Last Updated: April 28, 2024


Discover the intriguing world of rare elements with our comprehensive guide on Protactinium, a lesser-known player in the periodic table. Delve into the mysteries and applications of Protactinium, from its discovery to its unique properties and uses in various fields. This guide offers insights and examples that illuminate the significance of Protactinium in scientific research and technological advancements. Whether you’re a student, researcher, or science enthusiast, explore the fascinating aspects of Protactinium and its contribution to our understanding of the atomic world.

What is Protactinium?

Protactinium is a dense, silvery-gray metallic element that is characterized by its unique properties and limited applications. With the atomic number 91, Protactinium is notable for its radioactivity and scarcity in nature, making it one of the less common elements. This element does not occur freely in nature but is usually found in uranium ores from which it is extracted. Protactinium is mainly used in scientific research rather than widespread industrial applications, due to its radioactivity and scarcity. The element has been studied for potential use in nuclear reactors and as a tracer for geochronology and paleoceanography studies, but its high radiotoxicity and limited availability restrict its practical applications

Protactinium Formula

  • Formula: Pa
  • Composition: Consists of a single protactinium atom.
  • Bond Type: In its elemental form, protactinium does not have bonds as it is a pure element. However, protactinium can form covalent or ionic bonds when reacting with other elements.
  • Molecular Structure: As a pure element, protactinium does not form a molecular structure like compounds. At room temperature, protactinium is in a metallic state with an orthorhombic crystalline structure.
  • Electron Sharing: In compounds, protactinium typically shares electrons covalently or transfers electrons ionically, depending on the nature of the other element(s) it is bonding with.
  • Significance: Protactinium is known for its radioactivity and scarcity. It is significant in nuclear science, particularly in the study of the actinide series and nuclear fuel cycles. Due to its long half-life, Protactinium-231 is used in geological dating of natural waters and sediments.
  • Role in Chemistry: Protactinium plays a pivotal role in nuclear chemistry and reactor technology. Its compounds and isotopes are critical for research in nuclear physics, radiometric dating, and potential future applications in nuclear reactors, emphasizing its importance in advanced scientific and technological research.

Atomic Structure of Protactinium

Atomic Structure of Protactinium (3)


Electron Configuration

The electron configuration of Protactinium is [Rn] 5f² 6d¹ 7s². This indicates that Protactinium has two electrons in the 5f orbital, one electron in the 6d orbital, and two electrons in the 7s orbital, following the filled orbitals of radon (Rn). The configuration highlights its position as an early actinide, where the filling of the 5f orbital begins.

Atomic Properties

  • Atomic Number (Z): 91. This signifies the number of protons in the nucleus of Protactinium atoms, determining its identity as Protactinium.
  • Mass Number (A): The most stable isotope of Protactinium, ^231Pa, has a mass number of 231, indicating the total number of protons and neutrons in its nucleus.
  • Isotopes: Protactinium has several isotopes, with ^231Pa being the most stable, boasting a half-life of about 32,760 years. The presence of these isotopes contributes to the understanding of Protactinium’s radioactive properties.

Nuclear Composition

The nucleus of a Protactinium atom comprises 91 protons, imparting a positive charge, and a variable number of neutrons across its isotopes, with ^231Pa containing 140 neutrons. The delicate balance between protons and neutrons plays a crucial role in the stability and radioactivity of Protactinium isotopes.

Physical Properties

  • Atomic Mass: Approximately 231.03588 u (atomic mass units) for ^231Pa, reflecting its most abundant isotope’s mass.
  • Density: Protactinium has a density of about 15.37 g/cm³, showcasing its status as a dense, heavy metal.
  • State at Room Temperature: Solid. Protactinium exhibits a bright, metallic luster when freshly prepared but reacts with oxygen to form a coating of oxides.

Chemical Properties

  • Oxidation States: Protactinium commonly exhibits +4 and +5 oxidation states in its compounds. The +5 oxidation state is more stable and common, influencing its chemical behavior and the types of compounds it forms.
  • Reactivity: Protactinium is reactive, especially when finely divided. It reacts with oxygen, acids, and moisture, but is resistant to alkalis. Its chemistry is dominated by the formation of oxides, halides, and other complex compounds.

