Last Updated: April 28, 2024


Dive into the enigmatic world of Promethium, a rare and fascinating element nestled within the lanthanide series of the periodic table. This comprehensive guide unveils Promethium’s unique characteristics, shedding light on its elusive nature, intriguing uses, and the compelling science behind its compounds. From enhancing the luminosity in watches to powering space exploration devices, Promethium’s applications are as diverse as they are remarkable. Embark on a journey to explore how this scarcely found element impacts technology, science, and beyond, enriched with examples that bring its story to life.

What is Promethium?

Promethium is a chemical element with the symbol Pm and atomic number 61, making it one of the rare earth elements within the lanthanide series of the periodic table. It is unique among the lanthanides as it does not occur in significant amounts in the earth’s crust in a natural, stable form due to its highly radioactive nature. All its isotopes are radioactive, with promethium-145 being the most stable, having a half-life of 17.7 years.Discovered in 1945 by Jacob A. Marinsky, Lawrence E. Glendenin, and Charles D. Coryell, the element was named after Prometheus, the Titan from Greek mythology who stole fire from the gods and gave it to humanity. The name reflects the discovery of the element amidst the development of nuclear technology and the atomic bomb in the mid-20th century.

Promethium Formula

Formula: Pm

Composition: Comprised solely of promethium atoms, making it an elemental substance.

Bond Type: As an element, promethium does not form bonds in its pure state. However, it can form various types of chemical bonds, such as ionic and covalent bonds, when it reacts with other elements. This ability enables promethium to create a multitude of compounds.

Molecular Structure: In its elemental form, promethium doesn’t exhibit a molecular structure. It assumes a metallic structure, likely adopting a hexagonal close-packed crystalline form, indicative of its properties as a potentially lustrous, silvery metal, although as a radioactive element, it is not commonly observed in bulk metallic form.

Electron Sharing: Promethium can share electrons to form covalent bonds or transfer electrons to form ionic bonds. It commonly assumes a +3 oxidation state (Pm³⁺) in its compounds, contributing to its versatility in forming various chemical species.

Significance: Promethium’s importance is notable in niche applications due to its radioactive nature. It is used in beta voltaic nuclear batteries, luminous paint, and as a light source in signaling equipment. Despite its limited availability and specific uses, promethium’s potential in applications like space exploration and portable energy sources illustrates its unique value.

Role in Chemistry: Promethium’s chemical behavior is intriguing within the study of the lanthanide series, underscoring the complexity of rare earth elements. Its radioactive properties and potential for electron exchange make it an interesting subject for theoretical and applied chemistry research, contributing to our knowledge of rare earth metals’ behavior, particularly in how radioactivity influences chemical interactions and technological applications.

Atomic Structure of Promethium

Atomic Structure of Promethium

Promethium is a rare earth metal that belongs to the lanthanide series of the periodic table. It is defined by its atomic number 61, meaning it has 61 protons in its nucleus. The atomic structure of promethium is characterized by the following:

  • Protons and Neutrons: Promethium has 61 protons. The number of neutrons varies among its isotopes, with promethium-145, having 84 neutrons, being one of the more stable isotopes.
  • Electrons: Promethium has 61 electrons, with the electron configuration [Xe] 4f⁵ 6s². This configuration indicates that promethium has five electrons in the 4f orbital and two electrons in the 6s orbital, following the noble gas xenon.
  • Atomic Mass: The atomic mass of promethium varies depending on its isotope. For example, promethium-145, one of its more common isotopes, has an atomic mass of approximately 144.912749 amu.
  • Valence Electrons: As with other lanthanides, the valence electrons of promethium are those in the 4f and 6s orbitals, playing a crucial role in its chemical reactivity and bonding behavior.
  • Oxidation States: Promethium most commonly exhibits a +3 oxidation state in its compounds, similar to other lanthanides, which is reflective of its losing three electrons to achieve a stable electron configuration.
  • Radius: The atomic radius of promethium is approximately 183 pm (picometers), and its ionic radius for the Pm³⁺ ion is about 108 pm.

