Is there a way to find the distance between atoms? For example, if you have a pure gold film... how can you find out how far the gold atoms are spaced?
How about using good old fashioned chemistry (Avogadro's law, etc.)?
(Whoops, fluidistic beat me to it.
Check wikipedia. For at least some of the elements it gives you the Van der Waals radius which might be good enough for your purpuses.