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Hydrogen atom confussion

  1. Jul 19, 2010 #1
    You see hydrogen electron energy states labeled as 1s1/2, 2s1/2, 2p1/2 and 2p3/2.

    My confussion may be with understanding the definitions, but does not the 2s1/2 state imply that there are 2 electrons around as the 1st s orbital is filled. But, by definition doesn't that mean you are dealing with h- acid? ie a hydrogen proton with 2 electrons. Same thing with 2p - doesn't it imply a second electron?
  2. jcsd
  3. Jul 19, 2010 #2


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    No. In a hydrogen atom with one proton and one electron, the electron can be in any of the possible states. If it is in the 1s state, then the atom is in its ground state or unexcited state. If the electron is in any higher state, we are talking about an excited state that will eventually decay to the ground state. But there is still just one electron, or else we are not talking about a hydrogen atom.
  4. Jul 20, 2010 #3
    Thank you, if these 1s1/2, 2s1/2, 2p1/2 and 2p3/2 all represent a state of a single electron and single proton, how (or can I?) represent the states of a single proton and two electrons (H-) or the states of two protons and a single electron (H2+)?
  5. Jul 20, 2010 #4


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    First, something's not right here. A configuration is given like so:
    1s1 (1 electron in the 1s orbital, e.g. ground-state hydrogen),
    1s2 (2 electrons in 1s, ground-state helium, or H-), 1s12s1 (1 electron in 1s, 1 in 2s, which could be triplet helium or an excited singlet helium, for instance).

    You don't have fractional numbers when giving the orbital configuration. You must be confusing them with http://en.wikipedia.org/wiki/Term_symbol" [Broken], where a 1/2 subscript denotes a total angular momentum J=1/2. Term symbols give additional information, since as you can see from the above, the orbital configuration does not uniquely determine the state.
    Last edited by a moderator: May 4, 2017
  6. Jul 20, 2010 #5
  7. Jul 20, 2010 #6


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    Yes, it's all hydrogen. They're mixing it up a bit, putting J as a subscript as with term symbols. If you only have one electron, knowing J (and the orbital) is enough to determine the state completely.
  8. Jul 20, 2010 #7
    From the wiki page you posted:

    Calculate J as:
    if less than half of the subshell is occupied, take the minimum value J = | L − S | ;
    if more than half-filled, take the maximum value J = L + S;
    if the subshell is half-filled, then L will be 0, so J = S.

    Do you know the combination they use to get the 2P3/2?
  9. Jul 20, 2010 #8
    Was that my imagination or did this post just change??? Technical glitches??? My memory must be going.
  10. Jul 20, 2010 #9
    Here is a table of the atomic energy levels of neutral hydrogen:


    The first column lists the configuration for a single atomic electron; 1s1/2, 2s1/2, 2p1/2, 2p3/2

    the first # (before s or p) is n (the principal quantum number); the second number, listed in the third column, is J = L ± 1/2

    L is orbital quantum number; s stands for L = 0, and p stands for L = 1

    The energy levels are in inverse cm above the ground state. Divide level in cm-1 by 8061 to get electron volts.

    Bob S
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