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How to Draw all Resonance Structures & the Resonance Hybrid for a Given Lewis Structure

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  • 0:12 How to Draw all…
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Kyle Fisch, Kirsten Wordeman
  • Instructors
    Kyle Fisch

    Kyle has tutored general and organic chemistry as a part of the TRIO Rising Scholars and athletics programs for three years at Boise State University, where he earned his bachelor's degree in chemistry.

  •  
    Kirsten Wordeman

    Kirsten has taught high school biology, chemistry, physics, and genetics/biotechnology for three years. She has a Bachelor's in Biochemistry from The University of Mount Union and a Master's in Biochemistry from The Ohio State University. She holds teaching certificates in biology and chemistry.

Steps for Drawing all Resonance Structures & the Resonance Hybrid for a Given Lewis Structure

Step 1: Understand the rules of resonance and identify where electrons can flow to or away from.

Step 2: Draw curved arrows to show the movement of electrons.

Step 3: Confirm that no rules of resonance have been broken.

Step 4: Draw the resonance hybrid by combining all of the resonance structures drawn.

Vocabulary for Drawing all Resonance Structures & the Resonance Hybrid for a Given Lewis Structure

Resonance Structure: For molecules that can have resonance, a structure that represents an alternate distribution of electrons.

Resonance Hybrid: A combination of all of the resonance structures.

Rules of Resonance: Each resonance structure must have the same overall charge. The octet rule can't be violated. Resonance structures with charges larger than 1 are too unstable to exist. The resonance hybrid will favor the most stable resonance structure.

Next, we will look at two examples where we are given a Lewis structure, and we must draw its resonance structures and its resonance hybrid.

Example Problem 1 - How to Draw all Resonance Structures & the Resonance Hybrid for a Given Lewis Structure

Draw the resonance structures and resonance hybrid for {eq}NO_3^- {/eq}.

Lone pairs are not drawn as they do not affect the resonance of this molecule

Step 1: Understand the rules of resonance and identify where electrons can flow to or away from.

Any atom can have multiple bond states. Note here how we have three nitrogen to oxygen bonds. All three bonds are essentially the same as we can move the location of the double bond.

Step 2: Draw curved arrows to show the movement of electrons and resonance structures.

To draw the first resonance structure, we will take two electrons out of the double bond shown and shift them to another single bond.

This transition gives us the following structure:

There is one more possible resonance structure after the transition:

This gives us:

Step 3: Confirm that no rules of resonance have been broken.

Each structure has an overall charge of -1. There are no atoms with more or less than four electron groups. These resonance structures are correct.

Step 4: Draw the resonance hybrid by combining all of the resonance structures drawn.

This is done by drawing every bond that partakes in resonance with a solid/dashed bond as shown:

.

This hybrid is not shown with charges. This is because the electron density that usually provides a negative charge is dispersed through the molecule. Sometimes this partial charge is shown with a {eq}\delta^- {/eq} or {eq}\delta^+ {/eq}.

Example Problem 2 - How to Draw all Resonance Structures & the Resonance Hybrid for a Given Lewis Structure

Draw the resonance structures and resonance hybrid for {eq}CO {/eq}.

Step 1: Understand the rules of resonance and identify where electrons can flow to or away from.

Electrons are distributed between the carbon and oxygen atom. Electrons have the potential to flow towards either atom.

Step 2: Draw curved arrows to show the movement of electrons.

The transition:

Gives us:

The other possible transition:

Gives us:

Step 3: Confirm that no rules of resonance have been broken.

The first resonance structure is acceptable. The second resonance structure contains charges greater than 1 and does not exist.

Step 4: Draw the resonance hybrid by combining all of the resonance structures drawn.

Because there are only two atoms involved in this molecule, there is only one place for the electrons to exist. However, the only valid resonance structure was a result of shifting electrons towards the oxygen, which means it gained negativity. That being said, the original Lewis structure is the most stable and will contribute most to the resonance hybrid, which looks like this:

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