WEBVTT 00:00:00.030 --> 00:00:02.670 The following content is provided under a Creative 00:00:02.670 --> 00:00:03.830 Commons license. 00:00:03.830 --> 00:00:06.850 Your support will help MIT OpenCourseWare continue to 00:00:06.850 --> 00:00:10.550 offer high-quality educational resources for free. 00:00:10.550 --> 00:00:13.390 To make a donation or view additional materials from 00:00:13.390 --> 00:00:17.490 hundreds of MIT courses, visit MIT OpenCourseWare at 00:00:17.490 --> 00:00:18.740 ocw.mit.edu. 00:00:20.950 --> 00:00:21.755 Let's go to the lesson. 00:00:21.755 --> 00:00:27.380 So the last day we studied VSEPR, which allowed us to 00:00:27.380 --> 00:00:30.410 infer the shapes of molecules, covalent molecules. 00:00:30.410 --> 00:00:33.640 Today I want to talk about the state of aggregation. 00:00:33.640 --> 00:00:35.710 What do I mean by state of aggregation? 00:00:35.710 --> 00:00:39.680 Is something a solid, a liquid or a gas at a particular 00:00:39.680 --> 00:00:40.240 temperature? 00:00:40.240 --> 00:00:43.500 So 3.091 is introduction to solid state chemistry. 00:00:43.500 --> 00:00:47.010 One of the things we need to know is, under what conditions 00:00:47.010 --> 00:00:49.680 is the solid state stable? 00:00:49.680 --> 00:00:52.950 And the state of aggregation, when it applies to covalent 00:00:52.950 --> 00:00:55.750 molecules, is going to lead us to a discussion 00:00:55.750 --> 00:00:56.760 of secondary bonding. 00:00:56.760 --> 00:00:59.730 So today's lecture is state of aggregation 00:00:59.730 --> 00:01:01.270 or secondary bonding. 00:01:01.270 --> 00:01:03.630 Now let's just reflect upon what we've 00:01:03.630 --> 00:01:04.520 learned up until now. 00:01:04.520 --> 00:01:07.660 We studied ironic bonding and we knew that ionic bonding 00:01:07.660 --> 00:01:11.930 necessarily leads to crystal formation because we have 00:01:11.930 --> 00:01:13.750 unsaturated bonds. 00:01:13.750 --> 00:01:17.620 And that leads to an ion array of unlimited size until you 00:01:17.620 --> 00:01:18.860 run out of reagent. 00:01:18.860 --> 00:01:22.210 And something honking big made of ions is going to be a solid 00:01:22.210 --> 00:01:24.450 at room temperature. 00:01:24.450 --> 00:01:27.190 Last day we appreciated with covalent 00:01:27.190 --> 00:01:29.590 bonding we have two options. 00:01:29.590 --> 00:01:34.970 We can either make discrete molecules such as HCl. 00:01:34.970 --> 00:01:38.860 And HCl as a discrete molecule, depending on a 00:01:38.860 --> 00:01:41.010 number of factors that I'm going to show you today, could 00:01:41.010 --> 00:01:44.390 be a solid, liquid or gas. 00:01:44.390 --> 00:01:47.790 And we're going to understand more deeply how to sort out 00:01:47.790 --> 00:01:49.060 between the three of them. 00:01:49.060 --> 00:01:52.630 Or, I showed you at the end of the last lecture, you can make 00:01:52.630 --> 00:01:55.630 a three-dimensional network and diamond was one example. 00:01:55.630 --> 00:01:59.200 If it's a three-dimensional network that is a large array 00:01:59.200 --> 00:02:02.920 of solid then that means that you're going to end up with a 00:02:02.920 --> 00:02:05.670 formation of a crystal, which is going to give you a solid. 00:02:05.670 --> 00:02:08.040 Diamond is solid at room temperature, graphite is solid 00:02:08.040 --> 00:02:09.730 at room temperature. 00:02:09.730 --> 00:02:14.190 So let's now go to the one case that we haven't dealt 00:02:14.190 --> 00:02:18.570 with, and that's the formation of discrete molecules. 00:02:18.570 --> 00:02:20.920 So let's look at discrete molecules. 00:02:20.920 --> 00:02:23.270 And what we want to understand is whether they're going to be 00:02:23.270 --> 00:02:27.000 solid, liquid or gas at room temperature and what's the 00:02:27.000 --> 00:02:31.280 relevant physics here in order to make that determination? 00:02:31.280 --> 00:02:35.220 The relevant physics is the following. 00:02:35.220 --> 00:02:36.980 We're going to compare two forces. 00:02:36.980 --> 00:02:42.420 We're going to compare the cohesive force between 00:02:42.420 --> 00:02:46.920 molecules versus the disruptive force. 00:02:46.920 --> 00:02:50.120 And the disruptive force in 3.091 is 00:02:50.120 --> 00:02:52.360 always going to be thermal. 00:02:52.360 --> 00:02:53.530 It's thermal energy. 00:02:53.530 --> 00:02:54.060 We know this. 00:02:54.060 --> 00:02:57.190 As we heat things they go from solid to liquid to vapor as 00:02:57.190 --> 00:02:58.500 temperature increases. 00:02:58.500 --> 00:03:04.650 So thermal energy plays the role of the destructive force 00:03:04.650 --> 00:03:07.800 whereas the bonding is something that is 00:03:07.800 --> 00:03:09.230 the cohesive force. 00:03:09.230 --> 00:03:11.010 So let's go back to HCL. 00:03:11.010 --> 00:03:13.510 Last day we looked at HCl. 00:03:13.510 --> 00:03:16.840 So here's one HCl molecule. 00:03:16.840 --> 00:03:18.230 We have a covalent bond. 00:03:21.160 --> 00:03:24.690 It's a covalent bond within the molecule. 00:03:24.690 --> 00:03:29.510 We know this is a polar covalent molecule, with the 00:03:29.510 --> 00:03:32.690 chlorine having greater electronegativity and pulling 00:03:32.690 --> 00:03:35.250 the electrons towards its end. 00:03:35.250 --> 00:03:40.460 And furthermore, this bond I want to categorize as within 00:03:40.460 --> 00:03:44.290 the molecule so I'm going to call it intramolecular. 00:03:44.290 --> 00:03:46.510 Intramolecular. 00:03:46.510 --> 00:03:49.610 Now if I want to answer the question, is hydrogen chloride 00:03:49.610 --> 00:03:52.290 going to be a solid, liquid or gas at room temperature, I 00:03:52.290 --> 00:03:54.720 don't have the information on the board. 00:03:54.720 --> 00:03:57.890 The only way I can answer that question is to put another 00:03:57.890 --> 00:03:59.380 hydrogen chloride. 00:03:59.380 --> 00:04:02.470 This simply forms the bond between hydrogen and chlorine. 00:04:02.470 --> 00:04:05.760 To determine whether hydrogen chloride is a solid, liquid or 00:04:05.760 --> 00:04:10.290 gas, I need to look at how one hydrogen chloride molecule 00:04:10.290 --> 00:04:13.970 bonds to another hydrogen chloride molecule. 00:04:13.970 --> 00:04:19.260 So now this end is the delta plus this end is delta minus. 