Well, everyone else is apparently too stunned by the stupidity rays emanating from this question to answer it, so I'll take a shot.
a) if you mean homogeneously distributed atoms assembling into molecules and heterogenous clumps of stuff, than this can be observed in the formation of planets from dust. You can get the idea of how this could be by observing a child's toy made of iron filing under the influence of a magnet.
b) if you mean atoms producing other atoms, we have our sun for an example, which keeps us alive by zipping together heavier molecules from lighter molecules.