Avogadro´s constant is the number of atoms or
molecules in a mole of material. It´s also part of
the definition of the atomic mass unit (amu),
which is the unit given to the masses of the
1 amu=1/(Avogadro´s Number of
Carbon has been selected as the scientific
reference atom, so for carbon, there are exactly
Avogadro´s number of carbon atoms in 12 grams of
carbon, which is equal to 1 mole of carbon.
The first calculation of Avogadro´s constant was
done by Nobel Laureate Jean Baptiste Perrin in
1909, who estimated the number based on his
research in Brownian motion, which is the
constant, random motion of microscopic particles
in a fluid. His paper states that "The invariant
number N is a universal constant, which may be
appropriately designated `Avogadro´s Constant."
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