An Exact Value for Avogadro's Number Untangling this constant
from Le Gran K could provide a new definition of the gram
Avogadro's number, N A , is the fundamental physical constant
that links the macroscopic physical world of objects that we can
see and feel with the submicroscopic, invisible world of atoms.
In theory, N A specifies the exact number of atoms in a palm-
sized specimen of a physical element such as carbon or silicon.
The name honors the Italian mathematical physicist Amedeo
Avogadro (1776-1856), who proposed that equal volumes of all
gases at the same temperature and pressure contain the same
number of molecules. Long after Avogadro's death, the concept of
the mole was introduced, and it was experimentally observed that
one mole (the molecular weight in grams) of any substance
contains the same number of molecules. This number is Avogadro's
number, although he knew nothing of moles or the eponymous
number itself. Today, Avogadro's number is formally defined to
be the number of carbon-12 atoms i