Properties of Protactinium

Properties of Protactinium (1)


Physical Properties of Protactinium

Property Value
Appearance Bright, silvery metallic luster
Atomic Number 91
Atomic Weight 231.03588 u
Density 15.37 g/cm³ (near room temperature)
Melting Point 1568 °C (2854 °F; 1841 K)
Boiling Point 4027 °C (7281 °F; 4300 K)
State at 20 °C Solid
Crystal Structure Orthorhombic
Thermal Conductivity ~47 W/(m·K) (at 300 K)
Electrical Resistivity Not well characterized due to radioactivity
Thermal Expansion Not well characterized
Young’s Modulus Not well characterized
Shear Modulus Not well characterized
Bulk Modulus Not well characterized
Mohs Hardness Approx. 3-4
CAS Number 7440-13-3

Chemical Properties of Protactinium

Protactinium (Pa) is a dense, silvery-gray metal belonging to the actinide series. With its atomic number 91, it exhibits intriguing chemical properties due to its position in the periodic table.

1. Oxidation States: Protactinium primarily exhibits the +5 oxidation state in its compounds, which is the most stable and common. However, it can also show a +4 oxidation state in some compounds.

2. Reaction with Air: Protactinium is quite reactive with oxygen. In the air, it forms protactinium oxide. For the +5 oxidation state, the reaction can be represented as: 2 Pa+5 O₂→2 PaO₅

And for the +4 state, the reaction is: 4 Pa+5 O₂→2 Pa2O₄

3. Reaction with Water: Protactinium reacts with water, but the reaction is not as vigorous as with some other actinides. The reaction forms protactinium oxide and hydrogen gas: Pa+2 H₂O→PaO₂+2 H₂

4. Reaction with Acids: Protactinium dissolves in hydrochloric acid (HCl) and nitric acid (HNO3), forming protactinium(IV) or protactinium(V) solutions depending on the conditions, and releasing hydrogen gas: Pa+4 HCl→PaCl₄+2 H₂
Pa+5 HNO₃ →Pa(NO₃ )₅+H₂

5. Compounds and Complexes:Protactinium Oxides Protactinium forms oxides in both +4 and +5 oxidation states, PaO₂ and Pa2O₅, important for understanding its chemistry.
Protactinium Halides Including fluorides, chlorides, bromides, and iodides, such as PaF₄ and PaCl₅, showcasing its ability to form complex halide compounds.

6. Behavior with Halogens: Protactinium reacts with halogens to form tetra- and penta-halides. For example, with fluorine, it forms PaF4 and PaF5, indicating its reactive nature towards halogens: Pa+2 F₂→PaF₄
Pa+5 F₂→PaF₅

7. Radioactivity: Protactinium is highly radioactive, with isotopes such as Protactinium-231 playing a crucial role in the uranium-235 decay series. Its radioactivity is a significant aspect of its chemical behavior, influencing its handling and storage.

Isotopes of Protactinium

The table below lists some of the isotopes of protactinium, including their mass numbers, half-lives, and decay modes:

Isotope Mass Number Half-Life Decay Mode
Protactinium-230 230 17.4 days Beta decay to Uranium-230
Protactinium-231 231 32,760 years Alpha decay to Actinium-227
Protactinium-232 232 1.31 days Beta decay to Uranium-232
Protactinium-233 233 26.967 days Beta decay to Uranium-233
Protactinium-234 234 6.75 hours Beta decay to Uranium-234

Chemical Compounds of Protactinium

Chemical Compounds of Protactinium

1. Protactinium(IV) Chloride (PaCl₄)

Protactinium(IV) Chloride is a yellow crystalline solid, used in research applications. It forms through the reaction:

2. Protactinium(V) Oxide (Pa2O₅)

Protactinium(V) Oxide is a pale yellow powder, crucial for studying Protactinium’s chemical behavior. It’s synthesized by:

3. Protactinium(V) Fluoride (PaF₅)

A pale yellow crystalline solid, Protactinium(V) Fluoride is produced in the reaction:

4. Protactinium(IV) Iodide (PaI₄)

Protactinium(IV) Iodide, a yellow crystalline substance, is prepared through:

5. Protactinium(V) Chloride (PaCl₅)

A green-yellow crystalline solid, it’s obtained by combining Protactinium with chlorine:

