This explains the large-angle scatterings seen in the Geiger-Marsden experiments. When the α-particle approaches within 10^-13 meters of the compact nucleus of Rutherford's atomic model, it experiences a repulsive force around a million times more powerful than it would experience in the plum pudding model. The model suggested that most of the atom was empty space. Surrounding this tiny central core were electrons, and the distance at which they orbited determined the size of the atom. The Rutherford model of the atom, put forward in 1911, proposed a nucleus, where the majority of the particle's mass was concentrated, according to Britannica. The results did have a profound effect on Rutherford, however, who in 1910 set about determining a model of atomic structure that would supersede Thomson's plum pudding model, Manners wrote in his book. Initially, the data were unnoticed or even ignored, according to the book "Quantum Physics: An Introduction" by J. Rutherford explained just how extraordinary this result was, likening it to firing a 15-inch (38 centimeters) shell (projectile) at a sheet of tissue paper and having it bounce back at you, according to Britannica Rutherford model of the atom?Įxtraordinary though they were, the results of the Geiger-Marsden experiments did not immediately cause a sensation in the physics community. Even more shocking, around 1 in 10,000 α-particles were reflected directly back from the gold foil. Yet, when Geiger and Marsden conducted their eponymous experiment, they found that in about 2% of cases, the α-particle underwent large deflections. The chance of an α-particle being reflected back was just 1 in 10^1,000 (1 followed by a thousand zeroes). Even with this random scattering, the maximum angle of refraction if Thomson's model was correct would be just over half a degree. Of course, an α-particle passing through an extremely thin gold foil would still encounter about 1,000 atoms, and thus its deflections would be essentially random. Even in this case, the plum pudding model predicted a maximum deflection angle of just 0.06 degrees. The research team calculated that if Thomson's model was correct, the maximum deflection should occur when the α-particle grazed an atom it encountered and thus experienced the maximum transverse electrostatic force. The duo used a radioactive source of α-particles facing a thin sheet of gold or platinum surrounded by fluorescent screens that glowed when struck by the deflected particles, thus allowing the scientists to measure the angle of deflection. Marsden and Geiger conducted the experiments primarily at the Physical Laboratories of the University of Manchester in the U.K. (Image credit: BSIP/UIG Via Getty Images) Here, an illustration of Rutherford's particle scattering device used in his gold foil experiment. This is because α-particles are 7,000 times more massive than the electrons that presumably made up the interior of the atom. Rutherford reasoned that if Thomson's plum pudding model was correct, then when an α-particle hit a thin foil of gold, the particle should pass through with only the tiniest of deflections. He initially handed off his investigation to two of his protégés, Ernest Marsden and Hans Geiger, according to Britannica. His experiment would probe atomic structure with high-velocity α-particles emitted by a radioactive source. Rutherford's Nobel-winning discovery of α particles formed the basis of the gold foil experiment, which cast doubt on the plum pudding model. One scientist who was skeptical of this model of atoms was Rutherford, who won the Nobel Prize in chemistry for his 1899 discovery of a form of radioactive decay via α-particles - two protons and two neutrons bound together and identical to a helium-4 nucleus, even if the researchers of the time didn't know this.
The model had serious shortcomings, however - primarily the mysterious nature of this positively charged sphere. By 1904, Thomson had suggested a "plum pudding model" of the atom in which an atom comprises a number of negatively charged electrons in a sphere of uniform positive charge, distributed like blueberries in a muffin.
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