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Homework Help: Helium radius

  1. Feb 27, 2008 #1
    b]1. The problem statement, all variables and given/known data[/b]
    Given the observed spectrum of helium, estimate the distance between two electrons in a helium atom (a) in the ground state and (b) in the first excited state. Neglect the exchange energy.

    2. Relevant equations

    Given in my textbook,
    "Hartree theory predicts that the radius of the n=1 shell is smaller than that of the n=1 shell of hydrogen by approximately a factor of [tex]\frac{1}{Z-2}[/tex]"


    3. The attempt at a solution

    I'm confused by the text above. Doesn't [tex]Z_{helium}=2[/tex], and hence [tex]Z-2=0[/tex]?

    Another source I found says that,




    I can solve the first eq. for Z-2, but again this doesnt really make sense to me because I get Z-2=2.39 (for ground state) which would imply that Z=4.39? Also using this, I don't get the answers that are in the key.

    Please point me in the right direction... thanks.
  2. jcsd
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