Praseodymium

What is Praseodymium?

Praseodymium is a chemical element which is the 3rd member of the Lanthanide series and is placed in the 6th period. Symbol of the praseodymium element is Pr. It is a metal which is traditionally considered to be one of the rare earth metals. Its atomic number 59. Protactinium which is a member of actinide series is placed below praseodymium in the periodic table. Another metal cerium is found at the left of praseodymium and neodymium is present at the right in the 6th period of the periodic table. Cerium and neodymium metals are also members of the Lanthanide series. Praseodymium is a member of the f – block element. It is the 4th most common rare earth metal. It is found in earth’s crust and forms 9.1 parts per million of the earth’s crust. It is similar to boron in abundance in the earth’s crust. 

Praseodymium was discovered by Austrian Chemist Baron Carl Auer von Welsbach in 1885. Swedish chemist Carl Gustav Mosander extracted didymium (a rare earth oxide) from lanthana in 1841. Baron Carl Auer von Welsbach separated didymium into elements and these two elements were different from each other. One was praseodymium and another one was neodymium. Thus, discovery of praseodymium took place. The word praseodymium is derived from the Greek word ‘prasinos’ which means green colored and ‘didymos’ which means twin. Praseodymium is not found in pure elemental form in nature as it is a reactive metal and generally forms a green coating of its oxide when exposed to moist air. It is a soft, ductile, malleable and silvery colored metal. 

It is a monoisotopic element as it has only one natural isotope which is 141Pr. It is stable in nature. Although it has other synthetic isotopes. Out of synthetic isotopes of praseodymium 142Pr and 143Pr are most stable isotopes with a half - life period of 19.12 hours and 13.57 days respectively. 

Praseodymium Atomic Number and Electronic Configuration 

Atomic number of Praseodymium is 59. Its electronic configuration is 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f3 5d0 6s2 or it can be written as [Xe] 4f3 6s2. It has 2 electrons in K – shell, 8 electrons in L – shell, 18 electrons in M – shell and 21 electrons in its outermost shell N, 8 electrons in O shell and 2 electrons in P shell. 

Properties of Praseodymium 

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Physical and Chemical Properties - Physical and chemical properties of Praseodymium are listed below –

  • Its atomic number is 59. It means it has 59 protons in its nucleus. 

  • Its standard atomic weight is 140.9

  • It is a rare earth metal and lanthanide as well. 

  • It has a double hexagonal close packed structure.

  • It is found as solid at STP.

  • Its oxides are weakly basic in nature. 

  • Melting point of praseodymium is 935 .

  • Boiling point of praseodymium is 3130 .

  • Its density is 6.77 g.cm-3.

  • Like other rare earth metals its +3 oxidation state is most common. 

  • It is soft, malleable and ductile metals. 

  • It shows magnetic, electrical and optical properties as well.

  • According to the Pauling scale, its electronegativity is 1.13

  • It is a monoisotopic element. It is composed of only one isotope which is 141Pr.

  • It has a greyish white appearance. Its ions are found in yellow green color.  

  • It is paramagnetic at room temperature. 

  • Reaction with air – Praseodymium reacts with oxygen when left exposed to air and forms a green layer of its oxide Pr2O3. Reaction is given below –

4Pr + 3O2 🡪 2Pr2O3

  • Burning of Praseodymium – Pr burns readily at 150 on giving heat and forms praseodymium oxide. Reaction is given below –

12Pr + 11O2 → 2Pr6O11

  • Reaction with water – Pr reacts with hot water readily and forms praseodymium hydroxide. Reaction is given below –

2Pr(s) + 6H2O(l) → 2Pr(OH)3(aq) + 3H2(g)

  • Reaction with Halogens – Pr reacts with all halogens and forms trihalides. Reactions are given below –

2Pr(s) + 3F2(g) → 2PrF3(s) 

2Pr(s) + 3Cl2(g) → 2PrCl3(s) 

2Pr(s) + 3Br2(g) → 2PrBr3(s) 

2Pr(s) + 3I2(g) → 2PrI3(s)

  • Reaction with acid – Pr reacts readily with dilute sulfuric acid and forms Pr+3 ions in the solution. These ions form [Pr(H2O)9]3+ complexes. Reaction is given below –

2Pr(s) + 3H2SO4(aq) → 2Pr3+(aq) + 3SO4(aq)-2 + 3 H2 (g)

Uses of Praseodymium 

Due to its magnetic, electrical and optical properties praseodymium is used in various fields. Few of its main uses are listed below –

  • It is used in glass coloration.  Leo Moser discovered its use in glass coloration in the 1920s. 

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Green Praseodymium Glass Bead

  • Its small amounts are used in formation of alloys such as mischmetal and ferrocerium etc.

  • In combination with Nd, praseodymium is used to form high power magnets which are highly durable. 

  • Its alloy with Mg is used in aircraft engines.

  • It is used in carbon arc lights which are commonly used in film studios. 

  • It is used in coloration of ceramics and porcelain enamels as well. 

  • Its magnetic property is used with various other metals such as nickel and silicate crystals etc. for various purposes.

  • It is used as a single mode fiber optical amplifier. 

  • It is doped in fluoride glass and silicate crystals and then resultant substances are used in many purposes such as to slow a light pulse down to a few hundred meters per second. 

  • It is used as a catalyst with ceria. 

  • Its ions are used as activators in some UV phosphors. 

Praseodymium: Summary in Tabular form 

Praseodymium 

Symbol 

Pr

Discovered By 

Carl Auer von Welsbach 

Atomic number 

59

Standard atomic weight 

140. 9

Crystal Structure 

Double hexagonal close packed 

State at 20

Solid 

Melting point 

935

Boiling point 

3130

Period 

6th 

Series 

Lanthanide 

Block 

f

Electronic configuration 

1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 4f3 5d0 6s2 or [Xe] 4f3 6s2.

Main properties 

Paramagnetic 

Main use 

In coloration (specially glasses), alloys 

Disadvantage 

Intravenous injections of it may cause liver dysfunction


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