Whose Discovery Revealed the Structure of the Atom?

In 1897, J.J. Thomson discovered the electron and proposed the "plum pudding" model: atoms were a sphere of positive charge with electrons embedded like plums in a pudding. Ernest Rutherford, working at the University of Manchester with Hans Geiger and Ernest Marsden, tested this in 1909-1911 by firing alpha particles at a thin gold foil. Most passed straight through, as expected. But about 1 in 8,000 bounced back at large angles — which, Rutherford said, was "as if you fired a 15-inch shell at tissue paper and it came back and hit you." This could only be explained if the atom mass and positive charge were concentrated in a tiny nucleus, with electrons orbiting in mostly empty space. Niels Bohr improved the model in 1913 by proposing quantised electron orbits, and the modern quantum mechanical model (developed by Schrodinger, Heisenberg, and others in the 1920s) replaced definite orbits with probability clouds. But Rutherford nuclear atom remains the foundation.