If we could blow up an atom to be the size of a large professional football stadium, the nucleus would be about the size of a marble. It is worth emphasizing just how small the nucleus is compared to the rest of the atom. By the late 1800’s, John Dalton’s view of atoms as the smallest particles that made up all matter had held sway for about 100 years, but that idea was about to be challenged. The electrons are distributed around the nucleus and occupy most of the volume of the atom. This module is an updated version of Atomic Theory I. In the nuclear atom, the protons and neutrons, which comprise nearly all of the mass of the atom, are located in the nucleus at the center of the atom. 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. \) (while most of the alpha particles were indeed undeflected, a very small percentage (about 1 in 8000 particles) bounced off the gold foil at very large angles.
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