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Thorium - Th General Information Discovery Thorium was discovered by J.J. Berzelius in 1815 in Stockholm, Sweden. Appearance Pure thorium is a radioactive silvery-white metal which retains its lustre for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming first grey and then black. Source Thorium is found in large deposits in the USA and elsewhere, but these have not been exploited as a source of the element. Several methods are used to produce the metal, such as reducing thorium oxide with calcium and by the electrolysis of anhydrous thorium chloride. Uses The principal use of thorium is in the Welsbach mantle, which consists of thorium oxide amongst other compounds. This type of mantle glows with a dazzling flame when heated by gas, so is used in portable gas lights. Thorium is also an important alloying agent in magnesium, as it imparts greater strength and creep resistance at high temperatures. Thorium can be used as a source of nuclear power. It is about three times as abundant as uranium and about as abundant as lead, and there is probably more energy available from thorium than both uranium and fossil fuels. However, although work has been done in developing thorium cycle convertor-reactor systems, it will be many years before such a system is operative - if at all. Biological Role Thorium has no known biological role. It is toxic due to its radioactivity. General Information Pure thorium is soft and very ductile, and has one of the highest melting points of all elements. It is slowly attacked by water and acids. Powdered thorium metal is often pyrophoric. Thorium turnings ignite when heated in air and burn with a brilliant white light. |
| Physical Information | |||
| Atomic Number | 90 | ||
| Relative Atomic Mass (12C=12.000) | 232.04 | ||
| Melting Point/K | 2023 | ||
| Boiling Point/K | 5060 | ||
| Density/kg m-3 | 11720 (293K) | ||
| Ground State Electron Configuration | [Rn]6d27s2 |
| Key Isotopes | ||||||
| nuclide | 228Th | 229Th | 230Th | 231Th | 232Th | |
| atomic mass | 228.03 | 229.03 | 230.03 | 231.03 | 232.04 | |
| natural abundance | trace | 0% | trace | trace | 100% | |
| half-life | 1.9 yrs | 7340 yrs | 8x104 yrs | 25.5 h | 1.41x1010 yrs | |
| nuclide | 234Th | |||||
| atomic mass | 234.04 | |||||
| natural abundance | trace | |||||
| half-life | 24.1 days | |||||
| Other Information | ||
| Enthalpy of Fusion/kJ mol-1 | 19.2 | |
| Enthalpy of Vaporisation/kJ mol-1 | 513.7 | |
| Oxidation States | ||
| main | Th+4 | |
| others | Th+2, Th+3 | |
| Ionisation Energies/kJ mol-1 | ||
| M - M+ | 587 | |
| M+ - M2+ | 1110 | |
| M2+ - M3+ | 1978 | |
| M3+ - M4+ | 2780 | |
| M4+ - M5+ | ||
| M5+ - M6+ | ||
| M6+ - M7+ | ||
| M7+ - M8+ | ||
| M8+ - M9+ | ||
| M9+ - M10+ | ||
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