This is just what I've heard a long time ago so don't quote me lol. But no, splitting a single atom shouldn't do anything of note. I believe it's the same general reason that a nuke doesn't set the entire atmosphere on fire - you need a lot of energy to split atoms. That's why nukes need enriched materials.

I also believe that even a nuclear explosion won't be triggered by a single split atom in a bomb. For example, the Manhattan Project bomb was triggered by shaped explosives that surrounded the nuclear core. The blast of the charges "compressed" the nuclear material to the point it reached a critical mass that allowed a runaway fission reaction.