Rutherford's atomic model became known as the nuclear model. The nucleus is the tiny, dense, central core of the atom and is composed of protons and neutrons. He concluded that all of the positive charge and the majority of the mass of the atom must be concentrated in a very small space in the atom's interior, which he called the nucleus. In contrast, the particles that were highly deflected must have experienced a tremendously powerful force within the atom. Because the vast majority of the alpha particles had passed through the gold, he reasoned that most of the atom was empty space. Rutherford needed to come up with an entirely new model of the atom in order to explain his results. In a famous quote, Rutherford exclaimed that it was "as if you had fired a 15-inch shell at a piece of tissue and it came back and hit you." No prior knowledge had prepared them for this discovery. Some were even redirected back toward the source. Surprisingly, while most of the alpha particles were indeed not deflected, a very small percentage (about 1 in 8000 particles) bounced off the gold foil at very large angles. (Credit: (A) Christopher Auyeung (B) User:Fastfission/Wikimedia Commons Source: (A) CK-12 Foundation (B) (opens in new window) License: (A) CC BY-NC 3.0(opens in new window) (B) Public Domain)Īccording to the accepted atomic model-in which an atom's mass and charge are uniformly distributed throughout the atom-the scientists hypothesized that all of the alpha particles would pass through the gold foil with only a slight deflection, or none at all. Rutherford found that a small percentage of alpha particles were deflected at large angles, which could be explained by an atom with a very small, dense, positively-charged nucleus at its center (bottom). (B) According to the plum pudding model (top), all of the alpha particles should have passed through the gold foil with little or no deflection. \) : (A) The experimental setup for Rutherford's gold foil experiment: A radioactive element that emitted alpha particles was directed toward a thin sheet of gold foil that was surrounded by a screen which would allow detection of the deflected particles.
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