Ch 4 #11 Part b and more

[Michelle Dong 1F]

Using Lewis structures and VSEPR, give the VSEPR formula for each of the following species and predict its shape:
(b) Iodine Trichloride

When I drew out the Lewis structure, there turned out to be 2 lone pairs on the Iodine atom. I understand that the name of the shape should be influenced only by the atom positions, which is why the answer key says it's T-shaped. However, when looking back on notes, I noticed that ammonia (NH3) is named trigonal pyramidal, even though the atoms located around N would also make it T-shaped. Why is it that ICl3 has a T-shape but Ammonia is trigonal pyramidal?

[Ethan-Van To Dis2L]

It's because the electron geometry of the iodine trichloride is trigonal bipyramidal and the electron geometry of NH3 is tetrahedral. Electron geometry simply refers to the number of electron dense areas around the central atom, while the molecular geometry takes into account whether or not it has lone pairs. Since iodine trichloride has an electron geometry of trigonal bipyramidal with 2 lone pairs it would be T-shape because it produces the most stable structure. NH3 is a tetrahedral with 1 lone pair making it a trigonal pyramidal shape since it is the most stable. NH3 cannot have a T-shape because the electron filled areas would be too close to each other making it unstable.

[Christina Cen 2J]

ICl3 has 5 regions of electron density with the 3 Cl atoms and 2 lone pairs, where as NH3 has 4 regions with 3 H atoms and 1 lone pair. The 5 regions of ICl3 makes the electron arrangement trigonal bipyramidal, and the 2 lone pairs make it T shaped unlike NH3 which has a tetrahedral arrangement and trigonal pyramidal shape with 1 lone pair.