# Bond angle in water vs in oxygen difluoride [duplicate]

My teacher taught that bond angle $\ce{H-O-H}$ is larger than $\ce{F-O-F}$ due to less repulsion in the latter's bond pairs.
I know that bond angle $\ce{H-O-H}$ is $104.5^\circ$, but I'm confused with that of $\ce{F-O-F}$ because variable angles are given in articles on websites and in books. Some are $109.47^\circ$, $101.55^\circ$, $103.1^\circ$.

I want to know which bond angle is greater and why?

• We prefer to not use MathJax in the title field, see here for details. Jul 27, 2018 at 17:54

Water has a bond angle of 105º and oxygen diflouride has a bond angle of 103.8º, which cannot be explained by repulsion since fluorine is larger than hydrogen$$. This is phenomenon is, however, explained by Bent's rule:

Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative.

p orbitals are oriented 90º from each other, so orbitals with more p character have smaller angles between neighboring atoms. The effects of this phenomenon can also demonstrated by comparing bond lengths.

$$ Bent, H. A. Chemical Reviews 1961, 61 (3), 288.

• Where did you get the value for oxygen difluoride from? I couldn't find anything reliable. Jul 27, 2018 at 18:41
• On the Wikipedia page for Bent's Rule. I'm trying to find another source now. Jul 27, 2018 at 18:42
• So Bent's original paper actually uses 103.8º for the bond angle of oxygen difluoride. He cites Ibers, J. A., and Schomaker, V.: J. Phys. Chem. 1953, 57, 699 . Jul 27, 2018 at 19:09

On the DF-B97D3/def2-TZVPP level of theory the bond angle of water is $104.2^\circ$. Which matches up quite well, see what is the bond angle of water? The bond angle of oxygen difluoride is $104.9^\circ$. Unfortunately I couldn't find a good source for an experimental value. (Also the CCCBDB currently only produces errors.)

The values are too close together to actually compare them on this level of theory. According to Bent's rule (What is Bent's rule?) I would have expected the bond angle to be smaller in $\ce{OF2}$.

Maybe CCCBDB starts working again: