MadSci Network: Physics |
From: Allan Ewings Grade: 10-12 City: Sydney, State/Prov.: NSW Country: Australia Area: Physics Message ID Number: 1087865185.Ph We are given that one of the down falls of the Bohr model of the atom was its inability to account for the difference in intensity of the lines of the Hydrogen spectra. How was that difference accounted for in later models? Bohr developed his theory to describe the behavior of hydrogen atoms with light. As such it was and is quite a good theory and when elaborated by the revelations of wave and quantum mechanics it allows a good basic understanding of what’s going on in the hydrogen atom and hydrogen-like ions such as He+ and Li++. Bohr’s theory describes transitions well but has no ability to describe the states of an atom these are described by wave mechanics, quantum mechanics and relativity. Descriptions of the states[1s, 2s, 2p,3s, 3p, 3d etc] allow the development of selection rules and calculation of transition probabilities. This and aspects of the quantum-wave mechanics theory are described elegantly in “Atomic Spectra and Atomic Structure” by Gerhard Herzberg. Others and I have discussed this before; search the Mad Scientist using “Balmer Series”. Check it out. I have one comment on the answer about the helium ion spectrum, the effect of increased nuclear charge increases the transition energies by a factor of 4 for He + and 9 for Li ++. The following site http://physics.nist.gov/Pubs/AtSpec/node17.html describes selection rules and gives emission and absorption intensities. All this considered the main contributor to the observed spectra is the distribution of states that the atoms are in. [This depends on the temperature [Boltzman distribution] ], the concentration of atoms usually the more the merrier, the presence of radiation flux that can alter state distribution thru photoexcitation or stimulated emission [lasers]. For example the balmer emission series is possible if there is a distribution among the n=2,3,4, etc states at too low a temperature or too high a temperature it diminishes. Similarly the absorption spectrum is observed with a high population of the n=2 state and is seen at lower temperatures. This is generally true for any atomic emission-absorption lower T shows absorption spectra; higher T shows emission spectra. If you are interested in spectroscopy I recommend Herzberg’s books
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