NO3- example in lecture

[Melody Haratian 2J]

Hi guys!
I was watching lecture #14 and I noticed that nitrogen was used as the central atom. I thought oxygen was an exception in ionization energies, so it would have a lower ionization energy than nitrogen due to its electron-electron repulsions. Why is nitrogen used as the central atom?

[Alen Huang 2G]

Using the lowest ionization energy atom as the central atom is just a guideline, I'm assuming N was used as the central atom due to the symmetry the polyatomic ion would have

[John Calonia 1D]

I often use atoms that outnumber the other atoms in a molecule as the outer ones surrounding the central atom due to symmetry reasons. It wouldn't make sense for O to be a central atom because that would throw off the molecule's symmetry.

[Jenny Chau 1I]

I was also curious about that when I saw it in the lecture. Should we just loosely use the guidelines then since it seems there are some exceptions?

[clairehathaway 2J]

I went to a step-up session today and they explained that ionization energies are very important and should be considered in drawing lewis structures but we should also consider symmetry because it will play a role in the stability of the molecule. I think Dr. Lavelle mentioned that we would be learning the structure/geometry of molecules soon and there we will probably learn more about symmetry and how to decide what element will be the central atom.