Ionization Energy [ENDORSED]

[Timothy Kim 1B]

Why does Oxygen go against the trend of having an increasing ionization energy to the right of the periodic table?

[Dylan Davisson 2B]

Oxygen doesn't follow this trend due to repulsion between electrons of the same orbital. In this case, you can see that nitrogen (the element directly to the left of oxygen in the periodic table) has one electron in each of its p-orbitals, while oxygen has a paired electron within one of its p-orbitals. Because the repulsion between the two electrons in the same orbital raises their energy, it is easier to remove one of the paired electrons than it is to remove an unpaired electron.

Breaks in this trend of ionization energy are not exclusive to oxygen, but they occur for the same reason that it occurs for oxygen: repulsion between electrons of the same orbital raises their energy, making one of the electrons easier to remove.

[Chloe Blume 1F]

Usually when you go across the periodic table the ionization energy will increase but when going from N to O this is not the case. This is because when adding another electron into the px orbital the electrons repel against each other due to their similar charges which causes the ionization energy to decrease rather than increase.