WEBVTT 00:00:00.090 --> 00:00:02.430 The following content is provided under a Creative 00:00:02.430 --> 00:00:03.820 Commons license. 00:00:03.820 --> 00:00:06.030 Your support will help MIT OpenCourseWare 00:00:06.030 --> 00:00:10.150 continue to offer high quality educational resources for free. 00:00:10.150 --> 00:00:12.690 To make a donation, or to view additional materials 00:00:12.690 --> 00:00:16.445 from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:16.445 --> 00:00:17.070 at ocw.mit.edu. 00:00:26.260 --> 00:00:28.660 PROFESSOR: So, moving to today's handout, 00:00:28.660 --> 00:00:32.150 we're going to talk about crystal field theory. 00:00:32.150 --> 00:00:34.570 And we're going to talk about how 00:00:34.570 --> 00:00:37.390 the shapes of those orbitals can explain 00:00:37.390 --> 00:00:40.180 the special properties of transition metals, 00:00:40.180 --> 00:00:42.790 like color and magnetism. 00:00:42.790 --> 00:00:45.250 And really, as I said, the transition metals 00:00:45.250 --> 00:00:48.460 have amazing properties that can be absolutely gorgeous. 00:00:48.460 --> 00:00:50.500 They can do incredible things. 00:00:50.500 --> 00:00:52.480 They're very, very useful elements. 00:00:52.480 --> 00:00:54.910 I like to think of them as the super heroes 00:00:54.910 --> 00:00:56.650 of the periodic table. 00:00:56.650 --> 00:01:00.560 They're doing all the really spectacular stuff. 00:01:00.560 --> 00:01:02.740 So, today, we're going to talk about colors. 00:01:02.740 --> 00:01:05.560 And we're going to talk about whether things are magnetic, 00:01:05.560 --> 00:01:08.200 if they're paramagnetic, or diamagnetic. 00:01:08.200 --> 00:01:10.180 So, transition metals. 00:01:10.180 --> 00:01:13.840 I talked before about how they're useful in biology. 00:01:13.840 --> 00:01:18.480 They're also useful in terms of their beautiful colors. 00:01:18.480 --> 00:01:22.240 So, in the old days before you generated floor plans 00:01:22.240 --> 00:01:24.850 and drawings for buildings, on a computer 00:01:24.850 --> 00:01:27.130 you did blueprints for something. 00:01:27.130 --> 00:01:31.360 And the blue in the blueprint is actually a transition metal 00:01:31.360 --> 00:01:33.010 complex. 00:01:33.010 --> 00:01:37.150 And also, currently, it's an active area of research 00:01:37.150 --> 00:01:42.160 to design new imaging agents to use in MRIs, or to image 00:01:42.160 --> 00:01:43.780 the heart, or other things. 00:01:43.780 --> 00:01:47.170 And a lot of these also involve transition metal complexes. 00:01:47.170 --> 00:01:49.960 And the reason why they're useful, say, in an MRI 00:01:49.960 --> 00:01:52.510 is because they can have magnetic properties. 00:01:52.510 --> 00:01:55.340 So, scientists see these beautiful colors. 00:01:55.340 --> 00:01:57.700 It's kind of obvious that the transition metals often 00:01:57.700 --> 00:01:59.680 have these incredible colors. 00:01:59.680 --> 00:02:02.620 And they can put the transition metals in something 00:02:02.620 --> 00:02:05.792 with a magnet and see that they have magnetic properties. 00:02:05.792 --> 00:02:07.000 So these things were obvious. 00:02:07.000 --> 00:02:09.789 And then chemists want to try to understand why it's true. 00:02:09.789 --> 00:02:12.400 Why this particular metal behaves this way, or this metal 00:02:12.400 --> 00:02:14.110 has this particular color. 00:02:14.110 --> 00:02:16.390 And they like to try to categorize them and come up 00:02:16.390 --> 00:02:19.780 with theories that help to explain what 00:02:19.780 --> 00:02:21.580 they're observing in nature. 00:02:21.580 --> 00:02:23.740 And so, today, we're going to talk about one 00:02:23.740 --> 00:02:26.380 of those theories, which is Ligand field theory. 00:02:26.380 --> 00:02:28.660 And I'm also going to differentiate that-- or Crystal 00:02:28.660 --> 00:02:31.970 field theory and differentiate it from Ligand field theory. 00:02:31.970 --> 00:02:33.880 So both of these theories, again, 00:02:33.880 --> 00:02:38.140 are an attempt to explain the properties that we observe. 