For each of the following molecules, draw a 3-D representation...

Question

For each of the following molecules, draw a 3-D representation.

(c) CHBr₃

Accepted Answer

Hi, everyone. Let's take a look at the next problem. It says provide the 3d representation of CCL three F. We're given four answer choices A through D and each of them shows the carbon in the center with the three chlorine and the fluorine around the outside in four bonds from the carbon. But just in different arrangements with solid lines, wedges and hash marks for different of the atoms. So we'll look at them in more detail as we work our way through the choices. But essentially, we're given the same arrangements of the atoms. We're only given a molecular formula. So we could put them in any way. But this is multiple choice. We're given the choices. We just have to figure out the bond angles and where they are arranged in space. So we have a carbon with four bonds. So we know this will have a tetrahedral geometry and with the tetrahedral geometry, all bond angles are 109.5 degrees. Now, when we draw this in a two dimensional space, like a piece of paper, they're often drawn as if they are 100 and 20 degrees apart. But that's just a limitation of the two D uh medium that we're working in. So in this case, the, when we draw, I tend to draw the tetrahedral arrangement with one atom coming straight up. So like a vertical line and then having a dotted line or a wedge, in this case, going to another atom and then a wedge going straight down and then a straight line to the right in that representation, the wedge represents coming out of the plane of the screen. So I point the wedge saying coming out of plane of screen forward. So towards the viewer, the straight line going to the side and this line going up. So just the plain straight lines represent being in the plane of the screen or paper, if you're drawing on paper and the dotted line or dashed wedge represents going out the back. So behind the plane of the screen or paper, but in this case, it's not drawn with a line going straight up, it's sort of drawn with two lines going to either side. They have an angle of about 100 20 degrees between them, two straight lines in choice A and then sort of a wedge coming down to the left and a dotted wedge or dash wedge coming down to the right. With those being a lot closer together than 100 9 degrees. And then we're offered the choice of again and choice B two of them within the plane, two solid wedges. So choice B cannot be right because there's nothing coming going out behind the plane. When we think of our tetrahedral structure, imagine a tripod. So you have your three legs of the tripod that are resting, say on the ground. So if you're looking back at the structure that I drew, those represent the three legs of the tripod and then a part sticking straight up. So that can help you to sort of visualize how this molecule is structured. In this case, the way our answer choices are drawn, it's as if someone took the tripod and tipped it on its side. So the part that would be pointing up is now kind of angled up into the right and then the tripod legs are pointing down into the left so that can help you visualize. So you make sure you have something but choice B is incorrect because we have nothing going so nothing behind the plane. So these are two, they're two clustered together. You've got two in the plane, two in front of the plane. You don't have the proper arrangement. In choice C, we have two chlorine going back with the dashed wedges back behind the plane. A fluorine and a chlorine coming up towards the viewer out of the plane and nothing within the plane of the screen. So that's what's missing in choice C and makes it incorrect. Nothing in plain choice D has two chorines within the plane of the screen and a florine in a chlorine with the dashed wedges going behind the plane. So choice D is incorrect because there's nothing coming out of the plane in the front. So the only one we haven't eliminated is choice A. So by elimination, that's correct. And indeed, in choice A, we see two chlorine that are both within the plane of the screen. A fluorine with a solid wedge. So coming out forward from the plane of the screen and a chlorine on a dashed wedge going back behind the plane of the screen, the two chins in the plane of the screen are drawn about 100 and 20 degrees apart. But the other two have a narrower angle between them. And that's because if we actually were looking at this sort of sideways on those two forward and backwards out of the plane would be overlapping each other and you wouldn't be able to see them and that would really not make a good drawing. So they're kind of skewed a little bit so that you can see them both. So once again, the proper 3d representation of CCL three F is choice A, it represents that tetrahedral geometry where you see two bonds within the plane of the screen or paper, one projecting out towards the viewer and one projecting out the back away from the viewer, see you in the next video

For each of the following molecules, draw a 3-D representation.
(c) CHBr₃

Key Concepts

Molecular Geometry

VSEPR Theory

Stereochemistry

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