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Offline Chemistry4me

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Name a chemical and its origin or where it comes from?
« Reply #125 on: 25/01/2009 01:07:23 »
Holmium, silver-coloured metallic element. Holmium is one of the most paramagnetic substances known. The element has few practical applications, though it has been used in some electronic devices and as a catalyst in industrial chemical reactions. Holmium is one of the least abundant of the rare earth metals, ranking 55th in order of abundance of the elements in the Earth's crust. Holmium occurs in gadolinite and other minerals containing rare earths. Holmium oxide, Ho2O3, a greyish-white powder, and a few salts, such as the sulphate, have been prepared.
 

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« Reply #126 on: 26/01/2009 00:22:20 »
Erbium, metallic element. The Swedish chemist Carl Gustav Mosander discovered erbium in 1843. Erbium occurs mostly in the same minerals and in the same areas as dysprosium. One of the rare earth elements, erbium is 43rd in abundance among the elements of the Earth's crust. The atomic weight of erbium is 167.26. The element melts at about 1530°C , boils at about 2870°C , and has a relative density of 9.1. Metallic erbium has a bright silvery lustre. Erbium oxide, Er2O3, is a rose-red compound slowly soluble in many mineral acids, forming a series of rose-coloured salts, solutions of which have a sweet, astringent taste. Erbium is used in experimental optical amplifiers that amplify light signals sent along fibre-optic cables
 

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« Reply #127 on: 26/01/2009 00:24:21 »
Thulium, silver-grey metallic element that is the rarest of the rare earth elements. Thulium is in the lanthanide series of the periodic table the atomic number of thulium is 69. Thulim was discovered in 1879 by the Swedish chemist Per Teodor Cleve. Thulium ranks 61st in abundance among the elements in the crust of the Earth and is found in small quantities in such rare earth minerals as euxenite, gadolinite, and blomstrandine. The metal can be isolated by reduction of its oxide, Tm2O3, and is soft, malleable, and ductile. Thulium had little practical application until the development in the 1950s of a small, portable X-ray machine that utilizes artificially radioactive thulium as its X-ray source. Thulium melts at about 1545°C, boils at about 1950°C, and has a relative density of 9.34.
 

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« Reply #128 on: 26/01/2009 21:44:09 »
Ytterbium, soft, malleable, ductile metallic element that has a bright, silvery lustre. Ytterbium is one of the rare earth elements in the lanthanide series of the periodic table. Ytterbium is reasonably stable but reacts slowly with water to liberate hydrogen. Ytterbium occurs in combination with such minerals as xenotime, euxenite, monazite, and gadolinite. It ranks about 44th in natural abundance among the elements in the Earth's crust. Ytterbium has potential applications in alloys, electronics, and magnetic materials.
 

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« Reply #129 on: 26/01/2009 21:46:32 »
Lutetium, silvery-white metallic element with an atomic number of 71. Lutetium was discovered independently by two investigators, the French chemist Georges Urbain in 1907 and the Austrian chemist Carl Auer von Welsbach about the same time. It was named by Urbain, who derived the word from Lutetia, the ancient name of Paris. Lutetium occurs in various rare earth minerals, usually associated with yttrium. It was the rarest of the rare earth elements when classified in that group and it ranks 59th in order of abundance of the elements in the Earth's crust. Several trivalent salts are known. A natural radioactive isotope of lutetium that has a half-life of about 30 billion years is used in determining the age of meteorites in relation to the age of the Earth. Lutetium melts at about 1665°C, boils at about 3400°C and has a relative density of 9.84.
 

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« Reply #130 on: 27/01/2009 21:49:56 »
Hafnium, metallic element that closely resembles zirconium. Hafnium is one of the transition elements of the periodic table. On the basis of a prediction by the Danish physicist Niels Bohr that element 72 would resemble zirconium in structure, they looked for the element in zirconium ores. Hafnium is found in nearly all ores of zirconium and is 45th in order of abundance of the elements in the crust of the Earth. It resembles zirconium so closely in chemical properties and crystal structure that separation of the two elements is extremely difficult. Separation is accomplished most efficiently by means of the ion-exchange technique. Hafnium is used in the manufacture of tungsten filaments. Because of its resistance to high temperatures, it is used with zirconium as a structural material in nuclear power plants.
 

