## VSEPR Formula

(Polar molecules, Non-polar molecules, etc.)

Kellina Tran 2I
Posts: 50
Joined: Sat Jul 22, 2017 3:00 am

### VSEPR Formula

Why is it that molecules with the same general VSEPR formula can still differ in angle degrees?

Joshua Hughes 1L
Posts: 81
Joined: Sat Jul 22, 2017 3:01 am
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### Re: VSEPR Formula

Why is it that molecules with the same general VSEPR formula can still differ in angle degrees?

Do you mean how like H2O and say Cl2O or OF2 would have slightly different bond angle even though they should all have the configuration of AX2E2 giving them a bent molecular shape (tetrahedral in regions of electron densities)?
This is just due to differences in electronegativities I think between the different atoms...maybe? So in water the lone pairs on the oxygen repel the bonds and cause the bond angle to be less than the 109.5 degrees we would expect in a tetrahedral(the internet says it would be like 1045.5).
So electronegativity for the elements would be in this order: F>O>H.
In OF2 the electronegativity of fluorine is greater than that of oxygen(while in water, oxygen has greater electronegativity than hydrogen) and would pull the bonding electrons closer to the F atoms. I think it would also mean that the regions of electron density from the lone pairs would be smaller/closer and thus be able to repel the bond pairs more, causing a smaller bond angle than that of water. (If someone could confirm this line of thought please do because I'm not a 100% either).

Joshua Hughes 1L
Posts: 81
Joined: Sat Jul 22, 2017 3:01 am
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### Re: VSEPR Formula

Here is a link to a website that kind of explains the reasoning for the bond angles for H2O, OF2, and OCl2.
https://www.dartmouth.edu/~genchem/0102 ... SEPR2.html
OCl2 is kind of an exception because the bond angle is actually greater than the expected 109.5 because for some reason the repulsion between the bond pairs is greater than the bond-lone pair repulsion. The website explains why and how it is the way it is better than I possibly could. Hope it helps :)

Diane Bui 2J
Posts: 61
Joined: Sat Jul 22, 2017 3:00 am

### Re: VSEPR Formula

If I'm understanding this correctly, even though different molecules have the same AX2, AX3, AX4, etc structure, it is due to the lone pairs that create different bond angles due to their repulsion.