Everything about Carbon-12 totally explained
Carbon-12 is the most
abundant of the two
stable isotopes of the element
carbon, accounting for 98.89% of carbon; it contains 6
protons, 6
neutrons and 6
electrons.
Carbon-12 is of particular importance as it's used as the standard from which
atomic masses of all
nuclides are measured: its mass number is by definition 12.
History
Prior to
1959 both the
IUPAP and
IUPAC tended to use
oxygen to define the
mole, the chemists defining the mole as the number of atoms of oxygen which had mass 16 g, the physicists using a similar definition but with the
oxygen-16 isotope only. The two organizations agreed in
1959/
1960 to define the mole as:
"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 1961 the isotope carbon-12 was selected to replace oxygen as the standard relative to which the atomic weights of all the other elements are measured
In
1980 the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their
ground state.
Further Information
Get more info on 'Carbon-12'.
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