1 00:00:16,383 --> 00:00:23,523 Today, we are talking about bonding between molecules. 2 00:00:23,523 --> 00:00:27,660 Now, we have talked a lot about bonding within molecules. 3 00:00:27,660 --> 00:00:29,062 Right. 4 00:00:29,062 --> 00:00:30,563 And that got us to saying things like, 5 00:00:30,663 --> 00:00:32,232 well you can use electronegativity, 6 00:00:32,499 --> 00:00:33,366 You can use electronegativity, for example, to say, 7 00:00:33,366 --> 00:00:35,201 I got an ionic bond. 8 00:00:35,201 --> 00:00:36,503 All right. 9 00:00:36,503 --> 00:00:38,571 Or I got a non-polar covalent bond 10 00:00:38,571 --> 00:00:40,073 or I've got a polar covalent bond. 11 00:00:40,073 --> 00:00:41,975 But today, what we're going to do 12 00:00:41,975 --> 00:00:46,980 is talk about how these molecules-- 13 00:00:46,980 --> 00:00:49,949 how these molecules bond together. 14 00:00:49,949 --> 00:00:52,786 What sorts of interactions can they have? 15 00:00:52,786 --> 00:00:54,120 And those are really important. 16 00:00:54,120 --> 00:00:55,188 Right. 17 00:00:55,188 --> 00:00:56,856 So that's going to be the topic. 18 00:00:56,856 --> 00:01:01,261 Now, if we just get started with what we know what's up there. 19 00:01:01,261 --> 00:01:01,761 All right. 20 00:01:01,761 --> 00:01:02,962 Well, there's ionic. 21 00:01:02,962 --> 00:01:05,364 So listen, I'm going to fill this in. 22 00:01:05,364 --> 00:01:07,167 Bond, a model. 23 00:01:07,167 --> 00:01:08,134 You'll see what I mean. 24 00:01:08,134 --> 00:01:09,836 I'm going to draw a little cartoon. 25 00:01:09,836 --> 00:01:12,305 The attraction, how it's attracted, 26 00:01:12,305 --> 00:01:13,807 the energy range, and an example. 27 00:01:13,807 --> 00:01:14,307 Right. 28 00:01:14,307 --> 00:01:18,812 So for an ionic bond, we've got ionic-- 29 00:01:18,812 --> 00:01:20,447 ionic. 30 00:01:20,447 --> 00:01:21,414 OK. 31 00:01:21,414 --> 00:01:22,549 And here we go. 32 00:01:22,549 --> 00:01:23,416 Watch this. 33 00:01:23,416 --> 00:01:28,254 Plus and minus-- there's my model. 34 00:01:28,254 --> 00:01:29,021 OK. 35 00:01:29,021 --> 00:01:31,925 And the attraction here-- we'll get a little specific. 36 00:01:31,925 --> 00:01:35,895 It's a cation and an anion. 37 00:01:35,895 --> 00:01:39,799 And we know that that's going to go like Coulomb's Law. 38 00:01:39,799 --> 00:01:40,265 Right. 39 00:01:40,265 --> 00:01:44,137 So the attraction, the energy, not the force, the energy 40 00:01:44,137 --> 00:01:48,541 will go like 1 over R, roughly. 41 00:01:48,541 --> 00:01:49,542 Now, what is the energy? 42 00:01:49,542 --> 00:01:51,978 Well, the energy is pretty wide ranging. 43 00:01:51,978 --> 00:01:56,850 I'm going to do this in kilojoules per mole, 44 00:01:56,850 --> 00:01:58,218 since those are the units I have. 45 00:01:58,218 --> 00:01:59,384 I'll write that in a second. 46 00:01:59,384 --> 00:02:03,490 And an ionic bond can have lots and lots of range in here. 47 00:02:03,490 --> 00:02:05,458 And it typically can be very strong. 48 00:02:05,458 --> 00:02:07,026 Something we've already talked about. 49 00:02:07,026 --> 00:02:11,764 An example would be sodium chloride, right there. 50 00:02:11,764 --> 00:02:13,333 Let's put the units here. 51 00:02:13,333 --> 00:02:15,568 The energy units are in-- 52 00:02:15,568 --> 00:02:16,736 I'm going to write it here-- 53 00:02:16,736 --> 00:02:19,172 kilojoules per mole. 54 00:02:22,175 --> 00:02:23,977 Now, in a covalent bond-- 55 00:02:23,977 --> 00:02:26,513 so covalent wouldn't be here. 56 00:02:26,513 --> 00:02:27,013 OK. 57 00:02:27,013 --> 00:02:30,049 So in a covalent bond, remember, we've 58 00:02:30,049 --> 00:02:32,452 got something very different. 59 00:02:32,452 --> 00:02:34,988 We've got this carrying a sharing kind of thing, 60 00:02:34,988 --> 00:02:37,190 and we've got maybe two atoms. 61 00:02:37,190 --> 00:02:37,757 Right. 62 00:02:37,757 --> 00:02:39,025 Two atoms like this. 63 00:02:39,025 --> 00:02:40,927 And then the charge is sort of-- 64 00:02:40,927 --> 00:02:43,930 the negative charge is sort of floating around and sharing 65 00:02:43,930 --> 00:02:48,668 those two centers, like in H2 or Cl2. 66 00:02:48,668 --> 00:02:51,838 I'm going to use Cl, so let's keep using Cl, all right. 67 00:02:51,838 --> 00:02:55,175 That would also be an example of a covalent bond. 68 00:02:55,175 --> 00:03:01,347 And the energy range there is also quite large, 150 to 1100 69 00:03:01,347 --> 00:03:03,983 are the numbers I got. 70 00:03:03,983 --> 00:03:12,025 The attraction is shared electrons-- shared pair 71 00:03:12,025 --> 00:03:14,627 of electrons. 72 00:03:14,627 --> 00:03:18,531 And I'm not putting an R dependence, 73 00:03:18,531 --> 00:03:22,368 because for covalent bond, it's complicated. 74 00:03:22,368 --> 00:03:23,937 It's complicated. 75 00:03:23,937 --> 00:03:24,504 There is no. 76 00:03:24,504 --> 00:03:25,471 It is. 77 00:03:25,471 --> 00:03:28,841 It's a complicated-- but it's a very nice, happy relationship. 78 00:03:28,841 --> 00:03:30,777 But it's a complicated R dependence. 79 00:03:30,777 --> 00:03:34,280 So you can't simplify it like you can with a 1 over R 80 00:03:34,280 --> 00:03:36,015 or like some of the other interactions 81 00:03:36,015 --> 00:03:37,917 we'll talk about today. 82 00:03:37,917 --> 00:03:39,352 OK. 83 00:03:39,352 --> 00:03:41,921 1 over R, not for covalent. 84 00:03:41,921 --> 00:03:42,422 All right. 85 00:03:42,422 --> 00:03:44,724 Now that's where we've been. 86 00:03:44,724 --> 00:03:46,659 Mm. 87 00:03:46,659 --> 00:03:48,027 Mm. 88 00:03:48,027 --> 00:03:49,963 Here we go. 89 00:03:49,963 --> 00:03:50,930 Here we go. 90 00:03:50,930 --> 00:03:52,131 Look at this. 91 00:03:52,131 --> 00:03:54,601 I'm not even-- I'm just getting started. 92 00:03:54,601 --> 00:03:57,637 Because the thing is, now, we got 93 00:03:57,637 --> 00:03:59,906 to talking about how these molecules can 94 00:03:59,906 --> 00:04:00,807 talk to each other. 95 00:04:00,807 --> 00:04:02,742 And there's a variety of ways. 96 00:04:02,742 --> 00:04:07,180 What I want to focus on first is this thing here. 97 00:04:07,180 --> 00:04:10,650 That's that polar covalent bond that we've already 98 00:04:10,650 --> 00:04:11,284 talked about. 99 00:04:11,284 --> 00:04:13,987 So we've already got a grounding for it. 100 00:04:13,987 --> 00:04:15,455 Right. 101 00:04:15,455 --> 00:04:17,457 But I want to remind you of what happens. 102 00:04:17,457 --> 00:04:17,957 Right. 103 00:04:17,957 --> 00:04:20,493 So if I have, let's keep with HCl. 104 00:04:20,493 --> 00:04:23,763 If I have HCl, that's a nice version 105 00:04:23,763 --> 00:04:25,932 of a polar covalent bond. 106 00:04:25,932 --> 00:04:29,202 And remember what happens there is you've got 107 00:04:29,202 --> 00:04:31,704 a sharing but sort of unfair. 108 00:04:31,704 --> 00:04:32,205 Right. 109 00:04:32,205 --> 00:04:36,042 So one of the atoms took a little more of the charge. 110 00:04:36,042 --> 00:04:38,611 And so sometimes we represent that 111 00:04:38,611 --> 00:04:41,014 with like a more of the cloud, right, 112 00:04:41,014 --> 00:04:42,882 on one side than the other. 113 00:04:42,882 --> 00:04:44,550 But it's still a covalent bond. 114 00:04:44,550 --> 00:04:45,051 Yeah. 115 00:04:45,051 --> 00:04:46,586 But the thing is that-- and so what 116 00:04:46,586 --> 00:04:48,288 you're left with like in this case 117 00:04:48,288 --> 00:04:51,924 is some positive charge on the hydrogen atom 118 00:04:51,924 --> 00:04:54,127 and some negative charge on the chlorine atom. 119 00:04:54,127 --> 00:04:55,128 And we did this already. 120 00:04:55,128 --> 00:04:57,230 We used these symbols. 121 00:04:57,230 --> 00:04:59,799 And we also talked about how that leads you 122 00:04:59,799 --> 00:05:01,868 to a dipole moment. 123 00:05:06,572 --> 00:05:07,273 What is a dipole? 124 00:05:07,273 --> 00:05:12,578 Well, a dipole is just the description 125 00:05:12,578 --> 00:05:14,080 of what you have in this case, where 126 00:05:14,080 --> 00:05:18,451 you've got two charges of opposite signs separated 127 00:05:18,451 --> 00:05:20,286 by some distance. 128 00:05:20,286 --> 00:05:20,887 OK. 129 00:05:20,887 --> 00:05:22,488 Two charges. 130 00:05:22,488 --> 00:05:23,756 Those aren't full charges. 131 00:05:23,756 --> 00:05:25,091 Those are partial charges. 132 00:05:25,091 --> 00:05:25,591 Right. 133 00:05:25,591 --> 00:05:28,127 And they're separated by some distance, the distance 134 00:05:28,127 --> 00:05:29,629 between these two atoms. 135 00:05:29,629 --> 00:05:31,597 And you get a dipole moment. 136 00:05:31,597 --> 00:05:35,234 And it has a magnitude and a direction. 137 00:05:35,234 --> 00:05:38,738 And remember, just to remind you, 138 00:05:38,738 --> 00:05:41,841 I did share this with you in a previous lecture. 139 00:05:41,841 --> 00:05:45,478 But, you know, mu equals the charge 140 00:05:45,478 --> 00:05:47,413 times the distance between the charge. 141 00:05:47,413 --> 00:05:47,914 Right. 