Lead is a chemical element with symbol Pb (Plumbum in Latin) and atomic number 82. Lead is a soft and malleable metal, which is regarded as a heavy metal and when ingested, is poisonous. This metal is banned by the RoHS directive.
|Standard atomic weight Ar, std(Pb)||207.2(1)|
|Lead in the periodic table|
|Atomic number (Z)||82|
|Group||group 14 (carbon group)|
|Element category||Post-transition metal|
|Electron configuration||[Xe] 4f14 5d10 6s2 6p2|
|Electrons per shell||2, 8, 18, 32, 18, 4|
|Phase at STP||solid|
|Melting point||600.61 K (327.46 °C, 621.43 °F)|
|Boiling point||2022 K (1749 °C, 3180 °F)|
|Density (near r.t.)||11.34 g/cm3|
|when liquid (at m.p.)||10.66 g/cm3|
|Heat of fusion||4.77 kJ/mol|
|Heat of vaporization||179.5 kJ/mol|
|Molar heat capacity||26.650 J/(mol·K)|
|Oxidation states||−4, −2, −1, +1, +2, +3, +4 (an amphoteric oxide)|
|Electronegativity||Pauling scale: 1.87 (+2)|
|Atomic radius||empirical: 175 pm|
|Covalent radius||146±5 pm|
|Van der Waals radius||202 pm|
|Spectral lines of lead|
|Crystal structure||face-centered cubic (fcc)|
|Speed of sound thin rod||1190 m/s (at r.t.) (annealed)|
|Thermal expansion||28.9 µm/(m·K) (at 25 °C)|
|Thermal conductivity||35.3 W/(m·K)|
|Electrical resistivity||208 nΩ·m (at 20 °C)|
|Magnetic susceptibility||−23.0×10−6 cm3/mol (at 298 K)|
|Young's modulus||16 GPa|
|Shear modulus||5.6 GPa|
|Bulk modulus||46 GPa|
|Brinell hardness||38–50 MPa|
|Discovery||in the Middle East (7000 BCE)|
|Main isotopes of lead|
|Isotopic abundances vary greatly by sample|
Lead (//) is a chemical element with the symbol Pb (from the Latin plumbum) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cut, lead is silvery with a hint of blue; it tarnishes to a dull gray color when exposed to air. Lead has the highest atomic number of any stable element and three of its isotopes are endpoints of major nuclear decay chains of heavier elements.
Lead is a relatively unreactive post-transition metal. Its weak metallic character is illustrated by its amphoteric nature; lead and lead oxides react with acids and bases, and it tends to form covalent bonds. Compounds of lead are usually found in the +2 oxidation state rather than the +4 state common with lighter members of the carbon group. Exceptions are mostly limited to organolead compounds. Like the lighter members of the group, lead tends to bond with itself; it can form chains and polyhedral structures.
Lead is easily extracted from its ores; prehistoric people in Western Asia knew of it. Galena is a principal ore of lead which often bears silver. Interest in silver helped initiate widespread extraction and use of lead in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. In 2014, the annual global production of lead was about ten million tonnes, over half of which was from recycling. Lead's high density, low melting point, ductility and relative inertness to oxidation make it useful. These properties, combined with its relative abundance and low cost, resulted in its extensive use in construction, plumbing, batteries, bullets and shot, weights, solders, pewters, fusible alloys, white paints, leaded gasoline, and radiation shielding.
In the late 19th century, lead's toxicity was recognized, and its use has since been phased out of many applications. However, many countries still allow the sale of products that expose humans to lead, including some types of paints and bullets. Lead is a neurotoxin that accumulates in soft tissues and bones; it damages the nervous system and interferes with the function of biological enzymes, causing neurological disorders, such as brain damage and behavioral problems.