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Element Fact
In 1961, the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis of atomic weight, which has a mass of exactly 12.000 atomic mass unit.

Praseodymium, Pr

praseodymium sample

Atomic number: 59
Atomic mass: 140.90765(2)
Natural abundance: 9.1 ppm
141Pr (140.90765) - 100%

History and Production

From Greek prasios and didymos, meaning green and twin. It was discovered in didymia, a mixture of rare earth oxides by C.A. von Welsbach in 1885 via repeat fractional crystallizations. Nowadays, its compounds are isolated from monazite and bastnaesite via solvent extraction and ion-exchange techniques. The metal can be isolated by the reduction of its fluoride with calcium metal. Prasodymium is used among other rare earths for the misch metal to make flints for cigarette lighters. With magnesium, for high-strength jet-engine parts. It is also used as carbon arc in motion picture industry.

Physical Data

It is soft, silvery in appearance and is both malleable and ductile. It reacts slowly in air to give a green flaky oxide coating. It is subsequently best kept sealed or under a mineral oil. It is usually distrbuted (9.1 ppm of earth's crust) in monazite and bastnaesite.

Interatomic distance: 364 pm
Melting point: 931C
Boiling point: 3520C
Thermal conductivity/Wm-1K-1: 12.5 (27C)
Density/kgm-3: 6773 (20C)

Standard Thermodynamic Data (atomic gas)

Enthalpy of formation: 355.6 kJ/mol
Gibbs free energy of formation: 320.9 kJ/mol
Entropy: 189.8 J/mol K
Heat capacity: 21.4 J/mol K

Electronic data

Electronic configuration: [Xe] 4f8 6s2
Term symbol: 4I9/2
Electron affinity: -   Electronegativity (Pauline): 1.13
Ionization energy (first, second, third): 527.196, 1017.92, 2086.40 kJ/mol

Chemical properties

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