Drawing Molecular Orbitals

now that we know how to draw atomic Orbital's, I want to take things one step further and show you guys how atomic orbital's can be turned into molecular Orbital's. So guys here are seven rules for drawing Molecular Orbital's and just a heads up. You're not gonna find these rules anywhere because I made most of them up trying to look at all the different types of molecular Orbital's you might have to arrange and figuring out rules that would work for all of them. Now some of them are gonna be so straightforward, you know that you're not gonna need toe look all seven rules, but I just put the seven rules there, just in case you get to really complicated one. You don't know where to start. You could follow these rules and always know what to do. So let's go ahead and start with Rule number one, the simplest rule, which says that the number of total molecular orbital energy states should be equal to the total number of atomic orbital's. So if you have three atomic orbital's, you should have three molecular orbital's of different energy, pretty straightforward. Next one orbital of your molecular orbital's should never change phases. So what that means is that we're going to see that as thes molecular orbital increase in energy. Some of the orbital's will start to flip, but one orbital should always stay the same, so that could be any orbital you want. But I prefer that to be the first one because it just makes an easy reference to always see. Look at the first one to say that one is not going to change phases as energy increases. The last orbital, however, must do the opposite. It must always be changing phases with each increasing energy level, so you must always be flipping it back and forth for the number of nodes in your molecular. Orbital's must always begin at zero. So your first molecular orbital should have zero nodes and then increased with increased by one with each increasing energy level. So the more energy levels you have, you would just increase the number of nodes by one each time until you get to the very last energy love state. Five. Your notes should be as symmetrical as possible. Sometimes you're trying to fit three nodes into a molecular orbital, and you say, why can't I just put the three notes on this side and then zero notes on the other side. That's not the way it works. What you want to do is you want to space out your notes as symmetrically as possible. When in doubt, sometimes when a molecular orbital gets complicated. Like, for example, if you're doing eight atomic orbital's and you're trying to turn it into Molecular Orbital's, you're gonna get a lot of orbital's there. And when in doubt, you could actually draw a sine wave, Um, from a fake Adam zero to a fake Adam N Plus one. I'll show you how to do this, and this helps you to balance out your nodes evenly because you're using a sine wave system toe. Balance out your nodes, but we'll do that. We'll probably do that for more complicated example. Six. If a node passes through an orbital, so let's say that a node of your sine wave passes directly through an orbital. You must delete that orbital okay, so that orbital should not exist because by definition, if it's a node, electrons cannot exist there, so no electrons should be in that orbital. And then finally, once you have everything drawn. Fill the molecular orbital according to the rules of electron configuration, which would be off about principle. You have to build up Pauli exclusion. You can only put two electrons in each orbital and hunts rule. You have to fill degenerate or equal energy Orbital's one at a time symmetrically cool. So let's go ahead and try to do the next the following exam.

provide the molecular orbital's of 13 butadiene cool guys. So the first part should be really easy. All we have to do is fill in the atomic orbital, so let's go ahead and do that now. How many electrons should be in the atomic orbital's? It should be four. So should be 1234 Is everyone cool with that? Because we have two from each. Pi bon perfect. So remember that the number of basically this one's already filled out for you. Mostly, all I have to do is fill in the phases and that's because we're starting off slow. Typically, you would have to actually draw all these molecular orbital's from scratch. But I'm canning, too. You have the problem already so that we can practice part of it. Okay, so what we know by definition is that four atomic orbital's should turn into four molecular orbital's of increasing energy. Right? Cool. We also know that your first atomic, your first molecular orbital should have zero nodes me and there are no places that one that a phase changes. Okay, there are no phase changes happening in my first molecular orbital. That's good. Also, guys, I want to just talk a little bit about the nomenclature Here. It is common that when we're talking about molecular orbital's of three or more that we use the size symbol to represent each increasing energy state. So the first one would be sy one, then side to all the way to side four. And it should be up to whatever number of conjugated Adams you have now when you're only dealing with two conjugated atoms. Ah, lot of times you the letter pie will be used because pie would just be for a pie bond, which is too. So you may see pie one pie to for a double bond. But for anything bigger than a double bond, we use the size symbol. Cool. So, guys, we know that we have four electrons and we need to use the molecular orbital rules to fill in what the other phases should look like. Cool. So right now, how would we know what the phases should look like