00:02:38.140 --> 00:02:40.970 And the idea behind it is pretty simple. 00:02:40.970 --> 00:02:44.470 You have a metal ion and a set of ligands around it. 00:02:44.470 --> 00:02:49.390 And if you compare the energy levels of that free metal ion-- 00:02:49.390 --> 00:02:52.270 so here's a free metal ion-- with that metal 00:02:52.270 --> 00:02:54.380 ion in a coordination complex-- here 00:02:54.380 --> 00:02:57.220 is quite a pretty coordination complex-- 00:02:57.220 --> 00:03:00.100 the energy levels are different. 00:03:00.100 --> 00:03:02.920 That's really all these theories are getting at. 00:03:02.920 --> 00:03:05.260 That there's a change when you bring ligands 00:03:05.260 --> 00:03:08.710 in around a transition metal. 00:03:08.710 --> 00:03:11.650 It changes the energy levels of those d orbitals. 00:03:11.650 --> 00:03:14.350 And if we understand how those de-energy levels change, 00:03:14.350 --> 00:03:16.600 we can understand a lot about the properties 00:03:16.600 --> 00:03:21.760 of that particular metal in that coordination environment. 00:03:21.760 --> 00:03:25.750 So energy levels are altered. 00:03:25.750 --> 00:03:28.750 So there's these two theories: Crystal field theory 00:03:28.750 --> 00:03:30.910 and Ligand field theory. 00:03:30.910 --> 00:03:34.840 Crystal field theory is the more simple one. 00:03:34.840 --> 00:03:40.170 It just considers the ionic description of the metal ligand 00:03:40.170 --> 00:03:41.230 bond. 00:03:41.230 --> 00:03:44.067 And so we talked about ionic bonds. 00:03:44.067 --> 00:03:46.150 And mostly you're just kind of thinking about them 00:03:46.150 --> 00:03:48.104 as these point charges. 00:03:48.104 --> 00:03:49.520 And you have plus, you have minus, 00:03:49.520 --> 00:03:51.820 and they attract each other. 00:03:51.820 --> 00:03:54.627 Covalent bonding is a bit more complicated. 00:03:54.627 --> 00:03:56.710 Start talking about hybridization and other things 00:03:56.710 --> 00:03:57.670 like that. 00:03:57.670 --> 00:03:59.630 So Crystal field theory is really simple. 00:03:59.630 --> 00:04:02.200 It just considers the ionic nature. 00:04:02.200 --> 00:04:03.730 And it does pretty well. 00:04:03.730 --> 00:04:06.230 It can explain a lot, but not everything. 00:04:06.230 --> 00:04:09.790 Ligand field theory has the covalent and the ionic, 00:04:09.790 --> 00:04:11.350 so it's a more complete description 00:04:11.350 --> 00:04:13.030 of that metal ligand bond. 00:04:13.030 --> 00:04:15.670 But this is more of an advanced topic. 00:04:15.670 --> 00:04:17.570 I just want you to know that that exists. 00:04:17.570 --> 00:04:20.680 So if you take 503 here in organic chemistry, 00:04:20.680 --> 00:04:22.660 we'll talk more about Ligand field theory. 00:04:22.660 --> 00:04:25.570 In this class we're just going to do Crystal field theory. 00:04:25.570 --> 00:04:27.880 But I like Crystal field theory because I like it 00:04:27.880 --> 00:04:30.310 when something that's pretty simple theory 00:04:30.310 --> 00:04:31.720 can explain a lot. 00:04:31.720 --> 00:04:34.540 I think a lot of nature can be explained by this. 00:04:34.540 --> 00:04:36.640 So if you really want to understand 00:04:36.640 --> 00:04:39.610 particular properties of a specific compound, 00:04:39.610 --> 00:04:41.681 you probably want a more complicated way 00:04:41.681 --> 00:04:42.430 to think about it. 00:04:42.430 --> 00:04:44.990 But if in general you just want to say, 00:04:44.990 --> 00:04:48.880 why can some cobalt complexes can be so many colors? 00:04:48.880 --> 00:04:51.700 Crystal field theory works really well for that. 00:04:51.700 --> 00:04:54.430 All right, so Crystal field theory. 00:04:54.430 --> 00:04:57.730 Very simple idea behind this. 00:04:57.730 --> 00:04:59.380 It's almost disappointing, I think. 00:04:59.380 --> 00:04:59.980 But it's OK. 00:04:59.980 --> 00:05:01.960 You can go, yeah we're studying, you know, 00:05:01.960 --> 00:05:03.670 Crystal field theory in class. 