82
  Pb  
207.200000
Lead

Name: Lead
Symbol: Pb
Atomic Number: 82
Atomic Weight: 207.200000
Family: Carbon Family
CAS RN: 7439-92-1
Description: A bluish white metal, very soft, highly malleable, ductile, and a poor conductor electricity.
State (25C): Solid
Oxidation states: +2, +4

Molar Volume: 18.27 cm3/mole
Valence Electrons: 6p2

Boiling Point:  2013K, 1740C, 3164F
Melting Point:
600.75K, 327.6C, 621.7F
Electrons Energy Level: 2, 8, 18, 32, 18, 4
Isotopes: 34 + 4 Stable + 12 meta states
Heat of Vaporization: 177.7 kJ/mol
Heat of Fusion: 4.799 kJ/mol
Density: 11.35 g/cm3 @ 300K
Specific Heat: 0.13 J/gK
Atomic Radius: 1.81
Ionic Radius: 1.19
Electronegativity: 2.33 (Pauling); 1.55 (Allrod Rochow)
Vapor Pressure: 4.21E-07 Pa @ 327.6C
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 European Union's RoHS directive.  Lead may still be found in harmful quantities in stoneware, vinyl (Such as that used for tubing and the insulation of electrical cords), and brass manufactured in China.

1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d10 6s2p2

6
C
12.02
14
Si
28.08
32
Ge
72.15
50
Sn
118.7
82
Pb
207.2
114
Uuq
285.0
lead.gif (721 bytes)

Alchemical Symbol for Lead

Characteristics

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.  Like Mercury, another heavy metal, Lead is a potent neurotoxin which accumulates in soft tissues and bone over time.

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.  All Lead, except 204Pb, is the end product of a complex radioactive decay.

Known to the ancients, lead takes its name from the Anglo-Saxon word for the metal and its symbol comes from the Latin (from which we get the modern word "plumber" since old plumbing was done with lead pipes).

lead1.jpg (1479 bytes) lead2.jpg (1381 bytes) lead3.jpg (1147 bytes) lead4.jpg (1256 bytes) lead5.jpg (1434 bytes) lead6.jpg (1315 bytes) lead7.jpg (1453 bytes)
Additional Representations of Alchemical Symbols of Lead

Although lead is not very common in the earth's crust, what is there is readily available and easy to refine. Its chief use today is in lead-acid storage batteries such as those used in automobiles. In pure form it is too soft to be used for much else. Lead has a blue-white color when first cut but quickly dulls on exposure to air, forming Pb2O, one of the few lead (I) compounds.  Most stable lead compounds contain lead in oxidation states of +2 or +4.

Various isotopes of lead come at the end of the natural decay series of elements like uranium, thorium and actinium. These are Pb-206, Pb-207 and Pb-208

Occurrence

Native Lead occurs in nature making up only about 0.0013% of the earth's crust.  It is not considered to be a rare element since it is easily mined and refined.   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 (PbCO3) and Anglesite (PbSO4).   The largest source of raw Lead, however, is recycling, primarily of automobile batteries.

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10 4f14
5s2 5p6 5d10
6s2 6p2

In mining, the ore is extracted by drilling or blasting and then is crushed and ground.   The ore is then treated using extraction 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.

Applications

Former Applications

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.   When the pencil originated as a wrapped graphite writing tool, the particular type of graphite being used was named plumbago (lit. acts like lead).

Processing Methods

The principle ores of lead are Galena (PbS), Anglesite (PbSO4), and Cerussite (PbCO3).  Most ores contain less than 10% lead, and ores containing as little as 3% lead can be economically exploited. Ores are crushed and concentrated by froth flotation typically to 70% or more.  Sulfide ores are roasted, producing primarily Lead Oxide and a mixture of Sulfates and Silicates of Lead and other metals contained in the ore.

Lead Oxide from the roasting process is reduced in a coke-fired blast furnace.   This converts most of the Lead to its metallic form.  Three additional layers separate in the process and float to the top of the metallic Lead.  These are slag (silicates containing 1.5% Lead), matte (sulfides containing 15% Lead), and speiss (arsenides of Iron and Copper).  These wastes contain concentrations of Copper, Zinc, Cadmium, and Bismuth that can be recovered economically, as can their content of unreduced lead.

Metallic Lead that results from the roasting and blast furnace processes still contains significant contaminants of Arsenic, Antimony, Bismuth, Zinc, Copper, Silver, and Gold.   The melt is treated in a reverberatory furnace with air, steam, and Sulfur, which oxidizes the contaminants except Silver, Gold, and Bismuth.  The oxidized contaminants are removed by drossing, where they float to the top and are skimmed off.

Most Lead ores contain significant concentrations of Silver, resulting in the smelted metal also containing Silver as a contaminant.  Metallic Silver as well as Gold is removed and recovered economically by means of the Parkes Process.