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« Reply #131 on: 27/01/2009 21:51:42 »
Tantalum, white, ductile, malleable metallic element. Tantalum is one of the transition elements of the periodic table. Tantalum belongs to the group of metals that includes vanadium and niobium. It occurs mainly in the mineral tantalite, FeTa2O6. Tantalum ranks about 53rd among the elements in natural abundance in the Earth's crust. Principal deposits of the metal occur in Australia and Scandinavia. Most tantalum minerals contain some niobium metal, which is separated by solvent extraction or selective-crystallization procedures. Commercially, tantalum is prepared by the electrolysis of fused potassium tantalifluoride or of tantalum compounds dissolved in dilute sulphuric acid. Because it is more resistant than platinum to many corrosive agents, tantalum has largely replaced platinum in standard weights and in laboratory ware. The largest use of tantalum is for capacitors in electronic circuits and rectifiers in low-voltage circuits, such as railway-signalling systems. Because of its resistance to attack by acids of the human body and its compatibility with body tissue, it is used to pin together broken bones. Tantalum is also used in surgical and dental instruments and in chemical heat exchangers. The oxide is an ingredient in special optical glass for aerial camera lenses.
 

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« Reply #132 on: 28/01/2009 22:53:27 »
Tungsten, symbol W (from the earlier name, wolfram), metallic element that has the highest melting point of any metal. Tungsten is one of the transition elements of the periodic table. Pure tungsten is silver-white in colour and is ductile; the more easily obtained impure form is steel-grey and is hard and brittle. Tungsten is insoluble in hot and cold water and in alcohol, slightly soluble in ammonia and nitric acid, and soluble in hot, concentrated potassium hydroxide. Tungsten ranks 57th in abundance among the elements in the crust of the Earth. It is never found free in nature, but occurs in combination with other metals, notably in the minerals scheelite and wolframite, which are the important tungsten ores. Mines in South Korea, Portugal, Austria, and Australia produce more than half of the world's supply of these ores. To separate the element from its ore, the ore is first fused with sodium carbonate to give sodium tungstate, Na2WO4. The soluble sodium tungstate is then extracted with hot water and treated with hydrochloric acid to yield tungstic acid, H2WO4. The latter compound is washed and dried to produce the oxide WO3, which is reduced by hydrogen in an electric furnace. The resulting fine powder is reheated in moulds in an atmosphere of hydrogen and pressed into bars, which are hammered and rolled at high temperature to compact them and make them ductile. The principal uses of tungsten are as filaments in incandescent lamps, as wires in electric furnaces, and in the production of hard, tenacious alloys of steel. It is used also in the manufacture of spark plugs, electrical contact points, and cutting tools, and as a target in X-ray tubes.
 

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« Reply #133 on: 28/01/2009 22:54:18 »
Rhenium, rare, silvery-white, metallic element. Rhenium is one of the transition elements of the periodic table. The existence of rhenium and the similarity of its chemical properties to those of the element manganese were predicted in 1871 by the Russian chemist Dmitry Ivanovich Mendeleyev, who named it dvi-manganese. Rhenium metal is very hard; with the exception of tungsten, it is the least fusible of all common metals. Overall, it ranks about 79th in natural abundance among elements in crustal rocks. Rhenium is used in electrical filaments, welding rods, thermocouples, cryogenic magnets, and photographic flashbulb filaments; it is also used as a catalyst.
 

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« Reply #134 on: 29/01/2009 21:56:04 »
Osmium, bluish-white, brittle metallic element that has a density second only to iridium (although uncertainty has been expressed as to this and claims have been made for osmium having the highest relative density). The element is one of the transition elements of the periodic table. Osmium is not attacked by ordinary acids, but dissolves in aqua regia or fuming nitric acid. The metal occurs naturally in platinum ores and as an alloy, osmiridium, with iridium. Osmium ranks about 74th in natural abundance among the elements in crustal rock. The chief use of the metal is in the alloy osmiridium. Alloyed with platinum, it is used for standard weights and measures.
 

