90
Th
Thorium
232
Thorium (Th)
ActinidePeriod 7f-block-blockRadioactive
Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that still occur naturally in large quantities as a primordial element (the other being uranium). It was discovered in 1828 by the Norwegian Reverend and amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius, who named it after Thor, the Norse god of thunder.
Latin name: Thorium
Atomic Number
90
Atomic Mass
232 g/mol
Phase (STP)
Solid
Electron Config.
[Rn] 6d² 7s²
General
SymbolTh
Atomic Number90
Atomic Mass232 g/mol
CategoryActinide
Period7
Blockf-block
Electron Configuration[Rn] 6d² 7s²
Valence Electrons4
Coloursilvery-white metallic
Appearancesilvery, often with black tarnish
CAS NumberCAS7440-29-1
Physical Properties
Phase (STP)Solid
Density11.72 g/cm³
Melting Point1749.85°C · 3181.73°F · 2023.00 K
Boiling Point4787.85°C · 8650.13°F · 5061.00 K
Atomic Properties
Atomic Radius237 pm
Electronegativity1.3 Pauling
Ionization Energy587 kJ/mol
Oxidation States+4, +3
Ion ChargeTh4+
Thermodynamic
Molar Heat26.23 J/(mol·K)
Crystal Structure
Crystal Structurebody-centered cubic
Nuclear & Hazards
RadioactiveYes
Half-life1.405×10^10 years (Th-232)
Abundance
In Universe0.000000000001%
In Earth's Crust0.0270%
Discovery & History
Discovery Year1829
Discovered ByJöns Jakob Berzelius
Country of DiscoverySweden
Isotopes of Thorium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Th-228 | — | 1.9116 years | α |
| Th-229 | — | 7340 years | α |
| Th-230 | — | 7.538 × 10⁴ years | α |
| Th-231 | — | 25.52 hours | β⁻ |
| Th-232 | 100% | 1.405 × 10¹⁰ years | α |
| Th-234 | — | 24.10 days | β⁻ |