Desilvered Lead is freed of Bismuth according to the Betterton-Kroll Process by treating it with metallic Calcium and Magnesium, which forms a Bismuth dross that can be skimmed off.

Very pure Lead can be obtained by processing smelted lead electolytically by means of the Betts Process.  The process uses anodes of impure Lead and cathodes of pure Lead in an electrolyte of Silica Fluoride.

Descriptive Chemistry

Various oxidized forms of lead are easily reduced to the metal. An example is heating PbO with mild organic reducing agents such as glucose. A mixture of the oxide and the sulfide heated together without any reducing agent will also form the metal.

2PbO + PbS   rarrow.gif (63 bytes)   3 Pb + SO2

Metallic lead is attacked only superficially by air, forming a thin layer of oxide that protects it from further oxidation.  The metal is not attacked by Sulfuric or Hydrochloric Acids.  It does, however, dissolve in Nitric Acid with the evolution of Nitric Oxide gas gas to form dissolved Pb(NO3)2.

3 Pb + 8 H+ + 8 NO3   rarrow.gif (63 bytes)   3 Pb2+ + 6 NO3 + 2 NO + 4H2O

When heated with Nitrates of alkali metals, metallic lead oxidizes to form Litharge, PbO, leaving the corresponding Alkali Nitrate.  PbO is representative of lead's II oxidation state.  It is soluble in Nitric and Acetic Acids, from which solutions it is possible to precipitate Halide, Sulfate, Chromate, Carbonate (PbCO3), and basic carbonate (Pb3(OH)2(CO3)2) salts of lead. The Sulfide can also be precipitated from Acetate solutions . These salts are all poorly soluble in water.  Among the Halides, the Iodide is less soluble than the Bromide, which, in turn, is less soluble than the Chloride.

The II oxide is also soluble in Alkali Hydroxide solutions to form the corresponding plumbite salt.

PbO + 2OH + H2O   rarrow.gif (63 bytes)   Pb(OH)42–

Chlorination of plumbite solutions causes the formation of lead's IV oxidation state.

Pb(OH)42– + Cl2   rarrow.gif (63 bytes)   PbO2 + 2 Cl + 2 H2O

Lead Dioxide is representative of the IV state, and is a powerful oxidizing agent.   The Chloride of this oxidation state is formed only with difficulty and decomposes readily into the II Chloride and Chlorine gas.  The Bromide and Iodide of IV Lead are not known to exist.  Lead Dioxide dissolves in Alkali Hydroxide solutions to form the corresponding plumbates.

PbO2 + 2 OH + 2 H2O   rarrow.gif (63 bytes)   Pb(OH)62–

Lead also has an oxide that is a hybrid between the II and IV oxidation states.  Red Lead (also called minium) is Pb3O4.

Lead readily forms an equimolar alloy with sodium metal that reacts with Alkyl Halides to form organometallic compounds of Lead such as Tetraethyl Lead.

Compounds

Many compounds are formed from lead. Lead Monoxide (PbO), also known as Litharge, is a yellow solid used to make special types of glass, such as lead crystal and flint glass. It is used in the vulcanizing of rubber and as a paint pigment.  Lead Dioxide (PbO2) a brown material is used in lead-acid storage batteries.  Trilead Tetraoxide (Pb3O4), also known as red lead, is used to make a reddish-brown paint which prevents rust on steel structures.  Lead Arsenate, Pb3(AsO4)2,  has been used in insecticides but is being replaced with less harmful substances. Lead Carbonate (PbCO3), known as Cerussite, is a white, poisonous substance that was once widely used as a pigment for white paint.  Use of Lead Carbonate in paints has largely been replaced in favor of Titanium Oxide (TiO2).   Lead Sulfate (PbSO4), known as Anglesite, is currently used in a paint pigment known as sublimed white lead.  Lead Chromate (PbCrO4), known as Crocoite, is used to produce chrome yellow paint.   Lead Nitrate, Pb(NO3)2, is an ingredient used in the production of fireworks and other pyrotechnics.  Lead Silicate (PbSiO3) is also used in the production of certain types of glass as well as the production of rubber and paints.

Lead Dioxide, PbO2 Lead Monoxide, PbO, Litharge
Lead Sulfide, PbS, Galena Lead Sulfate, PbSO4, Anglesite
Lead Nitrate, Pb(NO3)2 Lead Carbonate, PbCO3, Cerussite
Lead Arsenate, Pb3(AsO4)2 Lead Chromate, PbCrO4, Crocoite
Lead Silicate, PbSiO3 Trilead Tetraoxide, Pb3O4, Minium,  Red Lead

Isotopes

Lead has four stable, naturally occurring isotopes204Pb (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 231Th, respectively.  The corresponding half-lives of these decay schemes vary markedly: 4.47 x 109, 7.04 x 108 and 1.4 x 1010 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.

