Carbon Facts - Atomic Number 6 or C

Carbon Chemical & Physical Properties

Graphite and diamond are two forms or allotropes of the element carbon.
Graphite and diamond are two forms or allotropes of the element carbon. Jeffrey Hamilton / Getty Images

Carbon is the element with atomic number 6 on the periodic table with symbol C. This nonmetallic element is the key to the chemistry of living organisms, primarily due to its tetravalent state, which allows it to form four covalent chemical bonds with other atoms. Here are facts about this important and interesting element.

Carbon Basic Facts

Atomic Number: 6

Symbol: C

Atomic Weight: 12.011

Discovery: Carbon exists free in nature and has been known since prehistoric time.

The earliest known forms were charcoal and soot. Diamonds were known in China at least as early as 2500 BCE. The Romans knew how to make charcoal from wood by heating it in a covered container to exclude air. René Antoine Ferchault de Réaumur showed iron was transformed into steel by the absorption of carbon in 1722. In 1772, Antoine Lavoisier demonstrated diamonds were carbon by heating diamond and charcoal and measuring the released carbon dioxide per gram.

Electron Configuration: [He]2s22p2

Word Origin: Latin carbo, German Kohlenstoff, French carbone: coal or charcoal

Isotopes: There are seven natural isotopes of carbon. In 1961 the International Union of Pure and Applied Chemistry adopted the isotope carbon-12 as the basis for atomic weights. Carbon-12 accounts for 98.93% of naturally-occurring carbon, while carbon-13 forms the other 1.07%. Biochemical reactions preferentially use carbon-12 over carbon-13.

Carbon-14 is a radioisotope that occurs naturally. It is made in the atmosphere when cosmic rays interact with nitrogen. Because it has a short half-life (5730 years), the isotope is almost absent from rocks, but the decay can be used for radiocarbon dating of organisms. Fifteen isotopes of carbon are known.

Properties: Carbon is found free in nature in three allotropic forms: amorphous (lampblack, boneblack), graphite, and diamond. A fourth form, "white" carbon, is thought to exist. Other allotropes of carbon include graphene, fullerenes, and glassy carbon. Diamond is one of the hardest substances, with a high melting point and index of refraction. Graphite, on the other hand, is extremely soft. The properties of carbon depend largely on its allotrope.

Uses: Carbon forms numerous and varied compounds with limitless applications. Many thousands of carbon compounds are integral to life processes. Diamond is prized as a gemstone and is used for cutting, drilling, and as bearings. Graphite is used as a crucible for melting metals, in pencils, for rust protection, for lubrication, and as a moderator for slowing neutrons for atomic fission. Amorphous carbon is used for removing tastes and odors.

Element Classification: Non-Metal

Toxicity: Pure carbon is considered to be non-toxic. It may be eaten as charcoal or graphite or used to prepare tattoo ink. However, inhalation of carbon irritates lung tissue and can lead to lung disease. Carbon is essential for life, as it is the building block for proteins, nucleic acids, carbohydrates, and fats.

Source: Carbon is the fourth most abundant element in the universe, after hydrogen, helium, and oxygen. It is the 15th most abundant element in the Earth's crust. The element forms in giant and supergiant stars via the triple-alpha process. When stars die as supernovae, carbon is scattered by the explosion and becomes part of the matter integrated into new stars and planets.

Carbon Physical Data

Density (g/cc): 2.25 (graphite)

Melting Point (K): 3820

Boiling Point (K): 5100

Appearance: dense, black (carbon black)

Atomic Volume (cc/mol): 5.3

Ionic Radius: 16 (+4e) 260 (-4e)

Specific Heat (@20°C J/g mol): 0.711

Debye Temperature (°K): 1860.00

Pauling Negativity Number: 2.55

First Ionizing Energy (kJ/mol): 1085.7

Oxidation States: 4, 2, -4

Lattice Structure: Diagonal

Lattice Constant (Å): 3.570

Crystal Structure: hexagonal

Electronegativity: 2.55 (Pauling scale)

Atomic Radius: 70 pm

Atomic Radius (calc.): 67 pm

Covalent Radius: 77 pm

Van der Waals Radius: 170 pm

Magnetic Ordering: diamagnetic

Thermal Conductivity (300 K) (graphite): (119–165) W·m−1·K−1

Thermal Conductivity (300 K) (diamond): (900–2320) W·m−1·K−1

Thermal Diffusivity (300 K) (diamond): (503–1300) mm²/s

Mohs Hardness (graphite): 1-2

Mohs Hardness (diamond): 10.0

CAS Registry Number: 7440-44-0

Quiz: Ready to test your carbon facts knowledge? Take the Carbon Facts Quiz

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  • Deming, Anna (2010). "King of the elements?". Nanotechnology. 21 (30): 300201. doi:10.1088/0957-4484/21/30/300201
  • Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.