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What is meant by Early atomic models predicted noble gas stable

  1. Oct 9, 2012 #1
    What is meant by "Early atomic models predicted...noble gas....stable"

    Hello,
    I am troubled by the following statement "Early models of atomic structure predicted that atoms and ions with noble gas electron arrangements should be stable"
    Is this referring to the Niels Bohr model or am I missing out on something?

    All opinions are appreciated.
    Michael
     
  2. jcsd
  3. Oct 9, 2012 #2

    mfb

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    Re: What is meant by "Early atomic models predicted...noble gas....stable"

    Do you have some context?

    My guess:
    You can try to model a nucleus similar to electron shells - both protons and neutrons are fermions, so they have to occupy different energy levels, similar to electrons. There, nuclei with 2, 10, 18, 36, ... electrons have closed shells, and they are very stable (high binding + ionisation energy). If you transfer that to atoms, you would expect that atoms with 2, 10, 18, ... protons and neutrons are very stable. While this is true for 2 (helium-4), it becomes wrong for larger numbers.
    The reason: The nucleus is a bit different, as you have a different potential shape (no 1/r-potential, but a sharp border) and different effects from proton<->proton repulsion for large nuclei.
     
  4. Oct 9, 2012 #3
    Re: What is meant by "Early atomic models predicted...noble gas....stable"

    That makes sense. I found the phrase in my specification under "Atomic Structure, Fundamental particles, Candidates should know that early models of atomic structure predicted that atoms and ions with noble gas electron arrangements should be stable". Which to be hones I found quite vague.

    Michael
     
  5. Oct 10, 2012 #4
    Re: What is meant by "Early atomic models predicted...noble gas....stable"

    I understand the question refers exclusively to electron shells, not to nuclei.

    Noble gas electron arrangements stable: onyl early, because meanwhile we know argon and xenon fluorides can be produced and kept for many minutes.
     
  6. Oct 10, 2012 #5
    Re: What is meant by "Early atomic models predicted...noble gas....stable"

    Knowledge of electrons had to predate any electron-proton models.

    In fact much was knownbefore the Bohr model and in particular the observation of periodicity in ionisation energies.

    I have shown pat of the graph, a proper search will show the whole picture, but the ionisation (negative) energies of helium and Neon are about five times as great as for lithium and sodium.

    So it stand to reason that the greater the I energy the less likely that the electron will be removed leading to the conclusion that the elements with greatest I energies will be the most stable.
     

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  7. Oct 10, 2012 #6
    Re: What is meant by "Early atomic models predicted...noble gas....stable"

    Thank you all. I'm glad I asked.

    Michael
     
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