[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

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.

[Chemistry4me]

Uranium, chemically reactive radioactive metallic element that is the main fuel used in nuclear reactors. Uranium has three crystalline forms, of which the one that forms at about 770° C  is malleable and ductile. Uranium is soluble in hydrochloric and nitric acids, and it is insoluble in alkalis. Uranium displaces hydrogen from mineral acids and from the salt solutions of such metals as mercury, silver, copper, tin, platinum, and gold. When finally divided, it burns readily in air at 150°to 175°C. At 1000° C , uranium combines with nitrogen to form a yellow nitride. Uranium never occurs naturally in the free state but is found as an oxide or complex salt in minerals such as pitchblende and carnotite. It has an average concentration in the crust of the Earth of about 2 parts per million, and, among the elements, ranks about 48th in natural abundance in crustal rocks. Pure uranium consists of more than 99 per cent of the isotope uranium-238, less than 1 per cent of the fissile isotope uranium-235, and a trace of uranium-234, formed by radioactive decay of uranium-238. In the classical procedure for extracting uranium, pitchblende is broken up and mixed with sulphuric and nitric acids.
Uranium dissolves to form uranyl sulphate, UO2SO4; radium and other metals in the pitchblende ore are precipitated as sulphates. With the addition of sodium hydroxide, uranium is precipitated as sodium diuranate, Na2U2O7•6H2O, known also as the yellow oxide of uranium.  After the discovery of nuclear fission, uranium became a strategic metal, and its uses were at first restricted mainly to the production of nuclear weapons. In 1954 the United States government relaxed controls to permit leasing of uranium enriched in the isotope uranium-235 to various private and foreign agencies for the development of nuclear power. The potential of uranium as a vast source of industrial power became apparent with the launching in 1954 of the first nuclear-powered submarine, the USS Nautilus. Conventional power plants producing 60,000 kW of electricity consume about 18 million kg of coal per month. A 60,000 kW nuclear power plant requires only 7kg of uranium-235 per month.

[Chemistry4me]

Neptunium, radioactive metallic element with an atomic number of 93. Neptunium is one of the transuranic elements in the actinide series of the periodic table. Neptunium is a silvery metal that exists in at least three different crystalline forms, hence the variations in relative density (from 18 to 20). The element is reactive and shows four ionic oxidation states. It is produced by bombardment of uranium-238 with neutrons; the resultant uranium-239 decays radioactively by emitting a beta particle to form neptunium-239. The neptunium isotope in turn emits a beta particle, forming the important isotope plutonium-239, one of the materials of which atomic bombs are made. Isotopes of neptunium with mass numbers from 228 to 242 are known. The most stable, neptunium-237, has a half-life of 2.14 million years. Neptunium occurs in nature in trace amounts in uranium ores but is produced artificially. It is used as a component in neutron detection devices.

[Chemistry4me]

Plutonium, radioactive metallic element that is used in nuclear reactors and nuclear weapons. Trace amounts of the element have been found in uranium ores, but plutonium is prepared in relatively large quantities today in nuclear reactors. Chemically, plutonium is reactive, its properties resembling those of the rare earth elements. The silvery metal, which becomes slightly yellow through oxidation caused by exposure to air, exists in six crystalline forms and has four different oxidation states. The metal gives off heat because of its radioactivity; 15 different isotopes of plutonium, ranging in mass number from 232 to 246, are known. The most important isotope, plutonium-239, has a half-life of 24,360 years, and is produced by   bombarding uranium-238 with slow neutrons. This forms neptunium-239, which in turn emits a beta particle and forms plutonium-239. Plutonium is the most economically important of the transuranic elements because plutonium-239 readily undergoes fission and can be both used and produced in quantity in nuclear reactors. It is also used in making nuclear weapons. It is an extremely hazardous poison due to its high radioactivity. Plutonium-238 has been used to power equipment on the Moon by means of the heat it emits.

[Chemistry4me]

Americium, symbol Am, artificially created, malleable, radioactive metallic element somewhat similar to lead. It was discovered in 1944 and 1945 by the American physicist Glenn Seaborg and his associates at the University of Chicago. They synthesized the americium isotope of mass number 241 by bombarding plutonium 239 with neutrons. Americium isotopes with mass numbers 237 to 247 have been formed; they are all radioactive, with half-lives of from 0.9 minute (americium 232) to about 7,400 years (americium 243). Americium 243 is used as target material in nuclear reactors or particle accelerators for the production of even heavier synthetic elements.

[Chemistry4me]

Curium, symbol Cm, radioactive element with an atomic number of 96. The element is made by bombarding the synthetic element plutonium with accelerated particles. Curium is a heavy metal similar in properties to uranium, plutonium, and americium. Thirteen isotopes, ranging in mass number from 238 to 250, have been discovered; the most stable isotope of curium has an atomic weight of 247. Most isotopes of curium decay by emission of alpha particles; because alpha radiation is not highly penetrating, curium isotopes, particularly curium-244, can be used without heavy shielding as sources of thermoelectric power for use in satellites and crewless space probes. In another application, curium-242 carried to the Moon by the Surveyor 5, 6, and 7 spacecraft was used to bombard the soil of the Moon with alpha particles. Measurements of the energy of alpha radiation backscattered from the soil revealed the kind and quantity of chemical elements in the soil.

[Chemistry4me]

Berkelium, artificially created radioactive metallic element. An isotope of mass number 243 with a half-life of 4.6 hours was produced by bombarding americium-241 with alpha particles accelerated in a particle accelerator called a cyclotron. Nine more isotopes were subsequently produced, bringing the total range of mass numbers from 242 to 251. The most stable isotope of berkelium, with a half-life of about 1,400 years, has a mass number of 247.

[Chemistry4me]

Californium, symbol Cf, artificially created radioactive element with an atomic number of 98. The scientists created californium-245 by bombarding curium-242 with alpha particles in a 152-cm cyclotron, a type of particle accelerator. Californium-245 rapidly decays, with the emission of alpha particles, having a half-life of 44 minutes. Isotopes, with mass numbers from 240 to 255, were subsequently prepared. Californium-249 is the result of beta decay of berkelium-249. The heavier californium isotopes are produced by neutron bombardment of berkelium-249, which increases the number of protons in the nucleus. Californium-252, with a half-life of 2.6 years, has an unusually high rate of spontaneous fission, with an abundant emission of neutrons. It has practical application as a high-intensity neutron source in electronic systems and in medical research. The most stable isotope of californium, with a half-life of about 900 years, has a mass number of 245.

[Chemistry4me]

Einsteinium, symbol Es, artificially created radioactive element with an atomic number of 99. Isotopes of einsteinium with mass numbers ranging from 243 to 256 are known. The element was discovered in 1952 in the debris produced by a thermonuclear explosion. The isotope first identified had an atomic mass of 253 and a half-life of 20 days. Subsequently, the most long-lived of all the known einsteinium isotopes, einsteinium-254, was prepared by irradiating plutonium in a nuclear reactor; however, only small amounts are now being produced.

[Chemistry4me]

Fermium, artificially created radioactive element with an atomic number of 100. Subsequently fermium was prepared synthetically in a nuclear reactor by bombarding plutonium with neutrons and in a cyclotron by bombarding uranium-238 with nitrogen ions. Isotopes with mass numbers from 242 to 259 have been produced; fermium-257, the longest-lived of these isotopes, has a half-life of 80 days. The element was named fermium in 1955 in honour of the Italian-American nuclear physicist Enrico Fermi. Fermium does not have any industrial applications.

[aysha]

what is the role of solutions[solute+solvent in chemistry?