00:04:19.260 --> 00:04:21.300 And we have again an intramolecular bond. 00:04:21.300 --> 00:04:24.580 So the question is, how does one hydrogen chloride bond to 00:04:24.580 --> 00:04:25.970 another hydrogen chloride? 00:04:25.970 --> 00:04:29.080 This is the intermolecular bond. 00:04:29.080 --> 00:04:30.330 Intermolecular bond. 00:04:32.100 --> 00:04:37.210 So intermolecular bonds govern the state of aggregation. 00:04:37.210 --> 00:04:38.880 And I'm going to show you the different types of 00:04:38.880 --> 00:04:40.310 intermolecular bonds. 00:04:40.310 --> 00:04:42.680 This intermolecular bond isn't the primary bond. 00:04:42.680 --> 00:04:46.740 The primary bond is here inside the molecule. 00:04:46.740 --> 00:04:51.840 So the intermolecular bond is known as a secondary bond. 00:04:51.840 --> 00:04:53.900 And there three types of secondary bonds. 00:04:53.900 --> 00:04:55.750 We're going to look at them in turn. 00:04:55.750 --> 00:04:59.340 So the first one is depicted here on the board. 00:04:59.340 --> 00:05:01.120 And it's called dipole-dipole interactions. 00:05:07.060 --> 00:05:12.370 And these obviously occur only between polar molecules. 00:05:12.370 --> 00:05:16.400 Operative and polar molecules. 00:05:16.400 --> 00:05:17.160 Not in. 00:05:17.160 --> 00:05:18.220 Between. 00:05:18.220 --> 00:05:19.700 Take out in. 00:05:19.700 --> 00:05:26.760 Operative between polar molecules. 00:05:26.760 --> 00:05:29.430 So we've made something covalent and now how does one 00:05:29.430 --> 00:05:30.920 stick to the other? 00:05:30.920 --> 00:05:35.990 Alright and I think I've got a cartoon here that shows this. 00:05:35.990 --> 00:05:36.460 There we go. 00:05:36.460 --> 00:05:39.260 That's taken from an old book that I had. 00:05:39.260 --> 00:05:43.280 So you see the H and the Cl and we have a dipole moment 00:05:43.280 --> 00:05:46.490 and the negative end of one dipole attracted to the 00:05:46.490 --> 00:05:49.480 positive end of another dipole. 00:05:49.480 --> 00:05:54.990 So we have a net dipole moment here and we can measure the 00:05:54.990 --> 00:05:58.375 distance between the center of the dipole-- 00:05:58.375 --> 00:06:01.190 center to center spacing and call it r. 00:06:01.190 --> 00:06:04.450 Center to center dipole spacing. 00:06:04.450 --> 00:06:09.250 And say that the energy in dipole-dipole interaction-- 00:06:09.250 --> 00:06:11.690 I don't expect you to know this by heart and do anything 00:06:11.690 --> 00:06:13.550 with it, but I just want you to realize 00:06:13.550 --> 00:06:15.460 that it's a weak force. 00:06:15.460 --> 00:06:17.680 This is very weak. 00:06:17.680 --> 00:06:20.270 It's proportional to the magnitude 00:06:20.270 --> 00:06:21.430 of the dipole moment. 00:06:21.430 --> 00:06:22.390 You'd expect that. 00:06:22.390 --> 00:06:24.460 Weak dipole moment, weak energy. 00:06:24.460 --> 00:06:26.350 Strong dipole moment, strong energy. 00:06:26.350 --> 00:06:28.800 Turns out it goes as the fourth order 00:06:28.800 --> 00:06:30.060 of the dipole moment. 00:06:30.060 --> 00:06:31.740 And it's inversely proportional to the 00:06:31.740 --> 00:06:32.990 separation. 00:06:32.990 --> 00:06:36.470 Only it's not coulombic, it goes as 1 over r cubed. 00:06:36.470 --> 00:06:38.770 And there's a temperature factor. 00:06:38.770 --> 00:06:39.850 1 over t. 00:06:39.850 --> 00:06:43.100 As temperature goes up, this energy goes down. 00:06:43.100 --> 00:06:46.780 And these are very weak forces on the order of about 5 00:06:46.780 --> 00:06:50.190 kilojoules per mole. 00:06:50.190 --> 00:06:52.130 You remember what the crystallization energy of 00:06:52.130 --> 00:06:53.700 sodium chloride was? 00:06:53.700 --> 00:06:56.310 787 kilojoules per mole. 00:06:56.310 --> 00:06:58.030 So this is very, very weak. 00:06:58.030 --> 00:07:02.140 It's operative at, between, at low temperatures. 00:07:02.140 --> 00:07:03.380 At very low temperatures. 00:07:03.380 --> 00:07:07.550 So for example, hydrogen chloride, in the case of 00:07:07.550 --> 00:07:12.170 hydrogen chloride, the melting point of hydrogen chloride is 00:07:12.170 --> 00:07:16.370 minus 115 degrees C and the boiling point is 00:07:16.370 --> 00:07:18.840 minus 85 degrees C. 00:07:18.840 --> 00:07:22.260 You can see at very low temperatures we already have 00:07:22.260 --> 00:07:24.880 enough thermal energy to disrupt. 00:07:24.880 --> 00:07:28.370 So if we have solid hydrogen chloride, the forces between 00:07:28.370 --> 00:07:31.480 the hydrogen chloride molecules in the solid are 00:07:31.480 --> 00:07:34.810 these very weak dipole-dipole interactions. 00:07:34.810 --> 00:07:37.180 And I think there's a couple more cartoons here. 00:07:37.180 --> 00:07:41.160 This is taken from your text. 00:07:41.160 --> 00:07:43.350 So there we go. 00:07:43.350 --> 00:07:43.770 There it is. 00:07:43.770 --> 00:07:47.380 That's the soup that might be HCl liquid. 00:07:47.380 --> 00:07:51.340 OK so that's the first type of secondary bond. 00:07:51.340 --> 00:07:53.910 Dipole-dipole interaction. 00:07:53.910 --> 00:07:55.050 Let's look at the second one. 00:07:55.050 --> 00:07:59.200 The second one is called induced dipole-induced dipole. 00:08:07.730 --> 00:08:11.850 And it's operative in non-polar species. 00:08:11.850 --> 00:08:18.170 Dominant in non-polar species. 00:08:18.170 --> 00:08:19.820 Why am I using the word, species? 00:08:19.820 --> 00:08:23.040 I'm trying to be a pedant and use fancy words? 00:08:23.040 --> 00:08:23.180 No. 00:08:23.180 --> 00:08:24.460 Because I'm going to make it generic. 00:08:24.460 --> 00:08:27.275 I'm going to show it works in atoms and in compounds. 00:08:30.110 --> 00:08:34.040 So as examples, what are some non-polar species? 00:08:34.040 --> 00:08:37.500 Well how about something like argon? 00:08:37.500 --> 00:08:40.450 Argon if you look on the periodic table it'll show you 00:08:40.450 --> 00:08:46.960 that it has a melting point of 84 kelvin and a boiling point 00:08:46.960 --> 00:08:49.600 of 87 kelvin. 00:08:49.600 --> 00:08:54.890 So if I cool argon to below 84 kelvin, I get argon ice. 00:08:54.890 --> 00:08:57.790 So what are the bonds between one argon atom and another 00:08:57.790 --> 00:08:58.430 argon atom? 00:08:58.430 --> 00:08:59.900 It can't be this. 00:08:59.900 --> 00:09:00.970 There's no net charge. 