Some of the important pollutants in the atmosphere are ozone...

Key Concepts

Lewis Structures

Lewis structures are diagrammatic representations of molecules that show the arrangement of atoms, the bonds between them, and the location of lone pairs of electrons. These structures help in visualizing the connectivity in a molecule and the distribution of valence electrons, which is crucial for understanding molecular geometry and reactivity.

Resonance Structures

Resonance structures are multiple valid Lewis structures for a molecule that cannot be accurately represented by a single drawing. They illustrate the delocalization of electrons within the molecule, indicating that the actual electron distribution is a hybrid of these structures, which helps in understanding molecules that exhibit stabilization through electron delocalization.

Octet Rule

The octet rule is based on the tendency of atoms (especially second-period elements) to have eight electrons in their valence shell, achieving a noble gas configuration. In drawing Lewis structures, electrons are arranged to fulfill this rule where possible, serving as a guideline for predicting the most stable structure.

Formal Charges

Formal charges are calculated for atoms within a molecule to determine the most likely distribution of electrons in a Lewis structure. By comparing the number of valence electrons in an isolated atom to those assigned in the molecule, formal charges help in identifying the most stable resonance structure or molecule by minimizing charge separation.

Transcript

00:01 So in this video we're going to talk about question 94 from chapter 8, which says some of the important pollutants in the atmosphere are ozone, o3, sulfur dioxide, and sulfur trioxide.

00:11 Brightly's structures for these three molecules.

00:14 Show all resonant structures where applicable.

00:18 So first we have ozone, o3, and we know that each oxygen atom is going to bring six valence electrons, so we have a total of 18 electrons to work with.

00:28 So i've gone ahead and drawn three possibilities for lewish structures and we'll talk about why each of them is good or bad.

00:37 So one possibility, the first possibility i've written is for each of our oxygen atoms to be singly bonded to the central oxygen atom.

00:46 Then i can fill in the octet on each of the oxygen atoms that are bonded and that leaves me two electrons remaining.

00:53 So i'll put those two electrons in my central atom.

00:56 Let's go ahead and calculate formal charges for this.

00:59 Well, for each of my electrons on the right and left, i have six valence electrons minus six electrons that are not bonding, minus half of the electrons in the bonds, that's one.

01:11 That gives me a formal charge of minus one.

01:14 Then for my central atom, i have six minus two, minus two.

01:18 That's a formal charge of plus two.

01:20 So with formal charges of plus two, minus one, and minus one, this is not a very good lewis structure.

01:25 Another possibility would be to take one of the oxygen atoms and double bond it.

01:31 So in that case, if i did that, one of my oxygen atoms would still have a minus one formal charge, but my central oxygen atom would now have 6 minus 2 minus 3, that's a plus 1 formal charge, and then my other oxygen atom making the double bond will have a formal charge of 6 minus 4, minus 2, that's 0.

01:53 Additionally, this structure is resonant stabilized.

01:56 So i could just move the electrons from this double bond to this single bond and end up with this resonant structure here.

02:08 Another possibility, you could say, well, won't i just have a formal charge of zero on every atom if i double bond both of the oxygen atoms to my central atom? so why don't we try that? well, if we do that, then yes, both of our oxygen atoms on the sides have formal charges of zero, and the central atom will have a formal charge of 6 minus 2 minus 4 that's also zero.

02:31 So this would seem like the best of both worlds.

02:35 But the problem is oxygen cannot have more than a noctet because of the energy level it's in.

02:42 It's only in the second row of the periodic table.

02:45 So we cannot have more than a octet with oxygen.

02:50 And this lewish structure would give the central atom more than an octet.

02:55 So the correct lewish structure is the resonant stabilized one here.

03:03 Now, what about so2? so in so2, each of our sulfur atoms and oxygen atoms bring six electrons.

03:10 So we have a total of 18 electrons to work with...

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