Using Electron Configuration to Figure out # of Bonds

[Alyssa Truong 1L]

Hi! I’m wondering how I am supposed to be able to use electron configuration of atoms to figure out how to draw out the Lewis structure of a molecule? In the TA session, N was used as the example. For example, Nitrogen has an electron configuration of 1s^2 2s^2 2p^3 so there is a pair of electrons on the 2s orbital and 3 unpaired electrons on the 3p orbitals. However, how come the 1s^2 isn’t accounted for? How come the TA wrote the configuration as 2s^2 2p^3 without the 1s^2? If anyone else has another explanation, I’d greatly appreciate it too!

[Kate Molnar 2J]

Hi!

The TA was probably referring to the configuration of nitrogen using [He] as a central core. In this method, you would ignore the 1s2 because it is covered by the helium core. You are right that nitrogen is capable of forming 3 bonds, because it has 3 unfilled electron shells. You look at the amount of unpaired electrons to determine this number, and that will be in the valence shells (like the 2p shell you identified here).