00:09:00.970 --> 00:09:02.460 It can't be ionic. 00:09:02.460 --> 00:09:05.590 It doesn't form a covalent network the way diamond does. 00:09:05.590 --> 00:09:09.150 How do you justify the existence of solid argon? 00:09:09.150 --> 00:09:11.590 It's just so cold that it just sits there and freezes? 00:09:11.590 --> 00:09:13.190 I mean, how does it bond? 00:09:13.190 --> 00:09:15.150 There needs to be some kind of bonding. 00:09:15.150 --> 00:09:16.700 And other non-polar species. 00:09:16.700 --> 00:09:19.540 So for example, the molecule iodine. 00:09:19.540 --> 00:09:23.320 Iodine melting point is above room temperature. 00:09:23.320 --> 00:09:26.330 It's a solid crystal at room temperature. 00:09:26.330 --> 00:09:29.700 Well there's a strong covalent bond inside iodine. 00:09:29.700 --> 00:09:32.635 But how does one iodine bond to another and to another and 00:09:32.635 --> 00:09:33.330 to another? 00:09:33.330 --> 00:09:35.040 And we can even go to polyatomic 00:09:35.040 --> 00:09:38.930 species, such as methane. 00:09:38.930 --> 00:09:41.610 You know there was data from the Cassini Probe. 00:09:41.610 --> 00:09:42.710 Look at this. 00:09:42.710 --> 00:09:45.110 This is an image from the Cassini Probe. 00:09:45.110 --> 00:09:47.270 This is an island group. 00:09:47.270 --> 00:09:48.770 The yellow is an island group. 00:09:48.770 --> 00:09:51.270 The blue is a methane sea. 00:09:51.270 --> 00:09:56.530 A sea of liquid methane on the moon of Saturn, Titan. 00:09:56.530 --> 00:09:58.700 So there's liquid methane. 00:09:58.700 --> 00:10:00.730 How does liquid methane form? 00:10:00.730 --> 00:10:05.830 What causes one methane to bond with another methane? 00:10:05.830 --> 00:10:07.630 That's the question that we're wrestling with. 00:10:07.630 --> 00:10:10.580 So let's look at it first in a simpler context. 00:10:10.580 --> 00:10:14.950 Let's look at it with argon. 00:10:14.950 --> 00:10:16.900 So I put argon here. 00:10:16.900 --> 00:10:20.480 It's a spherical atom. 00:10:20.480 --> 00:10:24.180 And the question we had before says, how does one argon bond 00:10:24.180 --> 00:10:28.300 to another argon, as has to be the case in the solid or 00:10:28.300 --> 00:10:29.680 liquid argon. 00:10:29.680 --> 00:10:35.490 So we know that this has a lot of electrons and the atom is 00:10:35.490 --> 00:10:36.380 net neutral. 00:10:36.380 --> 00:10:38.410 But the electrons are in motion. 00:10:38.410 --> 00:10:41.460 If I had an attosecond camera and I went in here and I went, 00:10:41.460 --> 00:10:46.760 snap, I could catch a freeze frame where the electrons 00:10:46.760 --> 00:10:48.100 aren't symmetrically 00:10:48.100 --> 00:10:51.010 distributed around the nucleus. 00:10:51.010 --> 00:10:55.220 This nucleus, the atom is in constant fluctuation. 00:10:55.220 --> 00:10:56.060 But net neutral. 00:10:56.060 --> 00:10:57.960 Time average it's symmetrical. 00:10:57.960 --> 00:11:01.500 So at some moment I might have a preponderance of electrons 00:11:01.500 --> 00:11:03.630 over here at around three o'clock. 00:11:03.630 --> 00:11:08.050 So this end of the argon is a little bit delta minus. 00:11:08.050 --> 00:11:11.240 Which means the other end is delta plus. 00:11:11.240 --> 00:11:13.060 Now what happens if this is delta minus, 00:11:13.060 --> 00:11:14.290 this is delta plus? 00:11:14.290 --> 00:11:19.000 Can you see that the positive end of this argon atom will 00:11:19.000 --> 00:11:21.730 then pull on the electron distribution of the adjacent 00:11:21.730 --> 00:11:25.280 argon atom rendering it delta minus at three o'clock and 00:11:25.280 --> 00:11:26.730 delta plus? 00:11:26.730 --> 00:11:34.350 So this is the dipole in one, induces a dipole in another. 00:11:34.350 --> 00:11:36.460 And why does it occur in the first place? 00:11:36.460 --> 00:11:41.080 It occurs because the electrons are in motion. 00:11:41.080 --> 00:11:46.100 Electrons in motion lead to time fluctuating dipoles. 00:11:46.100 --> 00:11:47.350 They're time fluctuating. 00:11:49.630 --> 00:11:51.800 Time average, there's no net dipole moment. 00:11:51.800 --> 00:11:53.700 I'm not going back on what I said before. 00:11:53.700 --> 00:11:56.000 There's no net dipole moment here, but this is time 00:11:56.000 --> 00:11:59.090 fluctuating dipole. 00:11:59.090 --> 00:12:00.340 Time fluctuating dipole. 00:12:06.560 --> 00:12:08.850 So who was the first to explain this? 00:12:08.850 --> 00:12:16.366 The first to explain this was Fritz London in 1930. 00:12:16.366 --> 00:12:20.530 In 1930 Fritz London gave us the explanation because this 00:12:20.530 --> 00:12:22.630 troubled people for a long time. 00:12:22.630 --> 00:12:26.350 And he did so in a quantitative manner. 00:12:26.350 --> 00:12:30.730 And the mathematics of the treatment are identical to the 00:12:30.730 --> 00:12:34.140 mathematics for the dispersion of light under certain 00:12:34.140 --> 00:12:35.170 conditions. 00:12:35.170 --> 00:12:37.660 This has nothing to do with the dispersion of light. 00:12:37.660 --> 00:12:41.240 The mathematical formulation imitates the formulation of 00:12:41.240 --> 00:12:44.450 the dispersion of light and hence the force here is known 00:12:44.450 --> 00:12:47.200 as the London Dispersion Force. 00:12:49.810 --> 00:12:53.540 So people will say that solid argon is held together by 00:12:53.540 --> 00:12:55.560 London Dispersion Forces. 00:12:55.560 --> 00:13:01.160 Or the bond is known by the name van der Waals. 00:13:01.160 --> 00:13:04.290 We either call them van der Waals bonds or London 00:13:04.290 --> 00:13:05.640 Dispersion Forces. 00:13:05.640 --> 00:13:07.110 Van der Waals was Dutch. 00:13:07.110 --> 00:13:08.490 I know how to spell the word wall. 00:13:08.490 --> 00:13:09.690 This is the dutch spelling. 00:13:09.690 --> 00:13:12.191 W A A L S. 00:13:12.191 --> 00:13:14.900 Van der Waals. 00:13:14.900 --> 00:13:21.100 So in this system here, the London Dispersion Force or the 00:13:21.100 --> 00:13:24.270 van der Waals bond is in fact not the secondary bond. 00:13:24.270 --> 00:13:26.270 It's the primary bond, isn't it? 00:13:26.270 --> 00:13:27.340 It's the only bond. 00:13:27.340 --> 00:13:31.480 So by definition it must be the primary bond. 00:13:31.480 --> 00:13:35.110 But can you see that in every compound, including diamond, 00:13:35.110 --> 00:13:38.900 we have time fluctuating dipoles in all of the atoms? 