## Bond Angles

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

Cytlalli 1B
Posts: 23
Joined: Fri Apr 06, 2018 11:02 am

### Bond Angles

How do you know if bond angles are exactly a number or less than a certain number because I know for some questions the answers are exactly 120 degrees but others are for example angles are less than 109.5 degrees

Anna De Schutter - 1A
Posts: 66
Joined: Wed Feb 21, 2018 3:01 am

### Re: Bond Angles

Hi!

Is there a specific hw problem you had in mind that showed this?

The only reason I can think of why we would say less than a certain bond angle instead of the actual value is because of the presence of lone pair electrons. We said in class, repulsion strength: lone pair - lone pair > lone pair - bonding pair > bonding pair - bonding pair. For example, with the molecule SO3(2-) we have the three oxygen surrounding S, each with a single bond, and then a lone pair on top of S. The reason why the bond length is less than the expected 109.5 of a tetrahedral shape is because the lone pair occupies a bigger volume and so pushes the three O's bound to S more down and closer together than another atom bound to S would; which is why we end up with a bond length of less than 109.5.

I hope this helps! :)
Anna De Schutter - section 1A