Determining Bond Angles

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

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Melanie Krahn 1C
Posts: 55
Joined: Wed Sep 30, 2020 9:34 pm

Determining Bond Angles

Postby Melanie Krahn 1C » Sun Nov 29, 2020 9:29 pm

How should we go about determining the bond angles of a molecule, since the VSEPR model only provides qualitative, not quantitative predictions? When given a problem, where would be the first place for us to start?

dana hu 1B
Posts: 60
Joined: Wed Sep 30, 2020 9:37 pm
Been upvoted: 2 times

Re: Determining Bond Angles

Postby dana hu 1B » Sun Nov 29, 2020 9:38 pm

determine valence electrons total and lewis structure of determining the number of bonding and lone pairs will help determine its shape.

Alex Benson
Posts: 40
Joined: Wed Sep 30, 2020 9:44 pm

Re: Determining Bond Angles

Postby Alex Benson » Sun Nov 29, 2020 10:03 pm

I begin by drawing out the shape of the molecule, then from there you are able to look at the bond angles and determine them!

Yun Su Choi 3G
Posts: 61
Joined: Wed Sep 30, 2020 10:09 pm

Re: Determining Bond Angles

Postby Yun Su Choi 3G » Sun Nov 29, 2020 10:08 pm

You don't have to know the exact bond angle of shapes with lone pairs. For example for trigonal pyramidal, you just have to know that the bond angles are less than 109.5. As long as you know the bond angles of basic geometry (linear, trigonal planar, tetrahedral,etc) you should be fine.

Samantha Pedersen 2K
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Joined: Wed Sep 18, 2019 12:21 am
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Re: Determining Bond Angles

Postby Samantha Pedersen 2K » Sun Nov 29, 2020 10:13 pm

One thing I find really helpful when determining bond angles is to consider the number of regions of electron density.

For example, consider a molecule with 3 bonding pairs and 1 lone pair. This has four regions of electron density, so the "parent structure" is tetrahedral. Tetrahedral molecules have bond angles of 109.5 degrees, and we can use this as a reference point. Since the molecule we're considering has one of the four bonding pairs replaced by a lone pair, its bond angles would be less than 109.5 degrees.

You can use the same logic with a molecule that has two bonding pairs and one lone pair. It has 3 regions of electron density, so the parent structure is trigonal planar which has bond angles of 120 degrees. One of the three bonding pairs is replaced by a lone pair in our molecule, so its bond angles would be less than 120 degrees. I hope this helps!


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