The evolution of atomic theory began with the ancient Greeks' philosophical idea of indivisible particles, progressed to John Dalton's scientific model of atoms as solid spheres, then saw J.J. Thompson's discovery of the electron and plum pudding model, followed by Ernest Rutherford's discovery of the nucleus and proton with the gold foil experiment, and Niels Bohr's planetary model. James Chadwick's discovery of the neutron, and the final Schrödinger's quantum mechanical model of electron cloud