VSEPR for four electron densities

[Jessica Yang 1J]

Hi I was wondering how to distinguish between a tetrahedral and a trigonal pyramid. I know both have four electron densities. Also how would hybridization would work differently for the two structures?

[K Stefanescu 2I]

Trigonal pyramidal structures have 4 regions of electron density, but one of those regions is a lone pair instead of a bonded atom. In contrast, tetrahedral structures have 4 regions of electron density that are all "attached" to a bonded atom.

I believe that hybridization of the central atom should be the same for either structure, but can anyone confirm this?

[Andrea ORiordan 1L]

Yes, the hybridization would be the same. Look at NH3 and NH4+ as examples, and you see that they both have sp3 hybridization. Hybridization does not depend on the number of lone pairs versus the number of bonded atoms- it only depends on regions of electron density, which can be either.