Properties of Promethium

Properties of Promethium

Physical Properties of Promethium

Property Value
Appearance Metallic, silvery-white luster
Atomic Mass Varies by isotope; for Pm-145, approximately 144.9127 amu
Density About 7.26 g/cm³ at room temperature
Melting Point 1042 °C
Boiling Point Estimated 3000 °C
State at Room Temperature Solid
Thermal Conductivity Lower than most metals
Electrical Resistivity High, characteristic of lanthanides
Magnetic Ordering Paramagnetic at room temperature

Chemical Properties of Promethium

Promethium, symbolized as Pm and atomic number 61, exhibits several chemical properties that reflect its position in the lanthanide series of the periodic table. Its chemical behavior is characterized by the following aspects:

  • Oxidation States: Promethium predominantly exhibits a +3 oxidation state in its compounds, aligning with the common oxidation state of lanthanides. A +2 oxidation state is also possible but less common.
  • Electronegativity: Promethium has an electronegativity of 1.13 on the Pauling scale, indicating its moderate tendency to attract electrons during chemical reactions.
  • Electron Configuration: The electron configuration of promethium is [Xe] 4f⁵ 6s², showcasing its placement within the f-block of the periodic table. This configuration plays a critical role in its chemical reactions and bonding behavior.
  • Reactivity with Oxygen: Promethium reacts with oxygen to form promethium(III) oxide: 2Pm + 3O₂ → 2Pm₂O₃Reactivity with Water: When exposed to water, promethium reacts to form promethium hydroxide and hydrogen gas, although this reaction is less vigorous than with alkaline metals: 2Pm + 6H₂O → 2Pm(OH)₃ + 3H₂Reactivity with Acids: Promethium dissolves in dilute acids, forming promethium(III) salts and releasing hydrogen gas, a common trait among active metals: Pm + 3HCl → PmCl₃ + (3/2)H₂
  • Formation of Compounds: Promethium forms a variety of compounds, including halides like promethium chloride (PmCl₃), oxides such as promethium oxide (Pm₂O₃), and sulfates (Pm₂(SO₄)₃), among others. These compounds are usually in the +3 oxidation state.
  • Solubility: Promethium compounds, such as PmCl₃, are soluble in water, which is significant for their chemical processing and purification.
  • Radioactivity: Being a radioactive element, promethium’s chemical properties are also influenced by its radioactivity. This aspect is crucial for applications that utilize its radioactive decay, such as in nuclear batteries and radioluminescent materials.

Thermodynamic Properties of Promethium

Property Value
Melting Point 1042 °C
Boiling Point Estimated 3000 °C
Heat of Fusion Estimated 7.7 kJ/mol
Heat of Vaporization Estimated 290 kJ/mol
Specific Heat Capacity Estimated 100 J/(kg·K)
Thermal Conductivity Low, specific value not provided
Thermal Expansion Estimated, similar to lanthanides

Material Properties of Promethium

Property Value
Density 7.26 g/cm³ at room temperature
Mohs Hardness Similar to lanthanides, estimated around 2.5
Young’s Modulus Not specifically known for Promethium
Shear Modulus Not specifically known for Promethium
Bulk Modulus Not specifically known for Promethium
Poisson’s Ratio Similar to lanthanides, not specifically provided for Promethium
Brinell Hardness Not specifically known for Promethium

Electromagnetic Properties of Promethium

Property Value
Electrical Resistivity High, specific value not provided
Magnetic Ordering Paramagnetic at room temperature
Curie Temperature Not applicable to paramagnets
Superconducting Point Promethium is not known to superconduct

Nuclear Properties of Promethium

Property Value
Natural Isotopes None, all isotopes are synthetic
Most Stable Isotope Pm-145 with a half-life of 17.7 years
Neutron Cross Section Varies with isotope, significant for Pm-149
Neutron Mass Absorption Specific to isotope, important for nuclear applications
Isotopic Abundance Not naturally occurring, produced in nuclear reactors

