According to:
http://www.4chemistry.co.uk/L5th-atom-notes1.htm
About five million million hydrogen atoms could fit. Some factors
would affect that number like the area of the head and the size of
atoms (as well as attractions between atoms). Some atoms are larger
than others.
Check this out:
http://www.monroecc.edu/wusers/flanzafame/PerRadii.pdf
(You'll need Adobe Acrobat to read it)
As atomic radii increases, you'll fit less and less atoms on the
pin of an atom. The atomic radii is the average distance between the
nucleus and the outermost electron.
Jason
(published on 10/22/2007)