"Counting (or calculating) the number of atoms in 28.0855 g of silicon is one way of determining the Avogadro constant, NA, and a way which is currently receiving a lot of attention (see below) although, as of the 2006 CODATA values of the physical constants, it is not the most accurate. It is only a method of determining NA because it is known by other means that 28.0855 g of silicon is equivalent to one mole. Those other means are:
- the very accurate determination of the ratios of the masses of each of the three silicon nuclides to the mass of an atom of carbon-12, in such a way that it is known that a silicon-28 atom is [27.976 926 5327(20)/12] times as massive as a carbon-12 atom;
- the determination of the isotopic abundance of silicon in the samples used to make the measurements, allowing the calculation of the atomic weight of silicon in each individual sample;
- the definition of 12 g of carbon-12 atoms to be equivalent to one mole."
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