Lead

This article is about the chemical element. For other meanings, see lead (disambiguation).

82 thallium ← lead → bismuth Sn ↑ Pb ↓ Uuq periodic table
General
Name, Symbol, Number	lead, Pb, 82
Chemical series	poor metals
Group, Period, Block	14, 6, p
Appearance	bluish white
Atomic mass	207.2(1) g/mol
Electron configuration	[Xe] 4f14 5d10 6s2 6p2
Electrons per shell	2, 8, 18, 32, 18, 4
Physical properties
Phase	solid
Density (near r.t.)	11.34 g/cm³
Liquid density at m.p.	10.66 g/cm³
Melting point	600.61 K (327.46 °C, 621.43 °F)
Boiling point	2022 K (1749 °C, 3180 °F)
Heat of fusion	4.77 kJ/mol
Heat of vaporization	179.5 kJ/mol
Heat capacity	(25 °C) 26.650 J/(mol·K)
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 978 1088 1229 1412 1660 2027
Atomic properties
Crystal structure	cubic face centered
Oxidation states	4, 2 (Amphoteric oxide)
Electronegativity	2.33 (Pauling scale)
Ionization energies (more)	1st: 715.6 kJ/mol
	2nd: 1450.5 kJ/mol
	3rd: 3081.5 kJ/mol
Atomic radius	180 pm
Atomic radius (calc.)	154 pm
Covalent radius	147 pm
Van der Waals radius	202 pm
Miscellaneous
Magnetic ordering	diamagnetic
Electrical resistivity	(20 °C) 208 nΩ·m
Thermal conductivity	(300 K) 35.3 W/(m·K)
Thermal expansion	(25 °C) 28.9 µm/(m·K)
Speed of sound (thin rod)	(r.t.) (annealed) 1190 m/s
Speed of sound (thin rod)	(r.t.) 16 m/s
Shear modulus	5.6 GPa
Bulk modulus	46 GPa
Poisson ratio	0.44
Mohs hardness	1.5
Brinell hardness	38.3 MPa
CAS registry number	7439-92-1
Notable isotopes
Main article: Isotopes of lead iso NA half-life DM DE (MeV) DP 204Pb 1.4% >1.4×1017 y Alpha 2.186 200Hg 205Pb syn 1.53×107 y Epsilon 0.051 205Tl 206Pb 24.1% Pb is stable with 124 neutrons 207Pb 22.1% Pb is stable with 125 neutrons 208Pb 52.4% Pb is stable with 126 neutrons 210Pb trace 22.3 y Alpha 3.792 206Hg Beta 0.064 210Bi

Lead (chemical symbol Pb, atomic number 82) is a soft, heavy, toxic metal. It is bluish white when freshly cut but tarnishes to dull gray when exposed to air. It is used in building construction, lead-acid batteries, bullets and shot, and is part of solder, pewter, and fusible alloys.

History

Lead is widely distributed in the world and is easy to extract and work with. For these reasons, it has been used by humans for at least 7,000 years. In the early bronze age, it was used with antimony and arsenic. Lead is mentioned in the Book of Exodus. Alchemists thought that lead was the oldest metal and associated it with the planet Saturn. Lead pipes that bear the insignia of Roman emperors are still in service.

This metal is also toxic, and lead poisoning was recognized even by the ancients. In the twentieth century, the use of lead in paint pigments was ended because of the danger of lead poisoning, especially to children [1] [2] [3]. By the mid-1980s, a significant shift in lead end-use patterns had taken place. 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. Recently, lead use is being further curtailed by the "Restriction of Hazardous Substances" directive.

Occurrence and production

Lead ore

Native lead does occur in nature, but it is rare. Currently, lead is usually found in ores with zinc, silver, and (most abundantly) copper, and is extracted together with these metals. The main lead mineral is galena (lead sulfide, PbS), which contains 86.6% lead. Other common varieties are cerussite (lead carbonate, PbCO₃) and anglesite (lead sulfate, PbSO₄). More than half the lead in current use comes from recycling.

Lead ore is mined by drilling or blasting operations, then crushed and ground. Lead is extracted from the ore by specialized metallurgical processes. A process called froth flotation is used to separate the lead mineral (and other minerals) from the waste rock to form a concentrate. The concentrate, which may contain 50–60% lead, is dried, heated (in the process of pyrometallurgy), and smelted, and a 97% lead concentrate is obtained. The lead is then cooled in stages, causing the lighter impurites (dross) to rise to the surface from which they are removed. The molten lead bullion is refined by additional smelting, when air is passed over the lead. This process forms a slag layer that contains the remaining impurities and produces 99.9% pure lead.

Notable characteristics

Lead is a chemical element that gets its symbol, Pb, from its Latin name, plumbum. The English word "plumbing" also derives from this Latin root.

In the periodic table, lead lies below tin (Sn) in group 13, and between thallium (Tl) and bismuth (Bi) in period 6. It is classified as a "poor metal" or "post-transition metal." Its atomic number of 82 indicates that there are 82 protons in the nucleus of each atom of lead. This gives lead the highest atomic number of all stable (nonradioactive) elements. (It should be noted, however, that bismuth, with an atomic number of 83, has a half life so long it can be considered stable.)

Lead is a very soft but dense metal, and a poor conductor of electricity. It is also highly malleable (can be shaped with a hammer or rollers), ductile (can be drawn into wires), and easy to smelt. As it is highly resistant to corrosion, it is used to contain corrosive liquids such as sulfuric acid. Lead can be toughened by adding a small amount of antimony or other metals to it. Lead is also poisonous.