here? What are the rules that we want to follow? Well, the first rule well, I mean, the first rule was that we have four orbital's Let's go to the next one, which is that your first atomic orbital should not change phases. So that means that on Just keep saying atomic total. But, I mean the first orbital of your molecular orbital. So that means that I'm gonna shade in this one here, just like it's shaded down here. Makes sense. And what I'm gonna do is I'm also gonna shade it inside three and side four because remember that the first rule is that remember that the rule for the first orbital is that it doesn't change. Cool. Now, what's the rule for the last orbital? The last orbital must always be changing. So let's go ahead and start flipping this one. So that means that over here it's gonna look like this. And then it's gonna flip again here and then it's gonna flip again. Here. Cool cellphones. Got that? So my first orbital is staying the same. My last orbital keeps flipping. Awesome. Now we look at nodes and what we say is that your nodes must increase one at a time. Right now I have my nodes is equal to zero for the first one, right? I have zero nodes. So that means that for sigh too. I should have one node for side three. I should have two notes. And for C four, I should have three notes. Quote So I'm gonna try to do is figure out symmetrical ways that I can keep these, uh, phases the way they are and have one place or not have one place but have have these phase changes happening in a symmetrical way. So if side to needs to have one note that symmetrical, where do you think is the best place to put it? Well, guys, hopefully what you're saying is that it should be right down the middle because putting it right down the middle would make it symmetrical on both sides. And what that tells us is that if there's only one phase change here, that means that this must be flipped up. And this one must have stayed down. Okay, Now notice. I'm using the colors blue and black for different reasons. Black means that I already knew that by definition of my rules, blue means I figured it out based on where the nodes were. Quote. So I have one note and this is what my side to molecular orbital looks like. So now we know what side one looks like and what side to looks like. Let's see if we can figure out side three. So Psy three needs to have two nodes. Where do you think is the best place to put those two notes that it's symmetrical. So I'm hoping that you guys are gonna pick this and this, Okay? Because what that does is it gives me symmetrical nodes that are there, not lopsided on one side. And it allows me to have to phase changes that are basically gonna make the thing looks symmetrical. Okay, So what that means is that my to note, my two orbital's in the middle. Oh, should look like this. Okay. And what this would do is it would allow my phase is my first one and my last one to follow the rule while also having two notes. Cool. And lastly, guys, what do you think for three notes. How do we do? Three notes. There's only one way, which is just in between each one. And that means that it's gonna be flipping back and forth. So that means that this one is going this way and this one's going this way cool. And now we have three phase changes and still overall their symmetry here. Cool. Awesome guys. So now we have our molecular orbital's filled in, and these are the rules we're gonna be using throughout any type of conjugated system. We're gonna be using these rules to figure out what our molecular orbital's look like. Okay, so now all we have to do is we have to use the principles of electron configuration to figure out in which psy molecular orbital's are those four electrons going to resign in. So, for example, I'm gonna draw something. Please don't draw this, But I'm just going to give you an example. Should I do something like this? Does that make sense where I distribute them evenly throughout all of my sigh Orbital's Please don't do that because what we learned is that the principles of electron configuration applied molecular orbital's as well. So that means after about principle, build up, always fill your lowest ones. First Pauli exclusion. You can only have two electrons at a time in an orbital Hans rule. If you have to equal energy level orbital's fill them symmetrically. What that means is that I should put two electrons inside one because that is the lowest energy. And I can only fit two and then two electrons inside, too. And I'm done. That's it. This is what the this is what the linear combination of atomic orbital's diagram, or m o theory should look like. You should have your molecular orbital filled in like this, and then you should fill in your sy one in your side to I just want to bring up one last thing, which is that I actually had failed to mention what that stars mean. Remember that star is just another description for anti bonding. So would you would you assume that this conjugated dying? Is it going to be stable or unstable, based on how these molecular orbital zehr filled stable? Because right now all I have is bonding orbital's that air filled anything basically below the halfway point is bonding. So right now what I have is to bonding orbital's. That air totally felt this. You're gonna encourage the atoms to be bonded together, and then I have the anti bonding elect, the anti bonding orbital's that have no electrons, which is good because you don't wanna have electrons in the anti bonding orbital's that makes the molecule more unstable. It increases the energy cool. Awesome guys. So that was that exercise. Let's move onto the next video.