142 00:05:47,914 --> 00:05:50,582 So that would be like the charge would be the deltas here 143 00:05:50,582 --> 00:05:53,286 and the distance between them, right, would be this. 144 00:05:53,286 --> 00:05:55,521 Right. 'r'. 145 00:05:55,521 --> 00:05:58,124 Now, remember the units are in Debye. 146 00:05:58,124 --> 00:06:06,799 So for this molecule, for here, mu is around 1.8D. 147 00:06:06,799 --> 00:06:16,909 And 1D is equal to 3.3 times 10 to the minus 30th Coulomb 148 00:06:16,909 --> 00:06:17,410 meters. 149 00:06:17,410 --> 00:06:19,679 Those are the units. 150 00:06:19,679 --> 00:06:21,147 Charge times distance. 151 00:06:21,147 --> 00:06:22,248 Charge times distance. 152 00:06:22,248 --> 00:06:22,915 Right. 153 00:06:22,915 --> 00:06:23,416 OK. 154 00:06:23,416 --> 00:06:27,186 3.3 times 10 to the minus 30th Coulomb meter is a Debye. 155 00:06:27,186 --> 00:06:29,922 And again, just to remind you, because we did talk about this 156 00:06:29,922 --> 00:06:32,358 when we talked about polar covalent bonds, 157 00:06:32,358 --> 00:06:34,727 the dipole moment of these molecules 158 00:06:34,727 --> 00:06:37,163 tends to range from 0-- 159 00:06:37,163 --> 00:06:39,565 mm-- right there. 160 00:06:39,565 --> 00:06:42,769 Right, no dipole, to 10 or so-- 161 00:06:42,769 --> 00:06:43,703 11. 162 00:06:43,703 --> 00:06:44,904 Right. 163 00:06:44,904 --> 00:06:46,305 Debyes. 164 00:06:46,305 --> 00:06:49,475 Now, why is this important? 165 00:06:49,475 --> 00:06:53,713 Because if you now think, well, what would happen? 166 00:06:53,713 --> 00:06:57,683 What would happen if I brought another charge up 167 00:06:57,683 --> 00:06:59,352 to the dipole? 168 00:06:59,352 --> 00:07:00,119 What would happen? 169 00:07:00,119 --> 00:07:00,620 Right. 170 00:07:00,620 --> 00:07:02,622 Let's say that I bring a positive charge. 171 00:07:02,622 --> 00:07:05,224 Let's say that I'm a sodium and I've 172 00:07:05,224 --> 00:07:08,394 lost that outer electron, which we know is pretty easy to lose, 173 00:07:08,394 --> 00:07:09,495 if you're sodium. 174 00:07:09,495 --> 00:07:09,996 Right. 175 00:07:09,996 --> 00:07:13,332 So I'm positively in charged, and I'm coming along, 176 00:07:13,332 --> 00:07:15,268 and I see this dipole. 177 00:07:15,268 --> 00:07:17,970 Well, it turns out that, as you can imagine, 178 00:07:17,970 --> 00:07:21,040 I'm going to be attracted to that negative charge. 179 00:07:21,040 --> 00:07:21,641 Right. 180 00:07:21,641 --> 00:07:25,545 So this molecule's going to orient in such a way 181 00:07:25,545 --> 00:07:32,351 that I can actually bond to the molecule 182 00:07:32,351 --> 00:07:34,754 and be attracted to the dipole of the molecule. 183 00:07:34,754 --> 00:07:37,123 So that is actually another type of bond. 184 00:07:37,123 --> 00:07:37,623 Right. 185 00:07:37,623 --> 00:07:41,594 And we'll call that ion-dipole. 186 00:07:41,594 --> 00:07:44,330 It's an ion-dipole bond. 187 00:07:44,330 --> 00:07:45,832 OK. 188 00:07:45,832 --> 00:07:51,103 Let's do this so that I stay within the lines. 189 00:07:51,103 --> 00:07:51,604 All right. 190 00:07:51,604 --> 00:07:52,238 Now, OK. 191 00:07:52,238 --> 00:07:53,406 So what does that look like? 192 00:07:53,406 --> 00:07:55,975 Well, we just said it's a charge. 193 00:07:55,975 --> 00:07:59,145 I'm taking a single charge, and I'm bringing it 194 00:07:59,145 --> 00:08:02,548 to this thing that has a shift of the charge within it 195 00:08:02,548 --> 00:08:04,350 that led to these two partial charges. 196 00:08:04,350 --> 00:08:06,285 So, as you as you can imagine, it's 197 00:08:06,285 --> 00:08:08,988 going to want to orient to form a bond. 198 00:08:08,988 --> 00:08:10,556 All right, so let's draw it that way. 199 00:08:10,556 --> 00:08:11,057 All right. 200 00:08:11,057 --> 00:08:13,860 So maybe if I were to take HCl, maybe I 201 00:08:13,860 --> 00:08:18,130 would have sort of like, you know, a cloud like that. 202 00:08:18,130 --> 00:08:18,631 Right. 203 00:08:18,631 --> 00:08:21,868 Where it had it's a minus and it's plus there. 204 00:08:21,868 --> 00:08:22,702 OK. 205 00:08:22,702 --> 00:08:23,603 Why did I-- 206 00:08:23,603 --> 00:08:27,673 I don't know why used dash lines, but there you go. 207 00:08:27,673 --> 00:08:29,775 And so you can see that is-- 208 00:08:29,775 --> 00:08:31,477 what I wanted to put is the dashed line 209 00:08:31,477 --> 00:08:33,111 for the bond itself. 210 00:08:33,111 --> 00:08:35,881 Give myself a little space. 211 00:08:35,881 --> 00:08:37,350 Right. 212 00:08:37,350 --> 00:08:39,051 That's the bond we're talking about. 213 00:08:39,051 --> 00:08:40,352 That's the bond we're talking-- 214 00:08:40,352 --> 00:08:43,489 Now, it turns out that this is an important type 215 00:08:43,489 --> 00:08:46,259 of interaction between molecules and ions. 216 00:08:46,259 --> 00:08:47,894 It's an ion dipole interaction. 217 00:08:47,894 --> 00:08:49,829 And it has a range-- 218 00:08:49,829 --> 00:08:51,330 I wrote it down. 219 00:08:51,330 --> 00:09:01,908 It has a range of 40 to 600, huge range, 40 to 600. 220 00:09:01,908 --> 00:09:05,244 And the kind of attraction is really not 221 00:09:05,244 --> 00:09:08,748 describable in any other way than what we just described. 222 00:09:08,748 --> 00:09:10,816 It's an ion and a dipole. 223 00:09:10,816 --> 00:09:14,053 And it goes as 1 over r squared. 224 00:09:14,053 --> 00:09:18,691 If you look at the separation, the distance between these, 225 00:09:18,691 --> 00:09:23,663 right, that distance-- the dependence on the energy, 226 00:09:23,663 --> 00:09:26,566 on the bond energy, will go like that distance, 227 00:09:26,566 --> 00:09:29,135 like, 1 over that distance squared. 228 00:09:29,135 --> 00:09:32,138 Now, these dependencies you can get from fairly 229 00:09:32,138 --> 00:09:33,506 simple electrostatics. 230 00:09:33,506 --> 00:09:35,007 I won't derive any of it. 231 00:09:35,007 --> 00:09:37,009 I'm telling you what it is. 232 00:09:37,009 --> 00:09:37,610 OK. 233 00:09:37,610 --> 00:09:38,110 Good. 234 00:09:38,110 --> 00:09:39,545 So an ion double-- now an example 235 00:09:39,545 --> 00:09:43,049 of that would be the system that I just drew. 236 00:09:43,049 --> 00:09:43,549 Right. 237 00:09:43,549 --> 00:09:50,156 So Na+ plus and HCl. 238 00:09:50,156 --> 00:09:51,023 OK. 239 00:09:51,023 --> 00:09:51,524 Good. 240 00:09:51,524 --> 00:09:52,858 That's a different kind of bond. 241 00:09:52,858 --> 00:09:55,261 But see, now, I could also have two dipoles. 242 00:09:55,261 --> 00:09:57,997 And I got a picture for that. 243 00:09:57,997 --> 00:09:58,864 So here's a dipole. 244 00:09:58,864 --> 00:10:00,499 There's my HCl dipole, and there it 245 00:10:00,499 --> 00:10:02,101 is with the negative partial charge 246 00:10:02,101 --> 00:10:03,369 and a positive partial charge. 247 00:10:03,369 --> 00:10:05,037 And it's also color coded. 248 00:10:05,037 --> 00:10:05,538 Right. 249 00:10:05,538 --> 00:10:06,038 OK. 250 00:10:06,038 --> 00:10:06,806 So that's cool. 251 00:10:06,806 --> 00:10:08,407 And there they are just floating along. 252 00:10:08,407 --> 00:10:10,810 And I put an electric field on. 253 00:10:10,810 --> 00:10:12,678 And I put an electric field on. 254 00:10:12,678 --> 00:10:14,814 And you can see that with the electric field-- 255 00:10:14,814 --> 00:10:17,049 so there's my positive plate and my negative plate-- 256 00:10:17,049 --> 00:10:18,584 they're going to try to align. 257 00:10:18,584 --> 00:10:19,452 Right. 258 00:10:19,452 --> 00:10:22,788 These dipoles mean that they're going to align with the field. 259 00:10:22,788 --> 00:10:24,357 They're going to align with the field. 260 00:10:24,357 --> 00:10:27,159 So all of those positive edges are 261 00:10:27,159 --> 00:10:29,128 going to try to turn and face the negative one. 262 00:10:29,128 --> 00:10:31,464 And all those negative ones are going to turn and face 263 00:10:31,464 --> 00:10:33,332 the positive one. 264 00:10:33,332 --> 00:10:37,069 And that's exactly what we just did with this ion. 265 00:10:37,069 --> 00:10:38,638 We basically did the same thing here. 266 00:10:38,638 --> 00:10:40,406 That's what the ion did. 267 00:10:40,406 --> 00:10:40,906 OK. 268 00:10:40,906 --> 00:10:41,907 That's what the ion did. 269 00:10:41,907 --> 00:10:45,144 It said, hey, come and face me and let's form a bond. 270 00:10:45,144 --> 00:10:49,315 But these can also be attracted to each other. 271 00:10:49,315 --> 00:10:49,815 All right. 272 00:10:49,815 --> 00:10:51,417 And so I've got a picture there. 273 00:10:51,417 --> 00:10:55,855 So you can see, like, if I have a dipole in another dipole-- 274 00:10:55,855 --> 00:10:58,124 so this is not an external field, and it's not an ion. 275 00:10:58,124 --> 00:11:02,895 It's two dipoles, two HCl molecules. 276 00:11:02,895 --> 00:11:03,562 Right. 277 00:11:03,562 --> 00:11:06,432 Well, they each have a plus charge and a minus charge. 