![]() This offered a mechanism for the emission of electromagnetic radiation by atoms. This implied that when an atom-for example, a hydrogen atom-is heated, its electrons should move away from the nucleus, then move back toward it again, giving up energy in the form of electromagnetic radiation (light). The classical planetary model of the atom allowed electrons to orbit at any distance from the nucleus. Some form of planetary model was necessary to explain the behavior of atoms. The plum-pudding model was disproved by 1911, when Rutherford showed that alpha particles fired at atoms sometimes bounce right back the way they came, as if they had struck a massive obstacle in the atom-a nucleus. In this alternative theory, negative electrons are embedded in a uniform globe of positive charge, much like plums in a pudding. Thomson proposed what was called the “plum pudding” model. However, this view was controversial, and in 1907, J.J. In those larger systems, small objects orbit a central, massive object: The planetary model suggested that in the atom, small, electrically negative electrons orbit a relatively massive, positively charged nucleus. It proposed that the atom is structured like the Saturnian ring system or the solar system. This theory was suggested by Japanese physicist Nagaoka Hantaro (1865–1950) in 1904 and further developed by Rutherford. ![]() Historical Background and Scientific Foundationsīefore Bohr, the foremost classical model of the atom was the Saturnian or planetary model. It was while working in England that Bohr developed his model of atomic structure. After graduation, Bohr worked in England with Thomson and subsequently with Rutherford. While working on his doctoral dissertation at Copenhagen University, Bohr studied the theory of radiation being developed by German physicist Max Planck (1858–1947). Thomson (1856–1940) and Ernest Rutherford (1871–1937), which were based on classical (Newtonian) physics. By using quantum theory, Bohr's model improved on the earlier atomic models of British physicists J.J. This idea was totally counter-intuitive and required a new physics.One early theory of the structure of the atom was the Bohr model, developed in 1913 by Danish physicist Niels Bohr (1885–1962). The releasing of the photons is responsible for the line spectra given off by elements when excited. Then the electrons would release the photons in quantized amounts to return to ground state. Why?īohr took the ideas of Rutherford (nuclear model), Planck (quanta), Einstein (photoelectric effect and spectroscopy and created the Planetary Model.īohr proposed that electrons were in energy levels (ground state) and absorbed photons of certain frequencies to move to a higher energy level (excited state). Classical physics says that opposites attract and likes repel, so the negative electrons should be attracted to the positive nucleus. ![]() Niels Bohr change the atomic theory by realizing that the electrons did not crash into the nucleus as would be expected in classical physics.
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