Write resonance forms that describe the distribution of...

Write resonance forms that describe the distribution of electrons in each of these molecules or ions. (a) sulfur dioxide, $\mathrm{SO}_{2}$ (b) carbonate ion, $\mathrm{CO}_{3}^{2-}$ (c) hydrogen carbonate ion, $\mathrm{HCO}_{3}^{-}$ (C is bonded to an OH group and two O atoms) (d) pyridine: (e) the allyl ion:

Write resonance forms that describe the distribution of electrons in each of these molecules or ions.
(a) sulfur dioxide, $\mathrm{SO}_{2}$
(b) carbonate ion, $\mathrm{CO}_{3}^{2-}$
(c) hydrogen carbonate ion, $\mathrm{HCO}_{3}^{-}$ (C is bonded to an OH group and two O atoms)
(d) pyridine:
(e) the allyl ion:

Key Concepts

Resonance Structures

Resonance structures are different Lewis structures for a single molecule or ion that depict the delocalization of electrons. They show alternative placements of electrons—especially in pi systems or lone pairs—without altering the position of the atoms in the molecule. None of the individual forms fully describes the electron distribution; instead, the actual molecule is best thought of as a resonance hybrid that is a weighted average of all the valid resonance forms.

Electron Delocalization

Electron delocalization refers to the dispersion of electrons over several atoms rather than being confined between a single pair of atoms. This phenomenon contributes to the stability of molecules by spreading out electron density, which reduces high-energy localized charges and results in more evenly distributed bonding characteristics across the molecule.

Formal Charge Distribution

When drawing resonance structures, assigning formal charges correctly is key to achieving stable arrangements. The concept involves calculating the charges on individual atoms based on assumptions regarding bond electrons, and more stable resonance forms are typically those that minimize formal charges while placing them on atoms that are better able to accommodate them, such as more electronegative atoms.

Canonical Forms

Canonical forms are the individual resonance structures that contribute to the resonance hybrid of a molecule. Each canonical form represents a possible electron arrangement, but none of them accurately represents the actual structure by itself. Instead, they collectively illustrate the concept of delocalization with some forms contributing more significantly than others based on factors like stability and minimal charge separation.

Transcript

00:01 Okay, so then for this problem, first of all, we need to draw the loose structure.

00:06 And then we'll have to determine resonance.

00:08 So for the resonance, we're basically going to see the double bond alternate between the oxen.

00:13 So when we draw the loose structure for sulfur dioxide, we get this as a result.

00:18 So what you would do is you would calculate the number of valance electrons, and then just form double bonds until we have the correct number of valence electrons from the molecule.

00:29 So you can see that this double bond can alternate between these.

00:31 These oxygens and those are the resonant structures.

00:34 So for the next one, we have the carbonate ion.

00:39 So this one is similar except now we have three of the oxygens that double bond can also.

00:46 So then for the next one, this is hydrogen carbonate ion.

00:52 So for this one, you can see that it will resonate in between these two oxygen, but it cannot resonate onto the one that is bonded to the oh.

01:03 So be sure that you're not resonating it there.

01:05 Also, if you see a charge on the ion, you need to add the charge on the ion to the valence electron count when you're making new structures as well.

01:15 So keep that in mind.

01:16 So then for the pyridine, the pyridine is a little bit more complicated, but you can see like the first resonance is like benzene, so the double bonds are just alternating.

01:29 Then what happens is there's a double bond right next to the nutrition with a loan pair.

01:33 So what will happen is this double bond is just going to go on to the nitrogen.

01:38 And then there's going to be a long pair on this nitrogen...

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