278 00:11:06,432 --> 00:11:09,035 They each have a plus charge and a minus charge and, you know, 279 00:11:09,035 --> 00:11:13,039 partial charge, right, polar covalent. 280 00:11:13,039 --> 00:11:15,341 And you can see that those can line up, actually, 281 00:11:15,341 --> 00:11:17,977 in different ways to form attraction. 282 00:11:17,977 --> 00:11:20,079 And they can also repel. 283 00:11:20,079 --> 00:11:20,813 Right. 284 00:11:20,813 --> 00:11:23,149 But overall, when they get together, or when two of them 285 00:11:23,149 --> 00:11:25,351 get together, they're going to find a way to attract, 286 00:11:25,351 --> 00:11:26,318 because they can-- 287 00:11:26,318 --> 00:11:27,687 because they can. 288 00:11:27,687 --> 00:11:33,192 And so that is another kind of inter-molecular attraction, 289 00:11:33,192 --> 00:11:35,761 and it's called a dipole-dipole. 290 00:11:35,761 --> 00:11:38,831 Dipole-dipole. 291 00:11:38,831 --> 00:11:41,033 But, let's draw this. 292 00:11:45,037 --> 00:11:49,208 And if we do that we have-- 293 00:11:49,208 --> 00:11:49,975 let's see. 294 00:11:49,975 --> 00:11:52,178 I'm going to try to draw this. 295 00:11:52,178 --> 00:11:54,747 So I've got one dipole. 296 00:11:54,747 --> 00:11:56,348 I'm going to stick to that picture-- 297 00:11:56,348 --> 00:11:57,983 oh, I'm going to stick to this picture, 298 00:11:57,983 --> 00:11:59,719 but it's the same as this picture, 299 00:11:59,719 --> 00:12:02,722 right, where I'm actually using the kind of shape 300 00:12:02,722 --> 00:12:05,791 here to show you that more charge has gone over 301 00:12:05,791 --> 00:12:07,126 to one side. 302 00:12:07,126 --> 00:12:07,626 OK. 303 00:12:07,626 --> 00:12:08,928 So let's go back to here. 304 00:12:08,928 --> 00:12:09,428 Right. 305 00:12:09,428 --> 00:12:11,764 And so if that happens, then I've got 306 00:12:11,764 --> 00:12:14,734 minus and plus, thank you. 307 00:12:14,734 --> 00:12:15,468 OK. 308 00:12:15,468 --> 00:12:18,104 And then I'm going to have another one that's going 309 00:12:18,104 --> 00:12:21,006 to want to line up like this. 310 00:12:21,006 --> 00:12:21,774 Oh. 311 00:12:21,774 --> 00:12:22,708 Did I do that right? 312 00:12:22,708 --> 00:12:23,509 Yeah. 313 00:12:23,509 --> 00:12:25,111 And this is the bond. 314 00:12:25,111 --> 00:12:27,346 This dashed line here is the kind of bond 315 00:12:27,346 --> 00:12:28,914 that we're talking about. 316 00:12:28,914 --> 00:12:33,185 Yeah, those are almost sort of asymmetric. 317 00:12:33,185 --> 00:12:34,854 OK. 318 00:12:34,854 --> 00:12:36,088 Now-- gesundheit. 319 00:12:36,088 --> 00:12:37,389 Now, that's a dipole-dipole. 320 00:12:37,389 --> 00:12:39,759 We don't really have a better way of calling that either. 321 00:12:39,759 --> 00:12:42,361 They're dipole charges interacting 322 00:12:42,361 --> 00:12:44,396 with dipole charges. 323 00:12:44,396 --> 00:12:49,301 And that's going to give you a 1 over r cubed dependence. 324 00:12:49,301 --> 00:12:52,671 And, you know, if you've taken some basic ENM or if you do, 325 00:12:52,671 --> 00:12:53,539 you'll learn this. 326 00:12:53,539 --> 00:12:54,039 Right. 327 00:12:54,039 --> 00:12:56,709 You'll learn how to derive these distance dependencies. 328 00:12:56,709 --> 00:13:01,380 So I've got two dipoles, right, because there are 329 00:13:01,380 --> 00:13:04,283 two molecules that have not-- 330 00:13:04,283 --> 00:13:05,451 is not a non-polar. 331 00:13:05,451 --> 00:13:07,019 It's a polar covalent bond. 332 00:13:07,019 --> 00:13:09,088 And those are attracted to each other in this way. 333 00:13:09,088 --> 00:13:12,525 And the range of that bonding strength for two dipoles 334 00:13:12,525 --> 00:13:14,593 is 5 to 25. 335 00:13:14,593 --> 00:13:16,362 So it's a lot less. 336 00:13:16,362 --> 00:13:17,229 Right. 337 00:13:17,229 --> 00:13:23,669 And well, if you had HCl and HCl, that would be an example-- 338 00:13:23,669 --> 00:13:29,642 now instead of an ion, I'm putting two polar molecules in. 339 00:13:29,642 --> 00:13:30,176 Right. 340 00:13:30,176 --> 00:13:34,380 So this could happen. 341 00:13:34,380 --> 00:13:40,286 This could happen from a molecule to a molecule. 342 00:13:40,286 --> 00:13:42,922 It could happen from an atom to a molecule. 343 00:13:42,922 --> 00:13:46,392 It could happen from a molecule to an atom. 344 00:13:46,392 --> 00:13:47,793 Right. 345 00:13:47,793 --> 00:13:51,463 So for example, you know, I could have-- 346 00:13:51,463 --> 00:14:01,574 if I have HCl, and more charge has gone to the chlorine side. 347 00:14:01,574 --> 00:14:02,074 Right. 348 00:14:02,074 --> 00:14:03,375 So this has my delta plus. 349 00:14:03,375 --> 00:14:05,211 This is what I wrote over on the other side. 350 00:14:05,211 --> 00:14:07,012 That's my delta minus. 351 00:14:07,012 --> 00:14:08,814 And if I have just a single atom-- 352 00:14:08,814 --> 00:14:11,016 I'm going to put a xenon atom here. 353 00:14:11,016 --> 00:14:13,786 Well, it's just sitting around happily, 354 00:14:13,786 --> 00:14:16,589 you know, minding it's own business. 355 00:14:16,589 --> 00:14:18,357 And what's going to happen to that? 356 00:14:18,357 --> 00:14:19,058 Right. 357 00:14:19,058 --> 00:14:20,359 What's going to happen to that? 358 00:14:20,359 --> 00:14:25,464 Well, see, if this comes up to an atom that 359 00:14:25,464 --> 00:14:29,969 didn't have a dipole, it still has feelings. 360 00:14:29,969 --> 00:14:31,136 It still has feelings. 361 00:14:31,136 --> 00:14:31,737 Why? 362 00:14:31,737 --> 00:14:34,573 Because electrons have feelings. 363 00:14:34,573 --> 00:14:35,374 That's why. 364 00:14:35,374 --> 00:14:38,611 Because it has electrons. 365 00:14:38,611 --> 00:14:43,382 So those electrons are in there, and it doesn't have a dipole. 366 00:14:43,382 --> 00:14:48,420 But that's OK, because those electrons still can feel. 367 00:14:48,420 --> 00:14:51,757 They can feel the dipole of this. 368 00:14:51,757 --> 00:14:56,595 They can feel the dipole of this molecule. 369 00:14:56,595 --> 00:14:59,698 And when they feel that dipole, they react to it. 370 00:14:59,698 --> 00:15:01,100 They react to it. 371 00:15:01,100 --> 00:15:03,068 So there's a whole other thing that can happen. 372 00:15:03,068 --> 00:15:04,703 By the way, it could happen-- 373 00:15:04,703 --> 00:15:07,406 it could happen with a sodium atom. 374 00:15:07,406 --> 00:15:13,946 Na+ also is a charge that this happy go lucky xenon, 375 00:15:13,946 --> 00:15:16,248 it doesn't know what's coming. 376 00:15:16,248 --> 00:15:19,985 But it's got electrons that feel charge. 377 00:15:19,985 --> 00:15:22,187 And so you bring in charge to it, 378 00:15:22,187 --> 00:15:24,456 and they're going to react to it. 379 00:15:24,456 --> 00:15:25,958 They're going to react to it. 380 00:15:25,958 --> 00:15:29,028 Whether it's a single charge or whether it's a dipole, 381 00:15:29,028 --> 00:15:32,965 these are charges that are going to change 382 00:15:32,965 --> 00:15:35,801 the charge around that atom. 383 00:15:35,801 --> 00:15:38,103 Now, there's another name for that. 384 00:15:38,103 --> 00:15:40,706 And that leads to another kind of bond. 385 00:15:40,706 --> 00:15:43,375 It actually leads to another kind of bond. 386 00:15:43,375 --> 00:15:44,143 Let's see. 387 00:15:44,143 --> 00:15:45,344 So I'm going to just-- 388 00:15:45,344 --> 00:15:46,645 let me draw the cartoon. 389 00:15:46,645 --> 00:15:48,380 I really want to make sure you understand 390 00:15:48,380 --> 00:15:52,351 this, because this sets up the next kind of bonding. 391 00:15:52,351 --> 00:15:59,091 And so let's suppose I take a sodium, and I'll use H2. 392 00:15:59,091 --> 00:16:00,960 H-- gesundheit. 393 00:16:00,960 --> 00:16:03,562 H. And mine could have been a single atom. 394 00:16:03,562 --> 00:16:06,398 It could be a non-polar molecule. 395 00:16:06,398 --> 00:16:06,899 Right. 396 00:16:06,899 --> 00:16:10,536 So this is what this looks like. 397 00:16:10,536 --> 00:16:14,606 And now this is going to-- 398 00:16:14,606 --> 00:16:16,275 these are kind of walking along happily, 399 00:16:16,275 --> 00:16:17,876 and then they see each other. 400 00:16:17,876 --> 00:16:20,212 And all of a sudden, this is going 401 00:16:20,212 --> 00:16:24,683 to induce a shift of the charge around that H2 molecule. 402 00:16:24,683 --> 00:16:28,721 So what you're going to see is now more-- 403 00:16:28,721 --> 00:16:31,156 which way is it going to go? 404 00:16:31,156 --> 00:16:33,659 Which should have the bigger side, the more charge? 405 00:16:33,659 --> 00:16:34,760 Right, yeah, here. 406 00:16:34,760 --> 00:16:36,962 Because that's positive, and electrons are negative. 407 00:16:36,962 --> 00:16:40,632 So now it's going to look like this. 408 00:16:40,632 --> 00:16:42,901 Now, that was not a dipole. 409 00:16:42,901 --> 00:16:44,870 It is not a molecule with a dipole. 410 00:16:44,870 --> 00:16:50,309 But it's an induced dipole, induced dipole, 411 00:16:50,309 --> 00:16:52,778 because of feelings. 412 00:16:52,778 --> 00:16:54,513 It comes down to feelings. 