Carbon (C)

Carbon (symbol C) is the chemical element with atomic number 6: a nonmetal, solid at 0 °C, with an atomic mass of 12.011 u. Known since antiquity.

Carbon has a unique ability to form long chains and rings by bonding to itself. That is why it is the backbone of every molecule of life, so much so that carbon chemistry is called “organic chemistry.” Depending on how its atoms are arranged, it becomes graphite, soft and black, or diamond, transparent and ultra-hard. Burned as coal, oil and gas, it powers the economy and drives global warming.

Key facts

Atomic number: 6
Symbol: C
French name: Carbone
Atomic mass: 12.011 u
Molar mass: 12.011 g/mol
Family: Nonmetals
Position: period 2, group 14, p-block
State at 0 °C: Solid
Melting point: 3,549.9 °C
Boiling point: 3,824.9 °C
Density: 2.27 g/cm³
Electronegativity (Pauling): 2.55
First ionization energy: 1,086 kJ/mol
Atomic radius: 70 pm
Electron configuration: [He] 2s² 2p²
Abundance in Earth's crust: 200 ppm (17th most abundant element)
Indicative price: 0.12 $/kg (order of magnitude)
Radioactive: no
Discovery: Antiquity

Origin of the name

From the Latin carbo, coal.

What does carbon look like?

Graphite: a shiny gray-black solid, smooth to the touch. Diamond: a transparent crystal, the hardest natural material. Charcoal and soot: dull black forms.

Where is carbon found?

The fourth most abundant element in the Universe, forged in stars. It makes up only about 0.02% of Earth's crust, mainly as limestone, but about 18% of the human body's mass. The atmosphere contains about 0.04% CO₂.

Natural sources

Graphite
Diamond
Coal
Calcite (limestone, chalk, marble)
Dolomite

How is carbon produced?

The world mines nearly 9 billion tonnes of coal a year. Natural graphite is mined (about 1.6 million tonnes a year), and synthetic graphite is made by heating petroleum coke to nearly 3,000 °C. Some 110 to 120 million carats of natural diamonds are mined each year, and far more industrial diamonds are synthesized.

Top producers

China
India
Indonesia
United States

What is carbon used for?

Fossil fuels: coal, oil, natural gas.
Coke for turning iron ore into steel.
Plastics, synthetic textiles and medicines.
Carbon fiber for bikes, aircraft and rackets.
Graphite anodes in lithium-ion batteries.
Carbon-14 dating in archaeology.

In everyday life

Your pencil “lead” (graphite and clay)
Barbecue charcoal
Plastic bottles
Your car's tires (carbon black)
A diamond ring

Role in living things

The foundation of life: proteins, sugars, fats and DNA are all built on carbon skeletons. Plants capture CO₂ from the air through photosynthesis, and we breathe it back out.

Hazards of carbon

Pure carbon is of low toxicity, but its compounds can be dangerous: odorless carbon monoxide (CO) is a deadly poison, and fine soot particles harm the lungs. CO₂ from fossil fuels is the main cause of climate change.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of carbon

Charcoal and soot have been known since prehistory: the cave paintings of Lascaux contain them. In the 1770s Lavoisier showed that diamond burns to give carbon dioxide, and in 1797 Smithson Tennant proved it is pure carbon. The name comes from the Latin carbo, “charcoal.”

Did you know?

Pencil “lead” contains no lead at all: graphite was long mistaken for a lead ore.
Graphene, a sheet of graphite just one atom thick, earned Andre Geim and Konstantin Novoselov the 2010 Nobel Prize in Physics; they had isolated it with sticky tape.
Diamonds are not forever at the surface: at ordinary pressure they very slowly tend to turn into graphite, but it would take billions of years.
Fullerenes, 60-carbon molecules shaped like a soccer ball, were discovered in 1985.

Isotopes of carbon

Two stable isotopes, including carbon-12, the yardstick for atomic mass. Radioactive carbon-14 is used to date the remains of living things.

carbon-11: radioactive, half-life 20.4 min. Tracer for PET (positron emission tomography) medical imaging.
carbon-12: 98.94% of natural carbon, stable. The atomic mass standard: one carbon-12 atom weighs exactly 12 u.
carbon-13: 1.06% of natural carbon, stable. Tracer in medicine (the breath test for Helicobacter pylori bacteria) and in NMR.
carbon-14: radioactive, half-life 5,730 years. Radiocarbon dating of organic remains up to ~50,000 years old.

Common compounds

Glucose (C₆H₁₂O₆) · Table sugar (C₁₂H₂₂O₁₁) · Alcohol (C₂H₅OH) · Caffeine (C₈H₁₀N₄O₂) · Urea (CO(NH₂)₂) · Citric acid (C₆H₈O₇) · Vitamin C (C₆H₈O₆) · Aspirin (C₉H₈O₄) · Paracetamol (C₈H₉NO₂) · Chlorophyll a (C₅₅H₇₂MgN₄O₅) · Baking soda (NaHCO₃) · Vinegar (CH₃COOH) · Limestone (CaCO₃) · Butane (C₄H₁₀) · Propane (C₃H₈) · Carbon dioxide (CO₂) · Methane (CH₄) · Malachite (Cu₂CO₃(OH)₂) · Silicon carbide (SiC) · Freon (CFC-12) (CCl₂F₂)

Related elements

Same family (nonmetals): Hydrogen (H), Nitrogen (N), Oxygen (O), Phosphorus (P), Sulfur (S), Selenium (Se).

Same column (group 14): Silicon (Si), Germanium (Ge), Tin (Sn), Lead (Pb), Flerovium (Fl).