Bent/Angular Bond Angles

[Alexander Chao 1L]

Hello! I'm a little confused when it comes to the bond angles of the bent VSEPR shape. When doing the textbook questions, I would see that the bond angles of the bent molecular shape would be slightly less than 120 degrees. However, I recall from one of the lectures that we did that the bond angles for the bent molecular shape would be slightly less than 109.5 degrees and would rather be approximately 104.5 degrees. Does this have something to do with the regions of electron density and the lone pairs attached to the central atom? Or am i just mistaken on the bond angles of bent molecular shape and it's just one of these two options? Anything will help thanks! :)

[Sloane Richie 3C]

Hi! When the linear central atom has two lone pairs, the bond angle is less than 109.5, but when the central atom has only one pair, it is less than 120. This is because when there are two lone pairs, they go on opposite sides of the central atom, creating something similar to a tetrahedral shape, which we know is 109.5. When there is just one lone pair on the central atom, it is a similar shape to trigonal planar, which is 120. The angles of bent are smaller than their similar shapes (tetrahedral and trigonal planar) due to the stronger electron repulsion from the lone pairs.

[Riya Agrawal]

Hi! So the bond angle of a bent shape depends on the number of electron density regions. If there are three regions (e.g. SO2), the bond angle is slightly less than 120 degrees due to lone pair repulsion in a trigonal planar geometry. If there are four regions (eg. H2)), the angle is slightly less than 109.5 degrees, typically around 104.5 degrees, due to long pairs in a tetrahedral geometry.