Element Thorium

Thorium ElementIt is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately hard, malleable, and has a high melting point.
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90.

Names and Identifiers

Chemical Formula:Th
CAS:7440-29-1
Molecular Weight:232.03800 g/mol
EC Number :231-139-7
MDL Number:n/a
Color:silvery-white
Other Names:n/a
PubChem CID:23960
IUPAC Name:Thorium
Inchl:InChI=1S/Th
InChI Key:ZSLUVFAKFWKJRC-UHFFFAOYSA-N
Canonical SMILES:[Th]
ICSC Number:0337

Physical & Chemical Properties

Phase:Solid
Density:11.7 g/cm³
Boiling Point:5061 K ​(4788 °C, ​8650 °F)
Melting Point:2023 K ​(1750 °C, ​3182 °F)
Molecular Formula:Th
Flash Point:n/a
Exact Mass:232.03800
Symbol:Globally Harmonized System of ClassificationGlobally Harmonized System of ClassificationGlobally Harmonized System of ClassificationGlobally Harmonized System of Classification
Signal Word:Danger
Hazard Statements:H272-H301-H373-H315-H319-H335
Precautionary Statements:P210
Hazard Codes:n/a
Risk Phrases:n/a
Safety Phrases:n/a
RIDADR:n/a
WGK Germany:3
RTECS:n/a
Packaging Group:n/a
Hazard Class:n/a

All but two elements up to bismuth (element 83) have an isotope that is practically stable for all purposes (“classically stable”), with the exceptions being technetium and promethium (elements 43 and 61).

Naturally occurring isotopes

IsotopeMass/DaNatural abundance (atom %)Nuclear spin (I)Magnetic moment (μ/μN)
232Th1000

Radiosotope data

IsotopeMass/DaHalf-lifeMode of decayNuclear spinNuclear magnetic moment
227Th227.02769918.72 dα to 223Ra3/2
228Th228.0287311.913 yα to 224Ra; 20O0
229Th229.0317547900 yα to 225Ra5/20.46
230Th230.03312675400 yα to 226Ra; SF0
231Th231.0362961.063 dα to 227Ra; β to 231Pa5/2
232Th232.0380508 (23)1.4 x 1010 yα to 228Ra; SF0
233Th233.04157622.3 mβ to 233Pa1/2
234Th234.03659624.10 dβ to 234Pa0

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