making high-strength metals for aircraft engines, and an alloy of praseodymium with nickel has been used by scientists to attain a temperature within one thousandth of a degree of absolute zero. A mixture of praseodymium with neodymium is used to make specialty goggles for welders and glass blowers. In addition, some praseodymium compounds are used to impart a yellow color to glasses and enamels.

Contents

Occurrence

Praseodymium is available in small quantities in the Earth’s crust—about 9.5 parts per million (ppm). It is found in the rare earth minerals monazite and bastnasite, and it can be recovered from these minerals by an ion exchange process. Praseodymium also makes up about five percent of Mischmetal, an alloy of rare earth elements in a range of naturally occurring proportions.

Etymology and history

The name praseodymium comes from a combination of two Greek words: prasios, meaning "green" and didymos, or "twin."

In 1841, Carl Mosander extracted a rare earth material called "didymium" (meaning "twin element") from lanthana. It was so named because of its remarkable similarity to lanthanum, with which it was found. Mosander wrongly believed didymium to be an element, under the impression that "ceria" (or cerite) isolated by Jöns Jakob Berzelius in 1803 was a mixture of cerium, lanthanum, and didymium. He was right about lanthanum being an element, but not about didymium.

In 1874, Per Teodor Cleve concluded that didymium was composed of two elements. Separately, in 1879, Lecoq de Boisbaudran isolated a new earth, samarium, from didymium obtained from the mineral samarskite. Eventually, in 1885, Austrian chemist Baron Carl Auer von Welsbach separated didymium into two elements that gave salts of different colors. These two elements were praseodymium and neodymium.

Notable characteristics

Praseodymium is an inner transition metal (or lanthanide) that lies in period 6 of the periodic table, between cerium and neodymium. This element is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium. Nonetheless, when exposed to air, it develops a green oxide coating that spalls off, exposing more metal to oxidation. For this reason, praseodymium should be stored under a light mineral oil or sealed in glass.

Isotopes

Naturally occurring praseodymium is composed of one stable isotope, 141Pr. In addition, many radioisotopes have been characterized. Of these, the longest-lived radioisotopes are 143Pr, with a half-life of 13.57 days, and 142Pr, with a half-life of 19.12 hours. All the remaining radioactive isotopes have half-lives that are less than 5.985 hours, and most of them have half-lives that are less than 33 seconds. This element also has six meta states.

The isotopes of praseodymium range in atomic weight from 120.955 atomic mass units (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.

Compounds

  • Praseodymium(III) chloride or praseodymium trichloride (PrCl3): This compound is a blue-green solid that rapidly absorbs water on exposure to moist air to form a light green heptahydrate. It can be used as a starting material for the preparation of other praseodymium salts. In addition, it can increase the activity of Pr6O11 catalysts, which are useful for the conversion of methane to ethene. This process is becoming an important route to ethene for the manufacture of polyethylene, a common plastic.

Additional praseodymium compounds

  • Fluorides
    • praseodymium(II) fluoride (PrF2)
    • praseodymium(III) fluoride (PrF3)
    • praseodymium(IV) fluoride (PrF4)
  • Bromides
    • praseodymium(III) bromide (PrBr3)
    • praseodymium bromide (Pr2Br5)
  • Iodides
    • praseodymium(II) iodide (PrI2)
    • praseodymium(III) iodide (PrI3)
    • praseodymium iodide (Pr2I5)
  • Oxides
    • praseodymium(IV) oxide (PrO2)
    • praseodymium(III) oxide (Pr2O3)
  • Sulfides
    • praseodymium(II) sulfide (PrS)
    • praseodymium(III) sulfide (Pr2S3)
  • Selenides
    • praseodymium(II) selenide (PrSe)
  • Tellurides
    • praseodymium(II) telluride (PrTe)
    • praseodymium(III) telluride (Pr2Te3]]
  • Nitrides
    • praseodymium nitride (PrN)

Applications

Praseodymium and its alloys and compounds can be used for various purposes, as follows.

  • Praseodymium can be used as an alloying agent with magnesium to create high-strength metals for aircraft engines.
  • Praseodymium forms the core of carbon arc lights that are used in the motion picture industry for studio lighting and projector lights.
  • Praseodymium compounds are used to impart a yellow color to glasses and enamels.
  • Praseodymium is a component of didymium[3] glass, which is used to make specialized goggles for welders and glass blowers.
  • Dr. Matthew Sellars of the Laser Physics Centre at the Australian National University in Canberra, Australia slowed down a light pulse to a few hundred meters per second using praseodymium mixed with silicate crystal.
  • Praseodymium alloyed with nickel (PrNi5) has a strong magnetocaloric effect, allowing scientists to approach within one thousandth of a degree of absolute zero[4].

Precautions

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

Notes

  1. Praseodymium is frequently misspelled as praseodynium.
  2. The term "rare earth metals" (or "rare earth elements") is a trivial name applied to 16 chemical elements: scandium, yttrium, and 14 of the 15 lanthanides (excluding promethium), which occur naturally on Earth. Some definitions also include the actinides. The word "earth" is an obsolete term for oxide. The term "rare earth" is discouraged by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are relatively abundant in the Earth's crust.
  3. Didymium is a mixture of praseodymium and neodymium.
  4. Emsley, John (2001). Nature's Building Blocks. Oxford University Press, pp. 342. ISBN 0198503415. 

References

  • Chang, Raymond. 2006. Chemistry. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.
  • Cotton, F. Albert, and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry. 4th ed. New York: Wiley. ISBN 0471027758.
  • Greenwood, N.N., and A. Earnshaw. 1998. Chemistry of the Elements. 2nd ed. Oxford, U.K.; Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654.
  • Jones, Adrian P., Frances Wall, and C. Terry Williams, (eds.). 1996. Rare Earth Minerals: Chemistry, Origin and Ore Deposits. The Mineralogical Society Series. London, UK: Chapman and Hall. ISBN 0412610302 and ISBN 978-0412610301.
  • Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford, UK: Oxford University Press. ISBN 0195080831.

External links

All links retrieved December 18, 2007.

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