CHEMISTRY : Metal Cation Identification

Information on LEAD

1. General Information


2. Occurence Uses and Properties


3. History of the Metal


4. Compounds
5. Back to Main Metal List

Lead has been mined and smelted for at least 8,000 years. This is confirmed by artifacts in various museums and by ancient histories and other writings, including the biblical Book of Exodus. Lead beads found in what is now Turkey have been dated to around 6500 BC, and the Egyptians are reported to have used lead along with gold, silver, and copper as early as 5000 BC. In pharaonic Egypt, lead was used to glaze pottery and make solder as well as for casting into ornamental objects. The British Museum holds a lead figure, found in the temple of Osiris in the ancient city of Abydos in western Anatolia, that dates from 3500 BC.

One of the most important historical appliCATions of lead was the water pipes of Rome. Lead pipes were fabriCATed in 3-metre (10-foot) lengths and in as many as 15 standard diameters. Many of these pipes, still in excellent condition, have been uncovered in modern-day Rome and England. The Roman word plumbum, denoting lead water spouts and connectors, is the origin of the English word plumbing and of the element's symbol, Pb.

Marcus Vitruvius Pollio, a 1st-century-BC Roman architect and engineer, warned about the use of lead pipe for conveying water, recommending that clay pipes be used instead. Vitruvius also referred in his writing to the poor colour of the workers in lead factories of that day, noting that the fumes from molten lead destroy the "vigour of the blood." On the other hand, there were many who believed lead to have favourable medical qualities. Pliny, a Roman scholar of the 1st century AD, wrote that lead could be used for the removal of scars, as a liniment, or as an ingredient in plasters for ulcers and the eyes, among other health appliCATions.

Many churches and major buildings constructed in the 15th and 16th centuries provide examples of lead employed as a roofing material and for water conveyance. Indeed, the stained-glass windows of many CAThedrals and castles of this period were made possible by the use of lead cames that held the glass elements together in a magnificent unity of colours and shapes.

In 1859 a French physicist, Gaston Planté, discovered that pairs of lead oxide and lead metal electrodes, when immersed in a sulfuric acid electrolyte, generated electrical energy and could subsequently be recharged. A series of further technical improvements by other investigators led to commercial production of lead-acid storage batteries by 1889. The huge growth of battery markets in the 20th century (eventually consuming about 75 percent of the world's lead production) largely paralleled the rise of the automobile, in which batteries found appliCATion for starting, lighting, and ignition. Another prominent lead product was tetraethyl lead, a gasoline additive invented in 1921 in the United States to solve "knocking" problems that had become commonplace with the development of high-compression engines operating at high temperatures. Soon after reaching its peak 50 years later, the use of this lead compound declined in the United States as the installation of CATalytic converters became mandatory on the exhaust systems of all American passenger cars.

Chemical compounds

Lead shows valences of +2 and +4 in its compounds. Among the many important lead compounds are the oxides: lead monoxide, or lead(II) oxide, PbO; lead dioxide, or lead(IV) oxide, PbO2; and trilead tetroxide, Pb3O4. Lead monoxide exists in two modifiCATions, litharge and massicot. Litharge, or alpha lead(II) oxide, is a red or reddish yellow solid, has a tetragonal crystal structure, and is the stable form at temperatures below 488 C (910 F). Massicot, or beta lead(II) oxide, is a yellow solid and has an orthorhombic crystal structure; it is the stable form above 488 C.

Both forms are insoluble in water but dissolve in acids to form salts containing the Pb2+ ion or in alkalies to form plumbites, which have the PbO22- ion. Litharge is produced by air oxidation of lead. Except for tetraethyllead [Pb(C2H5)4], an organic compound that has been used as a gasoline antiknock additive, litharge is the most important commercial compound of lead; it is used in large amounts directly and as the starting material for the preparation of other lead compounds. Considerable quantities of lead(II) oxide are consumed in manufacturing the plates of lead-acid storage batteries. High-quality glassware contains as much as 30 percent litharge, which increases the refractive index of the glass and makes it brilliant, strong, and resonant. Litharge is also employed as a drier in varnishes and in making sodium plumbite, which is used for removing malodorous thiols (a family of organic compounds containing sulfur) from gasoline. Lead(IV) oxide, found in nature as the brown-to-black mineral plattnerite, is commercially produced from trilead tetroxide by oxidation with chlorine. It decomposes upon heating and yields oxygen and lower oxides of lead. Lead(IV) oxide is used as an oxidizing agent in the production of dyestuffs, chemicals, pyrotechnics, and matches and as a curing agent for polysulfide rubbers. Trilead tetroxide (known as red lead, or minium) is produced by further oxidation of lead(II) oxide. It is the orange-red to brick-red pigment commonly used in corrosion-resistant paints for exposed iron and steel. It also reacts with iron(III) oxide to form a ferrite used in making permanent magnets.

Another economically significant compound is lead(II) acetate, Pb(C2H3O2)2, a water-soluble salt made by dissolving litharge in strong acetic acid. The common form, the trihydrate [Pb(C2H3O2)23H2O], called sugar of lead, is used as a mordant in dyeing and as a drier in certain paints. In addition, it is utilized in the production of other lead compounds and in gold cyanidation plants, where it primarily serves to precipitate soluble sulfides from solution.

Various other salts, most notably basic lead carbonate, basic lead sulfate, and basic lead siliCATe, were once widely employed as pigments for white exterior paints. Since the mid-20th century, however, the use of such so-called white lead pigments has decreased substantially because of a concern over their toxicity and attendant hazard to human health. The use of lead arsenate in insecticides has virtually been eliminated for the same reason.

atomic number 82 atomic weight 207.19 melting point 327.5 C (621.5 F) boiling point 1,744 C (3,171.2 F) density (20 C) 11.29 g/ml oxidation states +2, +4 electron config. 2-8-18-32-18-4 or 6s26p2 or 1s22s22p63s2 3p63d104s24p64d104f 145s2 5p65d106s26p2

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