Carbon

Carbon is the non-metallic chemical element of atomic number 6 in Group 14 of the periodic table, symbol C, atomic weight 12.01, specific gravity as graphite 2.25, as diamond 3.51. Its stable isotopes are ¹²C (98.90%) and ¹³C (1.10%). The weight of the ¹²C atom is the international standard on which atomic weights are based. It is defined as weighing exactly 12.00000 atomic mass units.

Carbon has been known since prehistoric times. It gets its name from carbo, the Latin word for charcoal, which is almost pure carbon. In various forms, carbon is found not only on Earth, but in the atmospheres of other planets, in the Sun and stars, in comets, and in some meteorites.

On Earth, carbon can be considered to be the most important of all the chemical elements, because it is the essential element in practically all of the chemical compounds in living things. Carbon compounds are what make the processes of life work. Beyond Earth, carbon-atom nuclei are an essential part of the nuclear fusion reactions that produce the energy of the Sun and of many other stars. Without carbon, the Sun would be cold and dark.

It is obviously impossible to summarize the properties of carbon's millions of compounds in one place. Introductory textbooks of organic chemistry generally run well over a thousand pages, and biochemistry textbooks run thousands more. But organic compounds can be classified into families that have similar properties, because they have certain groupings of atoms in common.