Who first split the atom?
The man credited with first having split the atom was Ernest Rutherford, who achieved the feat in 1917. In so doing, he verified the existence of the proton, thus demonstrating that the model of the atom proposed by Niels Bohr was essentially correct (in that it had a small nucleus surrounded by electrons, as opposed to the "plum pudding" model associated with J.J. Thomson.) Rutherford's famous "gold foil" experiments had already pointed in this direction a few years earlier. Rutherford also was the first to describe the implications of radioactivity, i.e. that new elements were formed over time, a controversial idea both because it sounded like alchemy and because the Curies were doing very similar work at almost exactly the same time.