Carbon-12 is the most abundant (98.89%) of the two stable isotopes of the element carbon. It contains 6 protons, 6 neutrons and 6 electrons.
Carbon-12 is of particular importance as it is used as the standard from which all other isotopes' atomic weight is measured and thus the measurement of Avogadro's number.
History
Prior to 1959 both the IUPAP and IUPAC tended to use used oxygen to define the mole, the chemists defining the mole as the number of atoms of oxygen which had mass 16g, the physisits using a similar definition but with the oxygen-16 isotope only. The two organisations agreed in 1959/1960 to define the mole as such:
"The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol.""
This was adopted by the CIPM (International Committee for Weights and Measures) in 1967, and in 1971 it was adopted by the 14th CGPM (General Conference on Weights and Measures)
In 1980 the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their ground state.
See also
