Atomic number: 6
Atomic weight: 12.0107 (8) g r
Group in periodic table: 14
Period in periodic table: 2
Block in periodic table: p-block
CAS registry ID: 7440-44-0
Carbon is a Group 14 element. Carbon is distributed very widely in nature. It is found in abundance in the sun, stars, comets, and atmospheres of most planets. The atmosphere of Mars contains 96 % CO2.
Carbon is found free in nature in three allotropic forms: amorphous, graphite, and diamond. Graphite is one of the softest known materials while diamond is one of the hardest. Carbon, as microscopic diamonds, is found in some meteorites. Natural diamonds are found in ancient volcanic "pipes" such as found in South Africa. Diamonds are also recovered from the ocean floor off the Cape of Good Hope. More recently, another form of carbon, buckminsterfullerene, C60, has been discovered. This new form of carbon is the subject of great interest in research laboratories today.
Carbon is present as carbon dioxide in the atmosphere and dissolved in all natural waters. It is a component of rocks as carbonates of calcium (limestone), magnesium, and iron. Coal, petroleum, and natural gas are chiefly hydrocarbons. Carbon is unique among the elements in the vast number of variety of compounds it can form. Organic chemistry, a 1/112th subset of inorganic chemistry, is the study of carbon and its compounds. While silicon might take the place of carbon in forming a host of related compounds, it is not possible currently to form stable compounds with very long chains of silicon atoms.
In 1961 the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope 12C as the basis for atomic weights. Carbon-14, 14C, an isotope with a half-life of 5730 years, is used to date such materials as wood, archeological specimens, etc. Carbon-13, 13C, is particularly useful for isotopic labelling studies since it is not radioactive, but is a spin I = 1/2 nucleus and therefore a good NMR nucleus.