00:05:03.670 --> 00:05:06.190 Yeah, you don't have to tell people that it's 00:05:06.190 --> 00:05:08.450 a really, very simple idea. 00:05:08.450 --> 00:05:12.310 So the idea is that the ligands are negative charges. 00:05:12.310 --> 00:05:15.550 They're like this big blob of negativity. 00:05:15.550 --> 00:05:19.570 And those ligands, with their lone pairs, 00:05:19.570 --> 00:05:21.310 their negativeness or negative charge-- 00:05:21.310 --> 00:05:24.970 they got those extra lone pair electrons-- are going to be 00:05:24.970 --> 00:05:28.780 repulsive to those d orbitals. 00:05:28.780 --> 00:05:30.330 Negative point charges, you bring 00:05:30.330 --> 00:05:34.380 a d orbital, And a lone pair, and there's some repulsion. 00:05:34.380 --> 00:05:36.090 That's basically it. 00:05:36.090 --> 00:05:38.160 Negative point charge repulsion. 00:05:38.160 --> 00:05:39.930 That's all that you have to think about 00:05:39.930 --> 00:05:41.430 with Crystal field theory. 00:05:41.430 --> 00:05:45.000 So it sounds really impressive to tell people you're 00:05:45.000 --> 00:05:47.190 doing Crystal field theory. 00:05:47.190 --> 00:05:50.460 And you can neglect to mention that it's just 00:05:50.460 --> 00:05:54.090 a really very, very simple idea that, sort of, negative charges 00:05:54.090 --> 00:05:54.810 repel each other. 00:05:54.810 --> 00:05:56.395 That's really all it is. 00:05:56.395 --> 00:05:58.020 All right, so we're going to talk first 00:05:58.020 --> 00:06:00.240 about the octahedral case. 00:06:00.240 --> 00:06:02.820 And then we're going to get into some other geometries 00:06:02.820 --> 00:06:05.010 on Friday, so that's going to be exciting. 00:06:05.010 --> 00:06:07.678 But here's our octahedral molecule. 00:06:10.290 --> 00:06:14.580 And here we have it, here. 00:06:14.580 --> 00:06:19.140 And I can think about the metal in the middle, M to the N plus. 00:06:19.140 --> 00:06:23.100 So this just indicates it's any metal and to the oxidation 00:06:23.100 --> 00:06:24.480 number. 00:06:24.480 --> 00:06:26.400 And the black balls, here, are the ligands 00:06:26.400 --> 00:06:29.470 and we can think of those as negative charges. 00:06:29.470 --> 00:06:35.970 So here, we have drawn sort of this octohedral shape 00:06:35.970 --> 00:06:38.490 around the metal in the middle. 00:06:38.490 --> 00:06:40.500 And we can think about these NH3 groups 00:06:40.500 --> 00:06:41.990 as these negative point charges. 00:06:41.990 --> 00:06:45.430 So these dots here are negative point charges. 00:06:45.430 --> 00:06:47.940 And so now if we think about the shapes of the d orbitals 00:06:47.940 --> 00:06:52.240 again, that we just looked at, we can look over here and say, 00:06:52.240 --> 00:06:55.552 wow, some of those ligands that are those negative point 00:06:55.552 --> 00:06:59.250 charges are basically right there up 00:06:59.250 --> 00:07:01.020 against that d orbital. 00:07:01.020 --> 00:07:03.960 Pointing directly toward the d orbital. 00:07:03.960 --> 00:07:05.880 So that's going to be pretty repulsive. 00:07:05.880 --> 00:07:09.690 The point charge is right there next to the d orbital. 00:07:09.690 --> 00:07:12.580 This also has a point charge kind of right toward it 00:07:12.580 --> 00:07:14.130 along z. 00:07:14.130 --> 00:07:18.670 But these, the point charges, are on axis. 00:07:18.670 --> 00:07:22.470 Octahedral, you have your ligands along z, 00:07:22.470 --> 00:07:24.840 along x, and along y. 00:07:24.840 --> 00:07:28.260 But these sets of orbitals, the negative point charges, 00:07:28.260 --> 00:07:30.930 aren't pointing directly at the d orbitals. 00:07:30.930 --> 00:07:32.310 So one could think about the fact 00:07:32.310 --> 00:07:35.820 that these are not going to be not as much repulsion. 00:07:35.820 --> 00:07:37.470 This is a lot of repulsion. 00:07:37.470 --> 00:07:40.770 All right, so let's go through orbital set by orbital set 00:07:40.770 --> 00:07:44.250 and consider how repulsive it's going to be 00:07:44.250 --> 00:07:46.740 compared to the other orbitals. 