Thorium (Th) Element: Detailed Properties, Uses, Hazard

The atomic number of thorium is 90. It is found in f-block and Period 7 of the periodic chart. The symbol ‘Th’ represents it. The name derives from the Scandinavian deity of war, ‘Thor’. Actinium is found only in trace amount in uranium and thorium ores. It is soft, silvery-white in appearance. Thorium is an electropositive actinide with a reactivity dominated by the +4 oxidation state; it is very reactive and, if finely split, is susceptible to ignition in air.

Thorium (Th) Element

Natural thorium is exceptionally plentiful in thorium-232; it is also the 41st most widely distributed element. It can be detectable in very small quantities in soil, rocks, water, plants, and animals. It is a solid under normal circumstances. There are both natural and man-made forms of thorium, all of which are radioactive. The thorium, which is utilized worldwide, is collected from monazite sands.

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History of Thorium

  • After receiving a sample of a strange black mineral from Hans Esmark that had been found on an island close to Brevik, Norway, Jöns Jacob Berzelius made the discovery of thorium in Stockholm, Sweden, in 1828. Berzelius knew nothing about the radioactivity of thorium.
  • Berzelius had already found two additional elements: cerium (Ce) in 1803 and selenium (Se) in 1817.
  • Thorium’s radioactivity was first detected 70 years later, in 1898, by Polish-French scientist Marie Curie and English chemist Gerhard C. Schmidt.
  • In 1925, Anton Eduard van Arkel and Jan Hendrik de Boer devised a technique for making high-purity thorium metal. On a white, hot tungsten filament, thorium iodide is broken down, producing a crystal bar of pure thorium.

Occurrence of Thorium

  • ‘Th’ may be found in trace levels in most rocks and soils, and it is three times more prevalent than uranium. Soil contains around 6 parts per million (ppm) of thorium on average.
  • ‘Th’ is particularly insoluble, which is why, unlike uranium, it is abundant in sands but not in seawater.
  • It is typically present in minerals such as thorite (ThSiO4) and thorianite (ThO2 + UO2).
  • The rare earth phosphate mineral monazite, which can contain up to 12% thorium phosphate but often only 6-7% of it, is the most common source of thorium.
  • Th metal is produced using following methods:
    • by reducing thorium oxide with calcium,
    • by reducing thorium tetrachloride with an alkali metal,
    • by electrolyzing anhydrous thorium chloride in a fused mixture of potassium and sodium chlorides or,
    • by electrolyzing thorium tetrachloride with anhydrous zinc chloride.
  • Th has 28 isotopes with identified half-lives and mass numbers ranging from 210Th to 237Th. They are, in fact, all radioactive. The most stable isotope is 232Th, which has a half-life of 14.05 billion years and a nearly 100% abundance.

Elemental Properties of Thorium

Electronic Configuration[Rn] 6d2 7s2
Atomic Number90
Atomic Weight232.0381 g.mol -1 , no stable isotope
State at 20°CSolid
Group, Period, and Block7, f-block
Density11.72 g/cm3 at 20 °C
Ionic radius0.110 nm (+4)
Van der Waals radius0.182 nm
Electron shells2, 8, 18, 32, 18, 10, 2
Neutrons in most abundant isotope142

Physical Properties of Thorium

  • Air-stable and silvery white, pure ‘Th’ metal can hold onto its brilliant luster for months.
  • Th has an atomic number of 90 and is a silvery-white metal. It has a melting point of 1750 °C (​3182 °F) and a boiling point of 4788 °C (​8650 °F).
  • Th has a density of 11.72 g/cm3 at the room temperature.
  • It is malleable; meaning it can be easily hit into sheets without any cleavage.
  • It is also ductile metal which can be drawn into thin wires without breaking it.
  • Th is a paramagnetic element.
  • Th is dimorphic, transitioning from a cubic structure to a body-centered cubic structure at 1400 °C.
  • It becomes a superconductor at temperatures below 1.4 K (-271.75 °C).
  • The melting point of thorium oxide is 3300°C, making it the highest among the oxides.
Color/physical appearanceLustrous, silvery-white
Melting point/freezing point2023 K ​(1750 °C, ​3182 °F)
Boiling point5061 K ​(4788 °C, ​8650 °F)
Density11.72 g/cm3 at 20°
Electronegativity1.3 (Pauling Scale)

Chemical Properties of Thorium

  • ‘Th’ is one of the most reactive metal.
  • ‘Th’ is an element that is electropositive.
  • Finely split thorium readily ignites in air.
  • Powdered thorium is pyrophoric and should be handled with caution.
  • When ‘Th’ is heated in the air, it ignites and emits a dazzling white light.
  • The interaction of pure ‘Th’ with air is sluggish, but when polluted by dioxide, the reaction is quick.
  • ‘Th’ tainted by its oxide will gradually tarnish to gray, then black.
  • With the exception of hydrochloric acid, it does not readily dissolve in most acids. The majority of regularly used acids fail to dissolve it.
  • ‘Th’ disintegrates to create radon gas, an alpha emitter and radiation threat, hence places where thorium is stored or handled must be well ventilated.

Uses of Thorium

Th and its associated compounds have a limited number of applications. Some of the important uses are mentioned here:

  • Thorium oxide (ThO2), commonly known as thoria, has one of the highest melting points of any oxide (3300 °C), making it useful in high-temperature ceramics. A ceramic is a substance made of earthy ingredients like sand or clay. Ceramics include bricks, tiles, cement, and porcelain.
  • Th is employed in magnesium alloying, to coat tungsten (W) wire used in electronic devices, and to regulate the grain size of plutonium used in electric lights and in the manufacturing of refractory materials for the metallurgical industries.
  • Thorium dioxide was employed in Welsbach gas mantles in the nineteenth century, and these mantles may still be found in camping lanterns today. (Thorium dioxide’s extremely high melting point guarantees that it remains solid, shining with an intense, dazzling white light at the temperature of the lantern’s burning gas.)
  • Because thorium dioxide-containing glass has a high refractive index and minimal dispersion, it is used in high-quality lenses and scientific equipment.
  • The thorium oxide is also utilized as a catalyst in the conversion of ammonia to nitric acid, the production of sulfuric acid, and petroleum cracking.
  • Th is being investigated as a possible source of nuclear energy since it is more common than uranium. Global energy crises might be resolved by utilizing it.
  • Because thorium dioxide-containing glass has a high refractive index and minimal dispersion, it is used in high-quality lenses and scientific equipment.

Health Hazards of Thorium

  • Everyone absorbs some thorium through food or drinking water, and the quantities in air are so little that it is frequently overlooked.
  • Breathing in thorium during work may raise the risk of developing lung problems, as well as lung and pancreatic cancer, many years later.
  • Th has the capability of altering genetic materials. People who are given thorium injections for specific X-rays may develop liver damage.
  • Th is a radioactive element that may be preserved in bones. Because of these features, it has the potential to induce bone cancer many years after exposure.

Environmental Effects of Thorium

  • Large-scale thorium discharges have been shown to affect the ecosystem, including plants, animals, and aquatic life-forms.
  • Inappropriate trash disposal contaminates the environment and damages ecosystems.

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Jyoti Bashyal

Jyoti Bashyal, a graduate of the Central Department of Chemistry, is an avid explorer of the molecular realm. Fueled by her fascination with chemical reactions and natural compounds, she navigates her field's complexities with precision and passion. Outside the lab, Jyoti is dedicated to making science accessible to all. She aspires to deepen audiences' understanding of the wonders of various scientific subjects and their impact on the world by sharing them with a wide range of readers through her writing.

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