why are double bonds equally weighted as single ones when drawing models?

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tonyhu
Posts: 57
Joined: Tue Sep 24, 2019 12:17 am

why are double bonds equally weighted as single ones when drawing models?

Postby tonyhu » Thu Nov 14, 2019 3:58 pm

shouldn't there be twice as much e- and therefore twice as much weight?

Michelle Chan 1J
Posts: 50
Joined: Thu Jul 25, 2019 12:16 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Michelle Chan 1J » Thu Nov 14, 2019 4:00 pm

I am not completely sure, but yes they are only counted as one. Maybe because e- are so light that it is insignificant.

Justin Vayakone 1C
Posts: 96
Joined: Sat Sep 07, 2019 12:19 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Justin Vayakone 1C » Thu Nov 14, 2019 4:39 pm

I think double/triple bonds can distort the molecule geometry slightly, but the VSEPR model ignores that for simplicity I guess. It's just a model, so there are probably limitations and exceptions.

Ally Huang- 1F
Posts: 93
Joined: Thu Jul 25, 2019 12:16 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Ally Huang- 1F » Thu Nov 14, 2019 4:47 pm

Double bonds are equally weighted as single ones when doing VSEPR models because it is just considering electron density. Whether it is one bond or two bonds, it is still one area of electron density.

Ellis Song 4I
Posts: 92
Joined: Thu Jul 11, 2019 12:17 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Ellis Song 4I » Thu Nov 14, 2019 8:10 pm

VSPER model only considers regions of high electron concentration not the actual concentration which is why multiple bonds are treated as a single region of high electron concentration

andrewcj 2C
Posts: 92
Joined: Thu Jul 11, 2019 12:17 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby andrewcj 2C » Thu Nov 14, 2019 9:30 pm

No. It's important to remember that in molecules with both single and multiple bonds, there only exist hybrid bonds of equal energy, and the localized double bonds depicted in lewis structures only exist as a limitation of lewis structures. This is why resonance structures exist: because the multiple bond is not fixed to one location in real life.

Jorge Ramirez_4H
Posts: 54
Joined: Wed Nov 21, 2018 12:19 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Jorge Ramirez_4H » Thu Nov 14, 2019 9:34 pm

Does weight not affect angles?

Alexandra Bartolome 2H
Posts: 82
Joined: Sat Jul 20, 2019 12:17 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Alexandra Bartolome 2H » Fri Nov 15, 2019 11:21 am

Single, double, triple bonds are all considered single regions of electron density in the VSEPR model.

Alexandra Bartolome 2H
Posts: 82
Joined: Sat Jul 20, 2019 12:17 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Alexandra Bartolome 2H » Fri Nov 15, 2019 11:23 am

Jorge Ramirez_4H wrote:Does weight not affect angles?


No because the bond angles are formed from the repulsion between lone pairs and bonding electrons.

Junwei Sun 4I
Posts: 115
Joined: Wed Oct 02, 2019 12:16 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Junwei Sun 4I » Fri Nov 15, 2019 4:11 pm

VSEPR model only takes in consideration of region of electron density. Therefore having a double bond or a single bond indicate the same, one region of electron density.

Alan Wu
Posts: 61
Joined: Sat Sep 14, 2019 12:16 am

Re: why are double bonds equally weighted as single ones when drawing models?

Postby Alan Wu » Fri Nov 15, 2019 6:37 pm

andrewcj 4I wrote:No. It's important to remember that in molecules with both single and multiple bonds, there only exist hybrid bonds of equal energy, and the localized double bonds depicted in lewis structures only exist as a limitation of lewis structures. This is why resonance structures exist: because the multiple bond is not fixed to one location in real life.


But I'm pretty sure this post is asking about when the double and single bond are between different atoms (not a resonance structure). For example in HCN, C has a triple bond with N and a single bond with H. There's no resonance involved here.


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