bond angles

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Roni Touboul
Posts: 31
Joined: Fri Sep 28, 2018 12:24 am

bond angles

Postby Roni Touboul » Thu Nov 15, 2018 11:05 am

how do we figure out what the bond angles are?

Nicole Lee 4E
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am
Been upvoted: 1 time

Re: bond angles

Postby Nicole Lee 4E » Thu Nov 15, 2018 11:14 am

You arrange the bonding pairs and lone pairs around the central atom in a way that minimizes electron pair repulsion. For molecules where there is no lone pair around the central atom, the bond angles are 180 degrees for molecules with 2 bonding pairs around the central atom, 120 degrees for 3 bonding pairs, 109.5 degrees for 4 bonding pairs, 120/90/180 degrees for 5 bonding pairs, and 90 degrees for 6 bonding pairs.

Sarah Jeong 4F
Posts: 30
Joined: Fri Sep 28, 2018 12:27 am

Re: bond angles

Postby Sarah Jeong 4F » Thu Nov 15, 2018 11:20 am

You could think logically for some of them, for example how a triangular planar is equal angles, and therefore is 360/3=120 degrees. For some, it's just pure memorization. This is a very useful chart I found!
image.png

taywebb
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

Re: bond angles

Postby taywebb » Mon Dec 03, 2018 11:51 pm

Does anyone know if there are ways to figure out if the bond angles are not the standard 90, 109.5, 120, 180 and how we would denote on the final if they were more or less than that?

Sydney Aurelio_Dis4B
Posts: 30
Joined: Fri Sep 28, 2018 12:28 am

Re: bond angles

Postby Sydney Aurelio_Dis4B » Mon Dec 03, 2018 11:54 pm

@taywebb Yes if there is a lone pair on the central atom it would make the bond angles slightly less than the standard. This is because the lone pairs repel the other atoms away from itself making their bond angles slightly smaller

jguiman4H
Posts: 31
Joined: Fri Sep 28, 2018 12:29 am

Re: bond angles

Postby jguiman4H » Mon Dec 03, 2018 11:59 pm

This chart also sums up the point made above. The presence of lone pairs typically alters the bond angles to less/greater than expected, except in the two cases seen (steric number 5, linear shape and steric number 6, square planar shape) as these electrons can be placed anywhere on the axis, so they repel equally.

https://web.chem.ucsb.edu/~devries/chem1C/handouts/Molecular%20Geometry%20chart.pdf


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