Carbon-12 Carbon-12 Carbon-12 (C) is the more abundant of the two stable isotopes of carbon (Carbon-13 being the other), amounting to 98.93% of the element carbon; its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured, thus, its atomic mass is exactly 12 daltons by definition. Its nucleus contains 6 protons and 6 neutrons. Before 1959 both the IUPAP and IUPAC used oxygen to define the mole; the chemists defining the mole as the number of
Chemical element Chemical element A chemical element is a species of atoms having the same number of protons in their atomic nuclei (that is, the same atomic number, or "Z"). For example, the atomic number of oxygen is 8, so the element oxygen consists of all atoms which have exactly 8 protons. 118 elements have been identified, of which the first 94 occur naturally on Earth with the remaining 24 being synthetic elements. There are 80 elements that have at least one stable isotope and 38 that have exclusively radionuclides, which decay over time into other elements. Iron is the most abundant