thorium

Also known as Th, element 90, 90Th

Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

AI overview

Thorium is a naturally radioactive metal with a silvery appearance that turns olive-grey when exposed to air, and it's relatively soft with a high melting point. It's notable for being highly reactive—particularly when finely divided—and for having chemistry dominated by a specific oxidation state that makes it chemically active.

AI-generated from the Wikipedia summary — may contain errors.

Key facts

Thorium.engvar: en-GB

via Wikipedia infobox

Chemical data

Formula: Th
Molecular weight: 232.038 g/mol
IUPAC name: thorium
SMILES: [Th]
InChIKey: ZSLUVFAKFWKJRC-UHFFFAOYSA-N
Polar surface area: 0 Å²
H-bond donors: 0
H-bond acceptors: 0
Formal charge: 0

via PubChem

Research

5,999 papers

Thorium ore dust research applicable to mineral sands industry workers.ReviewJournal of radiological protection : official journal of the Society for Radiological Protection · 2025Hewson GS, Ralph MI, Cattani MDOI: 10.1088/1361-6498/adacf6
Thorium inhibits human respiratory chain complex IV (cytochrome c oxidase).Journal of hazardous materials · 2022Yu L, Lin Z, Cheng X et al.DOI: 10.1016/j.jhazmat.2021.127546
Thorium bioassay of miners revisited.Journal of radiological protection : official journal of the Society for Radiological Protection · 2025Hewson GS, Ralph M, Cattani MDOI: 10.1088/1361-6498/adc312
Thorium(IV) triggers ferroptosis through disrupting iron homeostasis and heme metabolism in the liver following oral ingestion.Journal of hazardous materials · 2023Ma M, Wang R, Xu MDOI: 10.1016/j.jhazmat.2023.131217
Thorium promotes lung, liver and kidney damage in BALB/c mouse via alterations in antioxidant systems.Chemico-biological interactions · 2022Chaudhury D, Sen U, Sahoo BK et al.DOI: 10.1016/j.cbi.2022.109977
The role of thorium in endomyocardial fibrosis.ReviewHuman & experimental toxicology · 1990Singh NPDOI: 10.1177/096032719000900203
Thorium exerts hazardous effects on some neurotransmitters and thyroid hormones in adult male rats.Naunyn-Schmiedeberg's archives of pharmacology · 2020Abdel-Rahman M, Rezk MM, Abdel Moneim AE et al.DOI: 10.1007/s00210-019-01718-y
Construction of a thorium/actinium generator at the Canadian Nuclear Laboratories.Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine · 2020Perron R, Gendron D, Causey PWDOI: 10.1016/j.apradiso.2020.109262

via PubMed

Wikidata facts

Mass: 232.0377
Image: Thorium sample 0.1g.jpg

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time of discovery or invention: 1828-01-01
element symbol: Th
Commons category: Thorium
atomic number: 90
electronegativity: 1
oxidation state: 1
Mohs' hardness: 3
Unicode character: 釷
chemical formula: Th
canonical SMILES: [Th]
ionic radius: 1.21

Sources (5)

via Wikidata · CC0

~67 min read

Article

42 sections

Contents

Bulk properties
Isotopes
Radiometric dating
Chemistry
Reactivity
Inorganic compounds
Coordination compounds
Organothorium compounds
Occurrence
Formation
Abundance
On Earth
History
Erroneous report
Discovery
Initial chemical classification
First uses
Radioactivity
Further classification
Phasing out
Nuclear power
Nuclear weapons
Production
Concentration
Acid digestion
Alkaline digestion
Purification
Modern applications
Potential use for nuclear energy
Advantages
Disadvantages
Hazards and health effects
Radiological
Biological
Chemical
Exposure routes
See also
Explanatory notes
Citations
General and cited references
Further reading
External links

All known thorium isotopes are unstable. The most stable isotope, 232Th, has a half-life of 14.0 billion years, or about the age of the universe; it decays very slowly via alpha decay, starting a decay chain named the thorium series that ends at stable 208Pb. On Earth, thorium and uranium are the only elements with no stable or nearly-stable isotopes that still occur naturally in large quantities as primordial elements. Thorium is estimated to be over three times as abundant as uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare-earth elements.