How Lone Pairs Affect Bond Angles?

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

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Sophia Diaz - Dis 1B
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How Lone Pairs Affect Bond Angles?

Postby Sophia Diaz - Dis 1B » Thu Jun 14, 2018 12:09 pm

I don't think I understand how lone pairs change bond angles. Let's say there was a tetrahedral molecule. I know that those bond angles are 109.5, but when lone pairs start getting introduced, do the bond angles increase or decrease and why? Does this apply to all molecules that get lone pairs introduced to it? What if there is more than one lone pair?

AnnaYan_1l
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Re: How Lone Pairs Affect Bond Angles?

Postby AnnaYan_1l » Thu Jun 14, 2018 12:58 pm

Sophia Diaz - Dis 1G wrote:I don't think I understand how lone pairs change bond angles. Let's say there was a tetrahedral molecule. I know that those bond angles are 109.5, but when lone pairs start getting introduced, do the bond angles increase or decrease and why? Does this apply to all molecules that get lone pairs introduced to it? What if there is more than one lone pair?


So let's say you start off with a tetrahedral molecule (AX4) such as CH4. The bond angles H-C-H would be 109.5 degrees.

If you start removing elements and adding lone pairs (AX3E1, for example), such as CH3-, bond angles DECREASE because the lone pairs create more repulsion that just a normal element would (here, I am comparing CH4 to CH3-). Remember that bond angles only refer to angles between elements—so bond angles would not refer to the angle between the lone pair and the other elements.

Because lone pairs create more repulsion, the angles between the bonds of H-C-H in CH3- are less than 109.5 degrees.

Hopefully that makes sense!


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