Determining Shapes [ENDORSED]

[SammiOrsini_1B]

After the review session today I have come to learn that I am more confused about shapes than i thought i was. For starters, I understand the linear shape and I understand that when there is a lone pair the bond angle is less than 180. However, when it comes to the bent shape and the trigonal planar I run into confusion. For instance at the review session, the VSEPR Model was drawn as a linear shape, but then the central atom was said to have a lone pair on it and due to the fact taht the electron cloud of the lone pair is so big that it pushes the bond atoms down and creates a bent shape. It was further discussed that the shape actually was not bent because the lone pair that was added made it a trigonal planar. So i guess my confusion is, do lone pairs on a linear model make a bent shape? and does the bent shape with a lone pair on the central atom make the shape a trigonal planar? Also, can someone explain how to tell the difference between a tetrahedral, a see-saw, and a square planar? Thank you and i am so sorry that was so long and probably confusing!

[Myles Chang 1B]

I think your confusion lies within the fact that in one explanation you are describing the general shape using regions of electron density whereas in the other you are referring to bonded atoms. For example, both bent and trigonal planar have three regions of electron density, however bent is called bent because one of the regions of electron density is a lone pair that is not bonded to an atom. This is why it is called bent; when naming shapes, there is a difference between lone pairs and bonded electrons.