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

Posted: Thu Nov 14, 2019 3:58 pm
by tonyhu
shouldn't there be twice as much e- and therefore twice as much weight?

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

Posted: Thu Nov 14, 2019 4:00 pm
by Michelle Chan 1J
I am not completely sure, but yes they are only counted as one. Maybe because e- are so light that it is insignificant.

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

Posted: Thu Nov 14, 2019 4:39 pm
by Justin Vayakone 1C
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.

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

Posted: Thu Nov 14, 2019 4:47 pm
by Ally Huang- 1F
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.

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

Posted: Thu Nov 14, 2019 8:10 pm
by Ellis Song 4I
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

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

Posted: Thu Nov 14, 2019 9:30 pm
by andrewcj 2C
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.

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

Posted: Thu Nov 14, 2019 9:34 pm
by Jorge Ramirez_4H
Does weight not affect angles?

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

Posted: Fri Nov 15, 2019 11:21 am
by Alexandra Bartolome 2H
Single, double, triple bonds are all considered single regions of electron density in the VSEPR model.

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

Posted: Fri Nov 15, 2019 11:23 am
by Alexandra Bartolome 2H
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.

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

Posted: Fri Nov 15, 2019 4:11 pm
by Junwei Sun 4I
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.

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

Posted: Fri Nov 15, 2019 6:37 pm
by Alan Wu
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.