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Thorium
Thorium is a chemical element in the periodic General table that has the symbol Name, Symbol, Number Thorium, Th, 90 Th and atomic number 90. Chemical series Transition metals Group, Period, Block _ , 7 , f Density, Hardness 11724 kg/m3, 3.0 Appearance silvery white Atomic Properties Atomic weight 232.0381 amu uelmic radius (calc.) 180 (n/a) pm Covalent radius n/a pm van der Waals radius n/a pm Electron configuration [Rn]6d27s2 Notable Characteristics e- 's per energy level 2, 8,18,32,18,10, 2 Thorium is a naturally Oxidation states (Oxide) 4 (weak base) occurring, slightly Crystal structure Cubic face centered radioactive metal. When Physical Properties pure, thorium is a silvery white metal that State of matter solid (__) retains its lustre for Melting point 2028 K (3191 ¡F) several months. However, Boiling point 5061 K (8650 ¡F) when it is contaminated with the oxide, thorium Molar volume 19.80 ×10-3 m3/mol slowly tarnishes in air, Heat of vaporization 514.4 kJ/mol becoming grey and eventually black. Thorium Heat of fusion 16.1 kJ/mol oxide (ThO2), also called Vapor pressure n/a Pa at 2028 K thoria, has one of the Velocity of sound 2490 m/s at 293.15 K highest boiling points of all oxides (3300¡C). When Miscellaneous heated in air, thorium Electronegativity 1.3 (Pauling scale) metal turnings ignite and Specific heat capacity 120 J/(kg*K) burn brilliantly with a white light. Electrical conductivity 6.53 106/m ohm Thermal conductivity 54 W/(m*K) Applications 1st ionization potential 587 kJ/mol Applications of thorium: 2nd ionization potential 1110 kJ/mol * Mantles in portable 3rd ionization potential 1930 kJ/mol gas lights. These mantles glow with a 4th ionization potential 2780 kJ/mol dazzling light when Most Stable Isotopes heated in a gas flame. iso NA half-life DM DE MeV DP * As an alloying 228Th {syn.} 1.9116 years α 5.520 224Ra element in magnesium, imparting 229Th {syn.} 7340 years α 5.168 225Ra high strength and creep resistance at 230Th {syn.} 75380 years α 4.770 226Ra elevated 232Th 100 1.405 E10 years α 4.083 228Ra temperatures. * Thorium is used to SI units & STP are used except where noted. coat tungsten wire used in electronic equipment. * Thorium has been used in welding electrodes and heat-resistent ceramics. * The oxide is used to control the grain size of tungsten used for electric lamps. * The oxide is used for high-temperature laboratory crucibles. * Thorium oxide added to glass helps create glasses of a high refactive index and with low dispersion. Consequently, they find application in high quality lenses for cameras and scientific instruments. * Thorium oxide has been used as a catalyst: o In the conversion of ammonia to nitric acid. o In petroleum cracking. o In producing sulfuric acid. * Uranium-thorium age dating has been used to date hominid fossils. * As a fertile material for producing nuclear fuel. History Thorium was discovered in 1828 by the Swedish chemist Jšns Jacob Berzelius, who named it after Thor, the Norse god of war. The metal had virtually no uses until the invention of the lantern mantle in 1885. Biological Role This element has no known biological role. Occurrence Thorium is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium, and is about as common as lead. Soil commonly contains an average of around 6 parts per million (ppm) of thorium. Thorium occurs in several minerals, the most common being the rare earth-thorium-phosphate mineral, monazite, which contains up to about 12% thorium oxide. There are substantial deposits in several countries. Thorium-232 decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in its and in uranium decay chains. Most of these are short-lived and hence much more radioactive than Th-232, though on a mass basis they are negligible. Thorium as a nuclear fuel Thorium, as well as uranium, can be used as fuel in a nuclear reactor. Although not fissile itself, thorium-232 (Th-232) will absorb slow neutrons to produce uranium-233 (U-233), which is fissile. Hence, like uranium-238 (U-238), it is fertile. In one significant respect U-233 is better than uranium-235 and plutonium-239, because of its higher neutron yield per neutron absorbed. Given a start with some other fissile material (U-235 or Pu-239), a breeding cycle similar to but more efficient than that with U-238 and plutonium (in slow-neutron reactors) can be set up. The Th-232 absorbs a neutron to become Th-233 which normally decays to protactinium-233 and then U-233. The irradiated fuel can then be unloaded from the reactor, the U-233 separated from the thorium, and fed back into another reactor as part of a closed fuel cycle. Problems include the high cost of fuel fabrication due partly to the high radioactivity of U-233 which is always contaminated with traces of U-232; the similar problems in recycling thorium due to highly radioactive Th-228, some weapons proliferation risk of U-233; and the technical problems (not yet satisfactorily solved) in reprocessing. Much development work is still required before the thorium fuel cycle can be commercialised, and the effort required seems unlikely while (or where) abundant uranium is available. Nevertheless, the thorium fuel cycle, with its potential for breeding fuel without the need for fast neutron reactors, holds considerable potential long-term. Thorium is significantly more abundant than uranium, so it is a key factor in the sustainability of nuclear energy. India has particularly large reserves of thorium, and so have planned their nuclear power program to eventually use it exclusively, phasing out uranium as an input material. This ambitious plan uses both fast and thermal breeder reactors. Compounds Isotopes Naturally occurring thorium is composed of 1 isotope: 232-Th. 25 radioisotopes have been characterized with the most {abundant and/or stable} being 232-Th with a half-life of 14.05 billion years, 230-Th with a half-life of 75,380 years, 229-Th with a half-life of 7340 years, and 228-Th with a half-life of 1.92 years. All of the remaining radioactive isotopes have half-lifes that are less than 30 days and the majority of these have half lifes that are less than 10 minutes. This element also has 1 meta state. The isotopes of thorium range in atomic weight from 212 amu (212-Th) to 236 amu (236-Th). Precautions Powdered thorium metal is often pyrophoric and should be handled carefully. Thorium disintegrates with the eventual production of "thoron", an isotope of radon (220-Rn). Radon gas is a radiation hazard. Good ventilation of areas where thorium is stored or handled is therefore essential. Exposure to thorium in the air can lead to increased risk of cancers of the lung, pancreas and blood. Exposure to thorium internally leads to increased risk of liver diseases.
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