Aufbau Principle predicts that carbon would have two partially filled 2p orbitals, suggesting that carbon could only make 2 bonds. However, carbon actually makes 4 bonds.
How do we explain this?
Carbon Excites an Electron
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How carbon creates 4 partially-filled orbitals.
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So the first thing I want to talk about is just the theory of why this even is possible. Why this is a big deal. So the affable principle states that electrons can fill orbital's in order of increasing energy. Okay, remember that my orbital's in order of increasing energy were one s two s and then the three to peace. Okay, if we go ahead and draw the diagram for carbon, let's say let's just use carbon as an example we're gonna find is that the one s gets completely full. If the helium stage okay, then the two s gets completely full at the brilliant stage and then with carbon way, only have two electrons in those p orbital's. Okay, remember, there's three p orbital's total, and we only have two electrons in them. Okay, by the way, the notation that I'm referring to here has to do with electron configuration, which is something that you guys were supposed to remember from Gen com. Okay, so in this case, what that means they have two electrons in the two p orbital's. So if I were to draw the actual orbital diagrams for both of these, what you would realize or for the carbon. What you'd realize is that like I said, Oneness is full to us is full and then the peas air just a mess. Because what I have is basically to unfilled orbital's and then one completely empty orbital. Okay, so remember that I told you guys earlier we were talking about molecular orbital theory that unfilled orbital's like to bond with other unfilled orbital's. In order. Thio make them full in order to become more stable. So when you're looking at carbon, if it only has two unfilled like partially filled orbital's, you would think, Well, why wouldn't just make two Bonds? Why? Why does it make four okay, and remember, this is another way to think about it. We already talked about bonding preferences and stuff, but this actually has to do with Orbital. So why does it make four? Well, it turns out that this is just a really bad situation for carbon. Carbon does not like to look like this. The reason is because these orbital's are all messed up. The P organ ALS, some are partially filled, some are not filled, so that means that it would never really be able to be fully stable. So what carbon actually winds up doing is it winds up exciting one electron up into one of the P orbital. So what that does is it actually violates Affeldt the about principle. And it takes one electron from my two s orbital and it excites it to the one of the two p orbital's. So now what I went up getting is that instead of having one full orbital of lower energy and then three orbital's, that kind of just suck. Well, what's happening is that I wind up getting four orbital's of higher energy that all are partially filled. Why is that better? That even sounds worse now. We haven't excited Electron. That means it has more energy. So why is this better?
In terms of stability, now we have fewer filled orbitals, AND we had to excite an electron to do it. Why is it better to have 4 partially-filled orbitals?
Carbon Hybridizes Orbitals
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How carbon makes 4 sp3 orbitals.
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the reason is, and this is the crazy thing, it turns out that many of these atoms are gonna prefer to blend their second shell orbital's together. And what that's gonna do is it's gonna make new hybrid orbital's. Okay. So what that means is that instead of the two s orbital being lower energy and the P orbital's being higher energy well, ones of happening is that the carbon says, Hey, if I could just take these four different orbital's and make them combine them kind of mashed them up and make them all a little bit higher energy, but all equal. Then I could wind up filling them with bonds if I could fill them with bonds than I could become more stable because now I could have all of my orbital's filled. So what winds up happening is check this out. The two s orbital goes a little bit higher and because I'm blending the P orbital's with the S, the P orbital's dip down a little bit. So what winds up happening is that all the orbital's hybridized together and they all wind up being the same energy they all turn into what we call degenerate orbital's degenerate just means that they all have the same. They all have the same energy. Okay. And once they're degenerate, what that means is that I'm gonna follow hunts rule. So instead of the two s just having two electrons now, many follow hunts rule, which is that one? Each orbital gets one electron. Does that make sense? So now here's the interesting part since we blended one of the S Orbital's. And also since we had blended three of the P orbital's together and we made these four degenerate orbital's, these new orbital's are referred to as ehs p three. Okay, sp three. Because of the fact that one of them is the s and three of them are peace. Does that make sense now The reason that I have a two in front because these were all in the second shell. So this would be to s and two PS that air blending together to make sp three. So you could either just call it s p three and sometimes or sometimes we'll see it called to SP three. That just means that it's the orbital's from the second shell, that all coming together. All right, so Hopefully, that makes sense so far. Now, I'm gonna go ahead and show you guys how to apply this and how to use this knowledge to figure out hybridization and molecular geometry of atoms. So let's go ahead and get started.
Carbon “blends” its 2s orbital with the 2px, 2py and 2pz orbitals to create 4 new hybridized orbitals of equal energy. These are called 2sp3 orbitals or simply “sp3” orbitals.
