HI Ann, You have a very interesting question...and I'll try and help you here :) Looking at this, I would say....you can't have an atom of a plural....think about it....doesn't make sense. An atom could only come from one thing since it's soooo small! I would say this may be the best thing you could say: "...an atom of stone/an atom of a stone" "...an atom of one gadget / an atom of a gadget" Funny expression, but I hope this helps you some. Actually, when we were kids, we used to use this expressions quite extensively and had great fun creating insults for our friends! :) Keep learning English! David