Bond Angles

[Queena Chu 3E]

How do we determine bond angles if there are lone pairs? Would the bond angle be smaller or bigger?

[Ryan Laureano 3I]

I think it would just be helpful to look at a VSEPR chart. I am pretty sure Dr. Lavelle doesn't expect us to know the exact number, just if and why the bond angle is greater than or less than a specific number.

[Molly_Peterson_2F]

I don't think that we are expected to know or calculate the exact angles. I would agree that looking at a VESPR chart would be helpful to determine the approximate size of the angle. I would also suggest maybe rewatching lectures 20 and 21 because Dr. Lavelle goes through a lot of examples in those two lectures and explains the rationale behind the sizes of angles.

[Jillian Labador 3E]

Hi! Molecules with lone pairs have a molecular shape that is different from its electron density arrangement (since lone pairs aren't considered when determining shape; only the position of the atoms are). That being said, if you want to determine the bond angle of a molecule with lone pairs, I would suggest determining the electron density arrangement, but keep in mind that the bond angles are typically slightly smaller because of the strength of the lone pairs' repulsion compared to the repulsion of bonds. For example, if you have 3 bonded atoms and 1 lone pair attached to a central atom, the electron density arrangement would be tetrahedral (while the shape would be trigonal pyramidal) and if you know that the bond angle of a tetrahedral is 109.5 degrees, then you can determine that the bond angle of the molecule is slightly less than 109.5. Hope this helps!

[Violet Kwan 3H]

I agree with the post above. I do not think that we need to know the exact angle that is caused by a lone pair. You compare the slightly smaller or larger angles to angle degrees of the first few molecular shapes Dr. Lavelle showed us without lone pairs.

[MMorcus2E]

I also believe that we don't need to know the exact angles like Dr. Lavelle stated in the lectures. To answer your question about lone pairs, lone pairs decrease the bond angles. Lone pairs cause more repulsion than electrons within bonds because electrons within bonds are attracted by the nuclei of the atoms that are involved in the bond. Therefore, the more lone pairs that exist around an atom, the more repulsion there, which decreases the bond angles. Hope this helps :)

[Kyle Dizon 3A]

Lone pairs influence the bond angles by making them decrease because of the repulsion that it causes. In regards of knowing the actual bond angle, we do not need to know the exact angle, only the general idea of how it is influenced.

[Keon Amirazodi 3H]

The VSPER chart accounts for bond angles with certain numbers of lone pairs.

[reyvalui_3g]

In general, lone pairs will make the bond angles smaller than the angles if all the regions of electron density were atoms.

[IshanModiDis2L]

I don't think that we are expected to know or calculate the exact angles unless its a generally specific bond angle. I asked my TA and he agreed that looking at a VESPR chart would be helpful to determine the approximate size of the angle and that we may not to know some of them but I checked with him and he said we may need to know the general angles that are usually common, as he said it is fair game.

[Hannah Lechtzin 1K]

Lone pairs tend to cause bond angles to decrease sightly because they repel electrons surrounding the other bonded atoms. That said, I don't think we will need to know the exact bond angles, just general angles such as tetrahedral bond angles being 109.5 degrees.

[Ryan_Kien_1L]

The angles immediately near the electron would increase, while angles further away would increase because the electron pair creates more space for itself.