### Bond Angles

Posted:

**Thu Nov 22, 2018 9:52 pm**Does anyne have like a tip or trick to remember all the specific bond angles or is repetition my best bet?

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=38&t=37085

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Posted: **Thu Nov 22, 2018 9:52 pm**

Does anyne have like a tip or trick to remember all the specific bond angles or is repetition my best bet?

Posted: **Thu Nov 22, 2018 11:02 pm**

There's the normal ones like tetrahedral that you can just memorize, but for a lot of molecules where those angles are tweaked a bit you can't just memorize them other than knowing that they will be greater or less than the usual value.

Posted: **Fri Nov 23, 2018 10:35 am**

For planar geometries, you can just divide 360 by the number of angles, for example, a trigonal planar 360/3 and for 3-d geometries, it is best to memorize which should not be that hard.

Posted: **Fri Nov 23, 2018 11:59 am**

I would suggest memorizing the basic angles like tetrahedral is 109.5, trigonal planar is 120, and linear is 180. Then, you should understand how lone pairs affect those angles. Lone pairs push the bonded atoms together making the angles smaller. For instance, a trigonal pyramidal is <109.5.

Posted: **Fri Nov 23, 2018 12:01 pm**

For a tetrahedral shape (4 areas of electron density) with no lone pairs the bond angle is 109.5 degrees, and if there is a tetrahedral shape (4 areas of electron density) with one or more lone pairs, than the bond angle is less than 109.5.

Posted: **Fri Nov 23, 2018 2:37 pm**

Tetrahedral is typically the angle that trips people up because it is assumed that it would be 90 degrees since there are 4 molecules, when in fact it is 109.5 degrees. All the others are fairly straightforward (ex: trigonal planar, 120, or linear, 180) or are estimated instead of exact values (ex: trigonal pyramidal, which varies but is always <109.5).

Posted: **Fri Nov 23, 2018 6:20 pm**

Do lots of problems

Posted: **Fri Nov 23, 2018 7:07 pm**

I learned that it's easier to memorize each general one, but if you want to learn a trick then it's better to look at the shapes.

Posted: **Fri Nov 23, 2018 9:26 pm**

No better way than just memorizing them and more importantly understanding the 3-dimensional shapes and why the angles are what they are.