Ionization energy

[Lily Mohtashami]

Can someone explain why Oxygen has a lower first ionization energy than fluorine and nitrogen and what first ionization energy tells you?

[Chance Herbert 3A]

The first ionization energy is the amount of energy required to remove the first valence electron. This will vary depending upon the depending on the magnitude of electrostatic attraction towards the nucleus. Oxygen has a greater degree of electron-electron repulsion in its subshell than Nitrogen (2p^4 vs 2p^3) which results in a lesser center seeking force. Fluorine has a greater amount of attractive protons which would in turn make it more difficult to remove an electron (greater attraction evidenced by smaller atomic radius).

[705340227]

There is some electron-electron repulsion between the spin up and spin down electrons. Nitrogen does not have any spin up/down pairs in its outermost shell but oxygen does. This causes some electron-electron repulsion in oxygen so it is easier to remove an electron in oxygen than nitrogen. Ionization energy increases across a period so oxygen has a lower ionization energy than fluorine because of this fact.