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« Reply #135 on: 29/01/2009 21:57:19 »
Iridium, white, brittle, extremely hard, metallic element. Iridium is extremely inert chemically, resisting even the action of aqua regia. In its chemical compounds it forms tetravalent and trivalent salts. It is an extremely rare metal, ranking 77th in order of abundance of the elements in the crust of the Earth. Iridium is found in alluvial deposits alloyed with platinum as platiniridium and with osmium as osmiridium. Iridium is used chiefly as an alloying material for platinum; the alloy, which contains about 10 per cent iridium, is much harder than pure platinum. Platinum-iridium alloys containing larger percentages of iridium are used in making precision instruments, surgical tools, pen points, and standard weights and lengths. Iridium was discovered by the British chemist Smithson Tennant in 1804 and was named after the iridescent nature of some of its compounds.
 

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« Reply #136 on: 30/01/2009 21:32:14 »
Platinum, relatively rare, chemically inert metallic element that is more valuable than gold. The element is one of the transition elements in group 10 of the periodic table. Platinum is a greyish-white metal with a hardness of 4.3. It has a high fusing point, is malleable and ductile, expands slightly upon heating, and has high electrical resistance. Chemically the metal is relatively inert and resists attack by air, water, single acids, and ordinary reagents. It dissolves slowly in aqua regia, forming chloroplatinic acid (H2PtCl6); is attacked by halogens; and combines upon ignition with sodium hydroxide, sodium nitrate, or sodium cyanide. Platinum ranks about 72nd in natural abundance among the elements in crustal rock. Except for the mineral sperrylite, which is platinum arsenide and is found only sparingly in a few localities, platinum occurs in the metallic state, often alloyed with other platinum metals. Nuggets of the metal weighing up to 9.5 kg have been found. Because of its chemical inertness and high fusing point, platinum is valuable for laboratory apparatus, such as crucibles, tongs, funnels, combustion boats, and evaporating dishes. Small amounts of iridium are usually added to increase its hardness and durability. Platinum is also used for contact points in electrical apparatus and in instruments used for measuring high temperatures. Finely divided platinum in the form of platinum sponge or platinum black is used extensively as a catalyst in the chemical industry. A considerable amount of platinum goes into jewellery, in which it is often alloyed with gold. It is also used for dental fillings.

 

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« Reply #137 on: 30/01/2009 21:35:14 »
Gold, Au, (from Latin aurum, “gold”), soft, dense, bright yellow metallic element. Pure gold is the most malleable and ductile of all the metals. It can easily be beaten or hammered to a thickness of 0.000013 cm, and 29 g could be drawn into a wire 100 km long. It is one of the softest metals (hardness, 2.5 to 3) and is a good conductor of heat and electricity. Finely divided gold, like other metallic powders, is black; colloidally suspended gold ranges in colour from ruby red to purple. Gold is extremely inactive. It is unaffected by air, heat, moisture, and most solvents. It will, however, dissolve in aqueous mixtures containing various halogens such as chlorides, bromides, or some iodides. It will also dissolve in some oxidizing mixtures, such as cyanide ion with oxygen, and in aqua regia, a mixture of hydrochloric and nitric acids. Gold is found in nature in quartz veins or seams, nuggets, flakes, and secondary alluvial deposits as a free metal or in a combined state. There are several chemical and physical processes that may cause these formations, and it is also likely that colonies of soil bacteria and fungi play a part in gold agglomerations. Gold is widely distributed although it is rare, being 75th in order of abundance of the elements in the crust of the Earth. It is almost always associated with varying amounts of silver; the naturally occurring gold-silver alloy is called electrum. Gold occurs, in chemical combination with tellurium, in the minerals calaverite and sylvanite along with silver, and in the mineral nagyagite along with lead, antimony, and sulphur. It occurs with mercury as gold amalgam. It is generally present to a small extent in iron pyrites; galena, the lead sulphide ore that usually contains silver, sometimes also contains appreciable amounts of gold. Gold also occurs in sea water to the extent of 5 to 250 parts by weight to 100 million parts of water. Although the quantity of gold present in sea water is more than 9 billion tonnes, the cost of recovering the gold would be far greater than the value of the gold that could thus be recovered. The major portion of the gold produced is used in coinage and jewellery. For these purposes it is alloyed with other metals to give it the necessary hardness. The gold content in alloys is expressed in carats. Coinage gold is composed of 90 parts gold to 10 parts silver. Green gold used in jewellery contains copper and silver; white gold contains zinc and nickel, or platinum metals. Gold is also used in dentistry. Radioisotopes of gold are used in biological research and in the treatment of cancer.
 

