Atoms condensed from the plasma that followed the Big Bang, and the matter that composed the plasma condensed from the pure energy released from the Big Bang. Stars do produce new atoms, but that is through nuclear fusion which releases energy. As far as I am aware no one can fuse atomic particles into an atom in an endothermic reaction, so for now we cannot put Humpty Dumpty back together again. If we were to develop such technology though, it would take far more energy than is released from a fission reaction thanks to the laws of thermodynamics. We would also need to put it together relatively slowly, which means a lot of energy would be spent opposing the Strong Nuclear Force.