Avogadro's number

Avogadro's number, also called Avogadro's constant (NA) is a large constant used in chemistry and physics. Avogadro's number is formally defined as the number of carbon-12 atoms in 12 grams (0.012 kg) of carbon-12, which is approximately 6.022 × 1023. Historically, carbon-12 was chosen as the reference substance because its atomic mass could be measured particularly accurately.

Application

Avogadro's number can be applied to any substance. It corresponds to the number of atoms or molecules needed to make up a mass equal to the substance's atomic or molecular mass, in grams. For example, the atomic mass of iron is 55.847 amu, so Avogadro's number of iron atoms (i.e. one mole of iron atoms) have a mass of 55.847 g. Conversely, 55.847 g of iron contains Avogadro's number of iron atoms. Thus Avogadro's number corresponds to the conversion factor between grams (g) and atomic mass units:

Related Topics:
Atomic - Molecular mass - Amu

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:1 mbox{g}=N_{ m A} mbox{amu}.

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