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« Reply #138 on: 31/01/2009 21:44:01 »
Mercury, (Latin, hydrargyrum, “liquid silver”), metallic element that is a free-flowing liquid at room temperature. Mercury, once known as liquid silver and as quicksilver, was studied in alchemy. At ordinary temperatures mercury is a shining, mobile liquid, silvery-white in colour. Slightly volatile at room temperature, mercury becomes solid when subjected to a pressure of 7,640 atmospheres (5.8 million torrs), and this pressure is used as a standard in measuring extremely high pressures. The metal dissolves in nitric or concentrated sulphuric acid but is resistant to alkalis. Mercury is acutely hazardous as a vapour and in the form of its water-soluble salts, which corrode membranes of the body. Chronic mercury poisoning, which occurs when small amounts of the metal or its fat-soluble salts, particularly methylmercury, are repeatedly ingested over long periods of time, causes irreversible brain, liver, and kidney damage. Because of increasing water pollution, significant quantities of mercury have been found in some species of fish, which has aroused concern regarding uncontrolled discharge of the metal into the environment.
 

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« Reply #139 on: 31/01/2009 21:46:13 »
Thallium (Greek, thallos, “young shoot”), soft, malleable metallic element that acquires a bluish-grey colour upon exposure to the atmosphere. Thallium forms a hydroxide in water, and is soluble in nitric acid and sulphuric acid. Thallous oxide, Tl2O, a black solid that, when molten, attacks glass and porcelain, is made by heating thallium in air at very high temperatures. Thallium has a high index of refraction and is therefore important in the manufacture of several types of optical glass. Thallium ranks 60th in abundance among the elements in the crust of the Earth and is a member of the aluminium family of metals. Thallium sulphate, which is odourless, tasteless, and very poisonous, is used to exterminate rodents and ants. Thallium-activated sodium iodide crystals mounted in photomultiplier tubes are used in some portable scintillation counters to detect gamma radiation. The abilities of thallium bromoiodide crystals to transmit infrared radiation and of thallium oxysulphide crystals to detect the same radiation have been employed extensively in military communication systems. Thallium alloyed with mercury forms a fluid metal that freezes at -60°C; it is used in low-temperature thermometers, relays, and switches. Thallium salts, which burn with a bright green flame, are used in rockets and flares.
 

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« Reply #140 on: 02/02/2009 00:33:34 »
Lead, symbol Pb (Latin, plumbum, a lead weight), dense, bluish-grey metallic element that was one of the first known metals. Metallic lead is a soft, malleable, ductile metal. When gently heated it can be forced through annular holes or dies. It has a low tensile strength and is a poor conductor of electricity. A freshly cut surface has a bright silvery lustre, which quickly turns to the dull, bluish-grey colour characteristic of the metal. Lead is used in enormous quantities in storage batteries and in sheathing electric cables. Large quantities are used in industry for lining pipes, tanks, and X-ray apparatus. Because of its high density and nuclear properties, lead is used extensively as protective shielding for radioactive material. Among numerous alloys containing a high percentage of lead are solder, type metal, and various bearing metals. A considerable amount of lead is consumed in the form of its compounds, particularly in paints and pigments. Lead is widely distributed all over the world in the form of its sulphide, the ore galena. Lead ranks about 36th in natural abundance among elements in the Earth's crust. Ores of secondary importance are cerussite and anglesite. The principal method of extracting lead from galena is to roast the ore—that is, convert it to the oxide, and reduce the oxide with coke in a blast furnace. Lead is also used in ceramic glazes and in making other pigments. In recent years, however, because of the dangers of lead poisoning, the use of lead-based paints for interior use has largely been discontinued. The so-called Dutch process is the oldest method still in use for making white lead. In this process earthenware pots containing lead gratings and ethanoic acid are wrapped in tanbark (small pieces of bark that are rich in tannin); the reaction of the fermenting tanbark and the ethanoic acid is allowed to process the lead over a period of 90 days. More rapid processes, such as electrolysis or forcing hot air and carbon dioxide through large rotating cylinders containing powdered lead and ethanoic acid, are now industrially important. Lead monoxide, or litharge (PbO), a yellow, crystalline powder formed by heating lead in air, is used in making flint glass, as a drier in oils and varnishes, and in the manufacture of insecticides. Red lead, or minium (Pb3O4), a scarlet, crystalline powder formed by oxidizing lead monoxide, is the pigment in paint used as a protective coating for structural ironwork and steelwork. Lead(II) ethanoate (Pb(C2 H3O2)2•3H2O), a white, crystalline substance called sugar of lead because of its sweet taste, is prepared commercially by dissolving litharge in ethanoic acid. It is used as a mordant in dyeing, as a paint and varnish drier, and in making other lead compounds.
 

