Bond length

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Erik Buetow 1F
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Bond length

Postby Erik Buetow 1F » Fri Oct 25, 2019 9:23 am

In the example we did in class with the nitrate ion, he mentioned that the correct orientation was actually none of the Lewis structures but more likely a mix of all 3 due to the bond length being longer than a single but shorter than a double bond. What exactly is the significance of this and what is the importance of bond length?

Brittney Hun 2C
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Re: Bond length

Postby Brittney Hun 2C » Fri Oct 25, 2019 11:26 am

The longer the bond length the lower the energy it takes to break that bond. The further away the element is from the nucleus of the central atom, then the easier it is to break.

Haley Chun 4H
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Re: Bond length

Postby Haley Chun 4H » Fri Oct 25, 2019 11:28 am

I think he meant that resonance structures do not exist in real life and they just predict that a compound is more stable than expected (if you were to go to a lab and actually test it). In real life where quantum mechanics is considered, the bond length is an average of the 2 lengths. Resonance is just a simplification of this idea and one of the limitations of Lewis structures.

The bond length indicates strength/stability. The longer the bond, the less stable.

Sukanya Mohapatra 2G
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Re: Bond length

Postby Sukanya Mohapatra 2G » Fri Oct 25, 2019 11:28 am

The bond length is the average distance between the nuclei of two bonded atoms in a molecule. It is an average due to a bond not being a static structure, but instead one in which atoms vibrate because of thermal energy.

Alexa Mugol 3I
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Re: Bond length

Postby Alexa Mugol 3I » Fri Oct 25, 2019 11:30 am

As you saw in the resonance structures of nitrate, there are multiple places where you can place the double bond in the Lewis dot structure. Those different places for the double bond kind of exist all at the same time because the electrons are delocalized (think of delocalized electrons in metallic bonds). As Dr. Lavelle said, that's a flaw in the Lewis dot structure because it can't accurately depict the idea that those different bond placements exist simultaneously. I think the reason why Dr. Lavelle included the bond length is to further illustrate that the bonds are neither single nor double; they're somewhere in between, such that it's slightly stronger than a single bond but weaker than a double bond. Hope this helps!

Kassidy Ford 1I
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Re: Bond length

Postby Kassidy Ford 1I » Fri Oct 25, 2019 1:33 pm

Will bond length be given to us on tests or are we supposed to know bond lengths/assume resonance? Do you just base your lewis structure on the lowest formal charge?

lilymayek_1E
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Re: Bond length

Postby lilymayek_1E » Fri Oct 25, 2019 2:15 pm

Kassidy Ford 1J wrote:Will bond length be given to us on tests or are we supposed to know bond lengths/assume resonance? Do you just base your lewis structure on the lowest formal charge?


we probably don't need to memorize bond lengths, but in terms of resonance, I think that's something that we should be able to show (if it makes sense for that compound to have resonance; doesn't exceed valence electron capacity, e.t.c). So, if you have molecule C6H6, you'll probably draw out both structures with the double-sided arrow. I also think we'll really have to just understand that the more 0 the FC is, the more stable and more preferred(?) hope this helps!

405268063
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Re: Bond length

Postby 405268063 » Fri Oct 25, 2019 3:26 pm

Yes, Prof Lavelle did mention that the bond lengths of these atoms are not actually shorter or longer in real life. This is contrary to what a lot of textbooks will tell you (at least in my experience), and I think it's important in understanding conceptually what resonance structures really are.

Bradley Whitworth 4B
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Re: Bond length

Postby Bradley Whitworth 4B » Fri Oct 25, 2019 3:55 pm

The point is that electrons are rather unpredictable to us right now so to say we know there is a double bond in one spot when it could be in another is specifying something that we don't actually know because the electrons are delocalized. So, the resonance structure is meant to account for our degree of uncertainty with respect to where the electrons actually are and how they affect bond length.

Julieta Serobyan4D
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Re: Bond length

Postby Julieta Serobyan4D » Fri Oct 25, 2019 5:48 pm

Kassidy Ford 1J wrote:Will bond length be given to us on tests or are we supposed to know bond lengths/assume resonance? Do you just base your lewis structure on the lowest formal charge?

We don't have to know the actual values, but we have to know how bond length affects the behavior of the molecule

AprilPaz
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Re: Bond length

Postby AprilPaz » Fri Oct 25, 2019 6:04 pm

The significance of this example was resonance because we are visually seeing how different arrangements of electrons can be written in several ways. The importance of bond length in this example is that the average of the atom is a hybrid.

Madeline Phan 1E
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Re: Bond length

Postby Madeline Phan 1E » Sat Oct 26, 2019 10:29 am

When a molecule has resonance structures, its bond lengths don't actually look like any one resonance structure. It is actually has an average bond length of all the resonance structures.


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