Lead: the essentials
Lead is a bluish-white lustrous metal. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity. It is very resistant to corrosion but tarnishes upon exposure to air. Lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. Alloys include pewter and solder. Tetraethyl lead (PbEt4) is still used in some grades of petrol (gasoline) but is being phased out on environmental grounds.
Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements.
Lead: historical information
Lead has been known for ages and is mentioned in Exodus. Alchemists believed lead to be the oldest metal and associated it with the planet Saturn. They spent a lot of time trying to "transmute" lead into gold.
Lead is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for lead is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Lead: physical properties
Lead: orbital properties
Isolation: there is usually little need to make lead metal in the laboratory as it is so cheap and readily available. Lead is isolated from the sulphide, PbS. The process involves burning in a restricted air flow followed by reduction of the resulting oxide PbO with carbon.
PbS + 3/2O2 → PbO + SO2
PbO + C → Pb + CO
PbO + CO → Pb + CO2
This gives lead usually contaminated with metals such as antimony, arsenic, copper, gold, silver, tin, and zinc. A fairly complex process is used to strip out these impurities.
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