Understanding First Ionization Energy for Diatomic Gases

[Samson4]

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?

 

[mfb]

Always the isolated atoms.

 

[nasu]

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.

 

[Samson4]

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?

 

[nasu]

Molecular hydrogen has just two electrons per molecule. There is no double ionized molecule.

 

[Samson4]

Then what is second ionization energy?

 

[mfb]

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.

 

[nasu]

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.

 

[Samson4]

Thank you for your help everyone.

Mfb, that last bit was gold.

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