[sd79812]

How does spin-orbit splitting also affect this or anomalous zeeman effect or decrease in spin when you move from Nitrogen to Oxygen?

Bad Teacher: The addition of the second electron into an already occupied orbital introduces repulsion between the electrons, thus it is easier to remove. that is why there is a dip in the ionization energy.

Bad Teacher: In oxygen, the last electron shares a doubly occupied p-orbital with an electron of opposing spin. The two electrons in the same orbital are closer together on average than two electrons in different orbitals, so that they shield each other from the nucleus more effectively and it is easier to remove one electron, resulting in a lower ionization energy.[2][14]

The problem is then you can't use the same explanation to explain Fluorine is higher ionization energy than Oxygen because you're also adding repulsions.

Bad Teacher:Stability of half-filled orbitals or completely filled orbitals.

This quote is using is arguing a point not building evidence for it.

I've tried studying spin and that doesn't explain it.

I tried using term symbols. Can you compare ionization energies of different atoms using that via Highest spin highest J?