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Atomic symbol: Th |
Atomic number: 90 |
Atomic weight: 232.0381 |
Atomic volume: 19.9 cm3/mol |
Density: 11.7 g/cm3 |
Period Number: 7 |
Group number: none |
Group name: Rare Earth, Actinides |
Element classification: Metal |
Phase at room temperature: Solid |
Melting Point: 2023.2 K |
Boiling point: 5123 K |
Heat of fusion: 16.10 kJ/mol |
Heat of vaporization: 514.40 kJ/mol |
Ionization Energy: 6.08 eV |
1st ionization energy: 587 kJ/mole |
2nd ionization energy: 1110 kJ/mole |
3rd ionization energy: 1930 kJ/mole |
Electronegativity: 1.3 |
Electron affinity: kJ/mole |
Specific heat: 0.12 J/gK |
Heat atomization: 576 kJ/mole atoms |
Shells: 2,8,18,32,18,10,2 |
Electron Shell Configuration: [Rn] 6d2 7s2 |
Minimum oxidation number: 0 |
Maximum oxidation number: 4 |
Minimum common oxidation number: 0 |
Maximum common oxidation no: 4 |
Appearance & Characteristics |
Structure:: fcc: face-centered cubic |
Color: white |
Hardness: mohs |
Toxicity: ? |
Characteristics: Radioactive |
Uses: gas mantles (ThO2) |
Reaction with air: mild, w/ht ignites =>ThO2 |
Reaction with 6M HCl: mild |
Reaction with 15M HNO3: passivated |
Reaction with 6M NaOH: none |
Number of isotopes: 3 |
Oxide(s): ThO2 |
Hydride(s): ThH2 Th4H15 |
Chloride(s): ThCl4 |
Atomic Radius: 179 pm |
Ionic radius (1- ion): pm |
Ionic radius (1+ ion): pm |
Ionic radius (2- ion): pm |
Ionic radius (2+ ion): pm |
Ionic radius (3+ ion): pm |
Thermal conductivity: 54 J/m-sec-deg |
Electrical conductivity: 76.923 1/mohm-cm |
Polarizability: 32.1 A^3 |
Source: Monazite(phosphate),U extractn |
Relative abundance solar system: -1.475 log |
Abundance earth's crust: 1 log |
Estimated crustal abundance: 9.6 milligrams per kilogram |
Estimated oceanic abundance: 1×10-6 milligrams per liter |
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(Thor, Scandinavian god of war) Discovered by Berzelius in 1828. Much of the internal heat the earth produces has been attributed to thorium and uranium. Because of its atomic weight, valence, etc., it is now considered to be the second member of the actinide series of elements. |
Thorium occurs in thorite and in thorianite. Large deposits of thorium minerals have been reported in New England and elsewhere, but these have not yet been exploited. Thorium is now thought to be about three times as abundant as uranium and about as abundant as lead or molybdenum. Thorium is recovered commercially from the mineral monazite, which contains from 3 to 9% ThO2 along with rare-earth minerals. |
When pure, thorium is a silvery-white metal which is air-stable and retains its luster for several months. When contaminated with the oxide, thorium slowly tarnishes in air, becoming gray and finally black. The physical properties of thorium are greatly influenced by the degree of contamination with the oxide. The purest specimens often contain several tenths of a percent of the oxide. High-purity thorium has been made. Pure thorium is soft, very ductile, and can be cold-rolled, swaged, and drawn. Thorium is dimorphic, changing at 14000C from a cubic to a body-centered cubic structure. Thorium oxide has a melting point of 33000C, which is the highest of all oxides. Only a few elements, such as tungsten, and a few compounds, such as tantalum carbide, have higher melting points. Thorium is slowly attacked by water, but does not dissolve readily in most common acids, except hydrochloric. Powdered thorium metal is often pyrophoric and should be handled carefully. When heated in air, thorium turnings ignite and burn brilliantly with a white light. |
The metal is a source of nuclear power. There is probably more energy available for use from thorium in the minerals of the earth's crust than from both uranium and fossil fuels. Any sizable demand from thorium as a nuclear fuel is still several years in the future. Work has been done in developing thorium cycle converter-reactor systems. Several prototypes, including the HTGR (high-temperature gas-cooled reactor) and MSRE (molten salt converter reactor experiment), have operated. While the HTGR reactors are efficient, they are not expected to become important commercially for many years because of certain operating difficulties.
The principal use of thorium has been in the preparation of the Welsbach mantle, used for portable gas lights. These mantles, consisting of thorium oxide with about 1% cerium oxide and other ingredients, glow with a dazzling light when heated in a gas flame. Thorium is an important alloying element in magnesium, imparting high strength and creep resistance at elevated temperatures. Because thorium has a low work-function and high electron emission, it is used to coat tungsten wire used in electronic equipment. The oxide is also used to control the grain size of tungsten used for electric lamps; it is also used for high-temperature laboratory crucibles. Glasses containing thorium oxide have a high refractive index and low dispersion. Consequently, they find application in high quality lenses for cameras and scientific instruments. Thorium oxide has also found use as a catalyst in the conversion of ammonia to nitric acid, in petroleum cracking, and in producing sulfuric acid. |
Twenty five isotopes of thorium are known with atomic masses ranging from 212 to 236. All are unstable. 232Th occurs naturally and has a half-life of 1.4 x 1010 years. It is an alpha emitter. 232Th goes through six alpha and four beta decay steps before becoming the stable isotope 208Pb. 232Th is sufficiently radioactive to expose a photographic plate in a few hours. Thorium disintegrates with the production of "thoron" (220Rn), which is an alpha emitter and presents a radiation hazard. Good ventilation of areas where thorium is stored or handled is therefore essential. |
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