Predicting Hybridization for Other Atoms
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Using bond sites to predict hybridization
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now that we understand the theory behind hybrid orbital's, let's go ahead and just figure out the rules that are gonna help us determine what type of orbital's we're dealing with for different atoms. So hybridization, it turns out, instead of looking at just the electrons like we're doing it could be determined in a much easier way. Again, we predicted by the number of what we call bond sites on an Adam. Okay and Bonds. That's just, you know, some people refer to these as groups, okay, but I think groups is really general, where it it's like it's easy to forget what a group is, but a bond site is really, really way more specific. So a bond site is gonna be equal toe any Adam or Lone pair. Okay, so basically, any time that in Adam is attached to another Adam, regardless of what type of bond it is, it could be a single bond, double bond or triple bond. All of those count as just one bond site. Why? Because there's only one place that it's attached to an Adam. Okay, then a lone pair councils another bond site because that's a place that it could form another bond if it wanted to. Okay, So what I wanna do is I want to go through Ah, hybridization summary and help you guys realize how? Just by looking at bond sites, we can determine everything about these atoms in terms of hybridization. So let's start off with four bond sites. What happens if I have a combination off Adams and lone pairs? That gives me four bond sites, for example. Let's say that I just have a carbon with four bonds on it. Okay? All of these four single bonds, all of these bonds represent Adams that it's attached You Okay, Well, if I have a carbon that looks like this, the participating orbital's are gonna be that I have the two s orbital. Remember that I have that to us. Or will that spherical that is gonna be hybridized and then I'm gonna blend that with three of the p orbital's does that makes them so far. Remember that the P orbital's were of higher energy. The S was of lower, but I blend them all together for hybrid orbital's. So what that means is that instead of getting thes orbital's of different energies what I wind up getting is four orbital's of the same energy or those degenerate orbital's. And these orbital's look a little bit different. They're kind of a combination of the P and the S. So what winds up happening is that instead of just looking like a peanut or sphere, they look kind of like this with one big side and one small side, and you get four of these. Okay, so basically, oops, that one looks a little bad. I'm gonna draw it again. So basically, all of these orbital's combined together and what I wind up getting is is four of the hybridized orbital's. We're gonna talk more about what they are. Okay, on hybridized orbital's actually is none. Because all of these orbital's participated together and they all blended together to make these four degenerate orbital's does. That makes them so far that they all have the same energy. Okay, So now if I was talking about the hybridization, what would we call these Orbital's? What we call them P. What do you call them? S no would call them a combination of what they are. So remember what the name would be. It would be SP three Okay. The reason we call it S P three is because I have one s and three piece combining together to make these orbital's. What I would get is four sp three orbital's that are brand new orbital's that I can use. Does that make sense? I hope so. Well, now let's talk about the bond angle and the S character, because these air common things that professors want you to know about the hybridization bond angle has to do with how far apart these four orbital's can get from each other. And it turns out that if I was on a two dimensional space, let's say that this paper I had four different orbital's on it and I wanted to get them is far apart from each other as possible. The furthest would be 90 degrees like I have here. Notice that here I drew this at a 90 degree angle. Okay, First would be 90 degrees, but Adam's don't exist on a plane. They don't exist on a page. They actually actually exist in three D. So in three d, they can actually move in different directions. So what I could do is I could make to I could make two of them come out of the plane. And if they come out of the plane, what that means is that the bond angles they're gonna turn into the furthest way they could get from each other is gonna be 19.5. And this should be an angle that you kind of remember from Gen camp. Okay, The way that you can think of it is that basically two of them are going front and back, so imagine that my hands are two of the bond sites, and then two of them are going side to side like my legs. I know you can't see my legs, but I'm just explaining that if my legs were spread apart and if my hands were spread apart this way, that's what a tetra hydro or like, that's what a one on 9.5 would look like. I'm gonna explain with that with that, with shape is in a second. Okay, then finally, what's the s character percent s character? That doesn't even make sense. Um, well, all that is is it's a percentage of s. Okay. What part of the entire thing is the s? So I have four orbital's total. One of them is s. So overall, what