413 00:16:54,513 --> 00:16:55,614 That has a name. 414 00:16:55,614 --> 00:16:56,115 All right. 415 00:16:56,115 --> 00:16:57,149 That's ion. 416 00:16:57,149 --> 00:17:00,686 that one right there is ion-induced-- 417 00:17:00,686 --> 00:17:02,454 see if I can fit it all here-- 418 00:17:02,454 --> 00:17:06,558 induced dipole. 419 00:17:06,558 --> 00:17:07,893 Ion-induced dipole. 420 00:17:07,893 --> 00:17:09,528 And I'm going to try to draw this now. 421 00:17:09,528 --> 00:17:10,229 Let's see. 422 00:17:10,229 --> 00:17:11,163 OK. 423 00:17:11,163 --> 00:17:13,432 Hang on. 424 00:17:13,432 --> 00:17:13,932 OK. 425 00:17:13,932 --> 00:17:16,902 So the ion-induced dipole-- 426 00:17:16,902 --> 00:17:19,405 I'm going to have a plus charge here, 427 00:17:19,405 --> 00:17:21,205 and here's what I'm going to do. 428 00:17:21,205 --> 00:17:28,414 I'm going to draw the original shape as what it was. 429 00:17:28,414 --> 00:17:29,715 Oh, boy. 430 00:17:29,715 --> 00:17:30,582 Here we go. 431 00:17:30,582 --> 00:17:31,817 That's what it was. 432 00:17:31,817 --> 00:17:33,152 But then it got induced. 433 00:17:36,455 --> 00:17:37,289 OK. 434 00:17:37,289 --> 00:17:38,624 It got induced. 435 00:17:38,624 --> 00:17:40,659 And so then, once it's induced, you've 436 00:17:40,659 --> 00:17:44,596 got like a minus and a plus. 437 00:17:44,596 --> 00:17:46,832 Happens all the time. 438 00:17:46,832 --> 00:17:49,001 It happens all the time. 439 00:17:49,001 --> 00:17:52,504 Now, the way that it will-- we'll talk about this 440 00:17:52,504 --> 00:17:53,939 in a little bit of a different way, 441 00:17:53,939 --> 00:17:58,343 because this attraction is between an ion-- 442 00:17:58,343 --> 00:18:01,447 by the way, an ion just means an atom or something lost a charge 443 00:18:01,447 --> 00:18:03,982 or has a charge, plus or minus. 444 00:18:03,982 --> 00:18:07,219 Remember, cation anion. 445 00:18:07,219 --> 00:18:11,490 But the ion in this case is interacting with what 446 00:18:11,490 --> 00:18:14,526 is called a polarizable-- 447 00:18:14,526 --> 00:18:19,565 polarizable electron cloud. 448 00:18:19,565 --> 00:18:22,868 Now, the electron cloud is nothing new. 449 00:18:22,868 --> 00:18:24,536 We got an electron cloud nailed. 450 00:18:24,536 --> 00:18:26,271 We know about electron cloud. 451 00:18:26,271 --> 00:18:26,805 Right. 452 00:18:26,805 --> 00:18:29,741 Because those are orbitals. 453 00:18:29,741 --> 00:18:32,211 But what is this thing called polarizable? 454 00:18:32,211 --> 00:18:33,178 Right, polarizable. 455 00:18:33,178 --> 00:18:34,646 And that's a very important term. 456 00:18:34,646 --> 00:18:39,351 So I'm going to write down its definition. 457 00:18:39,351 --> 00:18:44,656 Because you can imagine if I have 458 00:18:44,656 --> 00:18:47,559 a way of being attracted to a non-polar molecule 459 00:18:47,559 --> 00:18:51,997 by shifting its charge, by shifting its cloud, then 460 00:18:51,997 --> 00:18:53,732 how easy was that? 461 00:18:53,732 --> 00:18:55,300 How much could I shift it? 462 00:18:55,300 --> 00:18:57,736 You can tell that that's going to affect the bond strength. 463 00:18:57,736 --> 00:18:59,638 By the way, which is-- 464 00:18:59,638 --> 00:19:04,476 let's see-- 3 to 15 and has a 1 over r 465 00:19:04,476 --> 00:19:08,213 to the fourth dependence. 466 00:19:08,213 --> 00:19:10,849 And let's give us-- let's give the example that I gave there. 467 00:19:10,849 --> 00:19:15,654 Na+ and H, H. 468 00:19:15,654 --> 00:19:17,256 OK, non-polar molecule. 469 00:19:17,256 --> 00:19:17,756 OK. 470 00:19:17,756 --> 00:19:19,458 It could have been an atom. 471 00:19:19,458 --> 00:19:23,228 But It could have been a non-polar molecule. 472 00:19:23,228 --> 00:19:23,996 Yeah. 473 00:19:23,996 --> 00:19:27,132 Now, polarizable-- polarizability, 474 00:19:27,132 --> 00:19:29,034 is a very important concept. 475 00:19:29,034 --> 00:19:35,541 Polarizability is the measure-- 476 00:19:38,177 --> 00:20:01,200 gesundheit-- Of how easy it is to temporarily distort 477 00:20:01,200 --> 00:20:03,168 the electron distribution. 478 00:20:09,508 --> 00:20:13,779 That is a very important concept for these types of bonds 479 00:20:13,779 --> 00:20:16,915 and for a lot of other properties and, of course, 480 00:20:16,915 --> 00:20:17,983 for life in general. 481 00:20:17,983 --> 00:20:20,419 How polarizable are my electrons? 482 00:20:20,419 --> 00:20:21,153 I need to know. 483 00:20:23,822 --> 00:20:28,393 Are they just willing to deform from their happy orbitals? 484 00:20:28,393 --> 00:20:32,030 Temporarily, because if they were 485 00:20:32,030 --> 00:20:33,865 going to deform permanently, then you'd 486 00:20:33,865 --> 00:20:36,101 have a dipole, a permanent dipole. 487 00:20:36,101 --> 00:20:38,503 These are induced dipoles. 488 00:20:38,503 --> 00:20:39,271 OK. 489 00:20:39,271 --> 00:20:41,607 That's important. 490 00:20:41,607 --> 00:20:43,275 OK. 491 00:20:43,275 --> 00:20:46,278 Now, OK, good. 492 00:20:46,278 --> 00:20:47,879 So that's an ion-induced dipole. 493 00:20:47,879 --> 00:20:50,449 Now you could also imagine, you know, 494 00:20:50,449 --> 00:20:53,952 this could have easily been a dipole over here. 495 00:20:53,952 --> 00:20:56,321 It didn't have to be an ion. 496 00:20:56,321 --> 00:20:57,489 It could have been a dipole. 497 00:20:57,489 --> 00:20:59,091 I could have had a dipole here that 498 00:20:59,091 --> 00:21:03,762 came up to a non-polar molecule or an atom, right, 499 00:21:03,762 --> 00:21:09,134 and it could have induced the same shift 500 00:21:09,134 --> 00:21:12,237 in the charge density, which then allows me to be attracted, 501 00:21:12,237 --> 00:21:14,106 because there's a little bit of a fluctuation 502 00:21:14,106 --> 00:21:15,807 of negative charge there. 503 00:21:15,807 --> 00:21:17,476 Right. 504 00:21:17,476 --> 00:21:18,443 So if I were to-- 505 00:21:22,147 --> 00:21:27,052 so the thing is, we've been talking about dimers. 506 00:21:27,052 --> 00:21:31,089 But you could talk about, what is the dipole of something 507 00:21:31,089 --> 00:21:32,024 more than a dimer. 508 00:21:32,024 --> 00:21:33,759 So this is polar. 509 00:21:33,759 --> 00:21:34,993 What about these other things? 510 00:21:34,993 --> 00:21:35,861 Right. 511 00:21:35,861 --> 00:21:40,799 So if I look at molecules, right, that are polar, 512 00:21:40,799 --> 00:21:44,436 it's not just about HCl, right, which 513 00:21:44,436 --> 00:21:46,138 is that first one up there. 514 00:21:46,138 --> 00:21:48,840 But that's kind of the obvious case. 515 00:21:48,840 --> 00:21:50,575 But what about CCl4? 516 00:21:50,575 --> 00:21:53,612 What if I take a carbon atom and I put 4 chlorines? 517 00:21:53,612 --> 00:21:54,846 Those are all polar bonds. 518 00:21:54,846 --> 00:21:57,115 And you can see-- well, it's hard to see-- but they've 519 00:21:57,115 --> 00:21:59,818 drawn in the dipole moment. 520 00:21:59,818 --> 00:22:01,620 You've lost some charge from the carbon. 521 00:22:01,620 --> 00:22:03,388 It's gone out to the chlorine atom. 522 00:22:03,388 --> 00:22:05,424 There's a dipole movement within each bond. 523 00:22:05,424 --> 00:22:08,327 But now here's where VSEPR comes in, 524 00:22:08,327 --> 00:22:14,800 because these are going to be tetrahedrally distributed 525 00:22:14,800 --> 00:22:17,102 and fully canceling out. 526 00:22:17,102 --> 00:22:18,704 So it's like you've got all these kind 527 00:22:18,704 --> 00:22:22,040 of electrostatic things going on that all cancel out. 528 00:22:22,040 --> 00:22:24,743 So this molecule is not a polar molecule. 529 00:22:24,743 --> 00:22:25,344 Right. 530 00:22:25,344 --> 00:22:30,782 On the other hand, molecules NH3 or CH3Cl-- 531 00:22:30,782 --> 00:22:31,249 right. 532 00:22:31,249 --> 00:22:34,186 Now, this is going to be polar, because these dipoles do not 533 00:22:34,186 --> 00:22:35,620 cancel out within the molecules. 534 00:22:35,620 --> 00:22:37,189 So you can kind of use this thinking. 535 00:22:37,189 --> 00:22:40,092 There's BF3, trigonal planar. 536 00:22:40,092 --> 00:22:41,159 Right. 537 00:22:41,159 --> 00:22:42,661 All those dipoles cancel. 538 00:22:42,661 --> 00:22:45,931 It's a non-polar molecule. 539 00:22:45,931 --> 00:22:47,899 But if you take a classic example-- 540 00:22:47,899 --> 00:22:49,534 which we'll come back-- 541 00:22:49,534 --> 00:22:55,073 of, say, water as a polar molecule, 542 00:22:55,073 --> 00:22:56,174 I could do the same thing. 543 00:22:56,174 --> 00:22:56,675 Right. 544 00:22:56,675 --> 00:23:01,446 I can take water, which is oxygen, hydrogen, 545 00:23:01,446 --> 00:23:04,750 hydrogen. And you see you've got delta plus there, delta 546 00:23:04,750 --> 00:23:08,019 plus there, and you've got some minus there. 547 00:23:08,019 --> 00:23:08,754 Right. 548 00:23:08,754 --> 00:23:14,793 Now, there's a dipole moment, so part of it cancels 549 00:23:14,793 --> 00:23:17,162 but not all of it. 550 00:23:17,162 --> 00:23:21,867 So there is a dipole moment for the net water molecule. 