These are the most common naturally occurring isotopes of oxygen and carbon, respectively. An atom of carbon-14 contains 6 protons and 8 neutrons and is denoted Certain isotopes of elements are unstable, giving off ionizing radiation, also known as radioactivity.
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. 1979, 1986 © Harper Collins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Cite This Source radiocarbon dating A technique for measuring the age of organic remains based on the rate of decay of carbon 14.
But in graphite, each carbon atom bonds only to three others in a much looser arrangement of layers, each of which is weakly bonded to neighboring layers.
Because individual layers of carbon in graphite are so loosely connected, they are easily scraped away, which is why it is used as pencil "lead" for writing.
Carbon 14 has a half-life of 5,780 years, and is continuously created in Earth's atmosphere through the interaction of nitrogen and gamma rays from outer space.
Because atmospheric carbon 14 arises at about the same rate that the atom decays, Earth's levels of carbon 14 have remained fairly constant.
Atomic number 6; atomic weight 12.011; sublimation point 3,825°C; triple point 4,489°C; specific gravity of amorphous carbon 1.8 to 2.1, of diamond 3.15 to 3.53, of graphite 1.9 to 2.3; valence 2, 3, 4. a nonmetallic element existing in the three crystalline forms: graphite, diamond, and buckminsterfullerene: occurring in carbon dioxide, coal, oil, and all organic compounds.
The isotope carbon-12 has been adopted as the standard for atomic wt; carbon-14, a radioisotope with a half-life of 5700 years, is used in radiocarbon dating and as a tracer. gr.: (of diamond) 3.51 at 20°C; (of graphite) 2.26 at 20°C.
In diamond, each carbon atom bonds to four others in a dense network that makes the material the hardest substance known.
Symbol: C; atomic no: 6; atomic wt: 12.011; valency: 2, 3, or 4; relative density: 1.8–2.1 (amorphous), 1.9–2.3 (graphite), 3.15–3.53 (diamond); sublimes at 3367±25°C; boiling pt: 4827°C 1. Symbol C A naturally abundant, nonmetallic element that occurs in all organic compounds and can be found in all living things. Proteins, sugars, fats, and even DNA all contain many carbon atoms.
a nonmetallic element found combined with other elements in all organic matter and in a pure state as diamond and graphite. Diamonds and graphite are pure forms, and carbon is a major part of coal, petroleum, and natural gas. The element carbon is also important, however, outside the chemistry of living things.
Symbol C An abundant nonmetallic element that occurs in many inorganic and in all organic compounds, exists freely in amorphous, graphite, and diamond forms and as a constituent of coal, limestone, and petroleum, and is capable of chemical self-bonding to form an enormous number of chemically, biologically, and commercially important molecules.
Other significant allotropes include fullerenes and nanotubes.The Table of Radionuclides documents the naturally-occurring radioisotopes.