Praseodymium (Pr)

Stable Isotopes of Praseodymium

Isotope Z(p) N(n) Atomic Mass Natural Abundance Nuclear Spin
Pr-141 59 82 140.907648 100.00% 5/2+


Praseodymium was discovered in 1885 by Carl F. Auer von Welsbach. It takes its name from the Greek phrase prasios didymos, meaning “green twin.”

A lanthanide-series rare earth element, praseodymium is a pale yellow metal which attains a green oxide coating on exposure to air. It exhibits two crystalline modifications: an alpha form that has a hexagonal close-packed structure, a density of 6.773 g/cm3 and a molar volume of 20.82 cm3/mol; and a beta form that has an open body-centered cubic structure, a density of 6.64 g/cm3 and a molar volume of 21.20 cm3/mol. The alpha form transforms to beta at 792 ºC.

Praseodymium is paramagnetic at ambient temperatures. There are several known compounds. Chloride, bromide and iodide salts are all hygroscopic and soluble in water and alcohol. Praseodymium salts containing oxo anions such as sulfate, hydroxide, carbonate, silicates, oxalate, thiosulfate, chromate, molybdate and borate are also known.

Praseodymium is a component of didymium glass used in welders' goggles. Its salts are used as colorants for glasses and enamels: when in glass, they produce an intense yellow color. Praseodymium's oxide is one of the most refractory substances known and is a core material for carbon arcs used in lighting and projection. A Misch metal that contains about 5% praseodymium is used to make cigarette lighters.

Properties of Praseodymium

Name Praseodymium
Symbol Pr 
Atomic number 59
Atomic weight 140.9077
Standard state Solid at 298° K
CAS Registry ID 7440-10-0
Group in periodic table N/A
Group name Lanthanoid
Period in periodic table 6 (Lanthanoid)
Block in periodic table f-block
Color Silvery white, yellowish tinge
Classification Metallic
Melting point 931 °C
Boiling point 3512 °C
Vaporization point 3510 ºC
Thermal conductivity 12.5 W/(m·K) at 298.2 °K
Electrical resistivity 68 µΩ·cm at 25 °C
Electronegativity 1.1
Heat of vaporization 330 kJ·mol-1 at 3512 °C
Heat of fusion 6.9 kJ·mol-1
Density of liquid 6.50 g/cm3 at 931 °C
Density of solid 6.77 g/cm3
Electron configuration [Xe]4f36s2
Atomic radius 1.828 Å
First ionization potential 5.46 eV
Oxidation states +2, +3, +4
Most stable oxidation state +3

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