   #copyright

Lead

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


               82                 thallium ← lead → bismuth
               Sn
               ↑
               Pb
               ↓
               Uuq

                                  Periodic Table - Extended 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] 4f^14 5d^10 6s^2 6p^2
                                   Electrons per shell 2, 8, 18, 32, 18, 4
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 11.34 g·cm^−3
                                   Liquid density at m.p. 10.66 g·cm^−3
                                                   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^−1
                                   Heat of vaporization 179.5 kJ·mol^−1
                         Heat capacity (25 °C) 26.650 J·mol^−1·K^−1

   CAPTION: 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^−1
                                                  2nd: 1450.5 kJ·mol^−1
                                                  3rd: 3081.5 kJ·mol^−1
                                                      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^−1·K^−1
                       Thermal expansion (25 °C) 28.9 µm·m^−1·K^−1
                              Speed of sound (thin rod) ( r.t.) (annealed)
                                                          1190   m·s^−1
                                                    Young's modulus 16 GPa
                                                     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
                                                         Selected isotopes

                   CAPTION: Main article: Isotopes of lead

                         iso    NA    half-life     DM    DE ( MeV)   DP
                        ^204Pb 1.4%  >1.4×10^17 y Alpha   2.186     ^200Hg
                        ^205Pb syn   1.53×10^7 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

                                                                References

   Lead ( IPA: /ˈlɛd/) is a chemical element in the periodic table that
   has the symbol Pb ( Latin: plumbum) and atomic number 82. A soft,
   heavy, toxic and malleable poor metal, lead is bluish white when
   freshly cut but tarnishes to dull gray when exposed to air. Lead is
   used in building construction, lead-acid batteries, bullets and shot,
   and is part of solder, pewter, and fusible alloys. Lead has the highest
   atomic number of all stable elements - although the next element,
   bismuth, has a half life so long it can be considered stable.

Notable characteristics

   Lead has a dull luster and is a dense, ductile, very soft, highly
   malleable, bluish-white metal that has poor electrical conductivity.
   This true metal is highly resistant to corrosion. Because of this
   property, it is used to contain corrosive liquids (e.g. sulfuric acid).
   Lead can be toughened by adding a small amount of antimony or other
   metals to it. Lead is the only metal in which there is zero Thomson
   effect. Lead is also poisonous.

Applications

     * Lead is a major constituent of the lead-acid battery used
       extensively in car batteries.
     * 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 products
       and ease of use due to relatively low melting point.
     * 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.
     * Lead is used as shielding from radiation.
     * Molten lead is used as a coolant, eg. for lead cooled fast
       reactors.
     * Lead glass is composed of 12-28% lead oxide. 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 as electrodes in the process of electrolysis.
     * Lead is used in solder for electronics, although this usage is
       being phased out to reduce the amount of environmentally unfriendly
       waste.
     * Lead is used in high voltage power cables as sheathing material to
       prevent water diffusion into insulation.
     * Lead is used for the ballast keel of sailboats. Its high
       weight-to-volume ratio allows it to counterbalance the heeling
       effect of wind on the sails while at the same time occupying a
       small volume and thus offering the least underwater resistance.
     * Lead is added to brass to reduce machine tool wear.
     * Lead sheets are used as roofing material.
     * Lead is frequently used in scuba diving weight belts to counteract
       the natural buoyancy of neoprene wetsuits.
     * It is also used in weights used in angling.

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. However, lead chromate is still in use.
     * Lead was used for plumbing in Ancient Rome and water mains and
       service pipes up until the early 1970's.
     * Tetraethyl lead was used in leaded fuels to reduce engine knocking;
       however, this is no longer common practice in the Western world due
       to health concerns.
     * Lead was used to make bullets for slings.
     * Lead was formerly used as a component of toys, though due to many
       toy safety regulations, this has been stopped.
     * Lead was used in car body filler, which was used in many custom
       cars in the 1940's-60's. Hence the term Leadsled.
     * Lead is a superconductor at 7.2K and IBM tried to make a Josephson
       Computer out of lead-alloy.

   Contrary to popular belief, pencil 'leads' have never been made from
   lead. The term comes from the Roman stylus, called the penicillus,
   which was made of lead. The pencil originated as a wrapped graphite
   writing tool, a particular type of graphite used being named plumbago
   (lit. acts like lead).

