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    lead (Pb)

    lead shielding
    Lead radiation shielding.
    Credit: L. Chang, wikipedia
    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 (see picture). 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.


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