551 00:23:21,867 --> 00:23:24,469 The net dipole is what matters to determine 552 00:23:24,469 --> 00:23:27,005 if a molecule's polar or not. 553 00:23:27,005 --> 00:23:30,709 So there's a net dipole, net dipole 554 00:23:30,709 --> 00:23:32,077 when you sum them all up. 555 00:23:32,077 --> 00:23:33,645 And that's what's going to determine 556 00:23:33,645 --> 00:23:37,215 if this can come along to that xenon atom, right. 557 00:23:37,215 --> 00:23:42,220 And so here's my xenon just sitting there doing nothing. 558 00:23:42,220 --> 00:23:46,024 And now when water comes up to xenon, what's going to happen? 559 00:23:46,024 --> 00:23:47,859 Well, what's going to happen is I've 560 00:23:47,859 --> 00:23:53,198 got my water molecule, my water molecule, my delta minus, 561 00:23:53,198 --> 00:23:55,200 my delta plus, my delta plus. 562 00:23:55,200 --> 00:23:59,171 And because it's got a net dipole, 563 00:23:59,171 --> 00:24:01,540 it's going to form the atom. 564 00:24:01,540 --> 00:24:03,508 And so I'm going to have-- 565 00:24:03,508 --> 00:24:05,177 let's see, make sure I draw this right. 566 00:24:05,177 --> 00:24:06,845 So it's going to look kind of like this. 567 00:24:11,082 --> 00:24:16,388 Delta minus, delta plus, and that allows a water molecule 568 00:24:16,388 --> 00:24:18,390 to bond to a xenon atom. 569 00:24:18,390 --> 00:24:24,729 It is bonding with another bond, which is very 570 00:24:24,729 --> 00:24:27,532 similar to what I just wrote-- 571 00:24:27,532 --> 00:24:34,105 gesundheit-- But it is a dipole-induced, not ion. 572 00:24:34,105 --> 00:24:39,611 It is a dipole-induced dipole. 573 00:24:39,611 --> 00:24:40,512 You see that? 574 00:24:40,512 --> 00:24:42,747 Because now, I didn't have an ion. 575 00:24:42,747 --> 00:24:48,720 I had a water molecule that had a dipole moment. 576 00:24:48,720 --> 00:24:50,989 So now I've got my dipole-induced dipole, 577 00:24:50,989 --> 00:24:52,457 and that's going to look-- 578 00:24:52,457 --> 00:24:53,458 oh let's draw it. 579 00:24:53,458 --> 00:24:53,959 Let's see. 580 00:24:53,959 --> 00:24:56,394 So I got my dipole-induced dipole. 581 00:24:56,394 --> 00:25:01,233 So we're going to go, kind of, oh, boy, there we go. 582 00:25:01,233 --> 00:25:02,667 OK. 583 00:25:02,667 --> 00:25:06,304 Minus, plus, and then-- 584 00:25:06,304 --> 00:25:09,107 now that might be the dipole of, say, the water 585 00:25:09,107 --> 00:25:10,242 molecule or something that. 586 00:25:10,242 --> 00:25:14,980 And then I've got another thing that didn't have a dipole, 587 00:25:14,980 --> 00:25:17,949 but it got induced to have one. 588 00:25:17,949 --> 00:25:20,652 OK. 589 00:25:20,652 --> 00:25:21,152 Oh, boy. 590 00:25:21,152 --> 00:25:23,421 I went out of the lines. 591 00:25:23,421 --> 00:25:24,356 Ah. 592 00:25:24,356 --> 00:25:25,891 I was so careful. 593 00:25:25,891 --> 00:25:28,560 But you can't-- you can't hold chemistry. 594 00:25:28,560 --> 00:25:30,495 Uh-uh. 595 00:25:30,495 --> 00:25:31,730 No way. 596 00:25:31,730 --> 00:25:35,500 No way. 597 00:25:35,500 --> 00:25:37,402 Mm. 598 00:25:37,402 --> 00:25:38,069 OK. 599 00:25:38,069 --> 00:25:42,040 Delta plus, delta minus, it's induced. 600 00:25:42,040 --> 00:25:44,476 That's what that means, right. 601 00:25:44,476 --> 00:25:48,780 Now, it turns out that this has an even weaker-- 602 00:25:48,780 --> 00:25:49,848 so this would be a dipole. 603 00:25:49,848 --> 00:25:51,583 Let's just-- right, let's finish this up-- 604 00:25:51,583 --> 00:26:00,258 dipole interacting with the polarizable electron cloud. 605 00:26:00,258 --> 00:26:07,265 And the value of this is even lower range, 2 to 10, 606 00:26:07,265 --> 00:26:10,502 and the dependence is 1 over r to the sixth. 607 00:26:10,502 --> 00:26:15,006 And the example-- let's go back to HCl. 608 00:26:15,006 --> 00:26:19,978 HCl, there's my dipole coming in ClCl. 609 00:26:19,978 --> 00:26:22,647 I like that because it's got three Cls. 610 00:26:22,647 --> 00:26:23,448 Why not? 611 00:26:23,448 --> 00:26:25,383 That's a non-polar molecule. 612 00:26:25,383 --> 00:26:26,384 That's a dipole. 613 00:26:26,384 --> 00:26:29,054 That induces a dipole in this by shifting 614 00:26:29,054 --> 00:26:31,590 its polarized electrons around. 615 00:26:31,590 --> 00:26:32,591 Right. 616 00:26:32,591 --> 00:26:36,094 And then it allows there to be a little bit of attraction. 617 00:26:36,094 --> 00:26:38,563 You might be saying, but that's so little. 618 00:26:38,563 --> 00:26:39,831 We'll get to that in a second. 619 00:26:39,831 --> 00:26:41,499 That's not so little. 620 00:26:41,499 --> 00:26:45,103 That's actually not so little when you've got a lot of it. 621 00:26:45,103 --> 00:26:46,137 OK. 622 00:26:46,137 --> 00:26:48,006 OK. 623 00:26:48,006 --> 00:26:54,079 Dipole interaction-- now it turns out that even-- 624 00:26:54,079 --> 00:26:57,182 and this is what's mind blowing. 625 00:26:57,182 --> 00:26:58,183 You knew this was coming. 626 00:26:58,183 --> 00:27:01,086 This moment today was going to come. 627 00:27:01,086 --> 00:27:07,192 I can have an interaction without any dipole 628 00:27:07,192 --> 00:27:08,593 to start with. 629 00:27:08,593 --> 00:27:09,961 It's true. 630 00:27:09,961 --> 00:27:12,030 I can take two non-polar covalent 631 00:27:12,030 --> 00:27:16,501 bonds, two non-polar covalent molecules, H2 and H2, 632 00:27:16,501 --> 00:27:20,805 and they are attracted to each other. 633 00:27:20,805 --> 00:27:22,841 How is that possible? 634 00:27:22,841 --> 00:27:24,743 Well, it's what explains this. 635 00:27:24,743 --> 00:27:25,877 I mean, we know-- 636 00:27:25,877 --> 00:27:28,079 why does helium, argon, and xenon-- 637 00:27:28,079 --> 00:27:30,115 why do these have different boiling points? 638 00:27:30,115 --> 00:27:33,518 By the way, the boiling point of these-- 639 00:27:33,518 --> 00:27:35,820 all right, so these can be made into liquids 640 00:27:35,820 --> 00:27:38,523 and you can boil them, right-- 641 00:27:38,523 --> 00:27:40,258 is really different. 642 00:27:40,258 --> 00:27:42,727 And it's a measure of how strongly they're 643 00:27:42,727 --> 00:27:43,662 bonded together. 644 00:27:43,662 --> 00:27:44,162 Right. 645 00:27:44,162 --> 00:27:47,399 So this is a direct kind of way of thinking about, 646 00:27:47,399 --> 00:27:50,168 of measuring something that's related to the bond strength. 647 00:27:50,168 --> 00:27:52,203 So why do these atoms-- 648 00:27:52,203 --> 00:27:55,306 they're all just atoms-- 649 00:27:55,306 --> 00:27:59,511 you know, they're all just like this. 650 00:27:59,511 --> 00:28:02,380 They don't have this dipole. 651 00:28:02,380 --> 00:28:03,014 Right. 652 00:28:03,014 --> 00:28:03,782 They're non-polar. 653 00:28:03,782 --> 00:28:06,851 They're just atoms sitting there with their symmetric charge 654 00:28:06,851 --> 00:28:07,452 clouds. 655 00:28:07,452 --> 00:28:08,753 How is it that they can be attracted 656 00:28:08,753 --> 00:28:10,188 to each other in the first place? 657 00:28:10,188 --> 00:28:14,693 And how is it that they can have such a strong trend? 658 00:28:14,693 --> 00:28:18,263 And that has to do with another kind of force. 659 00:28:18,263 --> 00:28:19,297 And there is a picture. 660 00:28:19,297 --> 00:28:21,399 So here's two examples. 661 00:28:21,399 --> 00:28:22,467 There's two helium atoms. 662 00:28:22,467 --> 00:28:25,070 So that's the first one in this list, boiling point 663 00:28:25,070 --> 00:28:27,072 minus 269 degrees Celsius. 664 00:28:27,072 --> 00:28:28,106 It's pretty cold. 665 00:28:28,106 --> 00:28:30,875 And there's two non-polar molecules, H2. 666 00:28:30,875 --> 00:28:35,113 What happens is that you get fluctuations. 667 00:28:35,113 --> 00:28:36,214 You get fluctuations. 668 00:28:36,214 --> 00:28:40,685 And what I mean by that is that, just randomly, literally, 669 00:28:40,685 --> 00:28:45,290 randomly, right, because of collisions or thermal energy-- 670 00:28:45,290 --> 00:28:49,828 randomly, one of those could form a dipole. 671 00:28:49,828 --> 00:28:50,662 I didn't mean it. 672 00:28:50,662 --> 00:28:53,231 It wasn't my happy place, but it happened. 673 00:28:53,231 --> 00:28:55,967 Now, if it happens and your charge kind of 674 00:28:55,967 --> 00:29:00,371 goes to one side, even if it's just for a split second, 675 00:29:00,371 --> 00:29:03,074 that's a dipole that then, if you're near another atom, 676 00:29:03,074 --> 00:29:05,610 can induce a dipole. 677 00:29:05,610 --> 00:29:09,114 And we know that if we can induce a dipole, if we're here, 678 00:29:09,114 --> 00:29:11,850 if we're at this stage, we've already got that covered. 679 00:29:11,850 --> 00:29:15,987 We already know that I can induce another dipole 680 00:29:15,987 --> 00:29:17,922 if I'm charged. 681 00:29:17,922 --> 00:29:18,656 Right. 