Ionization Potential

[MedPR]

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The ionizatione nergy of H(g) is 1312kJ/mol. A good approximation for the second ionization potential of helium(g) is:

A: 5248 kJ/mol
B. 2624 kJ/mol
C. 656 kJ/mol
D. 328 kJ/mol

 

[pfaction]

2nd IE is always greater than 1st IE, so cross out C and D. I'm between A and B, and I'm leaning towards A, as H2 has 2 electrons, and tearing apart that last electron is going to suck, so I'll go with A. B is just double the 1st ionization energy, and the 2nd one is supposed to be much more.

 

[chiddler]

I'd blindly choose A because it's helium.

 

[MedPR]

2nd IE is always greater than 1st IE, so cross out C and D. I'm between A and B, and I'm leaning towards A, as H2 has 2 electrons, and tearing apart that last electron is going to suck, so I'll go with A. B is just double the 1st ionization energy, and the 2nd one is supposed to be much more.

I'd blindly choose A because it's helium.

A, indeed. TBR says

Because the ionization energy is proportional to Z^2, the second ionization of helium should be four times as great as the ionization energy of hydrogen.

What are they talking about?

 

[pfaction]

Wow. I did it again. I ****ing misread the question. Someone kill me now.

That was my "logic" for "H2 gas" because i misread helium as H2. H2 and helium have the same electrons: 2 (I'm assuming H2 has 2 electrons right lol). If the 1st IE of H2 is 1300, the next one will completely remove any electrons - protons will be super attracted to that electron now, there's only one after all--will take massive energy to remove it. Esp since it's s shell.

 

[chiddler]

A, indeed. TBR says

What are they talking about?

I vaguely remember an equation...

I found it!
Once upon a time some 3 months ago:

Energy of electron orbitals, E, is related to nuclear charge, Z, and electron energy level, n, as follows:

E α Z^2 / n^2

"A 4-->2 drop is less than half as energetic as a 2-->1 drop". I don't think knowing this formula is important, but rather knowing the trend. Then again, you should have a stronger opinion on what to know thus far. What do you think?

 

[MedPR]

I vaguely remember an equation...

I found it!
Once upon a time some 3 months ago:

Energy of electron orbitals, E, is related to nuclear charge, Z, and electron energy level, n, as follows:

E α Z^2 / n^2

"A 4-->2 drop is less than half as energetic as a 2-->1 drop". I don't think knowing this formula is important, but rather knowing the trend. Then again, you should have a stronger opinion on what to know thus far. What do you think?

I think knowing that the second ionization energy > first ionization energy is the important thing. The relationship might be handy, but I doubt it will be tested directly.