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### "more or less than 109.5 degrees"?

Posted: Mon Nov 13, 2017 10:38 pm
Hi,
In the homework and in class I have a hard time following when we are asked whether or not the angle will be greater or less than 109.5 degrees. How is this answer determined? I can never tell! I think I am missing the concept here. Thank you for your help!

### Re: "more or less than 109.5 degrees"?

Posted: Mon Nov 13, 2017 11:46 pm
You are just supposed to understand that if you have molecules with lone pairs, it will "push" the other atoms to create an angle slightly less than what would usually be expected

### Re: "more or less than 109.5 degrees"?

Posted: Tue Nov 14, 2017 9:50 am
when molecules have lone pairs, it is going push the atoms so that the angle will be narrower and less than expected

### Re: "more or less than 109.5 degrees"?

Posted: Tue Nov 14, 2017 12:19 pm
Lone pairs are a little more electronegative than bonded pairs, so they "push away" a little more as well. This results in the angle of the bonds being smaller, since they are being pushed together by the electronegativity of the lone pairs.

### Re: "more or less than 109.5 degrees"?

Posted: Tue Nov 14, 2017 12:50 pm
Extra lone pairs will always push the bonds closer together, making bond angles that are more or less than the standard 109.5 degrees.