59
  Pr  
140.907650
Praseodymium

Name: Praseodymium
Symbol: Pr
Atomic Number: 59
Atomic Weight: 140.907650
Family: Rare Earth Elements
CAS RN: 7440-10-0
Description: A silvery white, soft, malleable, and ductile metal.
State (25C): Solid
Oxidation states: +3

Molar Volume: 20.8cm3/mole
Valence Electrons: 4f36s2

Boiling Point: 3785oK, 3512oC, 6354oF
Melting Point: 1204oK, 931oC, 1708oF

Electrons Energy Level: 2, 8, 18, 21, 8, 2
Isotopes: 38 + 1 Stable + 5 meta states
Heat of Vaporization: 296.8 Kj/mol
Heat of Fusion: 6.89 kJ/mol
Density: 6.77 g/cm3 @ 300oK
Specific Heat: 0.192 J/gK
Atomic Radius: 2.67
Ionic Radius: 1.013
Electronegativity: 1.13 (Pauling), 1.07 (Allrod Rochow)
57
La
138.9
58
Ce
140.1
59
Pr
140.9
60
Nd
144.2
61
Pm
(145)
62
Sm
150.4
63
Eu
152.0
64
Gd
157.3
65
Tb
158.9
66
Dy
162.5
67
Ho
164.9
68
Er
167.3
69
Tm
168.9
70
Yb
173.0
71
Lu
175.0

1s2 2s2p6 3s2p6d10 4s2p6d10f3 5s2p6 6s2

History

The name praseodymium comes from the Greek  prasios, meaning green, and didymos, or 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. 

It was prepared in relatively pure form in 1931.  Ion-exchange and solvent extraction techniques have led to much easier isolation of the rare earths and the cost has dropped greatly. Praseodymium can be prepared by several methods, such as by calcium reduction of the anhydrous chloride of fluoride.

Today, praseodymium is primarily obtained through an ion exchange process from monazite sand, (Ce, La, Th, Nd, Y)PO4, a material rich in rare earth elements.

Characteristics

Pure praseodymium is silvery-white and fairly soft.  It oxidizes slowly in air and reacts vigorously with water to release hydrogen gas.  It is used as an alloying agent along with magnesium for parts in aircraft engines.  Misch metal is 5% praseodymium and is used for alloying steel and in flints used to create sparks in lighters.  The glass in welder's goggles contains a mixture of praseodymium and neodymium.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f3
5s2 5p6
6s2

It is somewhat more resistant to corrosion in air than europium, lanthanum, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air, exposing more metal to oxidation.  For this reason, praseodymium should be stored under a light mineral oil or sealed in glass.

As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide.

Occurrence

Praseodymium is available in small quantities in Earth’s crust (9.5 ppm). It is found in the rare earth minerals monazite and bastnasite, and can be recovered from bastnasite or monazite by an ion exchange process.

Praseodymium also makes up about 5% of Misch metal.

Applications

Uses of praseodymium:

Compounds

Praseodymium compounds include:

Fluorides Chlorides Bromides
  • PrF2
  • PrF3
  • PrF4
  • PrCl3
  • PrBr3
  • Pr2Br5
Iodides Oxides Sulfides
  • PrI2
  • PrI3
  • Pr2I5
  • PrO2
  • Pr2O3
  • PrS
  • Pr2S3
Selenides Tellurides Nitrides
  • PrSe
  • PrTe
  • Pr2Te3
  • PrN

Isotopes

Naturally occurring praseodymium is composed of one stable isotope141Pr.   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 (t 2.12 hours), 142mPr (t 14.6 minutes) and 134mPr (t 11 minutes).

The isotopes of praseodymium range in atomic weight from 120.955 (121Pr) to 158.955 (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 Cerium-58 isotopes and the primary products after are element Neodymium-60 isotopes.

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
121Pr 120.95536 1.4 seconds
122Pr 121.95181 ~500 ms
123Pr 122.94596 ~800 ms
124Pr 123.94296 1.2 s
125Pr 124.93783 3.3 s
126Pr 125.93531 3.12 s
127Pr 126.93083 4.2 s
128Pr 127.92879 2.84 s
129Pr 128.92510 32 s
130Pr 129.92359 40.0 s
131Pr 130.92026 1.50 min
132Pr 131.91926 1.49 min
133Pr 132.916331 6.5 min
134Pr 133.91571 ~11 min
134mPr   17 min
135Pr 134.913112 24 min
136Pr 135.912692 13.1 min
137Pr 136.910705 1.28 h
138Pr 137.910755 1.45 min
138mPr   2.12 h
139Pr 138.908938 4.41 h
140Pr 139.909076 3.39 min
141Pr 140.9076528(26) STABLE
142Pr 141.9100448 19.12 h
142mPr   14.6 min
143Pr 142.9108169 13.57 d
144Pr 143.913305 17.28 min
144mPr   7.2 min
145Pr 144.914512 5.984 h
146Pr 145.91764 24.15 min
147Pr 146.918996 13.4 min
148Pr 147.922135 2.29 min
148mPr   2.01 min
149Pr 148.92372 2.26 min
150Pr 149.926673 6.19 s
151Pr 150.928319 18.90 s
152Pr 151.93150 3.63 s
153Pr 152.93384 4.28 s
154Pr 153.93752 2.3 s
155Pr 154.94012 ~1 s
156Pr 155.94427 ~500 ms
157Pr 156.94743 ~300 ms
158Pr 157.95198 ~200 ms
159Pr 158.95550 ~100 ms

Precautions

Like all rare earths, praseodymium is of low to moderate toxicity.  Praseodymium has no known biological role.  As with other rare-earth metals it should be kept under a light mineral oil or sealed in plastic.

atom.gif (700 bytes)

Praseodymium Data

 

Atomic Structure

Atomic Radius (): 2.67
Atomic Volume cm3/mol: 20.8
Covalent Radius: 1.65
Crystal Structure: Hexagonal (HEX)
Ionic Radius: 1.013

Chemical Properties

Electrochemical Equivalents: 1.7524 g/amp-hr
Electron Work Function: unknown
Electronegativity: 1.13 (Pauling), 1.07 (Allrod Rochow)
Heat of Fusion: 6.89 kJ/mol
First Ionization Potential: 5.46
Second Ionization Potential: 10.551
Third Ionization Potential: 21.62
Valence Electron Potential (-eV): 42.64 -eV
Ionization Energy (eV): 5.464 eV

Physical Properties

Atomic Mass Average:
Boiling Point: 3793K, 3520C, 6368F
Melting Point: 1204K, 931C, 1708F
Heat of Vaporization: 296.8 Kj/mol
Coefficient of Lineal Thermal Expansion/K-1: unknown
Electrical Conductivity: 0.0148 106/cm
Thermal Conductivity: 0.125 W/cmK
Density: 6.77 g/cm3 @ 300oK
Enthalpy of Atomization: 368 kJ/mole @ 25C
Enthalpy of Fusion: 6.89 kJ/mole
Enthalpy of Vaporization: 296.8 kJ/mole
Molar Volume: 20.8cm3/mole
Specific Heat: 0.192 J/gK
Vapor Pressure: unknown
Estimated Crustal Abundance: 9.2 milligrams per kilogram
Estimated Oceanic Abundance: 6.410-7 milligrams per liter

Miscellaneous

Fusion Heat: 11.3 kJ/mol
Evaporation Heat: 331 kJ/mol
First Ionizing Energy (kJ/mol): unknown
Electronic Configuration: [Xe] 4f3 6s2
Lattice Constant: 3.670
Lattice C/A Ratio: 1.614
First Ionization Energy: 526.6 kJ/mol