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Hydrogen Spectral Series Question

  1. May 28, 2010 #1
    I do not understand the distinction between the Lyman, Balmer, Pascher series etc. I understand that you calculate the values in each series with the corresponding n' values but I dont understand the need for multiple series. Why can't you have one overarching series that covers the entire spectrum and why would you use one series instead of another? Also, how to the series compare to each other?
  2. jcsd
  3. May 28, 2010 #2


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    Science Advisor

    Simple answer: There isn't a need!
    They're just named that way because they were discovered experimentally before we knew how it all fits together. It's historic.

    Well, the different series represent different electronic transitions. But there is an important equation, the http://en.wikipedia.org/wiki/Rydberg_formula" [Broken] which describes all of them.. I think you've learned of it since you mention the n values. This lead to the Bohr model of the hydrogen atom, which explained _why_ you had these levels.

    Or, almost. See, it turned out that those lines were not actually single lines, but several lines very close together.. And so they had to add more variables to describe how these levels-within-levels fit together.. and the answer to that eventually came from quantum mechanics.

    (Edit: Ooh - My 900th post!)
    Last edited by a moderator: May 4, 2017
  4. May 28, 2010 #3
    Heres what I am having trouble with. My understanding is that these spectral series correspond to energy levels of the hydrogen atom and that these levels are therefore necessarily quantized. However, as one series overlaps another series, the spectral lines of the previous series becomes quazi continuous at lower frequencies. I dont understand how this quazi-continuous nature of one series can be logically compatable with discrete components of another series which it overlaps. I suppose what I am asking is what is the physical significance of n' in the Rydberg formula and the physical significance of the corresponding series. Here is the plot that I am having problems with: http://en.wikipedia.org/wiki/File:Hydrogen_spectrum.svg

    One series may be quazi-continuous at a frenquency where another series is decidedly discrete. How are these things reconcilable?
    Last edited by a moderator: May 4, 2017
  5. May 28, 2010 #4


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    Each spectral line corresponds to a transition between two atomic energy levels. The photon energy equals the difference in energy between the two levels. In the formula that you're looking at, n is the quantum number of the initial energy level (before the transition), and n' is the quantum number of the final energy level (after the transition).

    n' = 1 gives you the Lyman series, n' = 2 gives you the Balmer series, etc.
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