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A How Resonance in general, differ In Chemistry and Physics

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  1. Mar 4, 2016 #1
    Hi, I am just confused, regarding some definition above, I hope anybody can help explain differences.
    Does atoms resonate when subjected to some wave?
     
  2. jcsd
  3. Mar 4, 2016 #2

    BvU

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    Any stable equilibrium has some restoring force that goes against disturbances. Disturbances can cause oscillations around the equilibrium. Those oscillations have a preferred frequency. If the frequency of a repetitive disturbance is close to that preferred frequency there can be resonance.

    This harmonic oscillator phenomenon is ubiqitous in science. Kids on a swing have no difficulty with the issue. Why should you be confused ?

    Perhaps you can give some examples of where specifically you have problems ?
     
  4. Mar 4, 2016 #3
    Exactly, how do you relate that to chemical resonance? Are they the same?
     
  5. Mar 4, 2016 #4

    BvU

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    Boy, do these chemists make things complicated ! I had to look it up to find it's a way of describing a molecular bond with delocalized electrons. An intermediate structure is energetically favorable over canonical Lewis structures. There are a lot of similarities (a minimum in a potential), but I can't distinguish whether there is something resonating or not (I think there isn't, actually (*) -- it's just a way of describing a structure).

    By now I understand your confusion :smile:. Dimwit chemists ! Let's call for help: @Borek @Chestermiller ?

    (*) reading on in the link I find that confirmed under "misconception" ! And I heartily agree with the suggestion to abandon the "resonance" term. Confusing, as you found.
     
  6. Mar 4, 2016 #5
    I guess an english word sometimes has two different meaning.:cry: too bad if it falls on almost the same field. Digesting from the answer of yours, this is the next awkward question.--> Could we possibly, resonate a chemical resonant molecule?:woot: Boy, am I wrong, or I am wrong? Crazy isn't it?
     
  7. Mar 4, 2016 #6

    BvU

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    I think that would be pretty complicated.

    For e.g. the benzene ring I it seems as good as impossible to impose external conditions (a hexapole field?) that make the delocalized electrons swing back and forth between left and right neighbours.

    I see little physical difference between what you ask and e.g. letting H2 oscillate between H+H- and H-H+ which may be somewhat less impossible. But if it can be done ? No idea. Any ideas from the experts ?
     
  8. Mar 4, 2016 #7

    DrClaude

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    Resonance structures in chemistry are a classical approach to quantum mechanical phenomena. The example of benzene is a good one: resonance structures are necessary to move around the double bonds, while the actual electronic wave function is stationary and delocalized.

    While an imperfect representation, in his book The Nature of the Chemical Bond, Pauling argues that the use of resonant structures is on equal footing with drawing lines for single and double bonds, etc. It is not prefect, but it is still a useful classical representation of what happens in a molecules.
     
  9. Mar 7, 2016 #8

    DrDu

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    I wouldn't call it a classical representation. Rather, it is a quantum mechanical superposition of valence bond structures. It is not that different from the superposition of different Slater determinants in molecular orbital theory where this is called "configuration interaction". In solid state theory, "resonating valence bond" states are still a hot candidate for the ground state in high temperature superconductors.
     
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