percentage is made out of S 25%. So let's go ahead and write that in. Okay, when trying to say is that if you have four and one of them is the s, your percentage of s character is gonna be 25%. Why is this important? Because when we get to the acids and bases chapter, we're gonna need to know that we're actually gonna need to know the s character to predict some types of facilities. Okay, Now let's move on to the next situation. Which is what if we don't actually have three bonds for bond sets? How about if we have three? Okay, so this is also common. What if I have a molecule that looks like, let's say c with a dope on? Oh, and two carbons on the side. Okay, notice that here. I know that you can't really see the oh, that well, but notice that this carbon now would have how maney bond sites Onley three. Because remember that I said that any Adam councils of bond site and any lone pair accounts is a bond site do I have any lone pairs? Know how many atoms do I have attached to that carbon Onley three I have a carbon on one side, carbon on the other side and then the oxygen of the top. So what that means is that in this case I'm only going to get three orbital's hybridizing together. The reason is because I only have three places where I'm making bonds. Okay, Does that kind of makes sense? I only have three places where I'm taking sharing an electron with another atom. So that's the only ones that are gonna hybridize. So what I'm gonna hybridize is one of the s Orbital's same as before. But now I'm on Liana hybridized to of the p orbital's. Alright, So I've won us and two peas and what that's going to give me is three hybridized orbital's. Does that make sense so far? But now, when it comes toe unhampered iced orbital, is there gonna be anything that's not making a bond to anything? Yes, there is. And it's gonna be one of the P Orbital's one of the P orbital's. I'm just gonna put here one p or I'm just gonna put here Pete. Okay, One of the P orbital's is not going to participate because it's not making a bond to anything, so it's not high braising. Okay, So if I read it, find a new name for these orbital's. What are they called? What I would call them is just a combination of what they were. Originally One of the S is two of the peas, so this would be called SP two. Okay, so SP two is the name of these Orbital's and have three of them. So basically, in the first example, I had four of the S P threes. But in this next example, I only get three of the SP two s, and then I have a P orbital that's just left over, so I still have four overdose total, but they're not all hybridizing. Okay, Now, in terms of bond angles, how far apart can these guys get? They can get 120 degrees apart, Okay, because of the fact that now we only have three orbiters that have toe worry about only have three bonds that have to worry about getting moving apart from each other, repelling each other and the furthest away that three things could get from each other is 120 degrees. So what that means is that it's gonna be a slightly different bond angle. Then finally, if I were to analyze the S character for this, I would say what percentage of the total is the S? And the answer is, Well, the total is sp two. There's only one s and there's three or four days total, so it's gonna be 33% s character, and that shouldn't be so bad. You guys should understand where I'm going with that. Okay? It's kind of a pattern. So let's do this last one. What if I have a situation where I only have two bond sites? So what that means is that, for example, the example the one that I had with a resonance where I had an and on one side and then oh, on the other Okay, in this case, I have to double bonds, but both of them only counts as one bond site could only attached toe one. Adam. Okay, so if I had a situation like this and I'm looking at this carbon right there, how many bonds are making too So how? Maney Orbital's? I'm gonna hybridize Onley too, because only two of these air accepting electrons from other atoms. So I'm gonna taken s and I'm going to take a pee, Okay? And what that means is that when I go ahead and combine these together, these air also gonna make those weird looking orbital's. But I'm going to get even less than the less of them. In this case, I'm only going to get to okay, And that means in terms of unhygienic ized orbital's. Now I'm gonna have to peas just left over Crazy. Right? So now I'm gonna put here to peace. Okay, So if I were to go ahead and say what type of hybrid orbital's are these, Well, it would just be a combination of what's coming together. So this would be called SP okay. And the furthest that two things could get apart from each other because remember now I only have two things. Repelling is 180 degrees. And since only I'm combining one s and one p, the s character is gonna be 50%. Does that make sense? So this is your summary chart. This is what we're gonna use to predict hybridization and all you really have to do is look at the bond sites and that's going to tell you everything else you need to know, okay?
A bond site is the name that we give to any lone pair or atom attached to the hybridized atom. The number of bond sites is what determines the hybridization of the molecule (see above picture).
Hybridization of Reactive Intermediates
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Introduction to the reactive intermediates.
