Praseodymium

Praseodymium (Pr)

Introduction

Praseodymium is a chemical element with the atomic number 59 in the periodic table. It occurs naturally in Earth’s crust with an abundance of 9.5 parts per million. However, praseodymium can be rarely found in its pure, elemental form. 

 

Being a member of the lanthanides family of elements, this highly reactive chemical element is a divalent substance. It’s primarily used in a variety of alloys, such as in mischmetal or high-strength magnesium alloys. Praseodymium’s most popular application is pyrophoric alloys, which are used in cigarette lighter flints.

Fact Box

Chemical and Physical Properties of Praseodymium

The symbol in the periodic table of elements: Pr

Atomic number: 59

Atomic weight (mass): 140.91 g.mol-1

Group number: Lanthanides

Period: 6 (f-block)

Color: A silvery-yellow metal

Physical state: Solid at room temperature

Half-life: From 600(300) milliseconds to 13.57 days

Electronegativity according to Pauling: 1.1

Density: 6.8 g.cm-3 at 20°C

Melting point: 931°C, 1708°F, 1204 K

Boiling point: 3520°C, 6368°F, 3793 K

Van der Waals radius: Unknown

Ionic radius: 0.101 nm (+3)

Isotopes: 39

Most characteristic isotope: 141Pr

Electronic shell: [Xe] 4f3 6s2

The energy of the first ionization: 522 kJ.mol-1

The energy of the second ionization: 1016 kJ.mol-1

The energy of the third ionization: 2082.4 kJ.mol-1

The energy of the fourth ionization: 3752 kJ.mol-1

The energy of the fifth ionization: 5534 kJ.mol-1

Discovery date: In 1885 by Carl Auer von Welsbach

 

With the periodic table symbol Pr, atomic number 59, atomic mass of 140.91 g.mol-1, and electron configuration [Xe] 4f3 6s2, praseodymium is a silvery-yellow, ductile, and malleable metal. 

 

It reaches its boiling point at 3520°C, 6368°F, 3793 K, while the melting point is achieved at 931°C, 1708°F, 1204 K. This member of the lanthanides family of elements has an electronegativity of 1.1 according to Pauling, whereas the atomic radius according to van der Waals is unknown.

 

There are two allotropes of praseodymium:

 

  • The α-phase (a double close-packed hexagonal with a = 3.6721 Å and c = 11.8326 Å at room temperature); and
  • The β-phase (a body-centered cubic with a = 4.13 Å at 821 °C/1.510 °F/1094.15 K). 

 

The third member of the lanthanide series in the periodic table possesses strong chemical, paramagnetic, optical, and electrical properties. Praseodymium can rapidly displace hydrogen from H2O in dilute acids. Also, this lanthanide slowly oxidizes in air and forms a protective green oxide coating.              

How Was Praseodymium Discovered?

The story on the discovery of element 59 begins in 1841 when the Swedish chemist Carl Mosander (1797-1858) had incorrectly observed the new substance in a sample of a rare-earth oxide residue that he labeled as didymium. He isolated the didymium as a residue (lantana) from cerium salts.

 

In 1879, the French chemist François Lecoq de Boisbaudran (1838-1912) managed to detect samarium as a different substance from didymium. After the discovery of element 62 (Sm), didymium’s absorption spectrum changed. 

 

The chemists who studied didymium noticed this variability and formed a firm belief that there are two new elements mixed in the didymium substance. From this moment in science on, many of them put in their best knowledge and efforts to separate them from the chemical compound.

 

Eventually, the Austrian chemist and nobleman Carl Auer von Welsbach (1858 – 1929) had the best results in this scientific feat. In 1885, he succeeded in isolating the two elusive chemicals from the didymium sample. 

 

At the beginning of his experiment, von Welsbach produced nitrate salts from the didymium, after which he performed fractional crystallization. This step in the chemical trial of the Austrian discoverer resulted in greenish-brown praseodymium and pink neodymium salts.

How Did Praseodymium Get Its Name?

The name of element 59 was derived from the Greek words ‘prasios didymos‘. This phrase means ‘green twin’, and refers to the fact that the green-colored praseodymium salt was isolated together with its ‘twin’—the pink neodymium salt—in the same chemical trial. 

Where Can You Find Praseodymium?

Praseodymium is a highly reactive chemical element. As a result of its fast bonding to other chemical elements, it cannot be found freely in nature. 

 

Nowadays, metal praseodymium is mostly obtained from the bastnasite and monazite sand by solvent extraction and ion exchange techniques. This chemical element can also be isolated from samarium (III) chloride or anhydrous chloride through calcium reduction, as well as a nuclear fission product.

 

The richest deposits of praseodymium ores are found in mines located in the United States, China, and the Commonwealth of Independent States. On the other hand, Brazil, Russia, and China top the list of largest praseodymium producers in the world. 

