 All right, as promised, here is a little video on covalent shortcuts. There are some shortcuts that we can do when it comes to shapes. There are some shortcuts we can do when it comes to polarity because what we're dealing with in here are what we call binary covalent compounds. Binary compounds contain only two elements, so like H2O, CO2, NH3, and so on. The list goes on. Each of these contain only two elements, and the vast majority, if not everything that we do in CP chemistry when it comes to covalent bonding, should be about these binary compounds. When you're dealing with these binary compounds, there are some shortcuts that we can apply when it comes to dealing with VESPR, dealing with shapes. As far as shapes are concerned, we know a couple things already. Two atom molecules are automatically linear. There's no other way to put them together. You set them up in a straight line to put the two elements in a row. And we know the five atom ones are always tetrahedral. There's no other option. That's all they can be. So whenever we see one of those formulas in a question that asks us something about shape, if it is a two atom formula, like carbon monoxide, CO, not one that I would make you draw by the way, but just because it's a two atom molecule, we know that's going to be linear. Hydrogen fluoride. Again, just because it's a two atom molecule, we know it's going to be linear. The five atom ones, like methane, one carbon for hydrogens, I know automatically that's going to be tetrahedral or silicon tetra bromide. I know because there's one silicon for bromines, five atoms total, it's going to be tetrahedral. And there's nothing more I have to do with it. There's nothing more I have to think about it. I know those shapes. This with the three atoms and four atom ones, we have to be careful. We have to look at the center atom. Then we have a three atom with oxygen, sulfur, or selenium acting as the center atom. We know automatically that this is going to be bent. And the reason why we know automatically that this is going to be bent is because of the way the Lewis structures look for these. They're all going to be the same because they're all in group 16. We look at the Lewis structures, they're all the same. It's two pairs, two singles, two pairs, two singles, two pairs, two singles. And the reason why these are always going to be bent is because of the pairs. The pairs are what deform the linear molecule. Now how do you know it's the middle atom? How do you know what the center atom is? Well you look at the formula and you look at which one you only have one of. Because again, all we're dealing with is binary ones, so H2O. There's no subscript on the oxygen, that's how I know oxygen is the center atom. There's three atoms, two hydrogens, one oxygen, oxygen is the center atom. These two pairs of electrons here are what's going to make it bent and look like that. And again, I can do that without drawing the modeling. I can do that without thinking too hard about it. If we had SCL2, sulfur dichloride. Again, I know automatically this is a three atom molecule, two chlorines, one sulfur. Sulfur is the middle atom and because of those it's going to be bent. And I'm just going to draw it like that, again without having to do Lewis structures without having to think about it too much. That's how it works. If it's a three atom molecule, the only other elements that we're going to see are center atoms here, carbon and silicon. And if we see carbon or silicon as the middle atom, then we know it's going to be linear. And again, it all comes down to those Lewis structures. Carbon's got four valence electrons and silicon's got four valence electrons. They both belong to group 14. They look the same, they bond the same. And because these are all single dots, I know I have to use them all up in covalent bonding with the molecules we're working on. That's the way it's going to have to go. So carbon dioxide, CO2, again, I know which one's my center atom because it's the one that doesn't have a subscript on it. So carbon's the center atom. I know carbon's going to have to make four bonds. And the only way carbon's going to make four bonds in the situation is if it double bonds to each of the oxygens in that molecule. And I can, again, swap carbon for silicon any time I want to and talk about silicon dioxide and it's going to be the exact same thing. If silicon's got these four dots, it's got to make four bonds. Oxygen only has two that it can make, so I know it's going to be double bonded to both. Again, three atoms with oxygen sulfur or selenium as the middle atom is going to be bent. Three atoms with carbon or silicon as the center atom, they're going to be linear. Similar kind of story for the four atom molecules. Less variety, though. Four atoms with nitrogen or phosphorus in the middle. This is going to be pyramidal. And again, it comes down to paired up dots. Nitrogen group 15, five dots in its Lewis structure, phosphorus in the same group, so same Lewis structure. It's those dots that deform the molecule. Whenever