00:13:38.900 --> 00:13:41.770 It's not just argon that has time fluctuating dipoles. 00:13:41.770 --> 00:13:45.390 Every atom in you and me has time fluctuating dipoles. 00:13:45.390 --> 00:13:48.110 But we're held together by much greater forces. 00:13:48.110 --> 00:13:51.730 So that's why I say that in this case this is 00:13:51.730 --> 00:13:55.540 the dominant force. 00:13:55.540 --> 00:13:57.590 But it's operative in everything. 00:13:57.590 --> 00:14:01.240 Because wherever we have electrons, they're in motion. 00:14:01.240 --> 00:14:04.840 So this is the dominant one. 00:14:04.840 --> 00:14:08.360 Alright so we can look at it in a few other instances. 00:14:08.360 --> 00:14:12.260 So for example we can look at it in the case of iodine. 00:14:12.260 --> 00:14:14.200 We can look at it in the case of methane. 00:14:14.200 --> 00:14:15.080 All the same. 00:14:15.080 --> 00:14:16.680 Time fluctuating dipoles. 00:14:16.680 --> 00:14:18.860 And this is a very, very weak force. 00:14:18.860 --> 00:14:23.450 So the energy in London Dispersion Forces, or van der 00:14:23.450 --> 00:14:32.660 Waals bonds, is proportional to a quantity called the 00:14:32.660 --> 00:14:33.910 polarizability. 00:14:36.480 --> 00:14:39.620 The polarizability is-- 00:14:39.620 --> 00:14:42.950 and this was defined by London-- 00:14:42.950 --> 00:14:47.440 polarizability is the measure of how easy it is to induce 00:14:47.440 --> 00:14:49.440 this dipole. 00:14:49.440 --> 00:14:52.130 A measure of the ease of electron 00:14:52.130 --> 00:14:54.470 displacement within an atom. 00:15:08.190 --> 00:15:15.660 And it depends on, it's influenced by the size and 00:15:15.660 --> 00:15:21.620 it's influenced by the number of electrons in the atom. 00:15:21.620 --> 00:15:23.070 So what do I mean by that? 00:15:23.070 --> 00:15:30.310 Well let's take two systems. Suppose I've got argon and 00:15:30.310 --> 00:15:33.490 I'll go up two members in the same series 00:15:33.490 --> 00:15:34.740 and I've got helium. 00:15:37.160 --> 00:15:39.270 So what are the forces that hold helium together? 00:15:39.270 --> 00:15:40.480 Same thing. 00:15:40.480 --> 00:15:45.100 But the boiling point here is 87 kelvin. 00:15:45.100 --> 00:15:49.190 The boiling point here is 4.2 kelvin. 00:15:49.190 --> 00:15:51.590 Why does this have such a low boiling point? 00:15:51.590 --> 00:15:53.660 Well, polarizability. 00:15:53.660 --> 00:15:55.040 Size-- 00:15:55.040 --> 00:15:56.240 helium is smaller. 00:15:56.240 --> 00:16:00.490 So the degree, the corral in which the electrons can roam 00:16:00.490 --> 00:16:01.810 is smaller. 00:16:01.810 --> 00:16:04.960 So the extent of electron displacement is smaller. 00:16:04.960 --> 00:16:07.830 And secondly there are only two electrons. 00:16:07.830 --> 00:16:10.490 And they're in 1s, so they're tightly held. 00:16:10.490 --> 00:16:16.150 And so the delta minus delta plus capable of being created 00:16:16.150 --> 00:16:20.150 in helium is tiny compared to the delta minus delta plus 00:16:20.150 --> 00:16:22.570 that can be created in argon. 00:16:22.570 --> 00:16:28.120 So the energy goes as polarizability squared and 00:16:28.120 --> 00:16:32.140 divided by r to the sixth, where this is the separation. 00:16:32.140 --> 00:16:36.300 Not the radius but this is separation. 00:16:36.300 --> 00:16:37.430 Dipole separation. 00:16:37.430 --> 00:16:39.440 And this is a font issue. 00:16:39.440 --> 00:16:41.510 This is proportional to alpha. 00:16:41.510 --> 00:16:43.400 So you can tell the difference. 00:16:43.400 --> 00:16:44.870 This is a proportional that's to alpha. 00:16:44.870 --> 00:16:46.940 Of course you can't tell the difference. 00:16:46.940 --> 00:16:48.790 This is contextual. 00:16:48.790 --> 00:16:50.880 If I just wrote this by itself, you don't 00:16:50.880 --> 00:16:54.310 know what it is. 00:16:54.310 --> 00:16:56.150 My goodness you're nervous. 00:16:56.150 --> 00:16:57.590 So nervous. 00:16:57.590 --> 00:16:59.590 All right let's take a look at-- 00:16:59.590 --> 00:17:00.680 here's the cartoons. 00:17:00.680 --> 00:17:01.640 Induced dipole. 00:17:01.640 --> 00:17:04.160 And here's London's paper. 00:17:04.160 --> 00:17:07.710 Here's London's paper as it first appeared in 1930. 00:17:07.710 --> 00:17:10.190 Theory and System of Molecular Forces. 00:17:10.190 --> 00:17:12.930 And here's some cartoons from your book. 00:17:12.930 --> 00:17:15.630 This is helium, showing helium. 00:17:15.630 --> 00:17:17.680 It's kind of funny how the artist shows. 00:17:17.680 --> 00:17:20.150 Like there's these two helium atoms and they're absolutely 00:17:20.150 --> 00:17:23.160 immobile and all of a sudden one of the helium atom starts 00:17:23.160 --> 00:17:25.700 jiggling and then it induces a dipole moment 00:17:25.700 --> 00:17:26.750 in the other one. 00:17:26.750 --> 00:17:30.740 That's not how it happens, but anyway. 00:17:30.740 --> 00:17:32.560 Alright this is hydrogen. 00:17:32.560 --> 00:17:34.150 Same thing as iodine. 00:17:34.150 --> 00:17:37.000 All right so there's delta plus, delta minus. 00:17:37.000 --> 00:17:39.000 Because the electrons are moving even though there's a 00:17:39.000 --> 00:17:40.210 strong covalent bond inside. 00:17:40.210 --> 00:17:43.310 So let me just make the point, I want to make sure people are 00:17:43.310 --> 00:17:45.950 very clear about primary versus secondary bonding. 00:17:45.950 --> 00:17:47.610 So if I look at iodine. 00:17:47.610 --> 00:17:48.660 I2. 00:17:48.660 --> 00:17:50.080 This is a covalent bond. 00:17:50.080 --> 00:17:51.360 It's homonuclear. 00:17:51.360 --> 00:17:54.480 This covalent bond, there's no net dipole moment. 00:17:54.480 --> 00:17:56.840 Here's another iodine. 00:17:56.840 --> 00:17:59.000 But then we have time fluctuating dipoles. 00:17:59.000 --> 00:18:02.690 So this delta minus isn't because this is the bond here. 00:18:02.690 --> 00:18:05.020 This is the primary bond. 00:18:05.020 --> 00:18:07.660 This is the primary bond and it's covalent. 00:18:07.660 --> 00:18:10.110 And this is the secondary bond. 00:18:10.110 --> 00:18:14.073 And the secondary bond is London Dispersion Force or van 00:18:14.073 --> 00:18:17.360 der Waals bond because this is induced dipole. 