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
178Pb 178.003830 0.23 ms
179Pb 179.00215 ~3 ms
180Pb 179.997918 4.5 ms
181Pb 180.99662 45 ms
182Pb 181.992672 60 ms
183Pb 182.99187 535 ms
184Pb 183.988142 490 ms
185Pb 184.987610 6.3 seconds
185mPb   4.07 seconds
186Pb 185.984239 4.82 seconds
187Pb 186.983918 15.2 seconds
187mPb   18.3 seconds
188Pb 187.980874 25.5 seconds
189Pb 188.98081 51 seconds
189mPb   ~1 minutes
190Pb 189.978082 71 seconds
191Pb 190.97827 1.33 minutes
191mPb   2.18 minutes
192Pb 191.975785 3.5 minutes
193Pb 192.97617 ~5 minutes
193m1Pb   5.8 minutes
194Pb 193.974012 12.0 minutes
195Pb 194.974542 ~15 minutes
195m1Pb   15.0 minutes
196Pb 195.972774 37 minutes
197Pb 196.973431 8.1 minutes
197m1Pb   42.9 minutes
198Pb 197.972034 2.4 hours
199Pb 198.972917 90 minutes
199m1Pb   12.2 minutes
200Pb 199.971827 21.5 hours
201Pb 200.972885 9.33 hours
201m1Pb   61 seconds
202Pb 201.972159 52.5 x 103 years
202m1Pb   3.53 hours
203Pb 202.973391 51.873 hours
203m1Pb   6.21 seconds
204Pb 203.9730436 Stable
204m2Pb   67.2 minutes
205Pb 204.9744818 15.3 x 106 years
206Pb 205.9744653 Stable
207Pb 206.9758969 Stable
208Pb 207.9766521 Stable
209Pb 208.9810901 3.253 hours
210Pb 209.9841885 22.20 years
211Pb 210.9887370 36.1 minutes
212Pb 211.9918975 10.64 hours
213Pb 212.996581 10.2 minutes
214Pb 213.9998054 26.8 minutes
215Pb 215.00481 36 seconds

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) 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 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.  Even in these cases however, it should be noted that the Lead is not an additive but merely a contaminant that enters incidentally via for instance, metal particles accumulated during grinding processes.

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 schizophrena).   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.  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.

Trivia

A "Lead Pipe Cinch" is something that is absolutely certain.   In the 19th century a horse saddle that was safe when it was well "cinched".  The "lead pipe" qualifier is an obscure "intensifier".


atom.gif (700 bytes)

Lead Data

 

Atomic Structure

Atomic Radius (): 1.81
Atomic Volume cm3/mol : 18.17cm3/mol
Covalent Radius: 1.47
Crystal Structure: Cubic face centered
Ionic Radius: 1.19

Chemical Properties

Electrochemical Equivalents: 3.865 g/amp-hr
Electron Work Function: 4.25eV
Electronegativity: 2.33 (Pauling); 1.55 (Allrod Rochow)
Heat of Fusion: 4.799 kJ/mol
Incompatibilities: Strong Oxidizers, Hydrogen Peroxide, Acids
First Ionization Potential: 7.416
Second Ionization Potential: 15.028
Third Ionization Potential: 31.943
Valence Electron Potential: 24.2
Ionization Energy (eV): 7.417 eV

Physical Properties

Atomic Mass Average: 207.2
Boiling Point: 2013K, 1740C, 3164F
Melting Point: 600.75K, 327.6C, 621.7F
Heat of Vaporization: 177.7 kJ/mol
Coefficient of Lineal Thermal Expansion/K-1: 29.1E-6
Electrical Conductivity: 0.0481 106/cm
Thermal Conductivity: 0.353 W/cmK
Density: 11.35 g/cm3 @ 300K
Enthalpy of Atomization: 194.6 kJ/mole @ 25C
Enthalpy of Fusion: 4.77 kJ/mole
Enthalpy of Vaporization: 179.4 kJ/mole
Flammability Class: Non-combustible solid (except as dust)
Molar Volume: 18.27 cm3/mole
Optical Refractive Index: unknown
Relative Gas Density (Air=1): unknown
Specific Heat: 0.13 J/gK
Vapor Pressure: 4.21E-07 Pa @ 327.6C
Estimated Crustal Abundance: 1.4101 milligrams per kilogram
Estimated Oceanic Abundance: 310-5 milligrams per liter


(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. Native lead occurs in nature, but it is rare. Lead is obtained chiefly from galena (PbS) by a roasting process. Anglesite, cerussite, and minim are other common lead minerals. Lead is a bluish-white metal of bright luster, is very soft, 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. 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. 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 calbe covering, plumbing, ammunition, and in the manufacture of lead tetraethyl. 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. Care must be used in handling lead as it is a cumulative poison. Environmental concerns with lead poisoning has resulted in a national program to eliminate the lead in gasoline.

Source: CRC Handbook of Chemistry and Physics, 1913-1995. David R. Lide, Editor in Chief. Author: C.R. Hammond