I think mcatquestion.com made yet another mistake

[Postictal Raiden]

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"Under which conditions is the second ionization energy for an atom greater than its first ionization energy?"

A Only if the atom has an odd number of valence electrons.
B Only if the atom has one valence electron.
C Only if the atom is a nonmetal.
D The second ionization energy for an atom is always greater than its first.

The answer is D. However, I thought the answer was B, because if the atom has only one valence electron and then it loses it, it will acquire an a full valence shell, similar to the noble gas element that precedes it. Therefore, losing removing a second electron will require a significantly more energy.

What do you guys think?

 

[Jepstein30]

"Under which conditions is the second ionization energy for an atom greater than its first ionization energy?"

A Only if the atom has an odd number of valence electrons.
B Only if the atom has one valence electron.
C Only if the atom is a nonmetal.
D The second ionization energy for an atom is always greater than its first.

The answer is D. However, I thought the answer was B, because if the atom has only one valence electron and then it loses it, it will acquire an a full valence shell, similar to the noble gas element that precedes it. Therefore, losing removing a second electron will require a significantly more energy.

What do you guys think?

Right, but D is the best answer. The second ionization energy will ALWAYS be greater than the first (includes answer B).

If you pull off an electron, the remaining electrons are now being held onto even stronger by the protons in the nucleus than before because there's less electrons overall.

 

[Postictal Raiden]

Right, but D is the best answer. The second ionization energy will ALWAYS be greater than the first (includes answer B).

If you pull off an electron, the remaining electrons are now being held onto even stronger by the protons in the nucleus than before because there's less electrons overall.

Wouldn't pulling off the first electron from a noble gas element cost more energy input than pulling off a second one?

 

[Jepstein30]

Wouldn't pulling off the first electron from a noble gas element cost more energy input than pulling off a second one?

Nope. I think you're getting too stuck up upon atoms wanting to get a stable octet.

If you're comparing ionization energies between elements, you should consider such things.. but comparing successive ionization energies, you should think about Zeff. Since Zeff doesn't change when you pull off electrons, it becomes harder to pull off each successive electron because the protons in the nucleus hold on more tightly.

ex. Ionizing Neon will take a ton of energy (more than ionizing a Group I metal because of stable octets), leaving you with a cation with 10 protons and 9 electrons. Those 10 protons now pull on the 9 electrons even tighter than they did the 10 electrons from the step before.. and so on and so on. Think how hard it would be to pull off an electron from a species that has 10 protons and only one electron.

 

[Postictal Raiden]

Nope. I think you're getting too stuck up upon atoms wanting to get a stable octet.

If you're comparing ionization energies between elements, you should consider such things.. but comparing successive ionization energies, you should think about Zeff. Since Zeff doesn't change when you pull off electrons, it becomes harder to pull off each successive electron because the protons in the nucleus hold on more tightly.

ex. Ionizing Neon will take a ton of energy (more than ionizing a Group I metal because of stable octets), leaving you with a cation with 10 protons and 9 electrons. Those 10 protons now pull on the 9 electrons even tighter than they did the 10 electrons from the step before.. and so on and so on. Think how hard it would be to pull off an electron from a species that has 10 protons and only one electron.

You are right. Thank you for clarifying.

 

[Jepstein30]

You are right. Thank you for clarifying.

No problem. It is a little tricky nuance because we were always taught octet, octet, octet.

It's similar to pka's of multiprotic acids.

The first proton will always be more acidic than the second proton (pka1 < pka2) because it's harder to pull that second proton off the compound now that the electron density has one less proton to worry about.

 

[gwjib04]

It's similar to pka's of multiprotic hydrogens.
.

Nice connection

I always thought divalent cations would have low 2nd ionization energies because that forms a favorable e' arrangement.

Thanks

 

[Jepstein30]

Nice connection

I always thought divalent cations would have low 2nd ionization energies because that forms a favorable e' arrangement.

Thanks

Looking back, I meant multiprotic acids..

hydrogens can't be multiprotic