Lead

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Lead

This is lead.

Symbol Pb
Atomic number 82
Atomic mass 207.2 amu

Lead is the most familiar of the metallic elements. No one can claim to have discovered lead or to have been the first to isolate it. It can be traced back to the prehistoric times. The Bible mentions applications of lead in one of the oldest books, the Book of Job.

Distinguishing properties

Lead is a dense, soft, grey metal with a low melting point (327°C).

Occurrence

Lead is found in many regions of Canada, including the Northwest Territories, British Columbia, The Yukon, Manitoba, Northern Ontario, New Brunswick, and Cape Breton Island. The Sullivan Mine at Kimberly, B.C. is one of the world's largest producers of lead-zinc ore. A typical ore contains sulphides of lead, galena, zinc and iron, as well as small quantities of other metals.

  • Galena
    Galena, PbS, is the chief ore of lead. It is found throughout the world. The main commercial sources are in Australia, Russia, USA, and Canada.

Usage

Uses of lead include:

  • solder, in which an alloy of lead and tin containing about 50 to 70 % Pb, 30 to 50 % Sn is used to join copper wires in electrical circuits, and to seal joints in copper pipes
  • lead-acid batteries used in automobile
  • ammunition

As much as lead is useful, it is also a poison. Metallic lead can be absorbed through the skin because it reacts with the weak acids in perspiration and dissolves. Cases of lead poisoning have resulted from the repeated handling of lead foil, bullets, and other lead objects.

Lead ions are present in some foods, beverages, public water supplies (from lead pipes), and even air (from lead compounds in automobile exhausts). The body must be able to rid itself of lead, otherwise everyone would have died long ago of lead poisoning. The average person can excrete about 230 micrograms of lead a day through the kidneys and intestinal tract. The body can accumulate lead in bone cells, where it acts on the bone marrow. It can also interfere with the biochemical reactions that produce the iron-containing heme group in hemoglobin. In tissues, lead behaves like other heavy-metal poisons. When lead ions are bound to an enzyme, the enzyme will likely cease to function.

The principal sources of lead contamination now seem to be lead-based painted surfaces in old buildings and soldered joints in plumbing systems. The phasing out of leaded gasoline has resulted in a drastic drop in average lead blood levels. Mild forms of lead poisoning produce nervousness and mental depression. More severe cases can lead to permanent nerve, brain, and kidney damage.

Common compounds

Lead has an extensive variety of oxides and compounds, many of which are of commercially importance.

  • Lead(II) oxide (PbO) is an insoluble yellow solid frequently used in making glass, vulcanizing rubber, and colouring paints.
  • Lead(IV) oxide (PbO2) is an important ingredient in the operation of lead-acid storage batteries.
  • Trilead tetroxide (Pb3O4) is the primary ingredient in the reddish-brown rust-inhibiting paint that is applied to outdoor steel structures.
  • Lead arsenate (Pb3(AsO4)2) is a commercial insecticide.
  • Lead carbonate (PbCO3) is a white crystalline substance formerly used in the manufacture of white paints.
  • Lead sulfate (PbSO4) is also used in a paint pigment commonly known as sublimed white lead.
  • Lead chromate (PbCrO4) is a yellow crystal that is popular in chrome yellow paint.
  • Lead nitrate (Pb(NO3)2) is used in the manufacture of fireworks and other chemicals.
  • Lead silicate (PbSiO3) is used in glass-making as well as in the rubber and paint manufacturing industries.
  • Tetraethyllead (Pb(C2H5)4) is used as an antiknock agent in internal-combustion engine fuel.

See also

Periodic table of the elements