Understanding First Ionization Energy for Diatomic Gases

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Discussion Overview

The discussion revolves around the concept of first ionization energy for diatomic gases, specifically focusing on molecular hydrogen. Participants explore the definitions and implications of ionization energy in the context of isolated atoms versus diatomic molecules, and the challenges in defining second ionization energy for molecular hydrogen.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that ionization energy charts refer to isolated atoms, while others contend that for diatomic gases, it pertains to the molecule itself.
  • There is a distinction made between atomic and molecular ionization energies, with some noting that the energy to remove an electron can vary based on whether it is the first or subsequent electron.
  • One participant expresses confusion about the absence of a second ionization energy for molecular hydrogen, questioning if it relates to bond dissociation energy.
  • Another participant clarifies that molecular hydrogen, having only two electrons, does not have a classical second ionization energy, as removing both electrons results in no remaining molecule.
  • Participants discuss the energy required to dissociate molecular hydrogen into its constituent protons and electrons, suggesting it is not proper to label this as "ionization" energy.
  • There is a reiteration of the idea that while energy exists to remove a second electron, it does not correspond to a traditional ionization process.

Areas of Agreement / Disagreement

Participants express differing views on the definition and existence of second ionization energy for molecular hydrogen, with no consensus reached on the terminology or implications of the energy involved in dissociation.

Contextual Notes

Participants highlight the limitations in defining ionization energy for diatomic molecules, particularly in the case of molecular hydrogen, where the concept of second ionization energy becomes ambiguous.

Who May Find This Useful

This discussion may be of interest to those studying molecular chemistry, particularly in understanding ionization processes and energy definitions related to diatomic gases.

Samson4
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When looking at ionization energy charts; specifically for diatomic gasses, are we looking at the energy to take 1 electron from atomic or diatomic gasses?
 
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Always the isolated atoms.
 
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If it's for a diatomic gas, it is for a molecule of course. And it is different from the atomic ionization energy.
And yes, it means (usually) energy to remove one electron. But it can be also energy to remove a second one and so on.
 
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That's what I figured. What I don't get is why I can't find the second ionization energy of molecular hydrogen. I've searched everything I can think of. Would it be the 104 kcal per mole bond dissociation energy?
 
Molecular hydrogen has just two electrons per molecule. There is no double ionized molecule.
 
Then what is second ionization energy?
 
It does not have one in the classical sense. You can give the energy needed to completely split it apart (to two protons and an electron), but that is not a regular ionization.
If you don't find that number directly, take the dissociation energy and add the hydrogen atom ionization energy.
 
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Samson4 said:
Then what is second ionization energy?
You just said that you cannot find this second ionization energy, didn't you?
If you remove both electrons you don't have a molecule anymore. So there is no ion to talk about.
There is this energy, to remove the second electron, but it won't be proper to call it "ionization" energy.
 
Thank you for your help everyone.

Mfb, that last bit was gold.

Nasu, wouldn't there be 2 ions to talk about?
 

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