6. Protactinium(IV) Oxide (PaO₂)

Protactinium(IV) Oxide, a black powder, is essential for understanding Protactinium’s properties. It’s formed by:

Uses of Protactinium

Uses of Protactinium

Protactinium, due to its scarcity, radioactivity, and challenging handling requirements, has limited but specialized uses:

  • Scientific Research: Protactinium is primarily used in scientific research, particularly in the fields of nuclear physics and radiochemistry. Its isotopes, especially Protactinium-231, are of interest for understanding nuclear reactions and the decay chains of heavier elements.
  • Geochronology and Oceanography: Protactinium-231 is utilized in geochronology to date marine sediments and in oceanography to study the circulation patterns of ocean waters. The protactinium/thorium ratio in sediments helps in understanding the sedimentation rates and age of marine deposits.
  • Nuclear Applications: While not widely used in current nuclear reactor designs, the isotope Protactinium-233 is a potential fuel for future nuclear reactors. Protactinium-233 can be bred to Uranium-233, a fissile material, through neutron capture. This aspect is of interest in the development of thorium-based nuclear reactors.
  • Radiation Shielding: Due to its radioactivity, protactinium can be used in shields that protect against gamma radiation, although its use for this purpose is very limited due to the high radioactivity and scarcity of the element.
  • Superconductivity Research: Protactinium’s unique properties make it of interest in the field of superconductivity research. Superconductors are materials that can conduct electricity without resistance when cooled below a certain temperature. Protactinium’s electron configuration and metallic bonding characteristics offer a unique platform for studying the mechanisms of superconductivity under different conditions

Production of Protactinium

The production of Protactinium, a rare and highly radioactive element, is predominantly a byproduct of the nuclear industry. Its scarcity, combined with its hazardous radioactivity, makes its production complex and highly specialized. The most common isotope, Protactinium-231, originates from the decay of Uranium-235, while Protactinium-233 is produced through neutron irradiation of Thorium-232. Below are the main methods used in the production of Protactinium:

  1. Uranium Ore Processing: Protactinium-231 is produced naturally as a decay product of Uranium-235. When uranium ores are processed, small amounts of Protactinium can be extracted from the radioactive decay chains.
  2. Nuclear Reactors: Protactinium-233 is produced in nuclear reactors as part of the Thorium fuel cycle. Thorium-232 captures a neutron and transforms into Thorium-233, which decays into Protactinium-233 via beta decay. This isotope is significant for potential use in future nuclear energy systems.
  3. Chemical Separation: After its generation, Protactinium is chemically separated from the parent material and other byproducts. Due to its high radioactivity, this process requires specialized facilities to protect workers and the environment from radiation exposure.
  4. Targeted Production: For research purposes, Protactinium can be specifically produced by bombarding Thorium with neutrons in a nuclear reactor or using particle accelerators to induce reactions in Thorium or Uranium targets.

Applications of Protactinium

Despite its challenges, Protactinium has several niche applications, primarily in research and nuclear science:

  • Nuclear Reactor Research: The isotope Protactinium-233 is crucial for research in Thorium-based nuclear reactors. When it decays into Uranium-233, it becomes a potential fuel for nuclear reactors, offering a cleaner and safer alternative to conventional uranium fuels.
  • Radiometric Dating: Protactinium isotopes, particularly Protactinium-231, are used in the field of geochronology to date marine sediments and ice cores. This application takes advantage of the specific half-life of Protactinium-231 to provide age estimates for samples up to 175,000 years old.
  • Nuclear Forensics and Research: Due to its unique properties and part in the decay chain of Uranium-235, Protactinium is used in nuclear forensics and research to study the behavior of actinide elements in the environment and nuclear processes.
  • Potential Medical Applications: While still largely theoretical, isotopes of Protactinium have potential applications in targeted alpha therapy (TAT) for cancer treatment. Their high radioactivity can be harnessed to destroy cancer cells, though this application is in the early stages of research.

This article has explored the intricate properties and meticulous preparation processes of Protactinium, a rare and fascinating element. Through our detailed examination, we’ve uncovered the physical and chemical characteristics that make Protactinium unique, as well as the complex methods involved in its extraction and purification. This knowledge not only enriches our understanding of Protactinium but also highlights its potential applications in science and technology.

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