Atomic number 82

Lead

Pb
+ phase
− phase

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82 electrons in 6 shells: 2, 8, 18, 32, 18, 4.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Post-transition metal
Period: 6
Group: 14
Block: p
Standard atomic weight: 207.2(11) Da
Electron configuration: [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p²
Phase at 25 °C: solid
Melting point: 327.46 °C
Boiling point: 1749 °C
Density: 11.342 g/cm³
Electronegativity (Pauling): 2.33
Discovered: Prehistoric times

Neighbours in the table

Lead spreads 82 electrons across six shells, 2, 8, 18, 32, 18 and 4, and its configuration ends [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p². The filled d and f subshells count as core; the valence electrons are the four in 6s and 6p. Group 14 sets an oxidation state of +4, yet lead’s common ion is Pb²⁺: the two 6p electrons, added last, leave first, and the 6s pair stays behind. OpenStax names this the inert pair effect, a stable ion whose oxidation state sits two below the group’s.

Lead does reach +4, but in covalent compounds rather than as an ion; PbCl₄ is a low-boiling liquid. Lead(IV) tends to fall back to lead(II) by taking on two electrons, so lead dioxide, PbO₂, is a powerful oxidising agent. Burn the metal in air and the product is PbO, not the dioxide.

Group 14 runs from carbon, a nonmetal, through the metalloids silicon and germanium to the metals tin and lead. Metallic character grows down a group because an outer electron farther from the nucleus is easier to remove. Los Alamos describes lead as bluish-white and lustrous, very soft, malleable, ductile and, for a metal, a poor conductor of electricity. It melts at 327.46 °C, where transition metals need over 1000 °C, a gap OpenStax reads as weaker metallic bonding.

Where it is found

A kilogram of crust holds about 14 milligrams of lead on PubChem’s element record, and a litre of seawater 3 × 10⁻⁵ milligrams. Jefferson Lab’s text there still declines to call lead rare, because mining and refining it is easy. Native metal turns up, but seldom; the ores are galena, PbS, with anglesite, PbSO₄, cerussite, PbCO₃, and the red oxide Pb₃O₄.

The US Geological Survey puts world mine output for 2024 at about 4.3 million metric tons of contained lead, 1.9 million of it from China. Reserves stand at 96 million tons, over a third in Australia. American ore comes from five Missouri mines, with by-product lead from zinc mining in Alaska and silver mining in Idaho.

Roasting galena in hot air frees the metal, the route Jefferson Lab and Los Alamos both describe. Slag heaps in Asia Minor and on Aegean islands show silver being separated from lead by about 3000 BC. Most American lead is now recycled rather than mined: secondary refineries took about a million tons from old scrap in 2024, 70 per cent of US use. The last primary refinery closed in 2013.

Why it matters

Most lead goes into lead-acid batteries: 86 per cent of reported US consumption in 2024, by the US Geological Survey’s count. They start cars, back up computer and telecommunications networks, and supply motive power. Each spent battery is feedstock for the next: nearly all the secondary lead of 2024 came from old scrap, mostly batteries.

Jefferson Lab credits lead’s density for its use as shielding around X-ray machines and nuclear reactors. Tanks for sulfuric acid rely instead on its resistance to corrosion. Solder, about half lead and half tin, joins electrical parts because the alloy melts at a relatively low temperature. Tin, plastics, steel and zinc now replace it in solder, cable sheathing, cans and wheel weights.

Los Alamos counts four stable isotopes in natural lead, and three of them close the uranium, actinium and thorium decay series. Their parents decay far more slowly than the isotopes after them, so a rock’s radiogenic lead, the lead those decays have left, measures its age. Uranium-lead dating gave some of the first accurate ages for the Earth, about 4.55 × 10⁹ years. Because rocks of different ages and makeup leave different mixtures, lead from one place carries its own isotopic signature. That is how lead in the Iceman mummy’s teeth and bones helped fix his place of origin.

Properties

Properties of lead Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	82
Standard atomic weight	207.2(11) Da	Da	IUPAC/CIAAW 2024
Melting point	327.46 °C	°C	Los Alamos: 327.46 °C
Boiling point	1749 °C	°C	Los Alamos: 1749 °C
Density	11.342 g/cm³	g/cm³
Electronegativity (Pauling)	2.33
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p²
Phase at 25 °C	solid

The standard atomic weight of this element is an interval in nature, from 206.14 to 207.94 Da; the value shown is IUPAC's conventional abridged value.

Safety

Lead metal is a cumulative poison, and PubChem classifies both powder and solid pieces Danger for harm to fertility, unborn and breast-fed children, and aquatic life. Repeated exposure affects the blood, nervous system and kidneys, and the CDC has identified no safe level of lead in a child’s blood. Children under six are more likely to be exposed, through peeling paint in homes built before 1978 and water from lead pipes; workers who process the metal are NIOSH’s concern. The PubChem Laboratory Chemical Safety Summary, NIOSH pocket guide and CDC page are the sheets to read.

Questions

Why is lead used in car batteries?

A lead-acid cell stands an electrode of lead metal and one of lead dioxide in sulfuric acid, and OpenStax gives its output as about 2 V. Six cells wired in series make the 12 V battery in a car. The chemistry is inexpensive and delivers the high current a starter motor draws, which OpenStax says keeps it the usual choice. The batteries are heavy and hold caustic acid; spent ones need proper disposal, and recycled batteries supply most US lead.

Why does lead block X-rays?

Jefferson Lab's text in PubChem's record gives one reason, density: a cubic centimetre of lead weighs 11.342 g, against 7.874 g for iron and 2.7 g for aluminium. Los Alamos lists the same use, shielding around X-ray equipment and nuclear reactors, beside lead's work as an absorber of sound and vibration. The electronics industry has moved to flat-panel displays, which need no lead shield, and the US Geological Survey counts that among the substitutions for the metal.

Why is lead's symbol Pb?

The two letters abbreviate plumbum, the Latin name for the metal, according to the IUPAC history text in PubChem's element record. The English word has a separate ancestry: it comes from the Anglo-Saxon lead, whose own origin is unknown. Symbol and name descend from two languages and have no letter in common. Los Alamos adds that the alchemists held lead to be the oldest of the metals and linked it with the planet Saturn.

Is lead still used in gasoline and paint?

Far less than it was. Los Alamos records a national programme to take lead out of gasoline and says its use in paint has been sharply cut for health reasons. White lead paint was lead carbonate, now largely replaced by titanium dioxide. The CDC names chipping paint in buildings put up before 1978 as a source of childhood exposure. PubChem's safety sheet quotes a 1997 book: about 90 per cent of pre-1940 homes hold lead-based paint.

Why are Roman lead pipes still in use?

Because lead reacts very slowly with air. OpenStax lists it among the metals that can be won from ore and used for that reason. The surface reacts with air to form a protective coating, which the book calls passivation. Lead is also only slightly easier to oxidise than hydrogen and normally needs a hot concentrated acid to attack it. Los Alamos reports drain pipes from Roman baths, stamped with emperors' insignia, still in service.