Chemistry. Chemical element with the symbol C. Carbon occurs in all organic life and is the basis of carbon compounds such as carbohydrates, proteins, lipids and nucleic acids. This nonmetal also has the chemical property of being able to bond with itself and can build chains and rings of any length and structure. It exists freely as graphite and diamond and as a constituent of coal, limestone, and petroleum. Carbon dioxide is a component of the atmosphere and of the oceans in form of bicarbonate (carbon cycle). The radioactive isotope Carbon-14 (14C) is used in radiocarbon dating.