Carbon
[He] 2s² 2p² · 2 · 4
The element life is built from. Four valence electrons let carbon bond to itself in endless chains, rings and cages — over ten million carbon compounds are known, more than for all the other elements combined.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 6
- Atomic mass
- 12.011 а.е.м.
- Electron configuration
- [He] 2s² 2p²
- Electrons per shell
- 2 · 4
- Block
- p-block
- Group
- Carbon group
- Period
- 2
- Electronegativity (Pauling)
- 2.55
- Electronegativity (Allen)
- 2.54
- Atomic radius
- 67 pm
- Covalent radius
- 76 pm
- Van der Waals radius
- 170 pm
- Ionisation energy 1
- 1 086.5 kJ/mol
- Ionisation energy 2
- 2 352.6 kJ/mol
- Ionisation energy 3
- 4 620.5 kJ/mol
- Ionisation energy 4
- 6 222.7 kJ/mol
- Ionisation energy 5
- 37 831 kJ/mol
- Electron affinity
- 153.9 kJ/mol
- Common oxidation states
- -4, +2, +4
- Oxidation states
- -4, -3, -2, -1, 0, +1, +2, +3, +4
Physical properties
- State at 25 °C
- solid
- Density
- 2.267 g/cm³
- Melting point
- 3 823 K · 3 549.9 °C
- Boiling point
- 4 098 K · 3 824.9 °C
- Speed of sound
- 18 350 m/s
Thermal properties
- Heat of fusion
- 117 kJ/mol
- Heat of vaporisation
- 355 kJ/mol
- Specific heat capacity
- 0.709 J/(g·K)
- Thermal conductivity
- 140 W/(m·K)
Mechanical properties
- Young's modulus
- 1 050 GPa
- Shear modulus
- 478 GPa
- Bulk modulus
- 33 GPa
- Poisson ratio
- no data
- Mohs hardness
- 10
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 7 837 nΩ·m
- Magnetic ordering
- diamagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal layered (graphite)
- Lattice constants
- a = 246.4 pm · c = 671.1 pm
Abundance
- In the crust
- 200 mg/kg
- In the ocean
- 28 mg/L
- In the universe
- 5·10⁶ mg/kg
- In the human body
- 230 000 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 12C | 98.93 % | stable | — |
| 13C | 1.07 % | stable | — |
| 14C | — | 5 700.8 yr | β− |
Carbon-14 is made in the atmosphere by cosmic rays and, with a 5700-year half-life, underpins radiocarbon dating; carbon-13 is the workhorse of NMR spectroscopy.
Discovery
- Year of discovery
- known since antiquity
- Discovered by
- known since antiquity
- Where
- no data
- Origin of the name
- from Latin carbo (coal, charcoal)
History
Carbon as charcoal and soot goes back to prehistory, and diamond has been prized for millennia. Lavoisier proved in 1772 that diamond and graphite are one substance, by burning a diamond at the focus of a lens and getting nothing but carbon dioxide.
Where it occurs
Only 200 mg/kg of the crust, but carbon is the element that circulates between atmosphere, ocean, rock and living matter. The main reservoirs are carbonate rock, coal, oil and gas.
How it is produced
Graphite is mined and also synthesised by the Acheson process from petroleum coke. Industrial diamond is made at 5 GPa and 1500 °C, or grown from the vapour phase.
Role in living things
Carbon is the second most massive element in a human body after oxygen, about 18 %. The backbone of every biomolecule — protein, DNA, lipid, sugar — is a carbon chain.
Safety
Carbon itself is non-toxic. The danger is in incomplete combustion: carbon monoxide binds haemoglobin 200 times more tightly than oxygen, and soot is carcinogenic.
Uses
- Steel: a fraction of a per cent of carbon turns soft iron into something you can harden
- Graphite electrodes for arc furnaces and anodes for aluminium smelting
- Carbon fibre and composites, from aircraft to bicycle frames
- Activated charcoal for water and air purification and in medicine
- Diamond tooling for cutting, drilling and grinding
Curiosities
- Diamond and graphite differ only in how the atoms are joined, yet differ by a factor of thousands in hardness.
- Graphene — carbon one atom thick — is two hundred times stronger than steel at the same cross-section.
- Carbon does not melt at ordinary pressure: it sublimes at around 3900 K.
- Carbon-12 has an atomic mass of exactly 12 by definition; the whole atomic mass scale is built on it.
- The C₆₀ fullerene is shaped like a football, and its discovery won the 1996 Nobel Prize.