682 00:29:18,656 --> 00:29:22,427 And so what happens is you get this kind of fluctuation 683 00:29:22,427 --> 00:29:25,663 that leads literally to a bond. 684 00:29:25,663 --> 00:29:28,199 It leads to a bond. 685 00:29:28,199 --> 00:29:28,700 Right. 686 00:29:28,700 --> 00:29:32,170 And that is called London dispersion. 687 00:29:32,170 --> 00:29:34,839 That's called the London force, and the London dispersion 688 00:29:34,839 --> 00:29:38,576 is the name of a kind of bonding you have. 689 00:29:38,576 --> 00:29:40,078 Let me just make sure-- 690 00:29:40,078 --> 00:29:41,412 ha. 691 00:29:41,412 --> 00:29:43,815 OK. 692 00:29:43,815 --> 00:29:48,419 London dispersion. 693 00:29:54,058 --> 00:29:55,760 Notice there's room for one more. 694 00:29:55,760 --> 00:29:56,728 It's coming. 695 00:29:56,728 --> 00:29:58,763 There's more. 696 00:29:58,763 --> 00:30:00,865 We're not done. 697 00:30:00,865 --> 00:30:01,933 We are not done. 698 00:30:01,933 --> 00:30:07,138 I can literally take two non-polar atoms or molecules, 699 00:30:07,138 --> 00:30:12,010 and I can find a way for them to be attracted. 700 00:30:12,010 --> 00:30:15,580 And the way it happens is thermal fluctuations. 701 00:30:15,580 --> 00:30:20,952 This is such an important force, and it's such a strange one 702 00:30:20,952 --> 00:30:24,189 that I want to write down what it is. 703 00:30:24,189 --> 00:30:28,092 It's that non-polar-- we've been talking about polar 704 00:30:28,092 --> 00:30:31,763 and charges, but non-polar molecules 705 00:30:31,763 --> 00:30:34,999 are attracted by fluctuations. 706 00:30:43,174 --> 00:30:45,977 Fluctuations. 707 00:30:45,977 --> 00:30:48,313 I should say, by dipole fluctuations. 708 00:30:48,313 --> 00:30:50,615 That's really what's happening. 709 00:30:50,615 --> 00:30:51,282 Right. 710 00:30:51,282 --> 00:30:52,750 By dipole fluctuations. 711 00:30:52,750 --> 00:30:55,820 So one of them gets a little shift, and there's a dipole. 712 00:30:55,820 --> 00:30:58,122 And then that dipole, if there's another one around, 713 00:30:58,122 --> 00:31:02,093 can induce a shift, and then there can be a bond. 714 00:31:02,093 --> 00:31:07,765 And now, this gets back to something very important, 715 00:31:07,765 --> 00:31:10,568 which is that-- 716 00:31:10,568 --> 00:31:16,507 you can imagine, how easy was it for temperature-- 717 00:31:16,507 --> 00:31:20,044 how easy was it to create that shift? 718 00:31:20,044 --> 00:31:20,712 Right. 719 00:31:20,712 --> 00:31:25,483 Well that's going to have to do with your polarizability. 720 00:31:25,483 --> 00:31:30,788 Now, OK, so what is it that has to do with polarizability? 721 00:31:30,788 --> 00:31:31,289 Right. 722 00:31:31,289 --> 00:31:34,392 Well, if-- oh, I do have a board here. 723 00:31:34,392 --> 00:31:36,461 Ha. 724 00:31:36,461 --> 00:31:36,961 OK. 725 00:31:40,732 --> 00:31:46,237 You can already imagine, if I go back to this list here-- 726 00:31:46,237 --> 00:31:49,073 if I go from helium to argon, what have I done? 727 00:31:49,073 --> 00:31:51,142 I've gone down in the periodic table. 728 00:31:51,142 --> 00:31:52,944 And we've already talked about this. 729 00:31:52,944 --> 00:31:57,248 Those electrons that are going to do the shifting to cause 730 00:31:57,248 --> 00:31:58,716 the fluctuation-- 731 00:31:58,716 --> 00:32:02,387 those electrons are more loosely bound. 732 00:32:02,387 --> 00:32:02,887 Right. 733 00:32:02,887 --> 00:32:04,656 They're further out. 734 00:32:04,656 --> 00:32:06,157 They're more loosely bound. 735 00:32:06,157 --> 00:32:07,492 We've already talked about this. 736 00:32:07,492 --> 00:32:09,193 We've looked at this in a lot of ways. 737 00:32:09,193 --> 00:32:09,694 Right. 738 00:32:09,694 --> 00:32:13,564 Whether it's radius or ionization energy, those are-- 739 00:32:13,564 --> 00:32:16,734 if they're more loosely bound, then they're 740 00:32:16,734 --> 00:32:18,536 easier to shift around. 741 00:32:18,536 --> 00:32:19,837 I'm not taking them out. 742 00:32:19,837 --> 00:32:20,338 Right. 743 00:32:20,338 --> 00:32:21,406 I'm not taking them out. 744 00:32:21,406 --> 00:32:22,807 But I'm moving them. 745 00:32:22,807 --> 00:32:24,842 That's what London is. 746 00:32:24,842 --> 00:32:26,177 I got to fluctuate it. 747 00:32:26,177 --> 00:32:29,847 So you can imagine now, why, if it's heavier, 748 00:32:29,847 --> 00:32:32,817 and those electrons are further out, they're more polarizable. 749 00:32:32,817 --> 00:32:33,384 Right. 750 00:32:33,384 --> 00:32:34,519 So let's write that down. 751 00:32:34,519 --> 00:32:35,019 Right. 752 00:32:35,019 --> 00:32:39,857 So the London-- so we're going to get a stronger London-- 753 00:32:43,428 --> 00:32:44,329 two reasons. 754 00:32:44,329 --> 00:32:51,803 One, heavier atom, which really, in this case, 755 00:32:51,803 --> 00:32:53,504 right, it's heavier, but it really 756 00:32:53,504 --> 00:32:55,807 just means more polarizable. 757 00:32:55,807 --> 00:32:58,977 If it's more polarizable, that's the key. 758 00:32:58,977 --> 00:33:05,450 That's the chemistry key, more polarizable, more polarizable 759 00:33:05,450 --> 00:33:06,851 electron cloud. 760 00:33:06,851 --> 00:33:07,552 Write it all out. 761 00:33:10,188 --> 00:33:13,057 But the other thing that you can imagine with London-- 762 00:33:13,057 --> 00:33:14,592 right, so that explains that trend. 763 00:33:14,592 --> 00:33:16,594 The other thing that you can imagine with London 764 00:33:16,594 --> 00:33:19,964 is that these interactions, these fluctuations, they're 765 00:33:19,964 --> 00:33:22,200 happening all over the place. 766 00:33:22,200 --> 00:33:25,503 And the more contact I have-- 767 00:33:25,503 --> 00:33:30,808 the more places in a molecule I have to induce this, 768 00:33:30,808 --> 00:33:34,012 to have this fluctuation happen, the stronger these forces 769 00:33:34,012 --> 00:33:35,613 could be. 770 00:33:35,613 --> 00:33:37,181 And this is exactly what we see. 771 00:33:37,181 --> 00:33:38,282 Look at this trend. 772 00:33:38,282 --> 00:33:40,818 Methane, ethane, propane, and butane. 773 00:33:40,818 --> 00:33:42,887 All I've done is I've added another carbon atom. 774 00:33:42,887 --> 00:33:44,455 Oh, we're going to get to these. 775 00:33:44,455 --> 00:33:46,657 We'll talk a little bit about Orgel later. 776 00:33:46,657 --> 00:33:48,693 But for now, look at the boiling points of those. 777 00:33:48,693 --> 00:33:52,997 Again, boiling point being a proxy for the bonding strength. 778 00:33:52,997 --> 00:33:55,066 What bond could they have? 779 00:33:55,066 --> 00:33:58,636 None of those, only this. 780 00:33:58,636 --> 00:33:59,570 Ha. 781 00:33:59,570 --> 00:34:01,239 I got excited. 782 00:34:01,239 --> 00:34:04,542 Only in London, because look, they're non-polar molecules. 783 00:34:04,542 --> 00:34:05,810 They've got no charge on them. 784 00:34:05,810 --> 00:34:07,845 This is the only way they can talk to each other. 785 00:34:07,845 --> 00:34:09,914 But look at how much they talk to each other. 786 00:34:09,914 --> 00:34:10,614 Now, why? 787 00:34:10,614 --> 00:34:12,050 Because of the second thing, right. 788 00:34:12,050 --> 00:34:14,485 Which is that the greater the surface, 789 00:34:14,485 --> 00:34:16,154 the greater the surface. 790 00:34:16,154 --> 00:34:17,155 You can have more. 791 00:34:17,155 --> 00:34:19,524 The more surface you have-- 792 00:34:19,524 --> 00:34:27,364 the greater surface, more contact area, 793 00:34:27,364 --> 00:34:28,632 more contact area. 794 00:34:31,402 --> 00:34:33,304 And that's how this bond-- 795 00:34:33,304 --> 00:34:34,972 that's how this thing works. 796 00:34:34,972 --> 00:34:40,844 Because as long as I've got more surfaces see each other, 797 00:34:40,844 --> 00:34:43,246 then there can be more fluctuations, right, 798 00:34:43,246 --> 00:34:45,583 that are happening, that then induce the other one 799 00:34:45,583 --> 00:34:47,652 to have a fluctuation, that then create 800 00:34:47,652 --> 00:34:51,255 a little moment of bonding, that dramatically 801 00:34:51,255 --> 00:34:52,223 changes the properties. 802 00:34:52,223 --> 00:34:52,956 And look at this. 803 00:34:52,956 --> 00:34:56,127 This is a little bit small, but, you know, these are the-- 804 00:34:56,127 --> 00:34:58,396 so let's go all the way, right. 805 00:34:58,396 --> 00:35:00,865 CH4, OK. 806 00:35:00,865 --> 00:35:02,467 Let's go all the way, and look at this. 807 00:35:02,467 --> 00:35:06,270 It determines when you have a gas at room temperature 808 00:35:06,270 --> 00:35:10,174 or when you have a liquid at room temperature. 809 00:35:10,174 --> 00:35:13,878 Boy, is that important for how we use these molecules. 810 00:35:13,878 --> 00:35:14,378 Right. 811 00:35:14,378 --> 00:35:16,314 Boy, is that important. 812 00:35:16,314 --> 00:35:18,182 It's all London. 813 00:35:18,182 --> 00:35:19,417 there's no other option. 814 00:35:19,417 --> 00:35:19,917 Right. 815 00:35:19,917 --> 00:35:22,053 But that's what's dictating this trend. 816 00:35:22,053 --> 00:35:25,957 It's even more mind-blowing than that, because look at this. 817 00:35:25,957 --> 00:35:31,095 This is one molecule that's identical. 