00:18:22.350 --> 00:18:25.500 So now let's look at-- oh here's another one. 00:18:25.500 --> 00:18:27.970 This one gets on my nerves. 00:18:27.970 --> 00:18:29.460 Oh actually this is good. 00:18:29.460 --> 00:18:31.140 This is this the bad one. 00:18:31.140 --> 00:18:33.300 All right so I'm going to show you polarizability. 00:18:33.300 --> 00:18:38.510 So here's a series of sp3 hybridized chains. 00:18:38.510 --> 00:18:40.580 Propane, octane, icosane. 00:18:40.580 --> 00:18:41.630 They're all the same. 00:18:41.630 --> 00:18:43.330 They look like this. 00:18:43.330 --> 00:18:46.000 Ch is sp3 hybridized. 00:18:46.000 --> 00:18:47.650 And so you just have-- 00:18:47.650 --> 00:18:50.240 so what is that, C 3 H H. 00:18:50.240 --> 00:18:51.650 So it's just-- 00:18:51.650 --> 00:18:54.320 so you have 1, 2, 3 4. so there's hydrogen, hydrogen, 00:18:54.320 --> 00:18:56.780 hydrogen, and on the fourth one I'm going to make it flat 00:18:56.780 --> 00:18:59.130 instead of trying to make a tetrahedron. 00:18:59.130 --> 00:19:00.980 So 1, 2, 3 hydrogens. 00:19:00.980 --> 00:19:02.420 The fourth one is carbon. 00:19:02.420 --> 00:19:05.610 1, 2 hydrogens, carbon carbon. 00:19:05.610 --> 00:19:08.220 1, 2 3 hydrogens. 00:19:08.220 --> 00:19:09.740 So this is C3H8. 00:19:09.740 --> 00:19:12.620 And compare that to the longer one. 00:19:12.620 --> 00:19:16.170 Which is octane, which is C8H18. 00:19:16.170 --> 00:19:21.790 So it's 1, 2, 3, 4, 5, 6, 7, 8. 00:19:21.790 --> 00:19:24.970 And all you have got to do is, 1, 2, 3, 4, 5, 6, 7, 8. 00:19:24.970 --> 00:19:28.930 You put four sticks off of every carbon. 00:19:28.930 --> 00:19:29.900 You can't go wrong. 00:19:29.900 --> 00:19:30.540 You count them up. 00:19:30.540 --> 00:19:33.510 You got C8H18. 00:19:33.510 --> 00:19:34.500 Look at the structures. 00:19:34.500 --> 00:19:35.570 They are the same. 00:19:35.570 --> 00:19:41.220 So how come propane is a gas at room temperature? 00:19:41.220 --> 00:19:43.940 Whereas octane, which is the principal constituent of 00:19:43.940 --> 00:19:47.780 gasoline, is a liquid at room temperature? 00:19:47.780 --> 00:19:50.310 It all comes down to polarizability. 00:19:50.310 --> 00:19:52.060 This one's got a longer corral. 00:19:52.060 --> 00:19:56.320 So if you like the delta minus versus the delta plus, it's 00:19:56.320 --> 00:20:00.540 basically the same here except that separation is bigger. 00:20:00.540 --> 00:20:03.590 All right, so that's pretty good. 00:20:03.590 --> 00:20:05.380 This is the one that gets on my nerves. 00:20:05.380 --> 00:20:06.110 You see this? 00:20:06.110 --> 00:20:08.150 It's exactly what I just showed you. 00:20:08.150 --> 00:20:10.010 So here's methane. 00:20:10.010 --> 00:20:11.460 And there's the propane. 00:20:11.460 --> 00:20:15.120 Here's butane and somewhere between butane and pentane we 00:20:15.120 --> 00:20:17.250 cross the the line at room temperature. 00:20:17.250 --> 00:20:20.960 So pentane is liquid, butane is gas. 00:20:20.960 --> 00:20:24.220 And you keep going up, up, up, and finally if you get to C20 00:20:24.220 --> 00:20:27.420 you go from liquid to solid because now the van der Waals 00:20:27.420 --> 00:20:30.180 forces are strong enough that even at room temperature you 00:20:30.180 --> 00:20:30.810 make a solid. 00:20:30.810 --> 00:20:32.710 It looks like paraffin. 00:20:32.710 --> 00:20:35.450 That's why you can melt paraffin, because it's got 00:20:35.450 --> 00:20:37.280 weak van der Waals forces. 00:20:37.280 --> 00:20:40.420 So temperature disrupts and it reforms. If you try to break a 00:20:40.420 --> 00:20:42.980 covalent bond, you pyrolyze the thing and you 00:20:42.980 --> 00:20:44.320 don't get it back. 00:20:44.320 --> 00:20:47.540 Secondary bonds allow for ready processing. 00:20:47.540 --> 00:20:49.400 Here's what bothers me about this. 00:20:49.400 --> 00:20:52.310 Instead of talking about polarizability, which is a 00:20:52.310 --> 00:20:54.426 physical quantity that means something. 00:20:54.426 --> 00:20:55.480 They say molecular weight. 00:20:55.480 --> 00:20:58.340 Well it's true that these scales, these are heavier and 00:20:58.340 --> 00:20:59.460 it's monotonic. 00:20:59.460 --> 00:21:04.340 But to me what's the relevant physics between the ability to 00:21:04.340 --> 00:21:07.120 form van der Waals bonds and the mass. 00:21:07.120 --> 00:21:08.350 It's just a dumb thing. 00:21:08.350 --> 00:21:10.030 It's not a gravitational effect. 00:21:10.030 --> 00:21:11.760 So that's why this thing is stupid. 00:21:11.760 --> 00:21:14.800 And you see it all over in chemistry books. 00:21:14.800 --> 00:21:16.630 And it's just dumb. 00:21:16.630 --> 00:21:19.040 And if you put that on my exam you're not going to 00:21:19.040 --> 00:21:20.770 get points for it. 00:21:20.770 --> 00:21:22.020 Because that's dumb. 00:21:24.540 --> 00:21:25.810 OK let's go to the next one. 00:21:25.810 --> 00:21:29.270 There's a third type of bonding. 00:21:29.270 --> 00:21:31.950 There are certain things I feel strongly about and that's 00:21:31.950 --> 00:21:33.170 one of them. 00:21:33.170 --> 00:21:35.680 OK so let's look at the third type of secondary bonding. 00:21:35.680 --> 00:21:37.600 The third type of secondary bonding is 00:21:37.600 --> 00:21:40.120 called hydrogen bonding. 00:21:40.120 --> 00:21:43.010 Hydrogen bonding. 00:21:43.010 --> 00:21:45.560 It's a type of secondary bonding. 00:21:45.560 --> 00:21:54.300 And it occurs between hydrogen and the most electronegative 00:21:54.300 --> 00:21:57.760 elements, fluorine, oxygen, nitrogen. 00:22:00.760 --> 00:22:01.410 Why these? 00:22:01.410 --> 00:22:03.700 Because they have very, very high average 00:22:03.700 --> 00:22:05.000 valance electron energy. 00:22:05.000 --> 00:22:07.960 So the average valance electron energy I'm quoting in 00:22:07.960 --> 00:22:11.530 that second column, not megajoules per mole, but in 00:22:11.530 --> 00:22:14.190 sensible units like electron volts. 00:22:14.190 --> 00:22:18.440 And so you can see, when you get up around 18, 19 electron 00:22:18.440 --> 00:22:20.560 volts you cross a threshold. 00:22:20.560 --> 00:22:23.320 And that's the electronegativity as 00:22:23.320 --> 00:22:27.320 represented by average valance electron energy. 