Carbon (C)

Stable isotopes of carbon available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
C-13 6 7 13.00335484 1.10% >99.00% Gas

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Carbon has been known since ancient times, most familiarly as coal, charcoal, soot and diamond. Its name derives from the Latin word carbo, meaning “coal” or “charcoal.” Carbon exists in three allotropic forms — diamond, graphite and fullerenes — each differing distinctly from others in physical and chemical properties:

Diamond [7782-40-0] is one of the hardest substances known. It has a Mohs hardness of 10.0, a density of 3.513 g/cm3, and a melting point of about 3700 ºC. Carbon atoms in diamonds are arranged in cubic form, having stacking layers perpendicular to the diagonals of the cube. The diamond also occurs in hexagonal form, which is less stable than the cubic form. The hexagonal form of diamond is found in meteorites and can be synthesized.

Graphite [7440-44-0] is a black hexagonal crystal. The hexagonal layer has each carbon atom surrounded by three other carbon atoms. The C-C bond length is 1.415 Å. Because of the very weak van der Waal forces between the hexagonal layers, graphite is one of the softest solids, with a high lubricity and a density of 2.25 g/cm3. Graphite exhibits two manifestations: the stable hexagonal form that commonly occurs at ambient conditions, and a less stable rhombohedral form. Graphite can be converted to diamond under high temperatures (about 1400 ºC) and very high pressures (in the range of 4000-5000 atm) in the presence of a metal catalyst such as iron or nickel.

Fullerenes [99685-96-8] are polyhedral carbon allotropes consisting of large carbon molecules containing 60 to 120 carbon atoms. They are found in soot, charcoal, carbon black and many other carbonaceous matters, and they have high electrical conductivity and chemical reactivity.

Carbon is also produced and used in other forms — such as activated carbon, carbon black and coke — that have many commercial applications: purification of water and air, air analysis, waste treatment, removal of sulfur dioxide from stack gases, and decolorization of sugar. Carbon black includes several forms of artificially prepared carbon, such as furnace black, channel black, lamp black and animal charcoal, and is commonly used in typewriter ribbons, printing inks, carbon paper, paint pigments, and as an absorber for solar energy and UV radiation. Elemental carbon has many important applications: the diamond is a precious gem; graphite is used as an electrode and has numerous other applications; the isotope Carbon-14 is used in carbon dating; and the isotope Carbon-13 is used in tracer studies and nuclear magnetic resonance (NMR) imaging. 

Properties of Carbon

Name Carbon
Symbol C
Atomic number 6
Atomic weight 12.0107
Standard state Solid at 298 °K
CAS Registry ID 7440-44-0 (graphite)
Group in periodic table 14
Group name None
Period in periodic table
Block in periodic table p-block 
Color Graphite is black; diamond is colorless
Classification Non-metallic
Melting point 3500 °C
Boiling point 4027 °C
Thermal conductivity 140 W/(m·K)
Electrical resistivity About 1000 - direction dependent 10-8 Ω·m
Electronegativity 2.55 
Heat of vaporization 715 (sublimation) kJ·mol-1
Heat of fusion 117 (per mole carbon atoms) kJ·mol-1
Density of solid 2.267 g/cm3
Atomic radius 0.77 Å
Electron configuration [He]2s22p2
Oxidation state +4

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