Carbon Carbon Carbon (from "coal") is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Three isotopes occur naturally, C and C being stable, while C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique
Chemical file format element symbols B, C, N, O, F, P, S, Cl, Br, and I. The symbol "=" represents double bonds and "#" represents triple bonds. Branching is indicated by (). Rings are indicated by pairs of digits. Some examples are The XYZ file format is a simple format that usually gives the number of atoms in the first line, a comment on the second, followed by a number of lines with atomic symbols (or atomic numbers) and cartesian coordinates. The MDL number contains a unique identification number for each reaction and variation. The format is RXXXnnnnnnnn. R indicates a reaction, XXX