When to invoke hybridization

[Mrudula Akkinepally]

In lecture 23, Dr. Lavelle says that the electron configuration of Nitrogen would not give the proper structure of NH3 so we invoke hypridization and create the 2sp3 state. I was wondering if someone could explain how we know when to invoke hybridization if we don't know what the proper structure of the molecule is supposed to look like?

[emmaferry2D]

You have to draw out the lewis structure before you can determine the hybridization because you need to see if there are additional lone pairs attached to the central atom. In this specific example when you draw out the lewis structure you are to see that the central N atom has four regions of electron density (three from bonded atoms and on from a lone pair). From there you are able to determine the hybridization based on the correlating electron density number.

[Jordi M 2I]

Can someone give an example when you wouldn't need to hybridize orbitals?