Lead: the essentials
Lead is a bluish-white lustrous metal. It is very soft, highly malleable, ductile, and a relatively poor conductor of electricity. It is very resistant to corrosion but tarnishes upon exposure to air. Lead pipes bearing the insignia of Roman emperors, used as drains from the baths, are still in service. Alloys include pewter and solder. Tetraethyl lead (PbEt4) is still used in some grades of petrol (gasoline) but is being phased out on environmental grounds.
Lead isotopes are the end products of each of the three series of naturally occurring radioactive elements.
Cartoon by Nick D Kim ([Science and Ink], used by permission).
Lead: historical information
Lead has been known for ages and is mentioned in Exodus. Alchemists believed lead to be the oldest metal and associated it with the planet Saturn. They spent a lot of time trying to "transmute" lead into gold.
Lead is one of the elements which has an alchemical symbol, shown below (alchemy is an ancient pursuit concerned with, for instance, the transformation of other metals into gold).
Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions). This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for lead is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.]
Lead around us Read more »
Lead has no biological role. Lead affects the gut, central nervous system and causes anaemia.
Elemental lead is found in nature sparingly. Lead is present in ores such as galena (lead sulphide, PbS), anglesite (lead sulphate, PbSO4), minim (a form of lead oxide with formula Pb3O4), cerussite (lead carbonate, PbCO3) and other minerals. Galena is the most important source.
|Location||ppb by weight||ppb by atoms||Links|
|Human||1700 ppb by weight||50 atoms relative to C = 1000000|
Physical properties Read more »
Heat properties Read more »
- Melting point: 600.61 [327.46 °C (621.43 °F)] K
- Boiling point: 2022 [1749 °C (3180 °F)] K
- Enthalpy of fusion: 4.77 kJ mol-1
Crystal structure Read more »
The solid state structure of lead is: ccp (cubic close-packed).
Lead: orbital properties Read more »
Lead atoms have 82 electrons and the shell structure is 22.214.171.124.18.4. The ground state electronic configuration of neutral Lead is [Xe].4f14.5d10.6s2.6p2 and the term symbol of Lead is 3P0.
- Pauling electronegativity: 2.33 (Pauling units)
- First ionisation energy: 715.6 kJ mol‑1
- Second ionisation energy: 1450.5 kJ mol‑1
Isolation: there is usually little need to make lead metal in the laboratory as it is so cheap and readily available. Lead is isolated from the sulphide, PbS. The process involves burning in a restricted air flow followed by reduction of the resulting oxide PbO with carbon.
PbS + 3/2O2 → PbO + SO2
PbO + C → Pb + CO
PbO + CO → Pb + CO2
This gives lead usually contaminated with metals such as antimony, arsenic, copper, gold, silver, tin, and zinc. A fairly complex process is used to strip out these impurities.
Lead isotopes Read more »
Lead isotopes are used for medical and scientific purposes. Pb-206 and Pb-207 can both be used to produce the medical radioisotopes Bi-205 and Bi-206. Pb-204, Pb-206 and Pb-207 are used to measure lead levels in blood. Pb-208 has been used to produce neutron-rich isotopes of W and Lu. Pb-208 has also been used to study the configuration of neutron stars. Several Lead isotopes have also been used as target in the production of super heavy elements.
|204Pb||203.973020 (5)||1.4 (1)||0|
|206Pb||205.974440 (4)||24.1 (1)||0|
|207Pb||206.975872 (4)||22.1 (1)||1/2||0.58219|
|208Pb||207.976627 (4)||52.4 (1)||0|