<P> Rutherford overturned Thomson's model in 1911 with his well - known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus . Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure . If Thomson was correct, the beam would go straight through the gold foil . Most of the beams went through the foil, but a few were reflected . </P> <P> Rutherford presented his own physical model for subatomic structure, as an interpretation for the unexpected experimental results . In it, the atom is made up of a central charge (this is the modern atomic nucleus, though Rutherford did not use the term "nucleus" in his paper) surrounded by a cloud of (presumably) orbiting electrons . In this May 1911 paper, Rutherford only committed himself to a small central region of very high positive or negative charge in the atom . </P> <P> For concreteness, consider the passage of a high speed α particle through an atom having a positive central charge N e, and surrounded by a compensating charge of N electrons . </P> <P> From purely energetic considerations of how far particles of known speed would be able to penetrate toward a central charge of 100 e, Rutherford was able to calculate that the radius of his gold central charge would need to be less (how much less could not be told) than 3.4 × 10 meters . This was in a gold atom known to be 10 meters or so in radius--a very surprising finding, as it implied a strong central charge less than 1 / 3000th of the diameter of the atom . </P>

Who proposed the billiard ball model of the atom