Praseodymium (Pr)

Praseodymium (symbol Pr) is the chemical element with atomic number 59: a lanthanide (rare earth), solid at 0 °C, with an atomic mass of 140.91 u. Discovered in 1885 (Carl Auer von Welsbach).

Praseodymium was long mistaken for neodymium: together they made up a supposed element called “didymium” (“twin”). Its salts are a lovely green, and it gives ceramics a vivid yellow. Today it is used mainly alongside neodymium in the most powerful permanent magnets.

Key facts

Atomic number: 59
Symbol: Pr
French name: Praséodyme
Atomic mass: 140.91 u
Molar mass: 140.91 g/mol
Family: Lanthanides
Position: period 6, f-block
State at 0 °C: Solid
Melting point: 934.9 °C
Boiling point: 3,129.9 °C
Density: 6.77 g/cm³
Electronegativity (Pauling): 1.13
First ionization energy: 527 kJ/mol
Atomic radius: 185 pm
Electron configuration: [Xe] 4f³ 6s²
Abundance in Earth's crust: 9.2 ppm (39th most abundant element)
Indicative price: 100 $/kg (order of magnitude)
Radioactive: no
Discovery: 1885, Carl Auer von Welsbach

Origin of the name

From the Greek prasios didymos, “green twin.”

What does praseodymium look like?

A soft, malleable, silvery metal that forms a greenish oxide coat in air; the coat flakes off, exposing fresh metal.

Where is praseodymium found?

About 9 ppm of Earth's crust, more than tin. It always travels with the other light rare earths in bastnäsite and monazite.

Natural sources

Bastnäsite
Monazite

How is praseodymium produced?

It is separated from the other lanthanides by solvent extraction. Often it isn't even separated from neodymium: the “NdPr” mixture goes straight into magnet making.

Top producers

China
United States
Myanmar
Australia

What is praseodymium used for?

Neodymium-iron-boron magnets, alloyed with neodymium.
Yellow pigment for ceramics and enamels (praseodymium yellow).
Protective glasses for glassblowers and welders (“didymium” glass).
Magnesium alloys for aircraft engines.
Carbon electrodes for studio lighting.

In everyday life

Yellow tiles or glazed dishware
An electric-car motor
Glassblower's goggles

Role in living things

No known biological role; the body absorbs very little of it.

Hazards of praseodymium

Low to moderate toxicity. As with the other lanthanides, finely divided metal can ignite in air.

Cosmic origin

Neutron stars: Created when two neutron stars collide — the “forge” of gold.
Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).

History of praseodymium

In 1841 Mosander isolated “didymium,” which he believed was an element. In 1885 Carl Auer von Welsbach managed to split it in two through hundreds of fractional crystallizations: praseodymium (“green twin”) and neodymium (“new twin”).

Did you know?

Didymium glass blocks the intense yellow light of sodium, letting glassblowers see the molten glass through the flame.
In 2013, German physicists “stopped” light for a full minute inside a praseodymium-doped crystal.
It owes its name to the green color of its salts.

Isotopes of praseodymium

Praseodymium has only one stable isotope, praseodymium-141, which makes up the entire natural element.

praseodymium-141: 100% of natural praseodymium, stable
praseodymium-143: radioactive, half-life 13.6 days
praseodymium-144: radioactive, half-life 17.3 min. Daughter of cerium-144 in fission waste, and a very energetic beta emitter.

Related elements

Same family (lanthanides): Lanthanum (La), Cerium (Ce), Neodymium (Nd), Promethium (Pm), Samarium (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu).