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Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

1. A Review of General Chemistry


All bonds are not created equal. Some bonds perfectly share their electrons, and others barely share them at all. A dipole moment is the mathematical expression that describes this disbalance. 

Types of Bonds

General rules:

  • Bonds to carbon and hydrogen are always covalent.
  • Bonds between two identical atoms are always covalent
    • Adjacent atoms on the periodic table are polar.
    • Lone pairs are polar.

The sum of all dipole moments is equal to the net dipole. If all dipoles perfectly cancel out, the molecule with have no net dipole.   


Differences between ionic, polar and covalent bonds

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Now I want to talk about one of the most important concepts in all of chemistry, and that's electro negativity. So, as you guys already know, chemical bonds are formed by the sharing of valence electrons between two atoms. Alright, So when two atoms share their electrons with each other, that forms a bond. Okay. But the extent of that sharing okay will determine the identity and strength of that bond. What that means is that all bonds are not created equal. Some of them are very, very strong because they have intense sharing. And some of them are very, very weak because they have barely have any sharing it all. Okay, the unequal sharing of electrons in one direction or another is called a dipole moment. Okay. And that could be symbolized using the mu symbol, the mu peak letter. Okay, so just so you know, the dipole moment is calculated based on two variables. It's calculated based on the charge, and it's also calculated the charge difference between two atoms. And it's also calculated based on the distance between two atoms. Okay, so the charge between any two atoms is going to be related to the difference in election negativity. Okay, so I just wanted to point out that even though we used these two variables to deal with to figure out what the dipole moment is, the one that we're going to deal with the most is actually gonna be the charge. The reason is because the distances air gonna be very similar for a lot of these bonds. So that means the biggest difference is gonna be the election negativity it's gonna be Is it very, very charged or is it not very charged It all All right. So that's why we're gonna look at the charge, mostly, and to figure out what the charges were gonna use the following scale. Okay, Now this scale is called the Pauling Election Negativity Scale. You're going to see slightly different versions of it in your book. So, for example, um, thes are toe on li like two significant significant figures. So in your book, it might be 23 significant figures or there is possibility that the numbers will be slightly slightly different. So, for example, carbon might be like to four fours and like that, but in the end, thes relatively round thio each 0.5 which makes it really convenient when we're talking about what types of bonds were dealing with. So just to remind you guys, Florian is the most election negative, it goes all downhill from there. Another thing to point out is that hydrogen is actually unusually Electra negative for where it is in the periodic table. Check it out. Look what it's next to its next to a 1.9 point eight, and then all of a sudden you get 2.1 out of nowhere. There is, like it's like, what? What's going on? Okay, that's actually gonna make hydrogen able to make Covalin Bonds, and I'll show that in a second. Okay, so I want a couple this diagram that you guys should don't necessarily memorize it, but be familiar with it on. I wanna link that to my difference in election negativity. Now, when you were in Gen. Cam, your professor might have told you there's two types of bonds or there's three types of bonds. There's polar. And then there's Ionic, And then there's, like, just totally Covalin, And I remember when I was in Gen camp, my professor made very clear distinctions like there's one and there's the other and then they're two different things. But it turns out that it's really a spectrum. OK, it's really not just like one is completely polar or one is completely Ionic. Actually, it's a spectrum, and the way you figure out what the identity of that bond is is by taking the difference in the two election negativity is of the two atoms. So if that difference is less than 20.5, we're going to call that Covalin. That means that there's a lot of sharing. Okay, you can imagine that. For example, let's say that I had, um and F and an f, I guess. Cool with that. Both of these have the same election negativity. So this one has an electoral negativity of 4.0. This one has an electric negativity of 4.0. They both want electrons really, really bad, but they're both gonna pull equally. Think of this as a game of tug of war where you got you have these two heavyweights pulling on a rope. They're both pulling as hard as they can, but it doesn't budge. The reason is because they're both pulling exactly is hard. So the electrons get perfectly shared in between the two atoms. Does that make sense? That's a Covalin bond, meaning that the distribution of electrons is very similar amongst the two different atoms. Okay, then we have the range between five and two. These are gonna be polar or what's also known as polar co violence. So right that in just so you guys don't know that that means that they are Covalin in the sense that there is still some sharing. But they're polar. Polar means that it's a die pole. Remember that polar comes from the word die poll. Okay, so what that means is that there is unequal sharing. That means that one of these guys is going to get a little bit more than the other. Okay. And a good example of that would be Let's just say if I made this carbon and I made this flooring. Okay, So the election negativity of carbon is 2.5 election negativity of flooring is 4.0. Which one wants the electrons more? The floor in the way that I write a dipole is kind of like a vector. Back in physics, you write an arrow going in towards the direction of the greatest lecture negativity. But in order to be fancy like