electron configuration vs shape

[Romi Moore 3k]

What's the difference between the name of the electron configuration versus the shape of the molecule?

[katrinahuwang_1L]

The name for regions of electron density and the name for the molecular shape can be different depending on the molecule. For example, in BrF3, if you draw out the Lewis structure, the VSEPR formula is AX3E2, where Br has two lone pairs. There are 5 regions of electron density, which means that if you're asked for the electronic geometry of the molecule, the answer would be trigonal bipyramidal since you're basically treating the lone pairs as bonding pairs. However, the molecular geometry of the shape is T-shaped when you treat the lone pairs as they are.

Hope this helps!

[Leah Wildmann 1F]

Electron configurations accounts for all of the regions of electron density as the same, while shape thinks of them as different.

[Irene Kim 3E]

I think it helps to count the regions of electron density first and use it to determine the molecular geometry. Then, determine the actual shape of the molecule, or its electron geometry, based on how many of those regions of electron density are lone pairs. For example, in a molecule of NH₃, if you draw the Lewis structure, there are 4 regions of electron density, so it would have a tetrahedral geometry. However, since one of those regions is a lone pair, its electron geometry would be trigonal pyramidal. This also helps determine the bond angles associated with the shape, since it is based on the molecular geometry. A standard tetrahedral molecule would have all equal 109.5 degree angles, but since the lone pair of electrons pushes down on the bonding pairs in a trigonal pyramidal molecule, its angles will be slightly less than 109.5 degrees.

[Ashley Fakolujo 3H]

Why is then, that in some cases they both have the same name?