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GOB Chemistry
Learn the toughest concepts covered in your GOB - General, Organic, and Biological Chemistry class with step-by-step video tutorials and practice problems.
Molecular Compounds
Lewis Dot Structures: Exceptions (Simplified)
Lewis Dot Structure Exceptions happen when the central element violates the Octet Rule.
Lewis Dot Structure Exceptions
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Lewis Dot Structures: Exceptions (Simplified) Concept 1
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some elements can have less than eight or mawr than eight octet. Electrons around themselves and maintain stability. Now recall their non octet number of electrons is two x their group number. So for incomplete octet, where they have less than eight octet electrons around them for group to A and B two times two, which is four for Group three A would be three times to, which is six so they can have Group two elements. Can have four electrons, octet, electrons and be stable. Group 38 can have six or just multiplying their group number by two. So five they could have 10 electrons and me. Okay, Group six. They could have 12, 14 and 16. So just remember, sometimes the octet rule is broken and it's still okay in terms of the lewis dot structure.
Group 2A and 3A elements have incomplete octets. Group 5A-8A elements can have expanded octets.
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Lewis Dot Structures: Exceptions (Simplified) Example 1
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here. We have to draw the lewis dot structure for xenon di bromide molecule. So Zain on is in group eight A. It's a noble gas. So it has eight valence electrons, bro means a group seven. So it has seven, and there's two of them, so we have a 22 total valence electrons. Now, xenon will go in the center and here we're gonna be connected to our two bro means okay, Now, remember, your surrounding elements need to follow the octet rule. So we're gonna put our electrons around, bro Means so that they each have eight total valence electrons. Three lone pairs around them totalling six electrons. But remember, they're also sharing electrons from the single bond. So that's eight each one has. So that's using up 16 of my total 22 valence electrons. So we have six remaining here. The remaining six electrons. We have no choice but to put them around Zen on. So six electrons and we separate them evenly is lone pairs. And this would be the structure off xenon di bromide molecule. We can see here that Zen in has 2468 10 electrons around it. It's breaking the octet rule because it is an exception. Now it's non. It's ideal non octet number would have been 16, but again, that's when it's ideal here. We just don't have enough electrons to get to that number of 16. Instead, Xenon is okay with having 10 electrons around it. But here we're seeing that are central elements are breaking the octet rule, and it's still okay.
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Problem
Determine the Lewis Dot Structure for the following compound:SOCl2
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Lewis Dot Structures: Exceptions (Simplified) Concept 2
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When we discuss on electro molecules, we typically talk about free radicals. Now, free radicals are molecules or ions with a single UNP aired um paired electron around an element. We're going to say that these radical compounds or radical molecules always have an odd number of total valence electrons. And what's important understand here is that to draw them we place the electron on the element that is less electro negative. Except in the case of hydrogen itself. That's because if we show a single electron around hydrogen would be breaking the octet rule or in this case the duet role where it wants only two electrons around it. So if we take a look here at this molecule of nitrogen monoxide monoxide, we have a lone electron here. That's unfair on the nitrogen, nitrogen is less electoral negative than oxygen. So that's why it has the lone electron. And how do we know that nitrogen monoxide is a radical compound? Again, we would look at the total number of valence electrons and see if it's an odd number. Nitrogen is in group five A. So it has five valence electrons, oxygen's in group six A. So it has six valence electrons. So the total number of valence electrons from nitrogen monoxide is electrons. So it's an odd number. And that's why we have a rabble molecule or compound in this case. So just keep in mind we deal with these radical or free radical compounds. This is what you need to be on the lookout for to determine if it is a radical or not
Radical compounds always have an odd number of total valence electrons.
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Lewis Dot Structures: Exceptions (Simplified) Example 2
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here, it says, Draw the lewis dot structure for the radical of nitrogen dioxide. So nitrogen dioxide is a very common example used to talk about radicals. If we look at the total number of violence, we have five from nitrogen, since it's a Group five a six times to oxygen's in Group six A. So it has six and there's two of them. So this has a total off 17 total valence electrons. It's an odd number of Valence electrons, so that's a strong indication we're dealing with a radical. We place nitrogen in the center. It forms single bonds to the oxygen's. Initially, make sure that your surrounding elements follow the octet role. Right now, we have a total of 16 electrons being depicted, leaving us with one electron left. The issue now is that nitrogen is not fulfilling the octet rule. It has 235 electrons around it. So remember when the element is not fulfilling the octet role. What we can do is make double or triple bonds. Here. We can't make a triple bond because then that would be too many electrons around nitrogen. It can only go up to eight for the octet role. So we're just gonna use one of the lone pairs on oxygen, either one to make a double bond. And in that way, nitrogen has seven electrons around it, and that's the best that we can do. This year depicts what the nitrogen dioxide molecule would look like. It is a radical because we have that one lone electron on top of nitrogen.
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Problem
Draw the Lewis Dot Structure for the radical hydroxide, OH.
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Draw the Lewis Dot Structure for POCl3.
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Metalloids can sometimes adopt the bonding preferences of similar nonmetals. Based on your knowledge of expanded octets, draw the Lewis Dot Structure for the following ion, SiF62–.
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