Draw the molecular orbital picture for (a) ethene. Label the H...

Question

Draw the molecular orbital picture for (a) ethene. Label the HOMO and LUMO of each.

Accepted Answer

All right. Hello everyone. So for this question, let's go ahead and provide the molecular orbital diagram for protein label, the lowest unoccupied molecular orbital, the lumo and the highest occupied molecular orbital or the homo. So let's go ahead and get started. Recall first and foremost, when an amount of atomic orbitals combined together, they create an amount of molecular orbitals and each molecular orbital has its own distinct designation or SI N. Now as you go up from one energy level to another, for example, from P I one to psi two et cetera, the number of nodes should increase as a result. Now nodes refer to regions in successive molecular orbitals where there's no overlap between lobes of opposites. So what are lobes? Well recall that in a molecular orbital diagram, you might see this structure right here that looks like the number eight, one half referring to one lobe is above the line and another is below the line. Now, in this case, each lobe can have a positive or a negative sign but not referring to charge instead, the positive and the negative signs indicate their wave functions. So for the purposes of this video what you're going to notice is that one lobe or one half is going to be shaded and the other one will not be shaded. The shaded lobe represents a positive sign and the unshaded therefore represents a negative sign. And for the record, any nodes in the diagram are going to be represented as dots on the diagram and dotted lines actually. So let's talk about protein recall. Protein is a three carbon molecule with a double bond in between carbons, one and two. In this case, protein has three P orbitals, meaning that it is going to form three molecular orbitals. So in this case, there's going to be a SAS I one A side too. And AY three now because si one is going to be towards the very bottom, we're not going to have any nodes and all of the positive sides are going to be all of the positive signs are going to be on one side of the line and all of the negative signs are going to be at the bottom. Now, P si two on the other hand introduces one node which is therefore going to switch the orientation of the positive and the negative sign from one side to another. And then lastly py three is going to have two nodes where you will go ahead and see the orientation of the positive and the negative signs change twice. So I actually went ahead and pre drew this diagram just to save us a little bit of time, right? So first and foremost, we have P si one at the very bottom where all of the positive signs are going to be at the top and on the same side as each other. So I'm going to go ahead and shade in the upper lobes for each. Now, by the time we get to side two, we have one node at this point which is depicted by a dotted line going towards the middle. Now, in this case, on the left side, we're going to have the positive side or the lobe with a positive sign at the top. But on the right side, it's going to be flipped and it's going to face the bottom instead. And then once we get to si three, we're going to have two nodes or two dotted lines separating these three orbitals. So on the left side, I'm going to have the positive sign on the top. After the first note, its going to flip to the bottom instead. And then after the second node, it's going to return to the top, the positive sign. So now at this point, our task is to assign electrons to each molecular orbital two electrons at a time from the bottom upwards. So revisiting propane once again, because protein only has one pi bond, there are two pi electrons to distribute in this diagram. So I'm going to go ahead and start filling out each orbital two electrons at a time starting at the bottom. So si one is going to receive these two electrons and these electrons are going to be pointing in opposite directions inside of the orbital itself. And because I only have two electrons, that is all for this diagram. So now the question becomes, where is the homo? And where is the lumo recall that Homo stands for the highest occupied molecular orbital, meaning that it is the highest energy orbital that actually contains electrons. So because there's only one orbital here that contains electrons, in this case, si one si one is therefore the homo and therefore the lumo or the lowest occupied, excuse me, lowest unoccupied molecular orbital is the lowest energy molecular orbital that does not contain electrons. So normally the lumo lies just above the homo, meaning that si two is the lowest unoccupied molecular orbital and there you have it. So here is our final answer. We have the molecular orbital diagram for protein and the homo and the lumo have since been identified and labeled. So with all that being said, thank you so very much for watching. And I hope you found this helpful.

Draw the molecular orbital picture for (a) ethene. Label the HOMO and LUMO of each.

Key Concepts

Molecular Orbitals

HOMO and LUMO

Ethene Structure

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