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« Reply #141 on: 02/02/2009 00:35:00 »
Bismuth, rare metallic element that has a pinkish tinge. Ranking about 73rd in natural abundance among the elements in the Earth's crust, it is about as rare as silver. Most industrial bismuth is obtained as a by-product. There are several nitrates, notably bismuth nitrate, Bi(NO3)3, or bismuth trinitrate; and bismuth nitrate pentahydrate, Bi(NO3)3•5H2O. The latter form decomposes into bismuth nitrate. Bismuth nitrate is also known as bismuth oxynitrate, bismuthyl nitrate, pearl white, and Spanish white, and may be used in medicine and cosmetics. Bismuth expands on solidifying; this unusual property makes it useful for castings. Some of its alloys have unusually low melting points. One of the most strongly diamagnetic (difficult to magnetize) of all substances, bismuth tends to turn at right angles to a magnetic field. It is a poor conductor of heat and electricity, and its electrical resistance is further increased in a magnetic field; because of this property, it is used in instruments for measuring the strength of such fields. Bismuth is opaque to X-rays and can be used in fluoroscopy.
 

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« Reply #142 on: 02/02/2009 20:19:31 »
Polonium, rare, radioactive metallic element. Polonium is one of the elements in the uranium-radium series of radioactive decay, the first member of which is uranium-238. Polonium occurs in radium-containing ores and is found in isotopic forms with mass numbers ranging from 192 to 218. Polonium 210 (also called radium-F), the only naturally occurring isotope, has a half-life of 138 days. Because most polonium isotopes disintegrate by emitting alpha particles, the element is a good source of pure alpha radiation. It is also used in nuclear research with elements such as beryllium that emit neutrons when bombarded by alpha particles. In printing and photography equipment, polonium is used in devices that ionize the air to eliminate accumulation of electrostatic charges.
 

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« Reply #143 on: 02/02/2009 20:20:33 »
Astatine (Greek, astatos, “unstable”), symbol At, radioactive element that is the heaviest of the halogens. The first isotope synthesized had an atomic weight of 211 and a half-life of 7.2 hours. Subsequently, astatine-210 was produced and found to have a half-life of about 8.3 hours. Isotopes of astatine with mass numbers from 200 to 219 have been catalogued, some with half-lives measured in fractions of a second. Astatine is the halogen that behaves most like a metal and that has only radioactive isotopes. It is highly carcinogenic.
 

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« Reply #144 on: 03/02/2009 21:12:35 »
Radon, colourless, odourless radioactive gaseous element that is the heaviest of the noble gases of the periodic table. Radon-222, which is the most abundant isotope of radon, is formed by the radioactive decay of radium-226. Radon-222 has a half-life of 3.8 days, decaying by the emission of alpha particles into an isotope of the element polonium. Small quantities, formed by the decay of uranium minerals, are found in rock and soil, and radon makes up most normal background radioactivity. Concentrations of the gas, however, are believed to pose a serious health hazard. Radon-222 is obtained by passing air through a solution of radium salt and collecting the air and the radon gas that was present in the solution. This isotope can be used in the treatment of malignant tumours. The gas is enclosed in a tube, usually made of glass or gold, called a radon seed, which is inserted in the diseased tissue. Nineteen other isotopes of radon are known. The isotope of mass 220, discovered in 1899 by Ernest Rutherford, is a product of the radioactive decay of an isotope of thorium and is known as thoron; it has a half-life of 55 seconds. The isotope of mass 219, with a half-life of 4 seconds, is a product of the radioactive decay of an isotope of actinium and is known as actinon.
 

