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### Bond Angles

Posted: Sat Nov 16, 2019 11:25 pm
I might have missed when he said it, but did Lavelle specify if we're allowed to just write that bond angles in the presence of a lone pair are just less than their normal measure? For instance, a tetrahedral with two lone pairs, can we just write the bond angles as less than 109.5 degrees? Or would we need to approximate as closely as possible?

### Re: Bond Angles

Posted: Sat Nov 16, 2019 11:29 pm
I think you can just write what the textbook requires, which is <109.5. But you should write exact numbers for 90, 180, 120 degree angles.

### Re: Bond Angles

Posted: Sat Nov 16, 2019 11:33 pm
What I noted is that you should be able to tell when the bond angles are less than the expected (i.e. less than 109.5 deg in the example you give), but it is also helpful to be able to rank them when comparing various shapes, such as the bond angles on a molecule with one lone pair against a molecule with two lone pairs. This disparity is present because additional lone pairs force bonding electrons closer together with their repulsion power. The example that Lavelle used was with NH3 (one lone pair on central atom- angle 107 deg) and H2O (2 lone pairs on the central atom- angle 104.5 deg).

### Re: Bond Angles

Posted: Sat Nov 16, 2019 11:36 pm
Lauren Stack 4B wrote:What I noted is that you should be able to tell when the bond angles are less than the expected (i.e. less than 109.5 deg in the example you give), but it is also helpful to be able to rank them when comparing various shapes, such as the bond angles on a molecule with one lone pair against a molecule with two lone pairs. This disparity is present because additional lone pairs force bonding electrons closer together with their repulsion power. The example that Lavelle used was with NH3 (one lone pair on central atom- angle 107 deg) and H2O (2 lone pairs on the central atom- angle 104.5 deg).

Yeah, when Lavelle used that example for the H2O, and he said the angles had to be less than 107 degrees, it made me wonder if we are expected to reproduce the approximation on the test! Thank you for clarifying!

### Re: Bond Angles

Posted: Sun Nov 17, 2019 12:38 am
I believe you only need to be able to state that the bond angle is less than the expected angle. I don't think you need to give a more exact approximation.