Praseodymium (Pr)

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.

Chemical and Physical Properties of Praseodymium

Property	Value
Symbol	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.