Chemical Bonding: Dipole moments

dipole instants deciding at the molecule is polar the goal of this podcast is to take our knowledge of polar bonds along with our knowledge of how geometry jobs and be determined whether actual molecules are polar as opposed to exactly the bonds that we’ve done before so first let’s talk about what a dipole moment is a dipole moment is technically a vector add-on of the magnetic moment of polar bonds so what does that really mean so let’s take a 1 bata of one alliance molecule firstly so in other words two atoms with one bond if the attachment is polar the molecule ought to have gathered so that would be something like HF where we have hydrogen and then we have fluorine the most electronegative factor and we know that that ligament is polar and since that attachment is polar and there’s just the one ligament the whole molecule will be polar there’s different ways of writing it you can write it with this plus and minus notation that we have here and now or you can do this arrow with a plus sign and the plus feature gone on the plus place and then across now in multi bond atoms you need to look at the geometry and this is because sometimes these alliances can cancel so let’s look at something like clf3 so you may have to pause plot your framework gears or your toothpicks and candy think about what this geometry really looks like so when you write at your Lewis structure for this you see that you have two lone duets here in here and so overall you have this t-shaped molecule okay so let’s look at the polar bonds and look at the directions and ensure what cancels out and this is what they mean by vector additive so we know that each one of these alliances will be polar so we have three polar alliances now if we take all of these vectors and we supplement them up together what we can see is that some of these top two this one excuse me top and bottom ones these two are gonna cancel out and so what dissolves up happening is these cancel to talk the up-and-down part the horizontal part and then this whole horizontal part doesn’t have anything that cancels it so the full amounts of the overall dipole instant will be this mode so this is a polar the clf3 it’s a polar molecule and we can draw the dipole instant in as travelling this direction now let’s do some more practice with these and I’ll show you through these precedents how you can end up with designs that don’t actually have any that does not have a dipole even though they have polar attachments so these are the ones the relevant ones I’ve been working with so let’s start with and – so we know that it doesn’t have any polar alliances since it doesn’t have any polar bonds it’s not going to be polar if you have a molecule that has all nonpolar attachments you can go ahead and say that molecule isn’t polar now we have xef4 so let’s look at xef4 so this is the non ionic version this was the one without that electrons removed now we had a square planar shape I haven’t describe here in sort of a course that says that it’s 3d but you may want to build this for practice extremely so you have this square figure and we know that each of those attachments are polar fluorine is very electronegative XE is not so the fluorines are gonna be taking all of the electrons up not all but a good deal of the electron density so in this case we don’t have a dipole and why would that be well we look at all of those guidances up those arrows are moment and they immediately cancel out so one of the ways that I like to look at this and students seem to find helpful its think about what would happen if you had that person if you took this XE and you framed like a person there and then you bind lines to them and you four different parties gathered in each direction you’d see it all nullifies out because everyone would be draw in accurate antonym directions and so there’s no dipole now let’s look at the next one so you’ve sf6 and we retain from our discussion on the geometries that this was octahedral both electron and molecular geometry we don’t remember how we got that just go back and revisit the geometries video and and that’ll show you how to do it so you octahedral now “ve been thinking about” what that looks like in three magnitudes alright and again going to go and visit the other video if you need to so if it looks like it’s in three features all of the fluorines are coming off at accurately 90 measure inclinations and they’re all propagandize on each other precisely evenly so even though each one of these attachments would in fact be polar because they’re all going in opposite guidances we won’t have a dipole all right now let’s do another one so this one’s a little bit trickier so we have this figure we have four things is connected to the phosphorous which means we have a tetrahedral appearance now remember what that looks like in 3d if you need to go back in the old-fashioned videos feel free so we have this tetrahedral figure and all of the bonds are polar now interestingly enough though they are not all the same atom right now since oxygen and chlorine don’t have the same electronegativity that changes things a little bit if we were to look at this and we say there’s a polar bond running this path this road this acces in this way and again you’re arrange that in three features so they’re all coming out of each other evenly at 109 part five degrees or so they would all offset if everything of those were chlorines or if everything of this really is oxygens or if everything of those were the exact same atom these would all cancel out and you wouldn’t have a dipole nonetheles in this situation they aren’t the same the chlorine has a different electronegativity than the oxygen the oxygen is still much work electronegative and so they’re not all going to cancel and so yes here there would in fact be a dipole now let’s do another example this is a little bit more complicated than the other ones we have two and further drives home the same kind of principle that we were talking out with the PIO sale tip 3 ok so let’s outline the lewis organize for this firstly now when we go to draw the lewis structure for this there’s a couple of different ways that we have been able to outline it and in this case they’re not the same way so we could do this so we could say well here I have two chlorines two fluorines now these little speck wrinkles there’s smashed cables that indicates that it’s going back into the screen these shaded in areas point out that it’s coming toward you or out of the computer so if we instead leant the two fluorines going to the back “thats really not” actually fairly the same molecule they’re a little bit different and we would get different refutes depending on how we select it so let’s look at this a bit more so here we have our dipoles for chlorine and we have them for fluorine – but fluorines are gonna be a lot bigger so here we have a little bit of a attachment minute right there and a little bit of a sole time now now we have much bigger ones now on this one this chlorine in this chlorine are gonna immediately cancel out and this fluorine in this flooring you’re gonna instantly cancel out and so even though all of your ligaments are polar and though some of them are different sizes and the others they still cancel because of how they’re familiarized now let’s look at this one so here we have the two fluorines and the two chlorines where the big big attachment moment is going in the same direction back now and then here the smallest ones are going into the same direction forward now some of them would nullify and so the side to back now would cancel and the side to place now cancel the two sides to back now at nullify on the side to back now would cancel but they’re not gonna all counselor-at-law similarly and that’s because this direction this coming out of the board at U direction that is smaller than the moment going into the board or away from you and so because of that the overall dipole is going to be in the direction in between these two pink fluorines this side to back nullifies and it throws it in this direction now again you can kind of think about this in terms of what would happen if you had somebody sitting in the middle with lassoes held to them and beings were pulling on them so you could make this out to be the really strong beings plucking really hard and this may be you know hook up some like five-year-olds or something pulling the other direction trying to pull but not really being able to you know overall which space would they move if you did that and of course they would move in the direction of the two strong parties attracting them so that’s a good way to visualize it a little it’s obviously not a hundred percent accurate with how the chemical nonsense acts but it does help you remember it okay so here your right and left are gonna cancel oh you’re blue four paroles will cancel with some of the pink but not a hundred percent so the necktie total dipole is going to be going backwards in between the two fluorines okay so after watching this video now you’ve been able to take your knowledge of how polar attachments drive take your knowledge of how the geometry toils and how to decide on geometry and combine the two so you’re too starting to see now this building on each other right we build on the complication quite a bit now so if you don’t have your geometries down pat you’re gonna have a highly very hard if not completely impossible time with this section so make sure you go back and work through the geometry duty um and play around with your toothpicks and sugar and see how you can do so that you’re able to go on to this section well

As found on YouTube

Leave a Comment