Regions of e- density: Tetrahedral vs. trigonal pyramidal

[Jade Corpus-Sapida 1G]

If there are 4 regions of electron density, sp³, how would we know if it is tetrahedral shape or trigonal pyramidal? Or would we just have to draw the lewis structure to figure this out?

[Rebekah Kaufman 1L]

I believe that it depends on whether one or more of the regions of electron density are lone pairs. Lone pairs determine the shape so drawing the Lewis Structure would help you determine what shape it is.
(0 LP would mean tetrahedral and 1 LP would mean trigonal pyramidal)

[Katarina Ho -1B]

If one of the electron densities is a lone pair the repulsion force is much stronger and would push the others down into a trigonal pyramid.

[Alicia Beebe]

For four regions of electron density, it could even be angular if there were two lone pairs and two bonding pairs. I think of it as with four regions of electron density, your starting point is tetrahedral. If there's one lone pair, you "remove" it from the structure, but don't move any of the others. This would result in trigonal pyramidal. if there are two lone pairs, your result would be angular with the angle between at about 109 degrees, because you "removed" two of the attachments, without moving any of the others.