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.
|Name, symbol||lead, Pb|
|Lead in the periodic table|
|Atomic number (Z)||82|
|Group, block||group 14 (carbon group), p-block|
|Element category||post-transition metal|
|Standard atomic weight (±) (Ar)||207.2(1)|
|Electron configuration||[Xe] 4f14 5d10 6s2 6p2|
Electrons per shell
|2, 8, 18, 32, 18, 4|
|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, 3, 2, 1, −1, −2, −4 (an amphoteric oxide)|
|Electronegativity||Pauling scale: 1.87|
|Ionization energies||1st: 715.6 kJ/mol
2nd: 1450.5 kJ/mol
3rd: 3081.5 kJ/mol
|Atomic radius||empirical: 175 pm|
|Covalent radius||146±5 pm|
|Van der Waals radius||202 pm|
|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 (χmol)||−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||by Middle Easterns (7000 BCE)|
|Most stable isotopes of lead|
Lead is a chemical element with atomic number 82 and symbol Pb (after the Latin plumbum). When freshly cut, it has a bluish-white color that soon tarnishes to a dull gray upon exposure to air. Lead is a soft, malleable, and heavy metal; its density of 11.34 g/cm3 exceeds that of most common materials. Lead has the second highest atomic number of all practically stable elements. As such, it is located at the end of three major decay chains of heavier elements, which, in part, accounts for lead's relative abundance: its stability exceeds those of other similarly numbered elements.
Lead is a post-transition metal and is relatively inert unless powdered. Its weak metallic character is illustrated by its amphoteric nature—lead and lead oxides react with both acids and bases—and tendency to form covalent bonds. Compounds of lead are most commonly found in the +2 oxidation state, rather than +4, unlike the lighter group 14 elements of the periodic table; exceptions are mostly limited to organolead compounds. Like the lighter group 14 elements, lead exhibits a tendency to bond to itself; it can form chains, rings, and polyhedral structures.
Lead is easily extracted from ore, and it was known to prehistoric people in Western Asia. A principal ore of lead, galena, often bears silver, and interest in silver helped initiate widespread lead production and use in ancient Rome. Lead production declined after the fall of Rome and did not reach comparable levels until the Industrial Revolution. Today, lead is produced in quantities of around ten thousand tonnes annually; secondary production from recycling is gaining ground, accounting for around half of that figure.
Lead has several properties that make it useful: high density, low melting point, ductility, and relative inertness to oxidation. Combined with its relative abundance and low cost, these factors have led to its widespread use, including in building construction, batteries, bullets and shot, weights, solders, pewters, fusible alloys, and for radiation shielding. In the late nineteenth century, lead came to be recognized as poisonous, and since that time, lead has been and is being phased out for many applications. Lead is a neurotoxin that accumulates in soft tissues and bones, damaging the nervous system and causing brain disorders and, in mammals, blood disorders.