Question 2.81

[Annah Khan 1B]

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

I am not sure about how to answer this question and why that would be the answer. If anyone can help me, it would be much appreciated.

[Dabin Kang 1B]

The electron configuration of nitrogen is 1s2 2s2 2p3, which shows that each p-orbital contains one electron. However, the electron configuration of oxygen is 1s2 2s2 2p4, which shows that the px orbital contains two electrons. This leads to electron-electron repulsion which causes instability and makes it easier to remove the loosely held electron. However, fluorine has very high electronegativity, which makes it much harder to remove the outer electron even when there are electron-electron repulsions in the px and py orbitals, and is more likely to gain an electron instead of losing one.