What are resonance structures and how can I understand them better?

In summary, my teacher is explaining resonance structures in class, but I don't understand it that well. Can someone please help?
  • #1
emily(:
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My teacher is explaining resonance structures in class, but I don't understand it that well. Can someone please help? (:
 
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  • #3
The setup of them, I just don't understand them, like at all. I know that they provide more information than the Lewis structure, however I just don't know how to set them up correctly, or when you would want to use them over the Lewis structure or the electron dot diagram.
 
  • #4
You still haven't been too helpful in giving me a place a start... so again, I recommend reading the Wikipedia article, and doing a google search. That being said, let me say a few general things.

If you have a molecule---lets say NO2 (the example in the wikipedia article)---which has two (or more) possible configurations, it will often be in a combination between the possible states. In the figure, NO2 can have a double bond with either the left oxygen, or the right oxygen. In nature, NO2 will actual have kind of a 1 and a half bond on each side---more accurately, it will have partial double bond character. It other words it will 'resonate' between single and double bonds on each side.

Thus, the electron dot depictions aren't very accurate. Resonance structures are a way of trying to better describe the actual situation.

The reason molecules 'resonate,' is becomes it makes them more stable. The NO2 molecule is more stable with the double bond electrons shared between both sides of the molecule, than it would be if they were attached to only one side.

Let me know if there is something in particular I (or the forums in general) can try to elaborate on, or explain better. Please try to be precise.
 
  • #5
Emily, I don't blame you: the idea of resonance is kind of nebulous.

What it comes down to is that "resonance" is an artifact of valence bond theory/electron dot drawings on sheets of paper. We simply cannot draw a single structure that describes the chemical reactivities of certain molecules. So we draw several "contributing structures" with the understanding that none of them individually represents the "complete" description of the molecule. Instead, the best description of the molecule is that it is ALL of the contributing structures at the same time--pretty weird, eh? It's called quantum superposition :)

It's important to remember that the electrons aren't "shifting" between two resonance structures, so the term "resonance" is actually a bit misleading. The term "contributing structures" is more appropriate because multiple structures, frozen in drawings on paper, are contributing to the overall description of the chemical behavior of the molecule.
 
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  • #6
Thank you both for your responses. The description I gave is the best I way I could explain my problem.
 

What are resonance structures?

Resonance structures are different possible arrangements of electrons in a molecule that can be drawn to represent the same chemical structure. They are used to describe the delocalization of electrons in a molecule.

Why do we use resonance structures?

We use resonance structures to better understand the electronic structure of a molecule and to predict its reactivity and stability. They also help to explain certain properties of molecules, such as their bond lengths and strengths.

How do you determine the most stable resonance structure?

The most stable resonance structure is determined by following the rules of formal charge, where the structure with the lowest or most evenly distributed formal charges is considered the most stable. Additionally, the structure with the greatest number of covalent bonds and least number of formal charges is also typically the most stable.

Can resonance structures exist in all molecules?

No, not all molecules have resonance structures. Only molecules with conjugated systems, such as double bonds, triple bonds, or lone pairs of electrons, can have resonance structures. Molecules with only single bonds do not have resonance structures.

Do resonance structures actually exist in nature?

No, resonance structures are simply a representation of the different possible electron arrangements in a molecule. In reality, the molecule exists as a hybrid of all its resonance structures, with the actual electron distribution being somewhere in between the different resonance structures.

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