00:22:27.320 --> 00:22:30.660 So you can see that as the electronegativity gets beyond 00:22:30.660 --> 00:22:34.330 some threshold value, roughly 3, then you can 00:22:34.330 --> 00:22:36.160 form hydrogen bonds. 00:22:36.160 --> 00:22:44.280 So this is owing to high average valance electron 00:22:44.280 --> 00:22:47.600 energy, or if you like electronegativity. 00:22:47.600 --> 00:22:55.110 Which means very strong polarity in the covalent bond. 00:22:59.290 --> 00:23:02.420 So you say, well there's polar and there's even more polar. 00:23:02.420 --> 00:23:03.960 So let's see what happens. 00:23:03.960 --> 00:23:06.380 So I'm going to use a prototypical value here. 00:23:06.380 --> 00:23:07.860 I'm going to look at HF. 00:23:07.860 --> 00:23:11.250 So if I look at HF let's go through the Lewis structure. 00:23:11.250 --> 00:23:13.180 There's H with it's 1 electron. 00:23:13.180 --> 00:23:14.620 And F with the 7. 00:23:14.620 --> 00:23:17.770 1, 2, 3, 4, 5, 6, 7. 00:23:17.770 --> 00:23:19.570 And so we have a covalent bond here. 00:23:19.570 --> 00:23:22.440 We know fluorine is the most electronegative so we have a 00:23:22.440 --> 00:23:24.120 dipole moment here. 00:23:24.120 --> 00:23:29.060 Now the dipole moment is very strong here. 00:23:29.060 --> 00:23:31.450 This is an accounting procedure to put the two 00:23:31.450 --> 00:23:34.510 electrons, but it no way represents the physical 00:23:34.510 --> 00:23:35.810 position of these electrons. 00:23:35.810 --> 00:23:39.360 They're brought in very close to the fluorine. 00:23:39.360 --> 00:23:42.840 So it's not some symmetrically disposed between H and the F. 00:23:42.840 --> 00:23:45.500 So I can't tell anything about whether HF is a 00:23:45.500 --> 00:23:46.720 solid, liquid or gas. 00:23:46.720 --> 00:23:47.570 Why? 00:23:47.570 --> 00:23:48.890 Because there's only one sitting here. 00:23:48.890 --> 00:23:50.410 I have got to put at least one more. 00:23:50.410 --> 00:23:53.440 Because this is a primary bond. 00:23:53.440 --> 00:23:55.500 And it tells me how H bonds to F. 00:23:55.500 --> 00:23:58.570 It doesn't tell me how one HF bonds to another HF. 00:23:58.570 --> 00:24:01.980 So I'm going to put another HF over here. 00:24:01.980 --> 00:24:03.360 So here's another HF. 00:24:03.360 --> 00:24:06.380 And it's also dipole. 00:24:06.380 --> 00:24:08.910 But there's something special about that. 00:24:08.910 --> 00:24:11.640 Already there's a dipole-dipole interaction. 00:24:11.640 --> 00:24:14.090 But the hydrogen bond is much stronger. 00:24:14.090 --> 00:24:15.290 It's much stronger. 00:24:15.290 --> 00:24:17.390 And why is it stronger? 00:24:17.390 --> 00:24:21.960 The electron in this hydrogen on the right is pulled towards 00:24:21.960 --> 00:24:27.140 the fluorine to such an extent that this hydrogen is so 00:24:27.140 --> 00:24:31.950 denuded of its electrons that it's acting as proton-like. 00:24:31.950 --> 00:24:32.800 It's proton-like. 00:24:32.800 --> 00:24:35.890 Now don't tell people that Professor Sadoway said that 00:24:35.890 --> 00:24:38.370 hydrogen inside an HF is a proton. 00:24:38.370 --> 00:24:41.600 It's not a proton but it's starting to get more nearly 00:24:41.600 --> 00:24:42.435 like a proton. 00:24:42.435 --> 00:24:44.680 Now what do we know about a proton? 00:24:44.680 --> 00:24:46.030 Positive charge. 00:24:46.030 --> 00:24:48.100 Tiny high-charge density. 00:24:48.100 --> 00:24:54.820 So this hydrogen's looking forlornly over at its electron 00:24:54.820 --> 00:24:57.220 that's being hogged by the fluorine to a right. 00:24:57.220 --> 00:24:58.720 And what do we know about these? 00:24:58.720 --> 00:25:00.990 Oh it's time for colored chalk. 00:25:00.990 --> 00:25:02.100 It's time for colored chalk! 00:25:02.100 --> 00:25:03.790 What color are those? 00:25:03.790 --> 00:25:07.730 They're red because they're non-bonding. 00:25:07.730 --> 00:25:10.270 And the bonding are the blue in-between. 00:25:10.270 --> 00:25:13.040 And what do we know about the volume occupied by a 00:25:13.040 --> 00:25:16.010 non-bonding pair versus a bonding pair? 00:25:16.010 --> 00:25:17.090 It's larger. 00:25:17.090 --> 00:25:18.630 Because they're not constrained. 00:25:18.630 --> 00:25:20.990 So not only do we have a non-bonding pair, 00:25:20.990 --> 00:25:22.160 they're not just here. 00:25:22.160 --> 00:25:24.200 They're sort of flopping around. 00:25:24.200 --> 00:25:27.840 Hanging way out and there's this thing here that's almost 00:25:27.840 --> 00:25:30.830 denuded of its electrons, so it starts looking over here 00:25:30.830 --> 00:25:32.910 saying, if I can't get any action over 00:25:32.910 --> 00:25:34.160 here, what about here? 00:25:36.940 --> 00:25:41.645 So that proton starts establishing contact with the 00:25:41.645 --> 00:25:47.100 non-bonding pair of electrons on the adjacent fluorine And 00:25:47.100 --> 00:25:49.560 this is the hydrogen bond. 00:25:49.560 --> 00:25:52.320 The hydrogen bond is here. 00:25:52.320 --> 00:25:54.220 The hydrogen bond is not here. 00:25:54.220 --> 00:25:56.590 If you write this I will give you a 0. 00:25:56.590 --> 00:25:58.880 I'll give you a 0 with a circle around it. 00:25:58.880 --> 00:26:00.260 It's called the doughnut. 00:26:00.260 --> 00:26:02.860 That's what you get when you write something so stupid. 00:26:02.860 --> 00:26:05.200 This is not the hydrogen bond. 00:26:05.200 --> 00:26:06.870 This is the hydrogen bond. 00:26:06.870 --> 00:26:09.350 OK? 00:26:09.350 --> 00:26:10.620 So it works. 00:26:10.620 --> 00:26:12.390 It works. 00:26:12.390 --> 00:26:14.180 Now let's see the effect of it. 00:26:14.180 --> 00:26:15.320 Let's see the effect. 00:26:15.320 --> 00:26:22.190 Alright so here's a cartoon showing that in water the 00:26:22.190 --> 00:26:24.970 hydrogen-oxygen spacing is about 1 angstrom. 00:26:24.970 --> 00:26:29.360 And the hydrogen-oxygen spacing in adjacent water 00:26:29.360 --> 00:26:32.600 molecules can be less than 2 angstroms. So there's 00:26:32.600 --> 00:26:33.660 certainly a difference. 00:26:33.660 --> 00:26:34.610 I mean it can't be the same. 00:26:34.610 --> 00:26:37.120 If it were the same it would be a covalent primary bond. 00:26:37.120 --> 00:26:39.870 You'd have a network. 