lead (Pb)

Lead radiation shielding.
Credit: L. Chang, Wikipedia

Some traditional uses of lead and its alloys

A soft, malleable, ductile, dense, metallic element that is bluish-white when freshly cut but tarnishes to gray when exposed to air. Lead occurs in group IVA and period 6 of the periodic table and has the highest atomic number of any stable element. It is extracted chiefly from galena (lead sulfide, PbS) by converting the ore to the oxide by roasting, then smelting with coke. Anglesite (lead sulfate, PbSO₄) and cerussite (lead carbonate, PbCO₃) are two other lead-based minerals.

Lead dissolves in dilute nitric acid, but is otherwise resistant to corrosion, because of a protective surface layer of the oxide, sulfate, etc.

Lead is used in lead-acid batteries, cable-sheathing, lead crystal, some solders, bullets, and radiation shielding. Like mercury, lead is a potent neurotoxin which can gradually accumulate in soft tissues and bone. For this reason, it is no longer used in making water pipes, paints, and antiknock compounds (to raise the octane level of gasoline).

Lead has been known since ancient times. Its name is derived from the Anglo-Saxon laedan. The chemical symbol Pb comes from the Latin for "lead", plumbum, which is also the root for "plumbing". Lead was used in pipes, pewter, and paint by the Romans.

atomic number	82
relative atomic mass	207.2
electron configuration	1s²2s²2p⁶3s²3p⁶4s²3d¹⁰ 4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p²
ionization energy	1st: 716 kJ/mol 2nd: 1,450 kJ/mol 3rd: 3,081 kJ/mol 4th: 4,083 kJ/mol
oxidation states	+2, +4
covalent radius	154 pm
metallic radius	175 pm
ionic radius	119 pm (Pb²⁺), 78 pm (Pb⁺⁴)
relative density	11.35 (room temp)
melting point	327.5°C (621.5°F)
boiling point	1,749°C (3,180°F)

Compounds of lead

Lead forms two series of salts: the lead (II) compounds are more stable than the lead (IV) compounds. Lead (II) oxide (PbO), or litharge, is a yellow crystalline solid made by oxidizing lead; it is used in lead-acid storage batteries, glass, and glazes, and has a melting point of 880°C. Lead (IV) oxide (PbO₂) is a brown crystalline solid and a powerful oxidizing agent used in matches, fireworks, and dyes; it decomposes at 290°C. Trilead tetroxide (Pb₃O₄), or red lead, is an orange-red powder made by oxidizing litharge; it is used in paints, inks, glazes, and magnets. Lead tetraethyl (Pb[C₂H₅]₄) is a colorless liquid made by reacting lead/sodium alloy with ethyl chloride.

Lead poisoning

Lead and several of its compounds are poisonous. Lead poisoning (plumbism) may be acute or chronic. Acute lead poisoning, which may follow inhalation of lead fumes or dust, causes abdominal pain, vomiting, and diarrhea, with paralysis, convulsions, and sometimes encephalitis. In chronic poisoning a characteristic bluish marking of gums ("lead line") is seen and the peripheral nerves are affected; there is also anemia. Treatment is with edetate. The use of lead in paints is now strictly controlled. See also separate article on lead poisoning.

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• INORGANIC CHEMISTRY

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