Ionization Energy

[Eileen Si 1G]

Why does Oxygen have a lower ionization energy than Nitrogen? Are there are other elements that are special in the respect that they have lower ionization energies than the element to their right?

[KMenjivar_3A]

When writing down the electron configuration for each element, you will notice that oxygen has more electrons in the 2p orbital causing electron-electron repulsion. Therefore, oxygen has a lower ionization energy.

[Montana James 4G]

I don't know if this is the best way to explain it but here's how I think of it: Oxygen has four electrons in the p orbital (one pair and two unpaired). It is relatively easy to remove one of the paired electrons, making its ionization energy lower than nitrogen which is relatively stable with one electron in each of the three p subshells. The same is true for Boron, whose ionization energy is lower because it has only one electron in the p orbital and it's easier to remove that one than to disrupt an already full shell. (Someone please correct me if I'm wrong!)

[Lauren Tindall]

Since an electron is being added to an already half full orbital in oxygen, this results in electron electron repulsion, which lowers the ionisation energy. Nitrogen also has the added stability of a half filled shell of electrons in the 2p shell.