3502_02_sept11_LG

3502_02_sept11_LG - Chem 3502/5502 Physical Chemistry II...

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Physical Chemistry II (Quantum Mechanics) 3 Credits Fall Semester 2009 Laura Gagliardi Lecture 2, September 11, 2009 The state of Physics and Chemistry at the turn of the 20th Century To appreciate quantum mechanics, it is important to have some feel for the state of science, and in particular physics, in the years around 1900. Two key points should be made: 1) Many physicists felt that all of the key laws describing the manner in which the Universe worked had essentially been discovered. Dirac (about whom we will learn more later in the course) when looking for a field of study was advised by a senior physicist to avoid physics because "there is nothing important left to discover". The feeling was that all that was left was the polishing of a few details. 2) The bridge between physics and chemistry was beginning to be made solid. The enormous contributions of Gibbs in the United States and Boltzmann in Austria had forged links between chemistry and classical and statistical thermodynamics, respectively (these last two being primarily fields of physics at the time). The power of thermodynamic formulae to rationalize the behavior of gases, liquids, and solids had a tremendous impact on chemistry, which up to that point had tended to be a science in which rules were discovered empirically, without too much concern for explaining the physical foundation of those rules. In part, this derived from European politics, as Chemistry was fractured along nationalistic lines, with the Germans dominating organic chemistry, the English and Swedes dominating physical chemistry, and the French excelling in analytical and inorganic chemistry. After a long debate over the existence of atoms,* the matter was beginning to be considered settled. ____________________ * Ernst Mach (for whom the unit of speed is named) was a member of the Faculty of Philosophy at Vienna during this time, this being the same school where Boltzmann was the Head of Physics. The two engaged in many acrimonious debates about the existence of atoms, and about the utility of equations to represent physical laws. Mach held, as a philosophy , that nothing was real that could not be directly observed by an individual using only human senses—atoms being too small to be seen, any belief in their existence was simply faith, and not science. Mach also maintained that there were no physical laws, and that the suggestion that two events could be related as cause and effect was illegitimate. All one could do would be to note that, up until now, the effect always seemed to follow the cause, but going any further would not be justified. Mach especially objected to interpreting equations that successfully described some chemical or physical phenomenon so as to make predictions about the nature of the species involved (e.g., atoms or molecules)! Into this relative complacency, the philosophical bomb of quantum mechanics
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This note was uploaded on 12/14/2010 for the course CHEM 3502 taught by Professor Staff during the Spring '08 term at Minnesota.

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3502_02_sept11_LG - Chem 3502/5502 Physical Chemistry II...

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