chemist had to invent their own thing. So they make a little line, okay? And that little line just means it's a disciple. If I were to draw the electron cloud of this, remember that these electrons air just kind of going around in these clouds of areas that they were able thio circulate What it would look a lot like is like this worth of flooring, getting a ton of electrons and the carbon getting very few. Why? Because this is a tug of war where you've got a sumo wrestler on one side and, like I'm on the other side. So, like, I'm just screwed. Okay, So I am not keeping up with the sumo wrestler and he's just taking almost all the electrons from me. It's very selfish of him, but whatever. That's a polar covalin bond getting that so far. Okay, I also want to point out we're gonna talk about this a lot more in further chapters, but this is going to result in partial charges. What that means is that the flooring, on average is gonna have way more electrons so the flooring is gonna have a partial negative. Now, the partial sign is a lower case. Delta. So the squiggly is that lower case Delta, And what it means is that it's more negative than other atoms in the molecule. There's no number associated with it is just like, ah, qualitative thing like this is more negative, not quantitative, then the carbon. Since it's missing electrons, that's me, right? The guy just, like, destroyed my ass like I have no electrons left. So that would be a partial positive, all right, because I don't have any electrons left, so he took him off. All right, so that would I just want to show you guys that when you have polar bonds, that leads to a dipole moment, and that also leads to partial charges. Okay. And that's gonna be a huge part of organic chemistry. As we move forward, we're gonna be analyzing lots of partial charges. Then finally, we have Ionic ionic bonds are similar to what you learned in Gen Cam about like table salt. You have n a and you have cl can't remember n a c l. Let's go ahead and look at those differences N A. Is down at 0.9. CEO is at 30 So what is that difference? That difference is actually going to be if you subtract the 23. minus 0.9. I'm not gonna like through the carry overs, whatever that's going to give you 2.1. All right, 2.1 puts it in this range, which is Ionic. What that means is that that bond is actually kind of misleading. There's almost no sharing it. All the electrons almost fully rest on the one that's more Electra negative. So in this case, if I had to write the negative charge somewhere, where would I write it? The sodium or the chlorine? The chlorine? So actually, it turns out that this can be either written as a bond or it could be written as any positive c o negative. Why? Because there really is no sharing going on. Really. What's happening is that the C. L is really negative, and the n A is positive, so it's just attracted to it. But they're not sharing electrons between them, and it turns out I'm just gonna put like one of those little triple aero signs. That means that by definition they're the same thing. So when you have an Ionic bond, you can either right as a bond. And you just know that there's a disciple there or you can write it as the individual charges. Okay. And that's what happens with an A C. L. So hopefully you guys can see now is that there are some polar bonds that are more ionic and some polar bonds that are more Covalin. It just depends where you sit on that spectrum. Does that make sense? Cool. So now you're probably thinking okay, Johnny Wolf, I'm not going to have these numbers memorized all the time. Like or do I have to? How do I figure out these questions of polarity? What I would say is there are a few general rules that are gonna work for 99% of the time, So instead of memorizing each number, we could just remember these rules. So the first thing is that bonds to carbon hydrogen are always gonna be co violence. If you figure out the numbers, you're gonna find out that the difference is 0.4 and that difference is so small that that puts it right into the cold, violent area. Cool. So bond between carbon and hydrogen article Violent bonds between two identical atoms are always gonna be covalin. Okay, what I'm doing here is I'm giving you rules that you could just use as a generalization. Okay? Adjacent Adams on the periodic table. If there, attached to each other bonded are gonna be polar. Okay, so that's an example, right? Let's say I give you nitrogen and oxygen or nitrogen and carbon. There's gonna be a die poll in that direction towards the more on polar one. And then finally, lone pairs are also polar. Okay, so lone pairs are gonna have their own dipole moment that pulls in the direction of wherever the lone pairs facing. Okay, finally, we have our last thing, which is the net dipole net die Polls exist when Adam's have asymmetrical dipole moments. So what that basically means is remember when I talked about with, um, charges with formal charges and how you if you have a bunch of formal charges that equals a net charge, it's the same thing with the dipole. Ah, bunch of individual dipole moments will make an overall net dipole. Okay, now I do wanna let you guys know that for the sake of this course, I'm not going to make you guys calculate out with the net. Dipole is why? Because that would take a lot of math can that would actually take vectors and and decomposition of axes and stuff like that. So instead of we're gonna do is we're just going to try toe visualize. Okay, what would that net dipole kind of look like? In fact, many times I'm not gonna ask you to draw the net, dipole. I'm just gonna ask you, does it have a net, typo? So if all of the dipole moments perfectly cancel out, then I will not have a net cycle. But if it's asymmetrical, meaning that let's say, have a really big die pull in one direction and really small die pool in the other that will have a net type. Does that make sense? So now we're gonna do some practice problems because I know that you guys are eager to apply this, So let's go ahead and do that

Which molecule/s contain/s net dipoles?


Which molecule/s contain/s net dipoles?


Which molecule/s contain/s net dipoles?


Which of the solvents are apolar and polar?