 

Praseodymium in Everyday Life

Praseodymium has a wide variety of practical applications, mainly in the metal industries:

 

  • Praseodymium compounds are used to color glass and enamel;
  • Since praseodymium oxide is composed of oxygen and praseodymium, it is used to block or filter infrared radiation;
  • Welding goggles that are used as a protection of the eyes are made of didymium glass that contains some quantity of praseodymium. Praseodymium is one of the main components of this type of protective glass. It’s used by welders and glass blowers because it filters out the yellow light and infrared (heat) radiation;
  • The chemical industry applies element 59 in a ceria-zirconia or ceria solution as an oxidation catalyst;
  • Praseodymium is often used as an alloying agent with magnesium. The high-strength metals element 59 forms with magnesium are applied in the manufacturing process of aircraft engines;
  • There are about 5% of praseodymium in mischmetal, which is used in lighters, flints, and torch strikers;
  • Praseodymium is one of the main components of carbon arc lights. This type of light is excessively used by the motion picture industry for studio lighting and projector lights because they produce super-bright light that is capable of lighting a large length of a street or a film studio interior;
  • The alloys which are applied in the making of permanent magnets also contain some praseodymium. Praseodymium magnets can be used for wind turbines that convert wind energy into electricity by using the aerodynamic force from the rotor blades.
  • Probably the most popular everyday use of this chemical element is in the manufacturing of color TVs, as well as energy-saving and fluorescent lamps.

How Dangerous Is Praseodymium?

This rare-earth metal of the lanthanide series of the periodic table is considered a moderately toxic substance. While the soluble praseodymium salts are mildly toxic by ingestion, the insoluble salts are non-toxic. They can also lead to irritation of both skin and eyes. The fumes, dust, and powder of praseodymium are highly flammable and may pose a fire hazard. 

 

In case of overexposure to this chemical element and inhalation of praseodymium metal dust, the affected individual may experience pulmonary problems, such as difficulty breathing, bronchitis, lung emphysema, asthma, etc. 

 

Since the aforementioned adverse health effects belong to the category of chronic diseases, prolonged exposure to praseodymium could result in serious long-lasting consequences on human health and increase the risk of cell membrane damage. 

Environmental Effects of Praseodymium

Praseodymium is generally not considered a hazardous substance to geological, biological, or aquatic systems. However, if it’s released through the improperly disposed waste of the petrol-producing facilities, metal industry, or used household appliances. In this way, praseodymium gradually accumulates in soil and underground waters and may contaminate the air. In turn, the contaminated bio-systems may lead to negative effects upon all living forms in the environment. 

Isotopes of Praseodymium

There are 39 isotopes of praseodymium with atomic weight ranging from 121Pr to 159Pr. Naturally occurring praseodymium (59Pr) is made up of one stable isotope, 141Pr. All other forms of this chemical element are mildly radioactive isotopes. The most stable radioisotope among them is 143Pr, with a half-life of 13.57 days.

 

While the primary decay mode for the isotopes lighter than 141Pr is electron capture which forms cerium isotopes, the heavier forms of praseodymium undergo a beta decay to form neodymium isotopes. 

 

Nuclide

[n 1]

Z N Isotopic mass (Da)

[n 2][n 3]

Half-life

[n 4]

Decay

mode

[n 5]

Daughter

isotope

[n 6][n 7]

Spin and

parity

[n 8][n 4]