818 00:35:31,095 --> 00:35:31,963 This is C5. 819 00:35:31,963 --> 00:35:36,601 This is 5 atoms of carbon, n-Pentane. 820 00:35:36,601 --> 00:35:40,004 Same exact grams per mole, because it's the same chemical 821 00:35:40,004 --> 00:35:40,505 formula. 822 00:35:40,505 --> 00:35:44,308 But look here, 36.1 degrees C is the boiling point, 823 00:35:44,308 --> 00:35:45,710 and here it's 9.5. 824 00:35:45,710 --> 00:35:46,377 Why? 825 00:35:46,377 --> 00:35:48,379 It's all this. 826 00:35:48,379 --> 00:35:50,181 This is not the ground state. 827 00:35:50,181 --> 00:35:51,716 The most stable structure is here. 828 00:35:51,716 --> 00:35:54,452 But there is a version that's called neopentane. 829 00:35:54,452 --> 00:35:55,720 It's like a nickname for it. 830 00:35:55,720 --> 00:35:59,257 There's a version of it that you can make 831 00:35:59,257 --> 00:36:01,526 that has a different shape. 832 00:36:01,526 --> 00:36:05,663 And because this shape cannot come into contact with itself, 833 00:36:05,663 --> 00:36:07,798 look at this, you can see it from the red line. 834 00:36:07,798 --> 00:36:09,534 It's coming into contact with itself. 835 00:36:09,534 --> 00:36:13,404 In the liquid or gas, it can't have as much London forces, 836 00:36:13,404 --> 00:36:15,239 London potential. 837 00:36:15,239 --> 00:36:19,043 So it cannot bind as strongly, and therefore the boiling point 838 00:36:19,043 --> 00:36:21,012 is a lot lower. 839 00:36:21,012 --> 00:36:22,780 It's a lot lower. 840 00:36:22,780 --> 00:36:27,385 Now, there's a little bit of naming confusion. 841 00:36:27,385 --> 00:36:28,986 I want to clear this up. 842 00:36:28,986 --> 00:36:30,288 Oh, boy. 843 00:36:30,288 --> 00:36:31,556 I have nowhere to go here. 844 00:36:31,556 --> 00:36:35,059 So I'm going to get rid of London for a second. 845 00:36:35,059 --> 00:36:38,229 And I want to make something very clear 846 00:36:38,229 --> 00:36:42,433 that there's another word that's used, 847 00:36:42,433 --> 00:36:44,435 which is called Van der Waals. 848 00:36:44,435 --> 00:36:44,936 OK. 849 00:36:44,936 --> 00:36:50,708 Now, this ability of a fluctuation to happen, 850 00:36:50,708 --> 00:36:53,110 which then induces a fluctuation, that 851 00:36:53,110 --> 00:36:56,581 can happen no matter what molecule you have. 852 00:36:56,581 --> 00:36:57,215 It can happen. 853 00:36:57,215 --> 00:36:57,949 And it does. 854 00:36:57,949 --> 00:36:59,650 It's always there. 855 00:36:59,650 --> 00:37:00,184 All right. 856 00:37:00,184 --> 00:37:08,926 So all molecules, whether they are polar or non-polar-- 857 00:37:08,926 --> 00:37:18,970 polar or non-polar, all molecules are attracted 858 00:37:18,970 --> 00:37:32,049 by London plus any other attractive forces-- 859 00:37:32,049 --> 00:37:35,486 any other attractive forces present-- 860 00:37:42,059 --> 00:37:42,927 forces present. 861 00:37:42,927 --> 00:37:43,427 OK. 862 00:37:43,427 --> 00:37:45,830 So London is always there. 863 00:37:45,830 --> 00:37:54,672 Now, people interchangeably use the term Van der Waals. 864 00:37:54,672 --> 00:37:58,809 And what Van der Waals encompasses 865 00:37:58,809 --> 00:38:02,246 is more than London. 866 00:38:02,246 --> 00:38:06,117 Van der Waals, what you will sometimes see in textbooks, 867 00:38:06,117 --> 00:38:08,085 is the Van der Waals force. 868 00:38:10,921 --> 00:38:11,422 OK. 869 00:38:11,422 --> 00:38:20,231 So that is any or all added together. 870 00:38:20,231 --> 00:38:26,504 This is the combination of these weak forces of dipole-dipole-- 871 00:38:26,504 --> 00:38:27,605 dipole-dipole. 872 00:38:32,310 --> 00:38:41,619 Let's see, dipole-induced dipole, and London. 873 00:38:45,389 --> 00:38:50,361 Those taken together you will sometimes 874 00:38:50,361 --> 00:38:55,199 see referred to as Van der Waals forces, or weak forces. 875 00:38:55,199 --> 00:38:56,967 But we know more than that. 876 00:38:56,967 --> 00:38:58,769 We know the distinction. 877 00:38:58,769 --> 00:38:59,937 Right. 878 00:38:59,937 --> 00:39:06,544 We know that London started like this and then went like this. 879 00:39:10,948 --> 00:39:12,383 Ah! 880 00:39:12,383 --> 00:39:13,351 Really bad. 881 00:39:13,351 --> 00:39:14,719 Gesundheit. 882 00:39:14,719 --> 00:39:15,219 Right. 883 00:39:15,219 --> 00:39:17,588 We know that it started with non-polar, 884 00:39:17,588 --> 00:39:18,856 and that there's a difference. 885 00:39:18,856 --> 00:39:23,227 And so this is all about the polarizable electron cloud. 886 00:39:23,227 --> 00:39:27,832 Polarizable electron cloud, that's all you got. 887 00:39:27,832 --> 00:39:28,566 Right. 888 00:39:28,566 --> 00:39:34,739 And this can be really small, 0.5 to 40. 889 00:39:34,739 --> 00:39:35,239 Oh, yeah. 890 00:39:35,239 --> 00:39:40,444 Let's just keep with chlorine 2, chlorine 2. 891 00:39:40,444 --> 00:39:43,614 Two non-polar molecules, London dispersion, 892 00:39:43,614 --> 00:39:46,083 and this also has a dependence of-- 893 00:39:46,083 --> 00:39:48,552 in terms of the distance-- of 1 over r to the sixth. 894 00:39:48,552 --> 00:39:51,055 Now, in case you think that's small, 895 00:39:51,055 --> 00:39:53,557 I want to show you a little video of why this matters. 896 00:39:53,557 --> 00:39:57,361 So weak forces-- now, weak forces are really strong. 897 00:39:57,361 --> 00:40:00,865 We know this because of "Mission: Impossible". 898 00:40:00,865 --> 00:40:04,435 We know this also because of our own students. 899 00:40:04,435 --> 00:40:06,737 There was one of my former students, Rory, 900 00:40:06,737 --> 00:40:10,040 and he won all sorts of prizes, because he 901 00:40:10,040 --> 00:40:12,076 was trying to be like a gecko. 902 00:40:12,076 --> 00:40:14,912 And so he made gloves that were like gecko gloves, 903 00:40:14,912 --> 00:40:19,350 and much to the delight of the facilities people at MIT, 904 00:40:19,350 --> 00:40:23,821 he actually climbed one of the buildings using his gloves. 905 00:40:23,821 --> 00:40:28,225 In case you are wondering, it wasn't actually their delight. 906 00:40:28,225 --> 00:40:30,227 But really cool stuff. 907 00:40:30,227 --> 00:40:31,028 So let me show you. 908 00:40:31,028 --> 00:40:33,164 This is like a 30-second video. 909 00:40:33,164 --> 00:40:38,202 He found the answer in the sheer number and design of the hairs 910 00:40:38,202 --> 00:40:40,271 on the geckos feet. 911 00:40:40,271 --> 00:40:42,540 Geckos have millions of microscopic hairs 912 00:40:42,540 --> 00:40:43,207 on their toes. 913 00:40:43,207 --> 00:40:45,376 And of course, we can't see this with our naked eye, 914 00:40:45,376 --> 00:40:49,647 because each hair is only 1/10 the size of a human hair. 915 00:40:49,647 --> 00:40:52,149 And each of those hairs branch down to billions 916 00:40:52,149 --> 00:40:54,652 of little split ends. 917 00:40:54,652 --> 00:40:57,154 And they can make such close contact with the surface 918 00:40:57,154 --> 00:41:00,524 that weak intermolecular forces can begin to add up 919 00:41:00,524 --> 00:41:01,659 to something really strong. 920 00:41:04,328 --> 00:41:07,698 Turns out geckos exploit something called the Van der 921 00:41:07,698 --> 00:41:08,833 Waals force. 922 00:41:08,833 --> 00:41:09,600 No. 923 00:41:09,600 --> 00:41:10,835 London, London. 924 00:41:10,835 --> 00:41:13,771 If you think of an atom as a dancing couple, 925 00:41:13,771 --> 00:41:17,141 when you bring two atoms into very close contact, 926 00:41:17,141 --> 00:41:21,612 part of one atom can get attracted to part of the other. 927 00:41:21,612 --> 00:41:25,149 That very weak bond is the Van der Waals force, 928 00:41:25,149 --> 00:41:27,718 and it sticks atoms together. 929 00:41:27,718 --> 00:41:29,687 Proximity is the key. 930 00:41:29,687 --> 00:41:32,490 But bringing two materials that near each other 931 00:41:32,490 --> 00:41:34,458 is harder than you'd think. 932 00:41:34,458 --> 00:41:35,659 All right. 933 00:41:35,659 --> 00:41:38,863 Now, obviously, that got me very excited 934 00:41:38,863 --> 00:41:42,132 when I saw that, because that is how I see atoms, 935 00:41:42,132 --> 00:41:43,934 and that is how I see electrons. 936 00:41:43,934 --> 00:41:46,971 And I saw this, and I almost fell over. 937 00:41:46,971 --> 00:41:50,007 And of course, I played it, and I know all those moves. 938 00:41:50,007 --> 00:41:51,475 I would suggest you guys-- 939 00:41:51,475 --> 00:41:52,710 it's a Friday. 940 00:41:52,710 --> 00:41:54,678 There's some good moves in there. 941 00:41:54,678 --> 00:41:56,247 There's some good moves in there. 942 00:41:56,247 --> 00:41:57,681 And you can take this on your phone 943 00:41:57,681 --> 00:42:00,451 and just kind of work it out at the club. 944 00:42:00,451 --> 00:42:01,819 And speaking of the club, there's 945 00:42:01,819 --> 00:42:03,354 one more thing I've got to teach you. 946 00:42:03,354 --> 00:42:04,989 Because it's that last line. 947 00:42:04,989 --> 00:42:07,658 It's that last line. 948 00:42:07,658 --> 00:42:13,330 See, if you go along a trend like methane, silane, germane, 949 00:42:13,330 --> 00:42:16,100 right, these are non-polar molecules, 950 00:42:16,100 --> 00:42:18,669 and they're all attracted to each other 951 00:42:18,669 --> 00:42:19,637 by these Van der Waals. 