00:26:39.870 --> 00:26:44.530 Now this is interesting here because this shows the values 00:26:44.530 --> 00:26:46.890 that are given on your periodic table, which were 00:26:46.890 --> 00:26:48.730 obtained without the use the average 00:26:48.730 --> 00:26:50.250 valance electron energies. 00:26:50.250 --> 00:26:51.830 These trends are correct. 00:26:51.830 --> 00:26:52.560 But look at this one. 00:26:52.560 --> 00:26:54.920 They've got chlorine up at 3.16. 00:26:54.920 --> 00:26:56.660 And all of these have been revised. 00:26:56.660 --> 00:26:59.880 Now on a test, just use what you've been given on the 00:26:59.880 --> 00:27:00.740 periodic table. 00:27:00.740 --> 00:27:03.790 But I want you to understand how this is rationalized with 00:27:03.790 --> 00:27:07.400 better data coming from photoelectron spectroscopy. 00:27:07.400 --> 00:27:08.620 So now I want to show you the 00:27:08.620 --> 00:27:11.050 implications of hydrogen bonding. 00:27:11.050 --> 00:27:12.230 The implications. 00:27:12.230 --> 00:27:14.580 So I've got 4 homologous series. 00:27:14.580 --> 00:27:18.130 So they're all element plus hydrogen. 00:27:18.130 --> 00:27:20.930 So let's start with the group 14. 00:27:20.930 --> 00:27:22.180 That's shown here in purple. 00:27:24.820 --> 00:27:27.120 And what do we have? 00:27:27.120 --> 00:27:31.870 All of these, we'll start with methane. 00:27:31.870 --> 00:27:35.440 CH4, so that's a central atom. 00:27:35.440 --> 00:27:36.480 1, 2, 3 4. 00:27:36.480 --> 00:27:37.910 They're all tetrahedral. 00:27:37.910 --> 00:27:39.500 Hydrogens at the corners. 00:27:39.500 --> 00:27:41.160 Non-polar. 00:27:41.160 --> 00:27:43.440 And no hydrogen bonding capability. 00:27:43.440 --> 00:27:48.190 So one methane bonds to another methane by weak van 00:27:48.190 --> 00:27:49.890 der Waals forces. 00:27:49.890 --> 00:27:50.770 That's how it does it. 00:27:50.770 --> 00:27:53.910 It doesn't matter if I substitute the carbon with 00:27:53.910 --> 00:27:56.580 silicon or germanium or tin. 00:27:56.580 --> 00:27:57.840 I can put SnH4. 00:27:57.840 --> 00:28:02.020 And how does SnH4 bond to another SnH4? 00:28:02.020 --> 00:28:05.350 It's just by London Dispersion Forces. 00:28:05.350 --> 00:28:07.120 That's all that's operative here. 00:28:07.120 --> 00:28:10.250 And so we have, what makes sense here, is that the 00:28:10.250 --> 00:28:13.170 heavier, more massive-- 00:28:13.170 --> 00:28:17.040 no, the ones that have greater polarizability have a higher 00:28:17.040 --> 00:28:18.130 boiling point. 00:28:18.130 --> 00:28:20.660 Because their van der Waals forces are stronger. 00:28:20.660 --> 00:28:23.350 That means you have to go to a higher temperature to achieve 00:28:23.350 --> 00:28:24.600 disruption. 00:28:24.600 --> 00:28:28.540 Same temperature, weak van der Waals force: gas. 00:28:28.540 --> 00:28:30.540 Same temperature, strong van der Waals 00:28:30.540 --> 00:28:32.210 force: liquid or solid. 00:28:32.210 --> 00:28:34.870 And you see the boiling point here. 00:28:34.870 --> 00:28:38.080 Monotonic from the lightest to the heaviest. Now let's go to 00:28:38.080 --> 00:28:38.550 the next one. 00:28:38.550 --> 00:28:40.820 Let's go to the green line, group 15. 00:28:40.820 --> 00:28:42.540 Well group 15, what's that look like? 00:28:42.540 --> 00:28:44.690 Let's look at the structure of group 15. 00:28:44.690 --> 00:28:46.250 Group 15 is-- 00:28:46.250 --> 00:28:47.920 ammonia is one of them. 00:28:47.920 --> 00:28:50.230 So we can look at the structure of ammonia. 00:28:50.230 --> 00:28:52.690 And if we use VSEPR we'll end up with something 00:28:52.690 --> 00:28:54.370 that looks like this. 00:28:54.370 --> 00:28:55.350 I'll go through the whole thing. 00:28:55.350 --> 00:28:57.110 You're going to end up with three bonds like this. 00:28:57.110 --> 00:29:00.350 It's a tetrahedral skeleton with a lone pair. 00:29:00.350 --> 00:29:01.420 Ah, colored chalk. 00:29:01.420 --> 00:29:03.610 So now, what happens? 00:29:03.610 --> 00:29:05.180 I can't say anything about this. 00:29:05.180 --> 00:29:07.470 Why can't I say anything about whether this is a solid, 00:29:07.470 --> 00:29:08.730 liquid or a gas? 00:29:08.730 --> 00:29:10.030 It's the only one there. 00:29:10.030 --> 00:29:11.860 I have got to put another one. 00:29:11.860 --> 00:29:14.220 So put another one up here. 00:29:14.220 --> 00:29:15.470 N. 00:29:15.470 --> 00:29:16.120 H. 00:29:16.120 --> 00:29:16.690 H. 00:29:16.690 --> 00:29:19.210 H. 00:29:19.210 --> 00:29:21.990 Same gambit with the hydrogen fluoride. 00:29:21.990 --> 00:29:25.520 This hydrogen sees this lone pair and establishes a 00:29:25.520 --> 00:29:26.720 hydrogen bond. 00:29:26.720 --> 00:29:29.500 And that adds to what otherwise would have been a 00:29:29.500 --> 00:29:30.390 dipole-dipole. 00:29:30.390 --> 00:29:32.500 This has a net dipole along moment, agreed? 00:29:32.500 --> 00:29:34.320 There's a dipole-dipole moment here. 00:29:34.320 --> 00:29:36.230 But this bond is even stronger. 00:29:36.230 --> 00:29:38.750 The hydrogen bond is even stronger than dipole-dipole 00:29:38.750 --> 00:29:39.990 interactions. 00:29:39.990 --> 00:29:43.330 So now let's look at the graph up here. 00:29:43.330 --> 00:29:47.110 So what about in phosphene, PH3? 00:29:47.110 --> 00:29:49.410 No phosphorous isn't electronegative enough. 00:29:49.410 --> 00:29:54.760 So in phosphene, in arsine and in stibine we don't have 00:29:54.760 --> 00:29:56.000 hydrogen bonding. 00:29:56.000 --> 00:29:59.760 So you see this series in the group 4 here? 00:29:59.760 --> 00:30:04.740 It goes monotonic from the heaviest element down to the 00:30:04.740 --> 00:30:05.540 lightest element. 00:30:05.540 --> 00:30:08.800 But here, heaviest, less heavy, less heavy, and the 00:30:08.800 --> 00:30:11.900 lightest element that should be down here is up here. 00:30:11.900 --> 00:30:14.710 Why is the lightest compound not down here? 00:30:14.710 --> 00:30:17.070 Because of the addition of hydrogen bond. 00:30:17.070 --> 00:30:18.980 So ammonia is off the line. 00:30:18.980 --> 00:30:22.050 This line shows the trend based on dipole-dipole 00:30:22.050 --> 00:30:25.210 interactions only. 00:30:25.210 --> 00:30:26.280 And you can see the difference. 