Lead

Lead, ₈₂Pb
General properties
Pronunciation	/lɛd/ (LED)
Appearance	metallic gray
Standard atomic weight (Ar, standard)	207.2(1)
Lead in the periodic table
	thallium ← lead → bismuth
Atomic number (Z)	82
Group	group 14 (carbon group)
Period	period 6
Element category	post-transition metal
Block	p-block
Electron configuration	[Xe] 4f14 5d10 6s2 6p2
Electrons per shell	2, 8, 18, 32, 18, 4
Physical properties
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)
Atomic properties
Oxidation states	4, 3, 2, 1, −1, −2, −4 (an amphoteric oxide)
Electronegativity	Pauling scale: 1.87 (+2)
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
	Spectral lines
	Spectral lines
Miscellanea
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 ordering	diamagnetic
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
Poisson ratio	0.44
Mohs hardness	1.5
Brinell hardness	38–50 MPa
CAS Number	7439-92-1
History
Discovery	in the Middle East (7000 BCE)
Main isotopes of lead
	Isotopic abundances vary greatly by sample
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Lead is a chemical element with 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 has a relatively low melting point. When freshly cut, lead is bluish-white; 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 each conclude a major decay chain 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, rings and polyhedral structures.

Lead is easily extracted from its ores; prehistoric people in Western Asia knew of it. Galena, a principal ore of lead, often bears silver, interest in which 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, 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. Lead is a neurotoxin that accumulates in soft tissues and bones, damages the nervous system, and causes blood disorders. It is particularly problematic in children, in that permanent brain damage may result, even if blood levels are promptly normalized with treatment.