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Homework Help: Calculating second ionization energy of He

  1. Sep 12, 2012 #1
    1. The problem statement, all variables and given/known data

    The equation En=-Z2RH/n2 gives the energy (according to the Bohr model) of the energy levels available to an electron in any hydrogen-like atom. Calculate the second ionization energy of He(in J). The second ionization energy of He is the ionization energy of He+.

    2. Relevant equations

    En=-Z2RH/n2 where RH=2.178x10-18J


    3. The attempt at a solution

    I don't understand which value I am supposed to use for n. When I look up the second ionization energy of He I find that the answer is 54.4 eV or 8.712x10-18J, which is the answer I get when I input n=1 into the above equation. But it's asking for the second ionization energy of He, so why would I use n=1?
  2. jcsd
  3. Sep 13, 2012 #2


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    Gold Member

    n=1 is the orbit number of He. He has configuration of 1s2, meaning that both 2 electrons are in 1st orbit. 2nd Ionization energy refers to removal of 2nd electron, or removal of only electron of He+ ion, in this case.

    Z refers to the atomic number of the species. For He, Z = 2.
  4. Jul 18, 2013 #3
    Thanks for the question.
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