History

   Lead has been used by humans for at least 7000 years, because it is
   widespread, easy to extract and easy to work with. It is highly
   malleable and ductile as well as easy to smelt. In the early bronze age
   lead was used with antimony and arsenic. Lead was 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 and many Roman "pigs" (ingots)
   of lead figure in Derbyshire lead mining history and in the history of
   the industry in other English centres. Lead's symbol Pb is an
   abbreviation of its Latin name plumbum. The English word "plumbing"
   also derives from this Latin root.

   However, it is also toxic, and lead poisoning was recognized even by
   the ancients. Similarly, in the Twentieth Century, the use of lead in
   paint pigments was ended because of the danger of lead poisoning,
   especially to children. 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 RoHS directive.

Occurrence

   Lead ore
   Enlarge
   Lead ore

   Native lead does occur in nature, but it is rare. Currently lead is
   usually found in ore with zinc, silver and (most abundantly) copper,
   and is extracted together with these metals. The main lead mineral is
   galena (PbS), which contains 86.6% lead. Other common varieties are
   cerussite (PbCO[3]) and anglesite (PbSO[4]). But more than half of the
   lead used currently comes from recycling.

   In mining, the ore is extracted by drilling or blasting and then is
   crushed and ground. The ore is then treated using extractive
   metallurgy. The Froth flotation process separates the lead and other
   minerals from the waste rock ( tailings) to form a concentrate. The
   concentrate, which can range from 50% to 60% lead, is dried and then
   treated using pyrometallurgy. The concentrate is sintered before being
   smelted in to produce a 97% lead concentrate. The lead is then cooled
   in stages which causes the lighter impurites (dross) to rise to the
   surface where they can be removed. The molten lead bullion is then
   refined by additional smelting with air being passed over the lead to
   form a slag layer containing any remaining impurities and producing
   99.9% pure lead.
     * See Category:Lead minerals

Isotopes

   Lead has four stable, naturally occurring isotopes: ^204Pb (1.4%),
   ^206Pb (24.1%), ^207Pb (22.1%), and ^208Pb (52.4%). ^206Pb, ^207Pb and
   ^208Pb are all radiogenic, and are the end products of complex decay
   chains that begin at ^238U, ^235U and ^232Th, respectively. The
   corresponding half-lives of these decay schemes vary markedly: 4.47 ×
   10^9, 7.04 × 10^8 and 1.4 × 10^10 years, respectively. Each is reported
   relative to ^204Pb, the only non-radiogenic stable isotope. The ranges
   of isotopic ratios for most natural materials are 14.0 - 30.0 for
   ^206Pb/^204Pb, 15.0 - 17.0 for ^207Pb/^204Pb, and 35.0 - 50.0 for
   ^208Pb/^204Pb, although numerous examples outside these ranges are
   reported in the literature.

   Because lead is radiogenic and formed from the decay of most of the
   heavier elements that formed billions of years ago, it is much more
   common and much 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.
     * see isotope geochemistry

Health effects

   Enlarge

   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 PbO[2]) 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 which affected many
   of the 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 2004 scandal
   involving lead-laced Mexican candy being eaten by children in
   California.

   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). Lead-white paint has been withdrawn from sale
   in industralised countries. The yellow lead chromate is still in use;
   for example, Holland Colours Holcolan Yellow. Many older houses may
   still contain substantial lead in their old paint; see also lead 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 the
   manufacture of cider. Lead is considered to be particularly harmful for
   women's ability to reproduce. For that reason many universities do not
   hand out lead-containing samples to women for instructional laboratory
   analyses.

   Lead as a soil contaminant is a widespread issue, since lead may enter
   soil through (leaded) gasoline leaks from underground storage tanks or
   through a wastestream of lead paint or lead grindings from certain
   industrial operations.

   There has been an e-mail circulating about the lead content of various
   consumer products, such as shampoo and most notably lipstick, since
   2003. Though there are trace amounts of lead in some products, these
   levels are monitored by the FDA in the US and pose no real danger to
   health.

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 Through 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.

   Retrieved from " http://en.wikipedia.org/wiki/Lead"
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   with only minor checks and changes (see www.wikipedia.org for details
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