Chemistry

An Overview about the Chemical Element Lead



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Lead

Symbol: Pb

Atomic Number: 82

Atomic Mass: 207.2 amu (atomic mass units)

Melting Point: 327.5 C (600.65 K, 621.5 F)

Boiling Point: 1740.0 C (2013.15 K, 3164.0 F)

Number of Protons/Electrons: 82

Number of Neutrons: 125

Classification: Metal

Crystal Structure: Cubic

Density @ 293 K: 11.34 grams per cubic centimeter

Color: bluish

Lead has been known to man for thousands of years. The Romans who called the element "plumbum" used it to make water pipes. Some lead drainage pipes that carry the insignia of Roman emperors are still in use today. The symbol for the element comes from this Latin name. The word lead is of Anglo-Saxon origin.

Lead is a ductile and very malleable metal. It is very resistant to corrosion but it will tarnish in air. It is a poor conductor of electricity.

The element is toxic. It can affect the central nervous system and the gastrointestinal tract as well as causing anemia. Lead is an accumulative toxin causing damage over a prolonged period of time. Some historians have attributed the fall of the Roman Empire to lead poisoning from their water.

There are four naturally occurring isotopes of lead three of which are stable, lead-204 has an extremely on half life. In order of abundance, the naturally occurring isotopes on lead are: lead-208 (52.4%), lead-206 (24.2%), lead-205 (22.1%) and lead-204 (1.4%). Unstable isotopes of lead have mass numbers ranging from 180 to 214. Lead isotopes form the end products of the decay chains of three naturally occurring radioactive elements including uranium.

While lead can be found in its free state in nature most commercially available lead is extracted from the mineral ores: galena, anglesite, cerussite and minum. The most important lead ore is galena which will yield lead metal on roasting. Recycled lead provides nearly one third of the annual supply of the metal in the United States.

The automobile industry uses most of the lead produced today to make lead-acid batteries for use in vehicles. Because lead is so resistant to corrosion it is used to line corrosive liquid storage tanks which hold chemicals such as sulfuric acid. The high density of lead makes it a suitable material for shields against radiation for use around X-ray machines and nuclear reactors. Other uses of lead metal are the production of ammunition; covering cables to prevent corrosion and as a vibration or sound deadening material. Many countries are banning the use of lead shot used in shotgun cartridges because of the danger of lead poisoning to wild fowl that pick up spent shot in gravel for use within their digestive crops.

Solder is an alloy of tin and lead with a low melting point that is used to join electrical wires or metal piping. Type metal that is used to make the type blocks in printing presses is an alloy of lead, antimony and tin. The alloy Babbitt metal which reduces friction on bearings is also an alloy of lead.

Lead carbonate (PbCO3) was commonly used as a pigment in white paint but its poisonous nature has means it is being replaced by titanium oxide. Many houses still contain layers of this type of paint on old woodwork. Some paint still contains lead compounds; red lead or trilead tetraoxide (Pb3O4) is painted on outdoor steel structures to prevent corrosion, lead sulfate (PbSO4) is the pigment sublime lead white and lead chromate (PbCrO4) is used to make chrome yellow paint. Lead silicate (PbSiO3) as well as being found in paints also is also used in glass making and rubber production. Litharge or lead monoxide (PbO) is used to make lead crystal and flint glass as well as vulcanizing rubber. Another useful lead compound is lead nitrate (Pb(NO3)2) it is used in the production of fireworks.

Tetraethyl lead was commonly added to gasoline but this has been stopped in most countries owing to environmental concerns.

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