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The VSEPR Model

VSEPR is an acronym for valence shell electron pair repulsion theory. This theory is used to predict the molecular geometry of covalent molecules and ions.

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So the B S E P R model is very useful for understanding the geometry different molecules. So the S E p where stands for Fallon's Shall electron here Propulsion model. And so what this means is that we need to use the fact that electrons repel each other to help understand these young trees. And so when we use the little structures, it doesn't tell us how molecules are oriented in three dimensional space. On DSO, we can use thievy S E P R model Thio. Understand that And one important thing to note is that the VSC PR model does not tell us any information about the bomb link or the presence of multiple bonds. And so this gives us a very simple idea of again how these molecules exist in three dimensional space. And when we determine the geometries of these molecules, um, in some instances, we basically just used living structure and then from there, determine the geometry. But we could also do the same thing for residents structures. And in the case of president structures, you can use anyone to predict the molecular structure. And so what do we determined? The molecular geometry we have a couple of steps to help do this, and so we'll be going over the first two in this video and the next to the next one. And so for the first two, we need to write the loose structure well, the molecule, Which makes sense because before we determine the geometry, we need to know the bonding that is happening between the different atoms as well as the presence of any lone parents, because we know that this will introduce distortions in the geometry, and we also need to determine regions bonding and low in Paris. And again, this makes a lot of sense, because the number of bonds will influence the geometry as well as the presence of lone pairs. And so let's go into a couple of examples to refresh your memory about Lewis structures, as well as being comfortable with identifying the bonds and the lone pairs according to our new structure. And so, for our first example, let's look at B four minus, and so we've seen this in the previous videos, and so this is essentially a boron, which has three valence electrons. But with the addition off the negative charge for the town we know that we have an extra electron and we also know that for Florey we have seven valence electrons. And so first we can write the little structure for this. And so this would be be. And then we have the four F molecules oriented around Boron. And so we have an octet shown here. And so this would be you lose structure for be a four minus. And so from the little structure, we can actually simplify this into a line structure. Thio understand the bonding, so we can then assign the geometry. And so this would be be four. So this isn't do drastically different from our little structure, But this is a bit easier to look at when you are trying to figure out the geometry. And so now we can determine the region of bombings and lone pairs. And when we talk about lone pairs were talking about lone pairs on the central atom because the lone pairs on the atoms that are being bonded to do the central atom do not affect the geometry. That's in this case. We have four bonds, and so this will be important or determining the geometry on the market. And now, for another example, let's look at B B R. Three. And so, in this case we have four on Was Young has three valence electrons, and we also have the Britney, which also has seven valence electrons. And so, in this case, we will have six electrons around the boron because we will have three bonds until and so if we write the little structure, this is simply three room means around to be boron and we also of the Lynn Perez on each of the brew means. And so this would be the little structure for B B R three, and now you convert this to a line structure. We have more on being bonded to three brew means. And so in this case we have three bonds, which will dictate the geometry of the ball field. And now let's look at another example. So if we look at something like H 20 or water, we have hydrogen, which has one balance electron and oxygen, which has £6 electrons. And so for the living structure, we know that the oxygen will make a bond between both of the hydrogen and so the hydrogen will have Thio Electra's bonded to the oxygen, and then the oxygen will have a complete octet, and so this would be the Louis structure for water. And so if we draw the line structure, we actually have four regions where we have electrons. So we have to bonds from the oxygen and the hydrogen. And we also have two lone pairs with a total of four electrons because we have the lone pairs on the central up. And so we need to again take into consideration the bonds as well as the lone parents, because both will contribute to the overall geometry of the bomb. And for one last example, let's look at I didn't guess. And so nitrogen has five valence electrons and in I should guess, it will actually create a triple bond. So we have six electrons being shared between the nitrogen, and each will have lone parents on the side. And so if we draw the line structure, this is simply be triple bond. And so again, um, in this case, we have just two atoms, and the little pairs actually do not do anything to effect the geometry. And so the only thing that we need to take into consideration is the fact that we have this trouble bond. And one important thing to note is that what we're talking about? Regions with electrons, the regions with single bonds, double bonds, andro lawns take up the same area and three dimensions. And so we can think of this as just one bond. And so again, this is important to note because the the S E. P R model does not give us any information about the presence of multiple bonds, but rather just the overall geometry. And so, if this were a single bond or a double bond or, in this case a trouble, Juan, you would not be able to tell just from assigning the geometry. And so again, this is important to keep in mind a swell as the presence of the lone pairs around the central up. And one important thing to note is that there are lone pairs on the nitrogen, but this will only affect the geometry if this were bonded to another Adam, and so you only consider the loan. Paris When the central atom is bonded to more than one, but if not the lone parents should not affect the geometry

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Chemistry 101

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