May 2, 2005

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  the bohr model of the atom developed in 1913 was an attempt by neils bohr to come to an accommodation with two opposing schools of thought on the nature of particulate matter. the classical school maintained that all sub-atomic activity could be explained and understood in light of the classical laws of physics postulated by individuals such as sir isaac newton (laws of motion) and galileo. the laws of gravity, electrostatics, magnetism, and electricity were considered good predictors of the activity that occurred in the macrocosmic world that we live and function within. on the other hand, there was a new emerging school of thought that maintained the perception that the world of the atom could only be understood, if at all, by a complete set of new assumptions and postulates that would govern the way matter behaved at the sub-microscopic level. bohr maintained that both views of the atomic world could be correct. he tried an eclectic approach in his model. the model consisted of a massive very dense nucleus composed of the protons. the electrons (key to our understanding of the chemistry of matter) were assigned definitely predictable “orbits”. at first, the orbits were concentric circular paths, but, later, the model was modified to consist of elliptically shaped orbits. the electrons circled around the nucleus being held in position by a balance between the centrifugal force propelling them outward and the electrostatic force of attraction between the positive nucleus and the negative electrons. electrons assigned to orbits further out from the nucleus would possess a larger quantity of energy then those assigned to orbits closer to the nucleus. there were immediate problems with this model. the fact that moving charged particles such as the electrons should radiate energy. if this were so, then the electrons should spiral down into the center of the atom. in other words, we are faced with an absurdity that all atoms should collapse upon themselves. of course, that was not reality so the model was not predicting realty, as any theory ought to do. the model did accurately predict the parameters of a one-electron system like the hydrogen atom, but with multi-electron atomic systems the predicted parameters were not forthcoming. for these reasons the bohr model was not the definitive answer as to what an atom looked like. however, it was a step in the right direction. the model is still used as a way of keping up with the number of electrons in the various shells or orbits. this is important. it has to do with what we are doing here in the barn.

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