Defining VSEPR Theory

[IsabelMurillo3K]

Hey guys!
I was doing the sapling homework and I was struggling a bit with the situations revolving VSEPR theory. I was wondering if anyone could clarify the VSEPR theory and explain how I can apply it to find the smallest bond angle in a molecule. Thanks in advance!

[Danielle Goldwirth 3F]

The acronym says a lot about how to go about this.
The Valence-Shell-Electron-Pair-Repulsion Model focuses on the location of bonding electrons and lone pairs with respect to the central atom.
Bonding electrons and lone pair electrons repel each other (lone-lone pairs have the maximum repulsion while bonding-bonding pairs have the lowest repulsion).
If the repulsion between atoms' electron densities is higher, we must make the angle between these atoms longer.

[Nathan Tong 3G]

The VSEPR Theory allows us to determine the geometry of a molecule by using the repulsions between bonding and lone pair electrons. Essentially the bonding or lone pairs will repel each other as far from each other as possible, and using the ideal shapes of those molecules, you can determine the angles between the bonds. For example the bonding pairs in BF₃ will repel each other so that the angles between the bonds are all 120^o.

[Manseej Khatri 2B]

Hi. The VSEPR (valence shell electron pair repulsion) model is a model that helps find the shape of the molecule. Using the idea that electron repulsion is greatest between lone pairs regions, less so between a lone pair and a bonds, and the lowest between bonding regions, you can have a general idea of what the shape is. Knowing that, you can have an estimate for which bond angles are the smallest or largest depending on the shape or whether the atoms are different.

For example a molecule with a shape trigonal pyramidal would have 3 bond angles on one plane being around 120 degrees, with the other two bond angles being around 90 degrees.
If the shape is for example tetrahedral however, the bond angle would be uniform unless there are different atoms surrounding the central atom. I believe the larger the atom the larger the bond angle created between the other atoms but I am not particularly sure about this.

[SashaAnand2J]

VSEPR theory is a method by which we can better understand molecules' structures, which can help when scientists want to optimize reactions, for example. Molecular geometry can impact how a compound interacts with its environment. VSEPR specifically takes into account the amount of electron "clouds" around a central atom (including both bonds and lone pairs) and determines how each impacts the structure of a molecule. You can find tables online defining the impact a certain number of bonds and/or lone pairs has on this geometry in terms of bonding angles. Hope that helps!