Achieve #24

[Amanda Nguyen dis 2E]

Identify the reasons why oxygen has a lower first ionization energy than both nitrogen and fluorine:
- Oxygen has a smaller atomic radius than fluorine.
- The 2p electrons in fluorine are more highly shielded from the nuclear charge than the 2p electrons in oxygen.
- The 2p electrons in fluorine experience a higher effective nuclear charge than the 2p electrons in oxygen.
- Upon ionization, oxygen is relieved of electron‑electron repulsion.

I know the answers are the last two, but I don't understand why conceptually. If anyone can help that would be great!

[Nancy_La_1H]

The effective nuclear charge(Zeff) is the amount of positive charge(attraction) experienced by the valence electrons of an atom. Zeff increases as the number of protons increase because there would be a larger pull on the electrons. Therefore, F which has a larger atomic number than O would also have a larger Zeff.

In class we discussed how electrons are more stable when the have a half filled or fully filled valence shell. So oxygen with 4 e- in its valence shell would easily give up the 4th e- from it valence shell in order to have a half filled sub shell. The giving away of the electron would result in the ionization of the oxygen. Electron-electron repulsion decreases as the number of electron decreases. Therefore, when oxygen loses that e- during ionization, it lower/relives the electron electron repulsion occurring.

[Aliza Hacking 1A]

In addition to the other post, the second condition is false because one 2p orbital would not have more shielding than another, since they have the same number/organization of electrons in lower energy orbitals/shells to shield them. The first condition is false because, since fluorine has more protons, its effective nuclear charge is higher, meaning its electrons are held more closely/tightly, making the atomic radius smaller :)

[NaomiAbramowicz1H]

The third one is true because fluorine does, in fact, have a higher Z_eff than oxygen, because it has more protons and there is less of an attraction between the valence electrons and nucleus. The last one is true because when oxygen loses an electron during ionization, it lowers the electron-electron repulsion and thus the ionization energy.