Exceptions to periodic trends [ENDORSED]

[Aditya Narashim 1K]

Hi, I was looking at a chart and I saw that the ionization energy of oxygen is less than that of nitrogen and I was wondering why that is. I was also wondering about if this exception manifests in other molecules and if other trends like electronegativity have exceptions like this?

[Brian Kim 1L]

Hey Aditya, I believe nitrogen has a higher first ionization energy compared to oxygen because the 2p orbital is symmetrical. Because the three electrons in the 2p orbital are singularly occupied, there is minimal electron-electron repulsion within the orbitals. In oxygen, however, the singular electron with opposite spin experiences repulsion, which makes it easier to lose the electron. I also believe that in this case, the electron-electron repulsion is a trend exclusive to ionization energy.

[Sophia Henry]

In response to your question, I wanted to share a resource I found online that I found to be particularly helpful in understanding exceptions to the periodic trend of electronegativity involving Oxygen and Nitrogen. For me, I did not find the reasoning to be intuitive at first and that is why this video was so helpful for me: https://www.youtube.com/watch?v=bQHj2MrSbXE&t=2s. I hope that it clarifies for you.