Ionization Energy (10d on Midterm Review)

[Janet Nguy 2C]

10. d) Rank the following in order of increasing ionization energies: C N O F

This was one of the questions on the midterm review packet: the answer is C < O < N < F, but I'm still confused on why, since I thought that ionization energy increases across a period.

They mentioned that N's half-filled shell is more stable, but can someone explain why? And in the future, will I always have to write out the electron configurations to figure out which elements have the higher ionization energies?

[TYun_1C]

The half filled shell is more stable because with 4 electrons, there is electron to electron repulsion in the first orbital, making the electron easier to remove.

[Selena Yu 1H]

No, you don't always have to write out the full electron configuration because you just have to know the periodic trend for ionization energy, which is that it increases from bottom to top and left to right. As for the exceptions we need to know, they are oxygen and nitrogen, where nitrogen is greater than oxygen, and phosphorus and sulfur, where phosphorus is greater than sulfur.

[Claire Stoecklein 1E]

There are exceptions for Oxygen, Boron, and Calcium. To be safe, you should probably write out the electron configurations to see if there is a reason that certain elements could achieve lower energies.