Preparation of Promethium

Promethium is a unique element in that it does not naturally occur in significant amounts on Earth due to its radioactivity. All its isotopes are radioactive, with promethium-145 (Pm-145) being the most stable but still with a half-life of only about 17.7 years. The preparation of promethium primarily involves nuclear reactions, typically occurring within nuclear reactors or during the processing of nuclear materials. Here are the key steps involved in the preparation of promethium:

  1. Neutron Irradiation of Neodymium or Uranium: One common method involves the neutron bombardment of neodymium-146 (146Nd), which is present in mixed rare earth concentrates. The neutron bombardment converts 146Nd to 147Nd through neutron capture. 147Nd then undergoes beta decay to become promethium-147 (147Pm): 146Nd + n → 147Nd → 147Pm + β-.
  2. Extraction and Chemical Separation: After irradiation, the promethium must be chemically separated from the neodymium and other byproducts. This is typically achieved through a series of complex chemical separation processes, such as solvent extraction, ion exchange chromatography, or fractional crystallization. These processes exploit the slight differences in chemical properties between the lanthanides to isolate promethium.
  3. Purification: The separated promethium may still contain impurities or other radioactive materials. Further purification processes, including additional solvent extraction steps or distillation, are employed to obtain high-purity promethium.
  4. Conversion to Usable Forms: The pure promethium is often converted into compounds, such as promethium chloride (PmCl₃) or promethium oxide (Pm₂O₃), depending on its intended application. These compounds are easier to handle and integrate into devices, such as nuclear batteries or radioluminescent materials.

Chemical Compounds of Promethium

Chemical Compounds of Promethium

1.Promethium Oxide (Pm₂O₃)

  • Formed by the reaction of promethium metal with oxygen
  • 4Pm+3O₂→2Pm₂O₃

2.Promethium Fluoride (PmF₃)

  • Produced by reacting promethium oxide with hydrogen fluoride
  • Pm₂O₃+6HF→2PmF₃+3H₂O

3.Promethium Chloride (PmCl₃)

  • Prepared by treating promethium metal with chlorine gas
  • 2Pm + 3Cl₂ → 2PmCl₃

4.Promethium Sulfate (Pm₂(SO₄)₃)

  • Obtained by dissolving promethium oxide in sulfuric acid
  • Pm₂O₃ + 3H₂SO₄ → Pm₂(SO₄)₃ + 3H₂O

5.Promethium Carbonate (Pm₂(CO₃)₃)

  • Formed by reacting promethium chloride with sodium carbonate
  • 2PmCl₃ + 3Na₂CO₃ → Pm₂(CO₃)₃ + 6NaCl

6.Promethium Hydroxide (Pm(OH)₃)

  • Produced by adding a base like sodium hydroxide to promethium salt solution
  • PmCl₃ + 3NaOH → Pm(OH)₃ + 3NaCl

Isotopes of Promethium

Isotope Mass Number Half-Life Decay Mode
Pm-143 143 265 days Beta decay to Nd-143
Pm-144 144 363 days Beta decay to Nd-144
Pm-145 145 17.7 years Beta decay to Nd-145
Pm-146 146 5.53 years Beta decay to Nd-146
Pm-147 147 2.62 years Beta decay to Sm-147
Pm-148 148 5.368 days Beta decay to Sm-148
Pm-148m 148m 41.29 days Isomeric transition to Pm-148
Pm-149 149 53.08 hours Beta decay to Sm-149
Pm-150 150 2.68 hours Beta decay to Sm-150
Pm-151 151 28.40 hours Beta decay to Sm-151

Uses of Promethium

Uses of Promethium

Promethium, despite its scarcity and radioactivity, has several specialized applications due to its unique properties:

