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Homework Help: Calculating the radius

  1. Dec 13, 2008 #1
    1. The problem statement, all variables and given/known data
    Calculate the radius of the n = 6 Bohr orbit in O7+(oxygen with 7 of its 8 electrons removed).
    A) 190 pm B) 167 pm C) 238 pm D) 214 pm

    2. Relevant equations

    I believe that the relevant equation is
    r(sub n)=(n^2)*a(sub b) where a(sub b)= Bohr's radius= 5.29*10^-11 m

    3. The attempt at a solution
    I calculated it for what I believed to be n=6, but I got an incorrect answer. The correct answer is (C) 238 pm, but I do not understand why.

    Any help is greatly appreciated!
  2. jcsd
  3. Dec 14, 2008 #2


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    Homework Helper

    Your formula is not quite complete. You need to take into account the charge in the nucleus (so the number of protons).
  4. Dec 14, 2008 #3


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    Welcome to PF :smile:

    Your equation is for hydrogen, with a charge of +1 on the nucleus.
    Since oxygen has a charge of Z=8 for the nucleus, that equation should be different, containing Z somehow.

    Does your textbook discuss "hydrogen-like" or "hydrogenic" ions?

    EDIT: ah, I should know better than to wait a 1/2 hour and then respond without refreshing the page. :redface:
  5. Dec 14, 2008 #4
    I cannot find an equation that takes into account (Z). Anyone have the equation handy?
    Thanks for all your help!
  6. Dec 14, 2008 #5


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  7. Dec 14, 2008 #6
    Thank you very much!
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