Natural abundance (mole fraction)
Excitation energy[n 4] Normal proportion Range of variation
121Pr 59 62 120.95536(75)# 600(300) ms p 120Ce (3/2−)
β+ (rare) 121Ce
β+, p (rare) 120La
122Pr 59 63 121.95181(54)# 500# ms β+ 122Ce
123Pr 59 64 122.94596(64)# 800# ms β+ 123Ce 3/2+#
124Pr 59 65 123.94296(64)# 1.2(2) s β+ 124Ce
β+, p (rare) 123La
125Pr 59 66 124.93783(43)# 3.3(7) s β+ 125Ce 3/2+#
β+, p (rare) 124La
126Pr 59 67 125.93531(21)# 3.12(18) s β+ 126Ce (4, 5, 6)
β+, p (rare) 125La
127Pr 59 68 126.93083(21)# 4.2(3) s β+ 127Ce 3/2+#
127mPr 600(200)# keV 50# ms 11/2−
128Pr 59 69 127.92879(3) 2.84(9) s β+ 128Ce (3+)
β+, p (rare) 127La
129Pr 59 70 128.92510(3) 32(3) s β+ 129Ce (11/2−)
129mPr 382.7(5) keV 1# ms β+ 129Ce (11/2−)
130Pr 59 71 129.92359(7) 40.0(4) s β+ 130Ce (6, 7)(+#)
130mPr 100(100)# keV 10# s 2+#
131Pr 59 72 130.92026(6) 1.50(3) min β+ 131Ce (3/2+)
131mPr 152.4(2) keV 5.7(2) s IT (96.4%) 131Pr (11/2−)
β+ (3.59%) 131Ce
132Pr 59 73 131.91926(6) 1.49(11) min β+ 132Ce (2+)
132mPr 0(100)# keV 20# s β+ 132Ce (5+)
133Pr 59 74 132.916331(13) 6.5(3) min β+ 133Ce (3/2+)
133mPr 192.05(14) keV 1.1(2) μs (11/2−)
134Pr 59 75 133.91571(4) 17(2) min β+ 134Ce (5−)
134mPr 0(100)# keV ~11 min β+ 134Ce 2−
135Pr 59 76 134.913112(13) 24(2) min β+ 135Ce 3/2(+)
135mPr 358.06(6) keV 105(10) μs (11/2−)
136Pr 59 77 135.912692(13) 13.1(1) min β+ 136Ce 2+
137Pr 59 78 136.910705(13) 1.28(3) h β+ 137Ce 5/2+
137mPr 561.22(23) keV 2.66(7) μs 11/2−
138Pr 59 79 137.910755(15) 1.45(5) min β+ 138Ce 1+
138mPr 348(23) keV 2.12(4) h β+ 138Ce 7−
139Pr 59 80 138.908938(8) 4.41(4) h β+ 139Ce 5/2+
140Pr 59 81 139.909076(7) 3.39(1) min β+ 140Ce 1+
140m1Pr 127.5(3) keV 0.35(2) μs 5+
140m2Pr 763.3(7) keV 3.05(20) μs (8)−
141Pr[n 9] 59 82 140.9076528(26) Stable 5/2+ 1.0000
142Pr 59 83 141.9100448(26) 19.12(4) h β (99.98%) 142Nd 2−
EC (.0164%) 142Ce
142mPr 3.694(3) keV 14.6(5) min IT 142Pr 5−
143Pr[n 9] 59 84 142.9108169(28) 13.57(2) d β 143Nd 7/2+
144Pr 59 85 143.913305(4) 17.28(5) min β 144Nd 0−
144mPr 59.03(3) keV 7.2(3) min IT (99.93%) 144Pr 3−
β (.07%) 144Nd
145Pr 59 86 144.914512(8) 5.984(10) h β 145Nd 7/2+
146Pr 59 87 145.91764(7) 24.15(18) min β 146Nd (2)−
147Pr 59 88 146.918996(25) 13.4(4) min β 147Nd (3/2+)
148Pr 59 89 147.922135(28) 2.29(2) min β 148Nd 1−
148mPr 50(30)# keV 2.01(7) min β 148Nd (4)
149Pr 59 90 148.92372(9) 2.26(7) min β 149Nd (5/2+)
150Pr 59 91 149.926673(28) 6.19(16) s β 150Nd (1)−
151Pr 59 92 150.928319(25) 18.90(7) s β 151Nd (3/2)(−#)
152Pr 59 93 151.93150(13) 3.63(12) s β 152Nd 4+
153Pr 59 94 152.93384(11) 4.28(11) s β 153Nd 5/2−#
154Pr 59 95 153.93752(16) 2.3(1) s β 154Nd (3+, 2+)
155Pr 59 96 154.94012(32)# 1# s [>300 ns] β 155Nd 5/2−#
156Pr 59 97 155.94427(43)# 500# ms [>300 ns] β 156Nd
157Pr 59 98 156.94743(43)# 300# ms β 157Nd 5/2−#
158Pr 59 99 157.95198(64)# 200# ms β 158Nd
159Pr 59 100 158.95550(75)# 100# ms β 159Nd 5/2−#

Source: Wikipedia

List of Praseodymium Compounds 

As a part of a chemical compound, praseodymium mostly forms trivalent bonds. The +3 oxidation state of this chemical element is its only stable state in an aqueous solution. Such an example is the olive-green oxide Pr2O3, which produces green trivalent praseodymium salts when dissolved in acids. 

 

The most commonly prepared praseodymium compounds include the following items:


  • Didymium
  • Praseodymium(III) sulfate
  • Praseodymium(III,IV) oxide
  • Praseodymium(III) bromide
  • Praseodymium(III) chloride
  • Praseodymium(III) fluoride
  • Praseodymium(III) hydroxide
  • Praseodymium(III) nitrate
  • Praseodymium(III) oxide
  • Praseodymium(III) sulfide
  • Praseodymium(IV) oxide

5 Interesting Facts and Explanations

  1. Praseodymium is four times more abundant in Earth’s crust than tin. 
  2. Mischmetal is an alloy of rare-earth elements. This group of elements consists of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
  3. When exposed to air, praseodymium is more resistant to corrosion than the other rare earth elements. 
  4. Didymia refers to a chemical compound that contains a mixture of rare-earth praseodymium and neodymium.
  5. Praseodymium compounds give light green to yellow color to ceramics and other types of glass.