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What is Thorium

Thorium (pronounced as THOR-ee-em) is a less radioactive metal that belongs to the family of actinides and denoted by the chemical symbol Th [1]. Out of its thirty-two isotopes, thorium-230 and thorium-232 are the most stable ones with a half-life of 7.54×104 years and 1.4×1010 years, respectively, where the latter decays into radium-228 through alpha decay or spontaneous fission [2, 5].

Thorium Symbol

Where is it Found

Up to 12% of the element exists in monazite (Mt) ores in the form of thorium phosphate from where it’s mined. Its abundance is attributed to the presence of 16 million tones of Mt resources around the world out of which 12 million tones form heavy mineral sand deposits on the east and south Indian coasts [6].



How Did it Get the Name: Its name is derived from Thor, the Scandinavian god of war and thunder [1].

Who Discovered it: Jöns Jakob Berzelius was the discoverer of the metal [1].

When and Where was it Discovered

In 1829, Berzelius at the Royal Karolinska Institute, Stockholm, isolated a new metal from a rock sample that was sent to him by a mineralogist called Reverend Hans Morten Thrane Esmark who found it near Brevig. He even heated thorium fluoride with potassium to produce a sample of the same metal and named it as thorium. The rock mineral found by Esmark was later discovered to be thorium silicate (thorite) [1, 2].

Thorium Identification

Atomic number

90 [1]

CAS number

7440-29-1 [1]

Position in the periodic table [1]







Where is Thorium on the Periodic Table

Properties and Characteristics of Thorium

General Properties

Relative atomic mass 232.038 [1]
Atomic mass/weight 232.038 atomic mass units

Physical Properties

Color/appearance Grayish white [3]
Melting point/freezing point 1750°C (3182°F) [1]
Boiling point 4785°C (8645°F) [1]
Density 11.7 g/cm3 [1]
Natural state at standard room temperature (solid/liquid/gas) Solid [1]

Chemical Properties

Flammability Highly flammable [3]
Oxidation state/Oxidation number +2, +3, +4 [1]

Atomic Data of Thorium (Element 90)

Electron configuration (noble gas configuration) [Rn] 6d27s2
Quantum Numbers
– n 5 [10]
– ℓ 3
– mℓ -2
– ms +1/2
Atomic structure
– Number of Electrons 102 [5]
– Number of Neutrons 157
– Number of Protons 102
Radius of atom
Atomic Radius 2.45 Å[1]
– Covalent Radius 1.90 Å[1]
Ionization energy [1]


1st 2nd 3rd 4th 5th 6th 7th
608.504 1148.2 1930 2778.8

Thorium Bohr Model

 What is Thorium Used for

  • It is used as an alloying agent in magnesium to increase strength and creep resistance at a higher temperature required in the making of aircraft engines [1, 4].
  • The element is coated over tungsten filaments used in electronic devices such as television sets [2].
  • It is sometimes applied in the making of jewelry such as rings.
  • Thorium-229 might be useful in the treatment of cancer and infectious diseases even though no studies have been conducted to support its applications in the field of medicine [7].

Dangers and Health Hazards

Prolonged exposure or accidental inhalation/consumption may result in severe toxicity. If the radioactive metal enters the eyes or comes in contact with skin, it causes severe irritation [3].

Thorium Rod

Interesting Facts

  • Thorium-232, when targeted with neutrons, undergoes a series of beta decays to form uranium-233 that might be useful as a nuclear fuel in the future to power nuclear reactors [1, 2, 6,].
  • In 1898, the radioactivity of Th was first shown by Gerhard Schmidt, an organic chemist, and later confirmed by Marie Curie [1].

Thorium Pictures

Thorium Price

The costs of the element may vary somewhere between $130 and $160 [8].



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