Achieve hw #2 question #24 about oxygen ionization

[Megan McKenna Dis1A]

Hi! I was able to navigate through the question using the hints but I am still not 100% sure that I understand the reasoning behind the answer for this question. Could someone explain this to me?

[Paul Zhang 2F]

Hello! Since there are two answers that must be selected, I'll cover each of them.

Upon ionization, oxygen is relieved of electron‑electron repulsion.

Ionization energy is related to electron-electron repulsion. Greater repulsion between electrons in the atom means that the outermost electrons are already being "pushed" out more, so it's easier to ionize them (which involves pushing the electron out so far that it's removed). Thus, if ionization relieves a lot of electron-electron repulsion, that means the ionization energy is small. This answer is kinda misleading because there will still be electron-electron repulsion between the remaining electrons, but it'll be decreased (more so than if nitrogen or fluorine were ionized).

The 2p electrons in fluorine experience a higher effective nuclear charge than the 2p electrons in oxygen.

Higher effective nuclear charge means the electrons are more strongly attracted to the protons in the nucleus, which would require more energy to remove the outermost electrons. This suggests that oxygen would have a lower ionization energy.

Hope that's helpful!

[Carlotta Gherardi 2J]

Hi,

Fluorine's ionization energy is higher than Oxygen's because, as you move across the period, nuclear charge increases (ie more protons in nucleus attracting electrons), so electrons in F feel a greater pull of +9 (has 9 protons) to the nucleus than electrons in Oxygen that feel a pull of +8 (has 8 protons).

Nitrogen has 3 electrons in its 2p subshell, so they are spread out across the three orbitals, while Oxygen has 4 electrons in its 2p subshell, so two are in the same orbital and repel each other. This means that one of those two electrons will "want" to leave the Oxygen atom more than an electron in a Nitrogen atom.

Hope this helps!