ionization of oxygen

[705676154]

why does oxygen have a lower first ionization energy than both nitrogen and fluorine

[katrinahuwang_1L]

Oxygen is the first element encountered in which the p-electrons must be paired. This added electron-electron repulsion energy causes the ionization energy to be lower.

[KyleNagasawaDisc3C_Chem 14B2022W_]

Hey,

When you draw out the Aufbau diagrams for an electronically neutral atom of Oxygen and Fluorine, you realize that why Fluorine has 3 singly-filled p-orbitals, Oxygen has 2 singly-filled p-orbitals and 1 singly-filled p-orbitals. Due to the energetics of electron-electron repulsion, an orbital tends to be in a more energetically favored state when there is only one electron in an orbital. As a result, it is much easier to remove an electron from the doubly-filled orbital of Oxgen than it is to remove an electron from a singly-filled nitrogen p-orbital. This is seen with oxygen possessing a lower first ionization energy.

With regards to Fluorine, all the shielding provided by electrons is not as effective on an electron if they share the same subshell. As a result, even though Fluorine has more valence electrons, it has a higher effective nuclear charge, and thus, Fluorine hold onto its valence electrons much more strongly than oxygen. As a result, fluorine exhibits higher first ionization energy.

I hope this helps!