Draw a Lewis Structure for each species.
a. N₂

Question

Draw a Lewis Structure for each species.

a. N₂H₄

b. N₂H₂

c. (CH₃)₂NH₂Cl

d. CH₃CN

Accepted Answer

Hi everyone. Let's do this problem. It says write the appropriate lewis structures for each of the following species. NH two NH ch three, NH n ch three ch three NH three cl and CH three CH two c n Well, if you recall lewis structure show how the atoms are connected to each other and it shows all the electrons the valence electrons on our compound. Right, So that includes bonded electrons and non bonded electrons. So in order to know how many electrons we're adding to our structure, we first need to determine the total number of valence electrons for our structure by adding the valence electrons from each atom in our compound. And we do that using the group numbers on the periodic table. Right? So nitrogen is in Group five, so it has five valence electrons. And then once we have that we're going to sort of draw a rough draft structure of our compound, showing how they're connected. Using only sigma bonds are sigma sigma bonds. And then we're gonna note how many valence electrons we have used versus how many are left over. Okay, so the ones counting how many we used in the sigma bonds and then how many we have left over Because then we'll use those leftover electrons to complete the octet for our compound with by adding those electrons as lone pairs and even maybe forming some double bonds. Okay, so let's try this. So first we have N H two, N H CH three and if you add up all their valence electrons. So this would be five plus 25143. This would be 20 valence electrons. And now let's draw what that might look like. So we have nitrogen with our two hydrogen is bonded to another nitrogen with a hydrogen and our CH three or methyl group on the end. So this uses 2468, 10, 12 14, 16 valence electrons. So that means we have four more left over, which would be two lone pairs. Right? So where should we add those two lone pairs? Well, my eyes go immediately to these, nitrogen is right because this carbon is happy as a clam with those four sigma bonds and our nitrogen is only had 246 electrons each with those sigma bonds. So now adding a lone pair to each one, we have 2468. And do they have a formal charge? Do we need to make any double bonds? Well, each nitrogen is owning or touching 12345 electrons. Which as we said before, the the nitrogen is happy with five valence electrons. So this is actually the answer, Oops! four. Our first compound. Cool. Alright, let's do the next one. We have N H N CH three And this has 18 total valence electrons. So let's draw it out. It's kind of similar to the last one. Oops I was about to write the condensed CH three but we want to show all those sigma bonds. Alright, I'm just gonna draw this hydrogen out here. So we have 2468 10 12 advance electrons used that means we have six more which is three lone pairs. So again my eyes go straight to these nitrogen, they definitely need some electrons. So let's just add two here and one here. That's our three lone pairs. But is this it is this happy now? This nitrogen is missing some electrons. Right? It only has 246 octet electrons. And this one has 2468 octet electrons. But it has a formal charge. Right? One electron touching it 23456. So this nitrogen will contribute to the other nitrogen with a double bond. So that will look like this. So each nitrogen gets a lone pair and they share that double bond. So now they each have eight octet electrons and five or sorry, eight Yes, eight oct 8 electrons and five valence electrons. So that's our answer. How's it going you feeling feeling? Okay about this? Well, what about this next one? I think it might be a little bit different. So we have C H three and H three C O. Hm. Do you notice anything about the types of bonds in the structure? Is it all covalin? Is it all ionic or is it a mix? Well, it's a mix. Right, I see a chlorine ion and a poly atomic ion. So with an ionic compound first. We want to assign the charges. Okay, so assign the charges before counting the electrons and I'll show you why. So if we add a negative charge to our chlorine, right? We know chlorine is a acts as an an ion and this will be our positive cat ion. So now when you add up your electrons for each one separately, you're going to Add one for the negative charge and you're going to subtract one for the positive charge, right? Because this chlorine atom since it's negative will have one extra electron and this positive polly atomic ion will have one less electron. Okay, So with that being said chlorine will have eight valence electrons. Right? Because it usually has seven plus one and then this compound will have 14. Alright, so let's draw these. Are they gonna have a bond between these two? The between the an ion or between the ions rather know right ions exist sort of next to each other? Right. So we draw them separate. So let's draw them separate. So we have our CH three NH three and then we have our chlorine. Okay, and our chlorine has a negative charge. And I guess we can draw those eight electrons. It is a lewis dot structure after all. And then we already used our 14 valence electrons here in the sigma bonds. So we don't need to add any more electrons but we need to add our charge. Right? So where does that formal charge of? Plus one? Go on here. Well, carbon looks happy. It has four sigma bonds. But this nitrogen, although its octet is complete, it has a formal charge of plus one. Right? Because it's only owning four electrons touching it. Right. And we know it's happy with five. So, this will be our structure or lewis structure for this compound. All right. I know that was a little tricky, but I hope that made some sense. Alright, we're almost there. So, we have ch three CH two CN. Okay, this has 22 valence electrons. Let's draw it out. Draw it out. We have arm ethel C H two and C N. Okay, these sigma bonds total to 16 valence electrons. Which means I have six more. And how many lone pairs is that? Three? So, I can see that my lone pairs are going to go over here because these seas are saturated, Right? They have all their hydrogen. So let's add a lone pair to this carbon actually to write because then that will satisfy its octet and then we can add one to this nitrogen. Okay, are we done? No. Because although I said this carbon has its octet it has a formal charge right? 123456. So it has a formal charge of negative two. And this nitrogen is not happy at all. It has only four electrons total and its octet and it only has three electrons at its owning So we're gonna move both of these lone pairs over to that bond to that charge center. And let's see if that satisfies all the little atoms. So that will form a triple bond. Alright, so now we have 2468 octet electrons on the carbon and 1234 touching it. That carbon is happy are nitrogen has 2468 electrons, octet electrons with 12345 touching it. So these are happy. Also, if you remember, this is a night trial group, a night trial group. So being familiar with that group, this will also be easier to recognize. So when you see a CN on the end of a carbon chain, you'll probably remember that it has to have the triple bond in between it. Um or that's you'll instead of counting everything and thinking about it each time, you'll probably remember that this is what the the most stable form of that group looks like. Okay, I hope this video is helpful. Thanks for watching

Draw a Lewis Structure for each species.
a. N₂H₄
b. N₂H₂
c. (CH₃)₂NH₂Cl
d. CH₃CN

Key Concepts

Lewis Structures

Valence Electrons

Formal Charge

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