Why does an atomic bomb put out so much energy when it explodes?

now let me expand on that an atom is exponentially small and at no on an everyday basis does it ever put out the amount of energy the atomic bomb does. If i were to measure the total Energy an atom puts out in a day i would be no where near the total amount of energy an atomic bomb puts out within three milliseconds after detonation. So then where does it come from? Please be as technical and complex as you want (within reason of course no mindless babbling or any thing like that). And by the way i'm not planning anything sinister (yet) this is just something that intrigues me.