|
|
Atomic Number: |
82 |
Melting Point: | 327.46 ºC | |
| Atomic Symbol: | Pb | Boiling Point: | 1749 ºC | ||
| Atomic Weight: | 207.2 amu | Density: | 11340
kg/m 3 |
||
| Atomic Radius: |
175.0 pm |
Oxidation States: | 4, 2 | ||
| Covalent Radius: | 147 pm | Electron Configuration: | [Xe]6s24f145d106p2 | ||
| van der Waals Radius: |
202 pm |
State of Matter: | solid |
(Anglo-Saxon lead; L. plumbum) Long known, mentioned in Exodus. The alchemists believed lead to be the oldest metal and associated with the planet Saturn. Its historical use by the Roman Empire for water piping (and its salt, lead acetate, also known as sugar of lead, as a sweetener for wine) is considered by some to be the cause for the dementia that affected many of the emperors.
Lead has a dull gray appearance and is bluish white of bright luster when freshly cut but tarnishes to dull gray when exposed to air. It is very soft, heavy, toxic, highly malleable, ductile, and a poor conductor of electricity. It is very resistant to corrosion; lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. It is used in containers for corrosive liquids (such as sulfuric acid) and may be toughened by the addition of a small percentage of antimony or other metals.
Native lead occurs in nature, but is rare. Lead is obtained chiefly from galena (PbS) by a roasting process. Anglesite, cerussite, and minim are other common lead minerals.
The metal is very effective as a sound absorber, is used as a radiation shield around X-ray equipment and nuclear reactors, and is used to absorb vibration. White lead, the basic carbonate, sublimed white lead, chrome yellow, and other lead compounds are used extensively in paints, although in recent years the use of lead in paints has been drastically curtailed to eliminate or reduce health hazards.
Lead oxide is used in producing fine "crystal glass" and "flint glass" of a high index of refraction for achromatic lenses. The nitrate and the acetate are soluble salts. Lead salts such as lead arsenate have been used as insecticides, but their use in recent years has been practically eliminated in favor of less harmful organic compounds.
Its alloys include solder, type metal, and various antifriction metals. Great quantities of lead, both as the metal and as the dioxide, are used in storage batteries. Much metal also goes into cable covering, plumbing, ammunition, and in the manufacture of lead tetraethyl.
Natural lead is a mixture of four stable isotopes: 204Pb (1.48%), 206Pb (23.6%), 207Pb (22.6%), and 208Pb (52.3%). Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements: 206Pb for the uranium series, 207Pb for the actinium series, and 208Pb for the thorium series. Twenty seven other isotopes of lead, all of which are radioactive, are recognized.
Care must be used in handling lead as it is a cumulative poison. By the mid-1980s, a significant shift in lead end-use patterns had taken place do to its high toxicity. Much of this shift was a result of the U.S. lead consumers' compliance with environmental regulations that significantly reduced or eliminated the use of lead in nonbattery products, including gasoline, paints, solders, and water systems.
It can damage nervous connections (especially in young children) and cause blood and brain disorders. Long term exposure to lead or its salts (especially soluble salts or the strong oxidant PbO2) can cause nephropathy, and colic-like abdominal pains.
The concern about lead's role in mental retardation in children has brought about widespread reduction in its use (lead exposure has been linked to schizophrenia). Paint containing lead has been withdrawn from sale in industrialized countries, though many older houses may still contain substantial lead in their old paint: it is generally recommended that old paint should not be stripped by sanding, as this generates dust that can be inhaled.
Lead salts used in pottery glazes have on occasion caused poisoning, when acid drinks, such as fruit juices, have leached lead ions out of the glaze. It has been suggested that what was known as "Devon colic" arose from the use of lead-lined presses to extract apple juice in the manufacture of cider. Lead is considered to have particularly nasty consequences for mothers in spe, i.e. girls and young women. For that reason many universities do not hand out lead containing samples to girls for instructional laboratory analyses.
The earliest pencils actually used lead, though 'pencil leads' have been made for the last couple of centuries from graphite, a naturally occurring form of carbon.