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I want you guys to do is look at these examples here, and I want us to predict the hybridization off these different atoms. Okay, What I'm gonna do is I'm going to give you the name of all of these. These air called reactive intermediates, by the way. Okay, I'm going to give you the names of all of them. But then I want you to tell me how many bond sites it has, what the hybridization is and what the intermediate orbital is. Meaning that where is the negative for the positive charge actually going to reside? Okay, so let's go ahead and just talk about the names really quick. This is called this First one is a is a positive charge on a carbon. This is a very common reactive intermediate. What reactive intermediate means is that it's very unstable, so it reacts with lots of things. The reason it's unstable because it doesn't fulfill its octet, and that also doesn't fulfill its bonding preference. Okay, The name of this is a cardinal cat ion, and they want you guys to know that we're going to deal with these Ah, lot in organic chemistry. Carbon patterns are unstable because they don't fulfill their octet and they don't before they're bonding preference. So they want to bond with something else really bad. Okay, if I have a negative charge on a carbon that's called a carb an ion. Okay, if I have a single electron on a carbon, that's that's bad, because now that orbital is not fully filled, it only has one electron instead of two. This is called a radical. Okay, A radical radical. It's the same thing as free radicals. It's a new orbital that is not fully filled. It's only got one electron. Okay, And then finally, this is a very weird intermediate notice that this carbon here, in terms of its valence electrons, it has the right amount of valence electrons. Remember that carbon wants for violence. This one is for But the problem is that it has the wrong amount of octet electrons. Remember that Carbon wants eight, and this one only has six. This is a very reactive intermediate called a car bean. Okay, these are your four guys that you're dealing with. What I want you guys to do is use the rule for bond sites and figure out OK how? Maney. Basically, how many bond sites this each of these carbons have? Okay, from there. Tell me what The hybridization. Okay. And once you tell me what the hybridization is, then you'll be able to tell me, Okay, Where does this actually reside? Basically, where does the positive charge reside, or where does the negative charge reside? Okay, so I'm gonna give you guys an opportunity to solve that really quick. And then you guys go ahead, try to do all of these in terms of bond sites hybridization, and then we'll probably do the intermediate or pull together, So go ahead and try to do that now.
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Bond sites, hybridization, and intermediate orbitals
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so hopefully this wasn't too tricky. Let's go ahead and start with bond sites. All right. So bond sites for the Carvel cat eye on What are those? Well, let's go ahead and scroll up one more time just to see what bond sites where. Remember that I said that bond sites were equal to any Adam or any lone pair. Remember that? I also mentioned that some people call these groups. Okay, so some textbook, some online homeworks might call it groups. Some might call it bond sites. There's actually even another name that I've seen. And that name is Starik. Number Starik number. Okay, So what I want you guys to know is I really want you guys to know all three because your textbook might use one of these words. But your online homework, or maybe a supplemental book that you're using toe learn might use a different one. So I just want you guys to realize that if I say bond site group Starik number, that's all the same exact thing. All right. All has to do with is things around the atom that we're going to repel each other. All right, let's go ahead and talk about the carbon Catalan. So the caramel Catalan has three atoms. H h h. And then it has a positive charge. Does a positive charge count as a bond site? No, it doesn't remember that. I said the only thing that counts is atoms or lone pairs. So that means that I have three bond sites. All right, if I have three bond sites, then what is my hybridization? When my hybridization, I would look at my summary chart and I would say I have three. So my hybridization must be sp two. That must mean that one s is coming together with two piece and they're making three sp two orbital's. Okay, so I'm going to say that it's sp two and then we have the tricky one. What is intermediate orbital? What that means is, which is the left over orbital that isn't included in bonding where my positive charges Okay, let me put it this way. We just said that we have three sp two orbital's. Where are they? I'll show you The sp two orbital's are right here. There's one bonding to that h. There's one bonding to that h. And there's one bonding to that H. Okay, so those are the SP two orbital's, by the way. What is this bond gonna look like? Completely remember that? What kind of orbital doesn't h have? Do you remember? And h is just a one s orbital. Okay, so what I have here, let me use a different color for that. Since we have two different orbital's. What I have here is a one s a one s and one s So those are the one s is and those air overlapping with an SP two. So if I were to describe this, um, if I were to describe this bond, if I wanted to say, What kind of bond is this? What I would say is that it's a one s two s p to bond. Why? Because I have a oneness orbital from the hydrogen overlapping with an S P two orbital from the carbon. Remember, that has three of those. It's overlapping with one of those, and that's making a sigma bond that has that that has those properties. Isn't that interesting? So I just want to show you use that notation because in a lot of practice problems, professors will ask it just like that, they will say, What kind of bond is this or can you find all the bonds that are like this? All right, so that was a little bit of a detour, but I still think that's a good learning moment. Okay, so the question here, though, is that how