they're there, they bend the corners of the triangle downward. So if we have NH3, again, the one that has no subscript on it is the middle atom. Hydrogens will attach like this in a pyramid shape. Again, you don't have to draw all those structures to know that. PCL3, again, four atom molecule, one phosphorus, three chlorines. Phosphorus is the middle one. That pair is going to make it pyramidal, so it ends up looking like this. Simple enough. If it's four atoms and trigonal planar, again, keeping it to the CP chemistry level, it's going to have to have boron in the middle. Shape will be trigonal planar, flat triangle. And again, the only way to do this and keep it at the CP level is to put boron as a center atom. Sulfur can be in there to make a trigonal planar molecule, but the problem is it's got resonance. And resonance is not really a CP level concept. All the other ones, they're going to involve paired up electrons getting into the bonding process. And that's just beyond CP. Honors, maybe. AP for sure, but not in CP. So we have BCL3, four atom molecule, one boron, three chlorines. Boron is the middle atom. Boron's Lewis structure looks like that. It's similar to what we had going on here. When we had these carbons involved in our bonding, they all had single dots. So we know they all had to get involved in the bonding process. There would be no unshared electrons. All those are single dots too. So we know they have to all be part of the bonding process. That's what allows us to say it's going to be trigonal planar and draw it out without thinking too much about it. So again, these are shortcuts that should help you get through the testing on this, through regular exam, through the quarter exam, through the final exam. When you move on to higher levels, when you start learning this stuff in college, then you can start worrying about the more complicated stuff. Now, as far as polarity is concerned, there's shortcuts there too. Because again, we're dealing with these binary compounds. They only have two elements in it, and there's only so much you can do with that. There are certain shapes that will not be polar, and there are some shapes that may be. And again, this is a shortcut that only applies to CP chemistry because the molecules were dealing with their binary. They only have two elements in them. If we moved on into an honors level or an AP level or a college level one, we start mixing up elements, we'd start throwing in different combinations, and this all goes out the window. Again, we're talking about stuff like H2O, just hydrogen, just oxygen, carbon dioxide, just carbon, just oxygen. We're talking about sulfur, difluoride, one sulfur, two fluorides, it's still just two elements, sulfur and fluorine. Binary means two elements. It only works for this. And in these cases, 3-atom linear, trigonal planar, and tetrahedral will not be polar for us because of the way this all works out. If I have a 3-atom linear molecule, carbon dioxide, I end up with a negative charge here and a positive charge there, and I end up with negative charges on both ends. There's no way to divide that charge. There's no way to separate that charge. So even if it has polar bonds, it can't be a polar molecule. Same thing with a trigonal planar. I could have a positive charge here, and I could have negative charges there, but again, there's no way that I can draw a straight line through that and separate the charge, and again, that extends out to the tetrahedral as well. It's the same kind of story as the trigonal planar. I can have a negative charge in here and a whole bunch of positive charges surrounding it, but there's no way I can draw a straight line through it. So even if I have polar bonds, these shapes will not be polar molecules because of the binary nature of what we're working with. Now, of course, if this were something different, that could change the whole story. If that were something different, that could change the whole story, but that doesn't happen when it's binary. Shapes that may be polar are the only other three that are left. Two-atom linear, the opposite of the three-atom linear, which is bent, and the opposite of trigonal planar, which is pyramidal. These ones will allow for separation of charge, and that's why these things can be polar. Two atoms, the easiest one of all of them, find up with a positive and a negative, and I just draw my line straight like that, and I've got separation of charge, I've got a polar molecule. For the bends, because the ends have been pushed downward, if I have polarity, I can have separation, and it's the same story with the pyramidal, and it's very similar one to the bend. If I have polarity, I have a way of drawing a straight line through it and separating the charges. So again, in binary compounds, compounds that contain only two elements, these shapes will not be polar. These shapes will be polar, but if you have polar bonds, you have to meet that second criteria as well. So maybe those will help you, maybe they won't. Good luck to you either way.