Carbon C

Discovery

Carbon has been known since prehistory in the form of soot and charcoal, which early humans used for cave paintings and for smelting metals. Diamonds were prized in ancient India. What nobody knew was that these very different substances were the same element.

In the 1770s Antoine Lavoisier showed that diamond burns to form 'fixed air', the gas we call carbon dioxide, just as charcoal does. In 1796 Smithson Tennant demonstrated that equal masses of diamond and charcoal produce the same amount of carbon dioxide, proving that diamond is pure carbon. Graphite, long mistaken for a form of lead, was recognised as carbon in 1779 by Carl Wilhelm Scheele.

The twentieth century revealed new forms. Buckminsterfullerene, a football-shaped C60 molecule, was discovered in 1985 and earned a Nobel Prize in 1996. Carbon nanotubes were described in detail in 1991, and in 2004 Andre Geim and Konstantin Novoselov isolated graphene, a single atomic layer of graphite, winning the 2010 Nobel Prize in Physics.

Origin of the name

The name comes from the Latin carbo, meaning charcoal or coal. Lavoisier included carbone in his 1789 list of elements. The symbol is C.

Main uses

• Energy: coal, oil and natural gas, all carbon-based fuels, still supply most of the world's energy.
• Steel: small amounts of carbon turn iron into steel, and coke is used to reduce iron ore.
• Materials: graphite serves in pencils, lubricants and battery anodes; carbon fibre makes light, strong sporting goods and aircraft parts.
• Industry: diamonds cut and polish hard materials; activated carbon purifies water and air.
• Chemistry: plastics, medicines, dyes and solvents are all organic, carbon-based compounds.

Isotopes

Carbon has two stable isotopes: carbon-12, about 98.9 percent, and carbon-13, about 1.1 percent. Carbon-12 defines the atomic mass unit. Carbon-13 is used in NMR spectroscopy and in breath tests for stomach infections.

Carbon-14 is radioactive with a half-life of about 5,730 years. It forms continuously in the upper atmosphere and enters living things; after death the amount decays steadily, which lets scientists date organic remains up to around 50,000 years old. Willard Libby developed this radiocarbon method and received the 1960 Nobel Prize in Chemistry.

In everyday life

Carbon makes up about 18 percent of the human body by mass. Plants capture carbon dioxide by photosynthesis, and animals release it when they breathe. Burning fossil fuels has raised atmospheric carbon dioxide well above pre-industrial levels, driving climate change.

Carbon monoxide, produced by incomplete burning, is a colourless and odourless poison, which is why homes with fuel-burning appliances benefit from CO alarms.