History
Date: 2015-10-07; view: 502.
Text 2
Text 1
METALLURGY
UNIT 4
| 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·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 | ||||||||||||||
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| 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 |
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.
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