1s² 2s²p⁶ 3s²p⁶d¹⁰ 4s²p⁶d¹⁰f³ 5s²p⁶ 6s²

History

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. 

It was prepared in relatively pure form in 1931.  Ion-exchange and solvent extraction techniques have led to much easier isolation of the rare earths and the cost has dropped greatly. Praseodymium can be prepared by several methods, such as by calcium reduction of the anhydrous chloride of fluoride.

Today, praseodymium is primarily obtained through an ion exchange process from monazite sand, (Ce, La, Th, Nd, Y)PO₄, a material rich in rare earth elements.

Characteristics

Pure praseodymium is silvery-white and fairly soft.  It oxidizes slowly in air and reacts vigorously with water to release hydrogen gas.  It is used as an alloying agent along with magnesium for parts in aircraft engines.  Misch metal is 5% praseodymium and is used for alloying steel and in flints used to create sparks in lighters.  The glass in welder's goggles contains a mixture of praseodymium and neodymium.

It is somewhat more resistant to corrosion in air than europium, lanthanum, 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.

As with other rare earths, compounds of these elements in solution have distinctive sharp spectral absorption bands or lines, some of which are only a few Angstroms wide.

Occurrence

Praseodymium is available in small quantities in Earth’s crust (9.5 ppm). 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.

Applications

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 color.
• 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.
• Praseodymium alloyed with nickel (PrNi₅) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.

Compounds

Praseodymium compounds include:

Isotopes

Naturally occurring praseodymium is composed of one stable isotope,  ¹⁴¹Pr.   Thirty-eight 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-lives that are less than 5.985 hours and the majority of these have half lives that are less than 33 seconds. This element also has six meta states with the most stable being ^138mPr (t_½ 2.12 hours), ^142mPr (t_½ 14.6 minutes) and ^134mPr (t_½ 11 minutes).

The isotopes of praseodymium range in atomic weight from 120.955 (¹²¹Pr) to 158.955 (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 Cerium-58 isotopes and the primary products after are element Neodymium-60 isotopes.

Precautions

Like all rare earths, praseodymium is of low to moderate toxicity.  Praseodymium has no known biological role.  As with other rare-earth metals it should be kept under a light mineral oil or sealed in plastic.