For each of the following structures,
1. Draw a Lewis s...

Question

For each of the following structures,

1. Draw a Lewis structure; fill in any nonbonding electrons.

2. Calculate the formal charge on each atom other than hydrogen

d. [(CH₃)₃O]⁺

e. CH₃NC

f. (CH₃)₄NBr

Accepted Answer

Hey everyone, let's solve this problem. It says for each of the following structures draw lewis structure with the appropriate non bonding electrons and formal charge and we have CH 320 H plus H N C and C H +33 N H B R. So we're drawing our lewis structures and the first step for that is to count the total number of valence electrons in your structure which we do by adding up the group number of all the atoms. Right. And I see we have an eye on here. So if we have a plus charge we're going to subtract one electron from the total number. And if we have a minus charge, that's an extra electron. Right? So we're going to add one electron to the total then we can draw our sigma bond framework getting the connectivity of all the atoms correct then once we five, once we do that we can complete the octet with any extra electrons by adding them as lone pairs. And our question also asks for formal charge. So we can use our handy dandy formal charge equation which is group number or the number of valence electrons for that atom minus the number of bonds plus the number of non bonding electrons from our lone pairs. Right? And I like to call these touching electrons because they are the electrons that are directly touching that atom. Okay, so if I say that that is what I mean, it's kind of an umbrella term for both of those electrons. Okay, doke let's get this going. We have first our eye on CH 320 H plus, So that is four times two is 83 times two is 66 from oxygen and one from hydrogen and subtract one because of our positive charge. So that gives us 20 valence electrons. And oxygen has the highest bonding preference here. So that will be our central atom. So we have a hydrogen and two methyl groups in drawing this sigma bond structure that uses 18 valence electrons which means we have two more left over that we can add as one one that's not Quiet eligible one long pair. So I think it's pretty clear that lone pair is going on oxygen. Right? Those carbons are satisfied. They can't accept any more electrons. And oxygen only had six. So it needs two more to fill its octet. But are there any formal charges? So for oxygen, oxygen is in group six. So it likes to have six valence electrons and it has 12345 valence electrons. So that is a plus one formal charge on our oxygen. Okay, so that is it for that structure let's move on to H N C. Short and sweet. We have one plus five plus 4 10 valence electrons. And you can draw it left to right and nitrogen has the highest bonding preference. So that makes sense. This only uses for vance four valence electrons. So we have six left over Which would be three lone pairs. So we don't add lone pairs to hydrogen. But nitrogen and carbon definitely need some more electrons. Right, so carbon let's add two lone pairs there and let's add one to nitrogen. So carbon only has six electrons and it needs eight for its octet. Right. And nitrogen only has sex as well. It needs eight. So how about we donate these electrons to share with nitrogen? Right, sharing is caring. So let's see what that looks like. So we have double bond between nitrogen and carbon a lone pair on C n n mm They're still not happy. Right? They still only have, well, nitrogen is happy 246812345 electrons touching it. Carbon is not happy though. 246 total valence electrons or octet electrons now. So now nitrogen can share, Oh, that's so sweet. They're both sharing with each other. So we'll have a nitrile group. Right, H n triple bond C So carbon will still have a long pair. So there will be some formal charges here. Right, So nitrogen Likes to have five valence electrons but it has 1234. So, nitrogen will have a plus one formal charge. And how about carbon? It likes to have four but it has 12345. So carbon will have a negative one. And how did I know here that I should move the lone pair from the nitrogen instead of the carbon. Right, well, like I said, nitrogen was already happy. Right? So if I moved carbons electrons away from it towards the nitrogen that's just becoming more deficient. Right? Carbon doesn't have anything left to share here. The nitrogen is the one that has electrons that can that I can share. Okay, so This is our final structure for that one And one more to go. We have ch 33 N H B R. Okay, this is our biggest one yet. We have four for carbon times three is 12 plus three times three is nine. five for nitrogen, one for oxygen and seven for B. R. But I just realized something as I'm doing this. Is there anything different about this compound? B R likes to act as an ion. Right? That's an ion. So this is an ionic compound B R minus. And that means the rest of this will be our cat ion. Okay, so we have to add up their charges separately and apply our rules, subtracting an electron for the positive charge, adding an electron for the negative charge. Okay, I caught myself there. So B R likes to have seven electrons negative charge. That's eight valence electrons in our can ion we had 12 plus nine plus five plus one minus one. Now that we have a plus charge which gives us 26 valence electrons. Okay, let's draw it out. So we'll have B are on the outside here by itself with its eight valence electrons and its negative charge. And let's draw our cat ion. So it looks like nitrogen will be our central atom With the hydrogen and three methyl groups. See each three see age three, c H three and that uses all of our valence electrons for this cat ion. So let's calculate formal charge. These method groups are happy. The carbons all have four sigma bonds. How about that? Nitrogen though? Nitrogen Likes to have five valence electrons, but how many does it have here touching it? Only four. Right? 12341 from each sigma bond. So nitrogen will have a plus one formal charge. Which makes sense. Right. This compound we know needed to have a positive charge somewhere. So it's coming from the nitrogen. Okay, so that is it for this compound. That is it for this problem. I hope this video is helpful and thanks for watching.

For each of the following structures,
1. Draw a Lewis structure; fill in any nonbonding electrons.
2. Calculate the formal charge on each atom other than hydrogen
d. [(CH₃)₃O]⁺
e. CH₃NC
f. (CH₃)₄NBr

Key Concepts

Lewis Structures

Formal Charge Calculation

Nonbonding Electrons

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