Bond Angles

[salvadorramos3k]

How can you tell when a bond angle is going to get smaller or larger? Also, for example, if the angle gets smaller, how do you know it went from 120 degrees to 109.5? Is this just something I would have to memorize?

[Anish Patel 4B]

If there are more lone pairs present, the repulsion that they cause forces the bonding atoms away causing there to be a decrease in bond angle size. Lavelle said you do not need to know the exact numbers but the idea that more lone pair electrons force bonding electrons closer together, decreasing angle size.

[Wilson 2E]

Similarly, molecules that have more atoms will have decreased bond angles as there are more regions of electron density surrounding the central atom making it more cramped.

[Lauren Stack 1C]

For each of the different molecular geometry shapes (VSEPR), I am memorizing the possible angles. Otherwise, I believe that is important to understand why an angle might be slightly less than expected (such as 107deg instead of expected 109.5deg) by understanding the role that lone pairs play in repulsion. Further, it is important to compare the different numbers of lone pairs present on the central atom and see the different bond lengths (1 having larger bond angles than 2, etc).

[Jillian C 4C]

A bond angle gets smaller due to lone pairs being stronger in repulsions than bonded atoms. Because the lone electron pairs repel more, there is less space between atoms, causing smaller bond angles.

[Alexa Hernandez 3k]

You need to know the tendencies of the shape the molecule has, that can and will help a lot ...