00:30:26.280 --> 00:30:30.260 See if you have van der Waals forces alone, versus 00:30:30.260 --> 00:30:32.470 dipole-dipole, dipole-dipole are stronger. 00:30:32.470 --> 00:30:37.760 So SnH4 has a lower boiling point than SbH3. 00:30:37.760 --> 00:30:40.420 I can't predict this but I could ask you, if I gave you 00:30:40.420 --> 00:30:45.430 this data, I'd say, can you explain this to me? 00:30:45.430 --> 00:30:46.390 Let's keep going. 00:30:46.390 --> 00:30:48.420 Let's go to group 16. 00:30:48.420 --> 00:30:51.720 So, telluride, selenide, suphide, 00:30:51.720 --> 00:30:53.890 the oxide, H2O, water. 00:30:53.890 --> 00:30:58.580 It should have a boiling point of minus 100 centigrade were 00:30:58.580 --> 00:31:00.970 it not for hydrogen bonding. 00:31:00.970 --> 00:31:02.470 How does water work? 00:31:02.470 --> 00:31:05.340 Again, SP3 hybridization. 00:31:05.340 --> 00:31:11.000 Oxygen, 1, 2, 3, 4. 00:31:11.000 --> 00:31:12.570 Two lone pairs. 00:31:12.570 --> 00:31:16.440 1, 2, H, H. 00:31:16.440 --> 00:31:17.300 And now what happens? 00:31:17.300 --> 00:31:22.710 I bring another water molecule over here 00:31:22.710 --> 00:31:27.080 and hydrogen bonding. 00:31:27.080 --> 00:31:31.380 And that hydrogen bond raises the temperature, raises the 00:31:31.380 --> 00:31:33.920 requirement for thermal disruption and moves the 00:31:33.920 --> 00:31:37.250 boiling point of water up to 100 degrees celsius. 00:31:37.250 --> 00:31:39.090 It it weren't for this we wouldn't have this 00:31:39.090 --> 00:31:41.020 conversation. 00:31:41.020 --> 00:31:43.580 Because we wouldn't have evolved as a species capable 00:31:43.580 --> 00:31:48.010 of conducting business at room temperature if water boiled at 00:31:48.010 --> 00:31:49.750 minus 100 celsius. 00:31:49.750 --> 00:31:52.166 Hydrogen bonding is critical. 00:31:52.166 --> 00:31:56.040 It's absolutely critical. 00:31:56.040 --> 00:31:58.150 So now you know. 00:31:58.150 --> 00:31:59.990 And this isn't just some little bit of 00:31:59.990 --> 00:32:01.730 pedantry for a professor. 00:32:01.730 --> 00:32:03.080 This is very important. 00:32:03.080 --> 00:32:07.830 Because we're going to learn later that, when it comes to 00:32:07.830 --> 00:32:14.010 biochemistry, we will appreciate that most 00:32:14.010 --> 00:32:17.920 biochemicals are made of carbon, oxygen, 00:32:17.920 --> 00:32:20.670 nitrogen and hydrogen. 00:32:20.670 --> 00:32:23.400 And that means you can have hydrogen bonds here. 00:32:23.400 --> 00:32:24.990 And you can have hydrogen bonds here. 00:32:24.990 --> 00:32:28.160 Hydrogen bonding is critical to life. 00:32:28.160 --> 00:32:32.060 So this is a very important thing to know about. 00:32:32.060 --> 00:32:34.210 OK we have a minute or two. 00:32:34.210 --> 00:32:37.120 So you can see polarizability increases here but hydrogen 00:32:37.120 --> 00:32:38.690 bonding operative here. 00:32:38.690 --> 00:32:40.810 That's explains the mystery. 00:32:40.810 --> 00:32:42.390 All right we're going to jump over this because 00:32:42.390 --> 00:32:43.950 we are out of time. 00:32:43.950 --> 00:32:48.030 And so I will simply show you a few pictures. 00:32:48.030 --> 00:32:49.490 Pictures! 00:32:49.490 --> 00:32:53.770 So this is a conference in Copenhagen in June of 1936. 00:32:53.770 --> 00:32:56.160 And there's Fritz London. 00:32:56.160 --> 00:32:59.490 But look at who else is at the conference. 00:32:59.490 --> 00:33:05.810 Niels Bohr, Wolfgang Pauli, Werner Heisenberg, Max Born. 00:33:05.810 --> 00:33:07.430 Remember the Born Exponent? 00:33:07.430 --> 00:33:09.140 You better remember it for Wednesday. 00:33:09.140 --> 00:33:11.620 This is Lise Meitner, you haven't met her yet. 00:33:11.620 --> 00:33:12.880 We'll get to her. 00:33:12.880 --> 00:33:14.050 This is Walter Stern. 00:33:14.050 --> 00:33:15.510 Stern-Gerlach. 00:33:15.510 --> 00:33:17.470 And this is James Franck. 00:33:17.470 --> 00:33:20.440 That's just the first two rows! 00:33:20.440 --> 00:33:22.930 That's quite a conference. 00:33:22.930 --> 00:33:26.750 Here's a picture of Fritz London sitting on a bench in 00:33:26.750 --> 00:33:29.640 Berlin with Erwin Schrodinger. 00:33:29.640 --> 00:33:32.850 Schrodinger is brooding; he's thinking. 00:33:32.850 --> 00:33:34.270 Fritz London is smiling. 00:33:34.270 --> 00:33:34.980 You know why? 00:33:34.980 --> 00:33:36.330 Because he's figured it out. 00:33:36.330 --> 00:33:37.370 He's figured out. 00:33:37.370 --> 00:33:39.780 It's time-fluctuating dipole, but he's not going to tell 00:33:39.780 --> 00:33:40.570 Schrodinger. 00:33:40.570 --> 00:33:42.810 He's going to say, you have to read about it. 00:33:42.810 --> 00:33:44.340 But you have to go to the library. 00:33:44.340 --> 00:33:46.670 Because if you don't read the primary sources, if you go to 00:33:46.670 --> 00:33:48.560 Wikipedia, you won't find this. 00:33:48.560 --> 00:33:52.520 Because this is not going to be in Wikipedia in 1913. 00:33:52.520 --> 00:33:54.570 OK, last thing-- hold on, hold on, hey wait a minute! 00:33:54.570 --> 00:33:55.990 Where are you going? 00:33:55.990 --> 00:33:57.250 We're not done yet. 00:33:57.250 --> 00:33:59.710 Did the professor say class is dismissed? 00:33:59.710 --> 00:34:01.360 No. 00:34:01.360 --> 00:34:05.720 So here's a biography of Fritz London, which I would 00:34:05.720 --> 00:34:07.940 recommend if you have a few minutes and 00:34:07.940 --> 00:34:09.020 you'd like to unwind. 00:34:09.020 --> 00:34:11.060 Go out, sit in the sun and read something like this. 00:34:11.060 --> 00:34:14.130 It tells the story of how he came up with these ideas. 00:34:14.130 --> 00:34:16.480 The rise of fascism in the '30s. 00:34:16.480 --> 00:34:19.180 He comes to the United States, takes a teaching position at 00:34:19.180 --> 00:34:20.510 Duke University. 00:34:20.510 --> 00:34:23.020 All of the people that he met along the way. 00:34:23.020 --> 00:34:25.450 All these people that we study, all this stuff, it's 00:34:25.450 --> 00:34:27.360 all there from his perspective. 00:34:27.360 --> 00:34:29.480 And the perspective of his biographer. 00:34:29.480 --> 00:34:30.670 Plus the pictures. 00:34:30.670 --> 00:34:33.460 So anyway, primary sources. 00:34:33.460 --> 00:34:35.970 Go read the primary sources. 00:34:35.970 --> 00:34:38.010 All right, class dismissed.