Absorbing Energy Question

[justadream]

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I know energy is quantized but I'm unclear about absorbing energy when the energy is above the threshold.

For photoelectric effect, absorbing energy causes the electron to be excited. Here, if the energy being used is not above a certain threshold (the work function), then the electron fails to be excited. However, once it reaches that threshold, it will be excited. In addition, if it EXCEEDS that threshold then the electron can still be excited and the extra energy becomes kinetic energy.


What about for other applications like when bonds absorb energy (e.g., for spectroscopy)? In those situations, does the bond only absorb the energy if its at the exact threshold (and so if the energy exceeds that threshold, it won't be absorbed)?

 

[t5Nitro]

Bonds are simply electron domains so the same idea you detailed above applies. Depending on the energy, you can achieve different molecular transitions from (low to high): nuclear spin (e.g. NMR), electron spin (e.g. ESR), rotation of the molecule (microwaves), electron excitation of bonding electrons (UV-Vis), ionization of bonding electrons and electron excitation of core electrons (x-rays), and nuclear transitions with gamma rays. All I've done is walked through the electromagnetic spectrum, demonstrating different molecular transitions with varying energy intensities. So in short, yes, the "bond" (electrons) will absorb energy and undergo a transition as long as it reaches a certain threshold as you word it.

 

[justadream]

So to clarify, it does not have to be the exact minimum energy? For example, lets say that

1)If the bond receives X amount of energy, it will vibrate up and down
2)If the bond receives X+5 amount of energy, it will vibrate side to side

If I provide X+3 amount of energy, will it still vibrate up and down? How about if I provide X+5 (will it vibrate up and down and side to side)?

 

[t5Nitro]

So to clarify, it does not have to be the exact minimum energy? For example, lets say that

1)If the bond receives X amount of energy, it will vibrate up and down
2)If the bond receives X+5 amount of energy, it will vibrate side to side

If I provide X+3 amount of energy, will it still vibrate up and down? How about if I provide X+5 (will it vibrate up and down and side to side)?

Perhaps, and I do not know the exact answer to this question. I would say it still vibrates up and down with x+3, but if x+5 is sufficient added energy for the next molecular transition, then "something else" should happen. But before "something else" happens, it still begins by vibrating up and down (from your hypothetical description -- in fact, the first thing that should happen is nuclear spin with the lowest energy). If it is not sufficient energy, then I suspect it continues to only vibrate up and down. This type of chemistry is far beyond the scope of the MCAT (if you have an analytical chemistry professor to ask these questions, however, he or she should be able to clarify much better for you).

 

[pepocho]

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