Democritus, Newton, and Dalton all used atoms as philosophical ideas without worrying about the actual size of one such particle of matter. They would not have known how to begin to calculate the size of an atom. We can find out roughly how big a typical atom is with only a short scratch-paper calculation. The density of lithium metal is measured to be 0.534 g cm , but for this rough calculation two figures are good enough. Since 1 cm = 10 , we can express the density of lithium () in grams per cubic angstrom as . . .

 

We can convert this to moles per cubic angstrom by dividing by the atomic weight of Li, 7.0 g mole, and then to atoms per cubic angstrom by multiplying by Avogadro's number, 6.0 x 10 atoms mole :