952 00:42:19,637 --> 00:42:21,772 And you can see that the boiling point, remember, 953 00:42:21,772 --> 00:42:24,775 our proxy for the force, the bonding strength, is going up. 954 00:42:24,775 --> 00:42:26,076 That's what you'd expect. 955 00:42:26,076 --> 00:42:27,745 That's because these are getting larger, 956 00:42:27,745 --> 00:42:31,315 and there are going to be more polarizable electrons. 957 00:42:31,315 --> 00:42:34,685 But look at what happens as you go to other molecules. 958 00:42:34,685 --> 00:42:38,556 This is the expected trend until you get here. 959 00:42:38,556 --> 00:42:39,690 Right. 960 00:42:39,690 --> 00:42:43,794 NH3-- and that is because of one last type of bond. 961 00:42:43,794 --> 00:42:46,397 That is because of something called the hydrogen bond. 962 00:42:46,397 --> 00:42:50,267 It's a very unique kind of bond. 963 00:42:50,267 --> 00:42:55,406 And so a hydrogen bond is our last intermolecular bond. 964 00:42:55,406 --> 00:42:59,944 Hydrogen bond, right. 965 00:42:59,944 --> 00:43:01,712 And it's a very particular kind of bond. 966 00:43:01,712 --> 00:43:03,614 And it has to do is something very particular 967 00:43:03,614 --> 00:43:05,749 that hydrogen does. 968 00:43:05,749 --> 00:43:06,951 Look at those boiling points. 969 00:43:06,951 --> 00:43:08,619 Look at the change. 970 00:43:08,619 --> 00:43:12,957 I mean, H2O is H2O because of the hydrogen bonds. 971 00:43:12,957 --> 00:43:13,791 Right. 972 00:43:13,791 --> 00:43:18,529 Earth's operating conditions are luckily right here. 973 00:43:18,529 --> 00:43:21,298 But this is only good because of hydrogen bonds, 974 00:43:21,298 --> 00:43:24,001 and it's all the way up and not all the way down there. 975 00:43:24,001 --> 00:43:25,269 So hydrogen bonds are unique. 976 00:43:25,269 --> 00:43:27,204 This is the electronegativity scale, 977 00:43:27,204 --> 00:43:28,706 and there's something very important 978 00:43:28,706 --> 00:43:30,274 that happens for those three elements. 979 00:43:32,910 --> 00:43:35,245 Those are the three elements that are in this trend. 980 00:43:35,245 --> 00:43:36,480 Those are the three elements. 981 00:43:36,480 --> 00:43:39,249 See, nitrogen, chlorine, and oxygen, those 982 00:43:39,249 --> 00:43:40,684 are the three elements here. 983 00:43:40,684 --> 00:43:42,252 And what's important about them is 984 00:43:42,252 --> 00:43:45,255 that they have such a huge electronegativity. 985 00:43:45,255 --> 00:43:50,260 And so in a hydrogen bond, what's going to happen-- 986 00:43:50,260 --> 00:43:51,962 what's going to happen in a hydrogen 987 00:43:51,962 --> 00:43:55,065 is they're really going to pull a lot of charge 988 00:43:55,065 --> 00:43:58,168 from the hydrogen. 989 00:43:58,168 --> 00:44:03,841 So you have a very high positive charge on the hydrogen, 990 00:44:03,841 --> 00:44:05,976 but there's something else that happens. 991 00:44:05,976 --> 00:44:09,046 For hydrogen bonding to occur, you see, 992 00:44:09,046 --> 00:44:13,450 it's the H with say fluorine, and you 993 00:44:13,450 --> 00:44:17,454 have a delta plus and a delta minus, and this is high. 994 00:44:17,454 --> 00:44:18,856 This is very high. 995 00:44:18,856 --> 00:44:19,590 All right. 996 00:44:19,590 --> 00:44:23,527 But you also have a lone pair somewhere. 997 00:44:23,527 --> 00:44:25,129 You've also got a lone pair somewhere. 998 00:44:25,129 --> 00:44:29,033 And we know that we have that on the fluorine, right. 999 00:44:29,033 --> 00:44:31,268 We know that, and we've got those two. 1000 00:44:31,268 --> 00:44:34,471 And the bond that a hydrogen bond represents 1001 00:44:34,471 --> 00:44:38,242 is the fact that I've done two things with the same molecule. 1002 00:44:38,242 --> 00:44:40,310 I've taken a lot of charge off of hydrogen 1003 00:44:40,310 --> 00:44:43,347 and created a very strong delta plus on the hydrogen. 1004 00:44:43,347 --> 00:44:46,116 But I've also got a lone pair somewhere 1005 00:44:46,116 --> 00:44:48,052 that that can bond to. 1006 00:44:48,052 --> 00:44:51,922 And when I have those two things, which I really 1007 00:44:51,922 --> 00:44:53,924 have for these three elements, right. 1008 00:44:53,924 --> 00:44:56,860 When I have those two things, I can make this very special kind 1009 00:44:56,860 --> 00:44:58,262 of bond. 1010 00:44:58,262 --> 00:44:59,930 Now, this is what it looks like. 1011 00:44:59,930 --> 00:45:00,431 Right. 1012 00:45:00,431 --> 00:45:05,836 So there's an H2O molecule, and I want to make a point here. 1013 00:45:05,836 --> 00:45:08,539 There's the covalent bond between the oxygen 1014 00:45:08,539 --> 00:45:10,674 and hydrogen. There's the delta plus. 1015 00:45:10,674 --> 00:45:13,243 And there's that hydrogen bond right there. 1016 00:45:13,243 --> 00:45:14,044 Mm. 1017 00:45:14,044 --> 00:45:14,845 Mm. 1018 00:45:14,845 --> 00:45:15,512 There. 1019 00:45:15,512 --> 00:45:16,013 OK. 1020 00:45:16,013 --> 00:45:18,782 Hydrogen bond that forms between the delta plus 1021 00:45:18,782 --> 00:45:19,917 and the lone pair. 1022 00:45:19,917 --> 00:45:23,153 Now, you can see why water is so special. 1023 00:45:23,153 --> 00:45:24,054 You can see. 1024 00:45:24,054 --> 00:45:27,124 Because unlike NH3 or HF, you can 1025 00:45:27,124 --> 00:45:29,059 see where water had the biggest kick 1026 00:45:29,059 --> 00:45:31,261 up from what would be expected. 1027 00:45:31,261 --> 00:45:36,366 Because unlike NH3 or HF, you have exactly the right balance. 1028 00:45:36,366 --> 00:45:39,536 I've created two of these very strong delta pluses, 1029 00:45:39,536 --> 00:45:42,239 and I've got two lone pairs. 1030 00:45:42,239 --> 00:45:43,107 It all all works out. 1031 00:45:43,107 --> 00:45:45,342 There's no extra lone pairs, like here. 1032 00:45:45,342 --> 00:45:50,447 And all these extra lone pairs, right, that don't-- 1033 00:45:50,447 --> 00:45:52,983 you know, each molecule only has one hydrogen. Here, 1034 00:45:52,983 --> 00:45:54,384 it's two and two. 1035 00:45:54,384 --> 00:45:57,588 That's why water is so special. 1036 00:45:57,588 --> 00:45:59,123 This bond is so important. 1037 00:45:59,123 --> 00:46:01,125 I know you've probably heard about it for water, 1038 00:46:01,125 --> 00:46:04,795 but here's the example I want to give you for the club, 1039 00:46:04,795 --> 00:46:07,965 because some of you might be able to drink ethanol, 1040 00:46:07,965 --> 00:46:12,936 only if you're at the right age, please, of course. 1041 00:46:12,936 --> 00:46:15,272 This is what's in alcohol, right. 1042 00:46:15,272 --> 00:46:16,473 This is the ethanol molecule. 1043 00:46:16,473 --> 00:46:18,809 And it has a boiling point of 78.5 degrees. 1044 00:46:18,809 --> 00:46:21,445 Again, that tells you something about the bond strength 1045 00:46:21,445 --> 00:46:23,680 of this molecule to another molecule. 1046 00:46:23,680 --> 00:46:25,282 But look at this. 1047 00:46:25,282 --> 00:46:28,752 That's an oxygen with a hydrogen. 1048 00:46:28,752 --> 00:46:31,121 This took a lot of charge from the hydrogen, 1049 00:46:31,121 --> 00:46:32,856 right, so you've got a strong delta plus. 1050 00:46:32,856 --> 00:46:35,159 But you've got those two lone pairs there 1051 00:46:35,159 --> 00:46:37,961 ready to bond to the other ethanol molecule. 1052 00:46:37,961 --> 00:46:39,129 But look what happens. 1053 00:46:39,129 --> 00:46:42,432 Methoxymethane is a gas at room temp. 1054 00:46:42,432 --> 00:46:43,634 It's boiled off. 1055 00:46:43,634 --> 00:46:46,370 It's the exact same chemical formula. 1056 00:46:46,370 --> 00:46:47,938 It's the exact same chemical formula. 1057 00:46:47,938 --> 00:46:50,440 All I've done is shift the oxygen in, 1058 00:46:50,440 --> 00:46:52,709 and so now there's no hydrogen that's 1059 00:46:52,709 --> 00:46:55,145 had that big of a delta on it. 1060 00:46:55,145 --> 00:46:56,446 So it cannot hydrogen bond. 1061 00:46:56,446 --> 00:46:58,248 It can London. 1062 00:46:58,248 --> 00:46:58,982 You know. 1063 00:46:58,982 --> 00:47:01,218 But it can't hydrogen. It can't. 1064 00:47:01,218 --> 00:47:02,986 Because the oxygen has the lone pairs. 1065 00:47:02,986 --> 00:47:05,522 But there's no hydrogens that have that strong of a delta. 1066 00:47:05,522 --> 00:47:06,990 So when you're at the club tonight, 1067 00:47:06,990 --> 00:47:08,826 trying out those moves, go up to somebody 1068 00:47:08,826 --> 00:47:10,527 and say, it's a really good thing that's 1069 00:47:10,527 --> 00:47:13,664 not methoxymethane, isn't it. 1070 00:47:13,664 --> 00:47:15,032 Really good thing. 1071 00:47:15,032 --> 00:47:16,500 And tell them about hydrogen bonds. 1072 00:47:16,500 --> 00:47:18,502 Have a great weekend.