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59 ceriumpraseodymiumneodymium


Periodic Table - Extended Periodic Table
Name, Symbol, Number praseodymium, Pr, 59
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance grayish white
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·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
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
Crystal structure hexagonal
Oxidation states 3
(mildly basic oxide)
Electronegativity 1.13 (Pauling scale)
Ionization energies
( more)
1st: 527 kJ·mol−1
2nd: 1020 kJ·mol−1
3rd: 2086 kJ·mol−1
Atomic radius 185 pm
Atomic radius (calc.) 247 pm
Magnetic ordering no data
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
Selected 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 ( IPA: /ˌpreɪziə(ʊ)ˈdɪmiəm, ˌpreɪsi-/) is a chemical element in the periodic table that has the symbol Pr and atomic number 59.

Notable characteristics

Praseodymium is a soft silvery metallic element, and belongs to the lanthanide 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. For this reason, praseodymium should be stored under a light mineral oil or sealed in glass.


Uses of praseodymium:

  • As an alloying agent with magnesium to create high-strength metals that are used in aircraft engines.
  • Praseodymium forms the core of carbon arc lights which are used in the motion picture industry for studio lighting and projector lights.
  • Praseodymium compounds are used to give glasses and enamels a yellow colour.
  • Praseodymium is a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles.
  • 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.


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.


Praseodymium is available in small quantities in Earth’s crust (9,5ppm). 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.


Praseodymium compounds include:

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


Naturally occurring praseodymium is composed of one stable isotope, 141Pr. 38 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-lifes that are less than 5.985 hours and the majority of these have half lifes that are less than 33 seconds. This element also has 6 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.


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

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