maney sp two orbital's do I have? I have three. I have one sp to another sp two and another sp two. Alright. But how Maney Orbital's does this molecule? Does this carbon have total? It has four. So what is the left over orbital if you look up here, the left over orbital Is this p orbital that never hybridized. Alright, That P orbital is the one that's going to get the intermediate in it. Okay, where it's gonna get the positive charge. The reason is because I just showed you the sp two s are already bonding. All of these were taken up by an h. Okay, so that means that the positive charge must go where the positive charge must be in an empty P orbital. That is not bonding. Okay, I know that drawing is really messy, but that's the point of this question. OK, so the positive charges in the P and the other three SP two s are making three bonds. Does that kind of makes sense? Let's move on to the carbon ion. Okay, so for the carbon ion, how many bond sites do I have? I have three atoms, and then they have a negative charge is a negative charge. Ah, Bond site? Actually, not necessarily. I need to figure out what does that negative charge mean in this case, I need to convert this back to a Louis structure from a bond line so I can see. Yeah. I mean, it's not a true bond line right now, but having a negative charge kind of implies that we're implying lone pairs, so I have to figure out how many lone pairs that would have. So what I have to do is I have to say, Okay, Carbon once is in What group number four. Okay, I'm doing formal charges right now. Okay. And if as a negative charge, that means how many electrons does it have? If, as a negative charge, that means that it has one more electron than it's supposed to have. So that means that it must have five electrons. Okay? And that's why my charges negative one. Does that make sense? So if I have five electrons, that means that this carbon must necessarily have Ah, lone pair. Now, what I've just done is I just took the negative charge in the formal charge, and I converted back to a lone pairs. Whatever. You see, a charge. You have to do that for these because you have to figure out. Okay. Is there alone para not? Okay, so now that I have that lone pair that counts is my fourth bond site. Okay, So I have I basically have three atoms and have one lone pair, so I have four bond sites total. Does that make sense? Cool. Oh, my gosh. Almost dropped my pen. So if I have four bond sites than what's the hybridization? The hybridization is S p three. Okay. And that means how maney SP three orbital's do I have total. I have four of them because remember that when you use sp three, you have one s and three piece. They all come together and they all blends the other equally. So I have four hybridized orbital's. So what? That means is that one of the S P threes is going down and bonding to the H one of the SP three is bonded to that H One of the S P threes is bonded to that H but I still have an sp three left over. So that means that the orbital that the lone pair is going to be in is actually also gonna be sp three. Because that's the fourth SP three orbital. Cool. All right, so now let's move down to the radical, Okay? The radical. Let's just go a little bit quicker at this point. Has three atoms and a lone electron. Does that Lone Electron count as a group or as a bond site? No. So I have three bond sites. Okay. That means that my hybridization is gonna be SP two. These SP two orbital's are the ones that are making the bonding interaction. So I have one here, one here and one here. Those are my SP two s. So where do you think that this extra lone electron is going to go? Where this radical Where is it going to go? Once again, just like the Carvel Cat ion. It has to go in an empty P orbital. Why? Because remember I said for SP two, that means you only blend together one s and two p. And you have an extra P that's just left over. That's not hybridized at all. Okay? And that's where the radical would go. So once again, this would be in a p orbital. Okay, finally, we have a car bean car, beans a little bit interesting. How maney bond sites do I have? Well, I have two atoms, and I have a lone pair, so that means I have three barn sites. Okay, so what kind of hybridization would it be? Well, it would be SP two, okay? Because I have one s and have to piece coming together, and that's going to give me three hybridized orbital's. So let's look at where these orbital's are. One of the SP two s is coming down and making upon to that H one of the S P two is coming down and making up onto that H. Okay, where do you think the last SP two is? Well, in this case, my last SP two doesn't have anything to bond to, so that's actually gonna be the one that has the loan electrons in it. Why? Because I have to use up all my hybridized Orbital's first before I go to the UN hybrid iced ones. Okay, so what that means is that this lone electron pair is actually gonna be in my SP two in my third SP two orbital. Okay. And that is one that if I reacted it, I could make a bond right there. Okay, So for intermediate orbital, I'm going to say that the intermediate is actually SP to the the lone pair, which is my intermediate is going to go in an SP two hybridized orbital. Alright, So listen what I really want you guys to focus on, and I'm going to give you guys more practice problems in a little bit. Is the bond sites and the hybridization. As long as you guys can get that information from this chart that I made this awesome chart, then you're good. The intermediate orbital thing is a specific question that some professors ask, but it's not quite as important. Okay, So, for example, if this was an exam, most of the points would be on just figuring out bond sites and figuring out, um, hybridization. And not that many points would be on the intermediate orbital one. Alright. But I hope that you understood everything. Because in the end of the day, if you understand all of this, that's gonna help you later on. All right? So let's go ahead and move on.
So I know that was a loaded topic! If you found the part of intermediate orbitals a little confusing, that’s honestly fine as long as you know how to count bond sites and predict hybridization (will definitely show up on your exam).