Lead
Lead, symbol Pb (Latin plumbum, a lead weight), dense, bluish-gray metallic element that was one of the first known metals. The atomic number of lead is 82; the element is in group 14 (or IVa) of the periodic table (see Periodic Law ). Lead was mentioned in the Old Testament (see Bible ). It was used by the Romans for making water pipes, soldered with an alloy of lead and tin. PROPERTIES Metallic lead is a soft, malleable, ductile metal. When gently heated it can be forced through annular holes or dies. It has low tensile strength and is a poor conductor of electricity. A freshly cut surface has a bright silvery luster, which quickly turns to the dull, bluish-gray color characteristic of the metal. Lead melts at 328° C (662° F), boils at 1740° C (3164° F), and has a specific gravity of 11.34; the atomic weight of lead is 207.20. Lead is soluble in nitric acid but is little affected by sulfuric or hydrochloric acids at room temperature. In the presence of air, it slowly reacts with wate