  1. Radioluminescent Paint: Promethium is used in luminous paint for watches, aircraft dials, and compasses, where its radioactive decay energizes phosphorescent materials to emit light.
  2. Nuclear Batteries: Also known as radioisotope thermoelectric generators (RTGs), these devices use the heat released by promethium’s radioactive decay to generate electricity for spacecraft, buoys, and remote weather stations.
  3. Beta Voltaic Cells: Similar to nuclear batteries, these cells convert the beta radiation emitted by promethium into electricity, useful in small-scale, long-lasting power sources for electronic devices.
  4. Research: Due to its radioactive nature, promethium isotopes are valuable in scientific research for studying the structure of matter and nuclear processes.
  5. Thickness Gauging: Promethium-147 emits beta particles that can be used in devices to measure the thickness of materials by gauging the amount of radiation that passes through.
  6. Space Exploration: The long-lived isotopes of promethium can power instruments in space probes and satellites where solar power is insufficient.
  7. Signal Lights: Promethium’s radioluminescence is utilized in emergency exit signs and runway lights, providing illumination without the need for electrical power.
  8. Medical Devices: In some cases, promethium may be used in medical diagnostics equipment as a source of beta radiation, although this use is limited due to safety concerns and the availability of alternative isotopes.

Production of Promethium

Promethium is a rare and radioactive element, not found in significant quantities in nature due to its instability. Its production is predominantly synthetic, achieved through nuclear reactions in reactors or particle accelerators. Here are the primary methods for producing promethium:

  1. Uranium Fission: Promethium is also produced as a by-product of uranium fission in nuclear reactors. During the fission process, uranium nuclei split into smaller fragments, including various isotopes of promethium.
  2. Particle Accelerator: Another method involves bombarding lighter elements with particles in a cyclotron or other type of particle accelerator. This method is less common due to its higher cost and lower yield compared to reactor production.
  3. Chemical Separation and Purification: Following irradiation or fission, the promethium must be chemically separated from a complex mixture of products. This is typically achieved through solvent extraction or ion exchange chromatography, techniques that selectively isolate promethium from other elements.
  4. Final Processing: Once separated, promethium can be converted into various chemical forms depending on its intended use. Promethium-147, the most stable isotope, is particularly sought after for its applications in radioluminescent devices and nuclear batteries.

Applications of Promethium

Promethium, a rare and radioactive element, finds its use in a variety of niche applications due to its unique properties. Here are some of the key applications of promethium:

  1. Radioluminescent Paint: Promethium-147 is used in the production of radioluminescent paint. This paint glows in the dark and is used on watch dials, aircraft gauges, and emergency exit signs, providing illumination without external power sources.
  2. Nuclear Batteries: Promethium is utilized in the manufacture of nuclear batteries, also known as radioisotope thermoelectric generators (RTGs). These batteries convert the heat released from promethium’s radioactive decay into electricity, powering devices in remote locations, space probes, and medical equipment.
  3. Thickness Measurement: The beta radiation emitted by promethium-147 can penetrate materials and is used in thickness gauges. These devices measure the thickness of paper, sheet metal, and plastics in industrial manufacturing processes.
  4. Space Exploration: Due to its ability to provide a consistent power source through radioactive decay, promethium is considered for use in space exploration missions, powering instruments on spacecraft and satellites where solar power is ineffective.
  5. Signal Lights: The radioluminescence of promethium is employed in creating self-powered lighting for emergency signs, runway lights, and in military applications where reliability and independence from external power sources are crucial.
  6. Research and Development: Promethium isotopes are used in scientific research, particularly in studies related to nuclear physics and chemistry. Its radioactive properties make it a subject of interest for understanding radioactive decay processes and the behavior of lanthanides.
  7. Medical Devices: In some specialized cases, promethium may be used in diagnostic procedures or in treating certain medical conditions, taking advantage of its radioactive properties under controlled conditions.
  8. Environmental Testing: Promethium’s beta radiation is used in sensors and devices designed to monitor environmental conditions and pollution levels, providing data essential for environmental protection efforts.

Promethium, with its rare and radioactive nature, occupies a unique niche in scientific and technological applications. From powering self-luminous paint and nuclear batteries to contributing to space exploration and industrial processes, its utility extends across various domains. Despite handling challenges, the continued exploration of promethium’s potential underscores its invaluable role in advancing both technology and research.

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