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« Reply #145 on: 03/02/2009 21:13:31 »
Francium, symbol Fr, radioactive metallic element that closely resembles caesium in chemical properties. Francium is produced when the radioactive element actinium disintegrates. Francium is naturally radioactive; its longest-lived isotope, francium-223, or actinium-K, has a half-life of 22 minutes. It emits a beta particle of 1,100,000 electronvolts (eV) energy. Isotopes ranging in mass number from 204 to 224 are known. Francium is the heaviest of the alkali metals; it is the most electropositive element. All its isotopes are radioactive and short-lived.
 

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« Reply #146 on: 04/02/2009 21:54:36 »
Radium (Latin, radius, “ray”), chemically reactive, silvery-white, radioactive metallic element. The element oxidizes immediately upon exposure to air. The element is used and handled in the form of radium chloride or radium bromide and practically never in the metallic state. Radium is formed by the radioactive disintegration of uranium and is consequently found in all uranium ores. Radium is present in uranium ore to the extent of one part of radium to three million of uranium. Radiation from radium has a harmful effect upon living cells, and radium burns are caused by overexposure to the rays. Cancerous cells, however, are often more sensitive to radiation than normal cells, and such cells may be killed without seriously injuring healthy tissue by controlling the intensity and direction of the radiation. Radium is now used in the treatment of only a few kinds of cancer; radium chloride or radium bromide is enclosed in a sealed tube and inserted in the diseased tissue. When a radium salt is mixed with a substance such as zinc sulphide, the substance is caused to luminesce by the bombardment of the alpha rays emitted by the radium. Small amounts of radium were once used in the production of luminous paint, which was applied to clock dials, doorknobs, and other objects, to make them glow in the dark.
 

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« Reply #147 on: 04/02/2009 21:56:00 »
Actinium, radioactive metallic element found in all uranium ores. The element is found in uranium ores to the extent of 2 parts to every 10 billion parts of uranium. Two naturally occurring isotopes of actinium are known. Actinium-227 is a member of the actinium series, called the actinium decay series, resulting from the radioactive decay of uranium-235. It has a half-life of 21.8 years. The other isotope, actinium-228, is a member of the thorium series resulting from the decay of thorium-232. This isotope, known also as mesothorium-2, has a half-life of 6.13 hours. Isotopes ranging in mass number from 209 to 234 are known. Actinium melts at about 1050° C, boils at about 3200° C, and has a relative density of about 10.
 

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« Reply #148 on: 05/02/2009 21:22:50 »
Thorium, radioactive metallic element with an atomic number of 90. The element is dark in colour, slowly attacked by water, soluble in hydrochloric and sulphuric acids, and slightly soluble in nitric acid. It ranks 39th in abundance among the elements in the crust of the Earth. Small quantities of thorium are found in thorite, or thorium silicate; in orangite, a variety of thorite; and in thorianite, a radioactive mineral composed of thorium oxide and uranium. The larger deposits occur mainly as thorium oxide, ThO2, in the monazite sands of India and Brazil. Thorium-232 occurs naturally, has a half-life of about 14 billion years, and is the first member of the radioactive-decay series, ending with the stable lead isotope lead-208. Thorium is currently important as a potential atomic-fuel source, because bombardment of thorium-232 by slow neutrons yields the fissile isotope uranium-233. This process is comparable to the process by which fast neutrons “breed” fissile plutonium-239 from non-fissile uranium-238. The thorium-uranium fuel cycle is being studied by scientists as an alternative to the uranium-plutonium fuel cycle. Two types of reactors, the molten-salt breeder reactor and the light-water breeder reactor, are being considered. Thorium metal is used in magnesium alloys and as a stabilizing component of electronic tubes. Thorium oxide is used in light filaments and electrodes and also as a catalyst.
 

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« Reply #149 on: 06/02/2009 22:29:47 »
Protactinium, formerly protoactinium, symbol Pa, radioactive metallic element with an atomic number of 91. It was discovered in 1918 by the Austrian-Swedish physicist Lise Meitner and the German physical chemist Otto Hahn. Protactinium is a member of the uranium-actinium radioactive-decay series and is found in uranium ores. Isotopes of protactinium ranging in mass number from 215 to 238 are known. Protactinium-233 has a half-life of 27 days. Protactinium-231, the most stable isotope, has a half-life of more than 32,000 years; by emission of an alpha particle it decays to actinium. Protactinium melts at about 1550° C, boils at about 4230° C, and has a relative density of about 15.37.
 

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