Thorium
actinideProperties
| Property | Value |
|---|---|
| Atomic Mass | 232.04 amu |
| Category | actinide |
| Period | 7 |
| Electron Configuration | [Rn] 6d2 7s2 |
| Electronegativity | 1.3 (Pauling) |
| Oxidation States | 4 |
| Melting Point | 2023 K (1749.8 °C) |
| Boiling Point | 5061 K (4787.9 °C) |
| Density | 11.72 g/cm³ |
| Discovered By | Jons Jakob Berzelius (1829) |
About Thorium
Thorium occurs as a single primordial isotope, ²³²Th, with a 14.05-billion-year α-half-life — roughly the age of the universe — which makes it only mildly radioactive and explains why it sits in monazite sands at percent-level concentrations on beaches in Kerala and Brazil. It's a fertile, not fissile, fuel: ²³²Th captures a thermal neutron, β-decays through ²³³Pa, and ends up as ²³³U, which is fissile and the actual energy source in a thorium cycle. Oak Ridge's molten-salt reactor experiment (1965–69) ran on a FLiBe-dissolved uranium fluoride and demonstrated the chemistry; India's three-stage program is built around eventually breeding ²³³U from its monazite reserves. Outside reactor work, ThO₂ has the highest melting point of any oxide (3,350 °C), which is what made it useful in Welsbach gas mantles for a century and what still puts it into thoriated tungsten TIG electrodes (about 2% ThO₂) for steady arc starts in DC welding.
Fun Fact
Thorium is so abundant and energy-dense that the thorium contained in the average handful of beach sand could theoretically generate as much energy as 35 liters of oil in a thorium reactor.
Common Uses
- ²³²Th fertile feedstock in molten-salt and CANDU thorium fuel cycles
- ThO₂ refractory crucibles and high-temperature ceramic linings
- Welsbach gas mantles emitting bright incandescent light when heated
- Mg-Th alloys (HK31, HM21) for high-temperature aerospace castings
- 2% thoriated tungsten electrodes for stable DC TIG arc starts
- Th-bearing optical glass with high refractive index for camera lenses