Periodic Table


Atomic number: 59
Atomic weight: 140.90765
Symbol: Pr
Group number: (lanthanide)
Electronic configuration: [Xe].4f3.6s2


Praseodymium is soft, silvery, malleable, and ductile. It was prepared in relatively pure form in 1931. 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" away when exposed to air. The metal should be stored under an inert atmosphere or under mineral oil or petroleum. The rare-earth oxides, including Pr2O3, are among the most refractory substances known. It is a component of misch metal, used for lighter flints, and of the glass in welders' goggles.

General information

Discoveror: Carl F. Auer von Welsbach
Date discovered: 1885
Discovered at: Austria
Meaning of name: From the Greek words "prasios didymos" meaning "green twin"

Physical data

Standard state: solid at 298 K
Colour: silvery white, yellowish tinge
Density of solid at ambient temperature/kg m-3: 6640
Molar volume/cm3: 20.80

Radii /pm

Atomic: 247
Covalent (single bond):
Pauling radius for the ion [Pr]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius224.7no datano data36.1


Both values are quoted on the Pauling scale.

Pauling: 1.13
Allred Rochow: 1.07

Crystal Structure

structure: hcp (hexagonal close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1208
boiling point: 3563

Enthalpies /kJ mol-1

fusion: 9.0
vaporization: 332

single bond enthalpies:
Pr-F Pr-Cl Pr-Br Pr-I Pr-Pr
no data no data no data 338.5 no data

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
141Pr140.907647 (4)100

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/Pr.html