Isotopes

Lead has four stable, naturally occurring isotopes: lead-204 (²⁰⁴Pb, 1.4%), lead-206 (²⁰⁶Pb, 24.1%), lead-207 (²⁰⁷Pb, 22.1%), and lead-208 (²⁰⁸Pb, 52.4%). The last three of these isotopes are radiogenic—that is, they are the end products of radioactive decay chains that begin from uranium-238 (²³⁸U), uranium-235 (²³⁵U), and thorium-232 (²³²Th), respectively. The corresponding half-lives of these decay processes vary markedly: 4.47 × 10⁹, 7.04 × 10⁸, and 1.4 × 10¹⁰ years, respectively. Lead-204 is the only non-radiogenic, stable isotope. The isotopic ratios for most natural lead-bearing materials are in the following ranges: 14.0 - 30.0 for ²⁰⁶Pb/²⁰⁴Pb, 15.0 - 17.0 for ²⁰⁷Pb/²⁰⁴Pb, and 35.0 - 50.0 for ²⁰⁸Pb/²⁰⁴Pb, but numerous examples outside these ranges are also reported in the literature.

Given that three of the four stable isotopes are radiogenic and formed from the decay of heavier elements that were formed billions of years ago, lead is much more common and cheaper than most heavy elements. The cost has been further lowered in recent years with the phasing out of lead in many processes, including gasoline and paint.

Applications

• Lead is a major constituent of the lead-acid battery used extensively in automobiles.
• Lead is used as a coloring element in ceramic glazes, notably in the colors red and yellow.
• Lead is used as projectiles for firearms and fishing sinkers because of its density, low cost (compared to alternative materials), and ease of use (due to its relatively low melting point). For health concerns, see [4].
• Lead is used in some candles to treat the wick to ensure a longer, more even burn. Because of the dangers, European and North American manufacturers use more expensive alternatives, such as zinc [5].
• Lead is used to form shielding from harmful (ionizing) radiation, such as X rays.
• Molten lead is used as a coolant, such as in lead-cooled fast reactors.
• Lead glass contains 12–28% lead. It changes the optical characteristics of the glass and reduces the transmission of radiation.
• Lead is the traditional base metal of organ pipes, mixed with varying amounts of tin to control the tone of the pipe.
• Lead is used for electrodes in the process of electrolysis.
• Lead is used in solder for electronics.
• Lead is used as sheathing material for high-voltage power cables, to prevent water diffusion into insulation.
• Lead is used for the ballast keel of sailboats.
• Lead is added to brass to reduce the wear on machine tools.

Former applications

• Lead was used as a pigment in lead paint for white as well as yellow and red colors. It was discontinued because of the dangers of lead poisoning.
• Lead was used for plumbing in Ancient Rome, and it was used for water mains and service pipes up until the early 1970s.
• Tetraethyl lead was used in gasoline fuels to reduce engine knock. On account of health concerns, however, leaded gasoline is no longer used in the Western world [6].

Health effects

Main article: lead poisoning

Lead is a poisonous metal that 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 historical use of lead acetate (also known as sugar of lead) by the Roman Empire as a sweetener for wine is considered by some to be the cause of the dementia that affected many Roman Emperors. At one point in time, some lead compounds, because of their sweetness, were used by candy makers. Although this has been banned in industrialized nations, there was a recent scandal involving lead-laced Mexican candy being eaten by children in California [7].

The concern about lead's role in mental retardation in children has brought about widespread reduction in its use. Paint containing lead has been withdrawn from sale in industralised 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 inhalable dust.

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 manufacturing cider. Lead is considered particularly harmful for a woman's reproductive ability. For that reason, many universities do not hand out lead-containing samples to women for instructional laboratory analyses.

The earliest pencils actually used lead, but for the last couple of centuries, "pencil leads" have been made from graphite, a naturally occurring form (allotrope) of carbon.

Lead as a soil contaminant is a widespread issue, because lead may enter the soil by the leakage of leaded gasoline from underground storage tanks, or through wastestreams of lead paint, or lead grindings from certain industrial operations.

See also

• Lead compounds
• Derbyshire lead mining history

Literature

• Keisch, B., Feller, R. L., Levine, A. S., and Edwards, R. R.: Dating and Authenticating Works of Art by Measurement of Natural Alpha Emitters. In: Science, 155, No. 3767, p. 1238-1242, 1967.
• Keisch, B: Dating Works of Art Trough their Natural Radioactivity: Improvements and Applications. In: Science, 160, p. 413-415, 1968.
• Keisch, B: Discriminating Radioactivity Measurements of Lead: New Tool for Authentication. In: Curator, 11, No. 1., p. 41-52, 1968.

References

ISBN links support NWE through referral fees

• A Small Dose of Toxicology:Lead
• Los Alamos National Laboratory - Lead

External links

• Case Studies in Environmental Medicine - Lead Toxicity
• ToxFAQs™: Lead
• National Pollutant Inventory - Lead and compounds fact sheet
• WebElements.com - Lead
• The Lead Education and Abatement Design Group (Australia)
• Do lead fishing sinkers threaten the environment? (from The Straight Dope)

Credits

New World Encyclopedia writers and editors rewrote and completed the Wikipedia article in accordance with New World Encyclopedia standards. This article abides by terms of the Creative Commons CC-by-sa 3.0 License (CC-by-sa), which may be used and disseminated with proper attribution. Credit is due under the terms of this license that can reference both the New World Encyclopedia contributors and the selfless volunteer contributors of the Wikimedia Foundation. To cite this article click here for a list of acceptable citing formats.The history of earlier contributions by wikipedians is accessible to researchers here:

• Lead  ^history

The history of this article since it was imported to New World Encyclopedia:

• History of "Lead"

Note: Some restrictions may apply to use of individual images which are separately licensed.