Focus 1 Exercise 13

[Jared Limqueco 3E]

Q: Ionization energies usually increase on going from left to right across the periodic table. The ionization energy for oxygen, however, is lower than that of either nitrogen or fluorine. Explain this anomaly.

I don't know where to begin thinking. Does anyone know how to explain this?

[Varsha Ravi 3E]

I believe that the reason why it's different for oxygen is because it's the first element in which the electrons are paired in the p-orbitals (nitrogen has 3 unpaired electrons, fluorine has 2 paired 1 unpaired). Because of this, it has a slightly lower ionization energy than nitrogen despite being further to the right.

[Chance Herbert 3A]

Ionization energy is the amount of energy required to remove an electron from an atom. Oxygen is the first element in the p-block to have a paired electron. It is slightly easier to remove an electron from oxygen than it is in nitrogen and fluorine because this one paired electron is subject to a greater magnitude of repulsion from other electrons than if it were to have no paired electrons and one less attractive proton (center-seeking force) or two paired electrons and one more attractive proton, which would result in oxygen being an anomaly and having the lowest ionization of the three elements. Hope this helps.

[Jared Limqueco 3E]

I believe that the reason why it's different for oxygen is because it's the first element in which the electrons are paired in the p-orbitals (nitrogen has 3 unpaired electrons, fluorine has 2 paired 1 unpaired). Because of this, it has a slightly lower ionization energy than nitrogen despite being further to the right.

Ohhhhh I see, that makes sense. Definitely some good attention to detail. Thank you.