Lead – facts and properties
- Symbol
- Pb
- Atomic number
- 82
- Atomic mass
- 207.2 u
- Period
- 6
- Group
- 14
- Category
- metal
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p²
- Electronegativity
- 2.33
- Atomic radius
- 154 pm
- Valence electrons
- 4
- State at standard conditions
- solid
- Melting point
- 327.46 °C
- Boiling point
- 1749 °C
- Density
- 11.342 g/cm³
- Discovered
- known since antiquity
Lead is a soft, dense metal with atomic number 82. A fresh cut shines bluish white, but the surface quickly turns grey. Its symbol Pb comes from the Latin plumbum. Lead forms the plates of car batteries and shields against X-rays, and it once formed the water pipes of whole cities. It is also a poison that builds up in the body. For that reason it has been largely removed from petrol, paint and drinking water pipes.
Position in the periodic table
Occurrence and extraction
Lead is more common in the crust than most heavy metals. The main ore is galena, PbS, a grey, metallic-looking lead sulfide that grows in cube-shaped crystals.
To extract it, galena is roasted in air: the sulfur burns to sulfur dioxide and lead oxide is left behind. In a shaft furnace, coke then reduces the oxide to the metal. Today more than half of all lead comes from recycling, mainly from old car batteries.
Lead has been known since antiquity, so there is no year of discovery. The Romans mined it on a large scale as a by-product of silver production. Even Greenland ice shows raised lead levels from ancient smelting.
Properties and reactions
Lead is in period 6 and group 14, below tin, to the right of thallium and to the left of bismuth. Its electron configuration, [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p², ends in two 6p electrons, and its electronegativity is 2.33. A density of 11.342 g/cm³ makes the metal more than eleven times as dense as water. It melts as low as 327.46 °C but boils only at 1749 °C.
Lead belongs to the carbon group and has 4 valence electrons. Unlike carbon and silicon, however, it prefers the oxidation state plus two, because the two 6s electrons stay out of many reactions. Lead(IV) compounds such as brown lead dioxide, PbO₂, are therefore strong oxidising agents.
Lead ends the three natural decay series: uranium-238, uranium-235 and thorium-232 turn into the stable isotopes lead-206, lead-207 and lead-208 through many radioactive steps. Lead-208 is the heaviest stable nucleus of all. The ratio of uranium to lead in minerals reveals the age of rocks. In the 1950s Clair Patterson used lead isotopes from meteorites to date the Earth: about four and a half billion years.
Lead ions block enzymes needed for the red blood pigment, damage nerves and kidneys, and are stored in the bones. Children are at particular risk because their brains are still developing. No completely harmless intake is known. Lead compounds are unsuitable for school experiments.
Uses in everyday life and technology
The most important use is the lead-acid battery, invented by Gaston Planté in 1859. As a starter battery it sits in almost every petrol or diesel car. A plate of lead and a plate of lead dioxide dip into dilute sulfuric acid. On discharge, lead sulfate forms on both plates: Pb + PbO₂ + 2 H₂SO₄ → 2 PbSO₄ + 2 H₂O. Lead batteries are almost entirely recycled.
Because of its high density, lead weakens X-rays and gamma rays strongly. X-ray rooms are therefore lined with lead, and lead glass serves as a see-through window in radiation protection. Lead also goes into cable sheathing, weights and lead crystal, whose sparkle comes from lead oxide.
The Latin plumbum lives on in the symbol Pb, in the word plumber, a tradesman who once laid lead pipes, and in the German Plombe, a lead seal. Historians dispute whether lead poisoning helped bring down Rome.
In the twentieth century tetraethyl lead was added to petrol to stop engines knocking. The exhaust spread lead around the world. Because catalytic converters cannot tolerate lead and the health effects were known, leaded petrol was phased out step by step. It has been banned in the EU since 2000, and in 2021 the United Nations announced that it is no longer sold anywhere in the world. Lead paints, new lead pipes for drinking water and lead solder in electronics are largely banned in the EU as well.
Molecules containing this element
- Lead(II) oxide PbO
- Lead(IV) oxide PbO2
- Tetramethyllead Pb(CH3)4
Quick question
Which element is the main component of graphite in pencil cores?
FAQ
Is lead toxic?
Yes, lead and its compounds are toxic. Lead disturbs the formation of blood, damages nerves and kidneys, and is stored in the bones. Children are especially at risk. No completely harmless amount is known, which is why lead pipes, lead paint and leaded petrol were banned.
Why is the symbol for lead Pb?
The symbol comes from the Latin word plumbum. The English word plumber has the same origin, because the Romans made their water pipes from lead.
What is lead used for today?
Mainly for lead-acid batteries, which serve as starter batteries in cars. Lead also shields against X-rays and gamma rays and is found in weights, cable sheathing and lead glass. Most of it is recycled.