Lead




Lead

MELTING POINT: 327.5°C
BOILING POINT: 1,740.0°C
DENSITY: 11.34 g/cm
3
MOST COMMON IONS: Pb 2+ , Pb 4+

Lead makes up only about 0.0013 percent of Earth's crust but was well known in the ancient world and was even mentioned in the Book of Exodus. The word "lead" is derived from the Anglo-Saxon word laedan. Lead's symbol, Pb, comes from the Latin word for lead, plumbum. Because of lead's long use in piping, the word "plumber" comes from that same root. Lead is an extremely dense but malleable metal that is very resistant to corrosion.

Lead is sometimes found free in nature but is usually obtained from ores such as galena (PbS) or cerussite (PbCO 3 ), from which it is easily mined and refined. Most lead is obtained by simply roasting galena in hot air. About one-third of the lead used in the United States is obtained through recycling efforts.

Lead has seen many uses over the ages. As a constituent of pewter (an alloy of tin and lead), lead was a component of Roman eating and drinking utensils. It has been suggested that the decline of the Roman Empire may have been tied to this use, since acidic foodstuffs extract small amounts of lead, a cumulative human poison. Lead's use as a pottery glaze has been banned for the same reason—the danger of lead ingestion via the extraction of the lead by food and drink. During the twentieth century, a volatile form of lead—tetraethyl lead [Pb(CH 2 CH 3 ) 4 ]—was developed and widely used to improve the octane level of gasoline. That use has also been banned for health and environmental reasons.

Lead remains in wide use in electrical cable sheathing, automobile batteries, lead crystal, radiation protection, and some solders.

SEE ALSO Inorganic Chemistry ; Radioactivity .

George H. Wahl Jr.

Bibliography

Internet Resources

Jefferson Lab. "It's Elemental: The Element Lead." Available from http://education.jlab.org/itselemental/ele082.html .



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