With today's technology, for some compounds... you can count atoms by physical measurements and known structure, and figure mass by atomic weight. http://www.n

With today's technology, for some compounds... you can count atoms by physical measurements and known structure, and figure mass by atomic weight. http://www.nist.gov/pml/si-redef/kg_new_silicon.cfm http://www.nist.gov/pml/si-redef/kg_new_silicon.cfm