00:07:46.740 --> 00:07:51.110 OK, so if we look over here at the octahedral case-- 00:07:51.110 --> 00:07:53.844 and I have both, these drawings were on the first page 00:07:53.844 --> 00:07:54.510 of your handout. 00:07:54.510 --> 00:07:56.580 This is on the second page. 00:07:56.580 --> 00:07:57.830 But you can think about them. 00:07:57.830 --> 00:07:59.790 Here it's drawn more where they're all 00:07:59.790 --> 00:08:01.590 drawn kind of the same way. 00:08:01.590 --> 00:08:04.260 Here it's sort of moved a little so you can see better. 00:08:04.260 --> 00:08:07.080 So we can keep both of these in mind. 00:08:07.080 --> 00:08:10.320 So, again, the negative point charges around the orbitals 00:08:10.320 --> 00:08:10.890 here. 00:08:10.890 --> 00:08:13.320 And on these drawings, I have these little negative signs 00:08:13.320 --> 00:08:17.527 pointing in to give you a sense of where those negative point 00:08:17.527 --> 00:08:19.620 charge ligands are coming. 00:08:19.620 --> 00:08:23.670 So we have our dz2 and we can see the negative point charge 00:08:23.670 --> 00:08:27.120 right toward this maximum amplitude along z. 00:08:27.120 --> 00:08:29.170 So that's going to be repulsive. 00:08:29.170 --> 00:08:34.710 Dx2, y2, same thing, point charges right toward these. 00:08:34.710 --> 00:08:41.130 So the ligands point directly at dz2 and dx2 minus y2. 00:08:41.130 --> 00:08:44.110 So there's a large repulsion there. 00:08:44.110 --> 00:08:47.310 And, in this particular case, in the octahedral case, 00:08:47.310 --> 00:08:51.660 what turns out to be true, both of these are stabilized. 00:08:51.660 --> 00:08:54.900 And they're destabilized, actually, by the same amount. 00:08:54.900 --> 00:08:58.170 And so that means that they have the same energy, which 00:08:58.170 --> 00:09:00.120 we learned before, means that there-- you 00:09:00.120 --> 00:09:03.000 could say they're degenerate with respect to each other. 00:09:03.000 --> 00:09:06.120 So both of these, big repulsion. 00:09:06.120 --> 00:09:10.890 Both are destabilized by those negative charges, 00:09:10.890 --> 00:09:12.900 by the same amount. 00:09:12.900 --> 00:09:16.950 And you have much more repulsion, and much more 00:09:16.950 --> 00:09:20.670 destabilization, for these two orbitals compared 00:09:20.670 --> 00:09:22.770 to the other set of orbitals. 00:09:22.770 --> 00:09:25.870 The ones that are 45 degrees off axis. 00:09:25.870 --> 00:09:27.660 So now, let's look at these and look 00:09:27.660 --> 00:09:30.150 at where the point charges are. 00:09:30.150 --> 00:09:32.214 So this is the picture in your handout. 00:09:32.214 --> 00:09:33.630 I just kind of put these up there, 00:09:33.630 --> 00:09:37.200 too, so you can think about where those point charges are 00:09:37.200 --> 00:09:39.420 for octahedral geometry. 00:09:39.420 --> 00:09:41.790 So the ligands, again now, are not 00:09:41.790 --> 00:09:46.050 pointing right at the orbitals. 00:09:46.050 --> 00:09:47.820 They're off axis. 00:09:47.820 --> 00:09:51.180 Because of ligands are on axis, and the orbitals are off axis, 00:09:51.180 --> 00:09:53.470 and they're not directly pointing toward each other. 00:09:53.470 --> 00:09:55.944 And so this is a lot less repulsive 00:09:55.944 --> 00:09:57.360 than the other situation where you 00:09:57.360 --> 00:09:59.340 have the ligands and the orbitals, 00:09:59.340 --> 00:10:02.440 both on axis, pointing right toward each other. 00:10:02.440 --> 00:10:05.340 So now, this is why it's important to know which 00:10:05.340 --> 00:10:08.894 orbitals are 45 degree off axis because we, now, 00:10:08.894 --> 00:10:10.560 can think about the fact that there will 00:10:10.560 --> 00:10:13.680 be less repulsion in this case. 00:10:13.680 --> 00:10:20.790 So, we can say then, that the xy, xz, and yz orbitals 00:10:20.790 --> 00:10:28.560 are stabilized compared to dz2 and dx2 minus y2 orbitals. 00:10:28.560 --> 00:10:31.810 And they're also stabilized by the same amount. 00:10:31.810 --> 00:10:33.810 So these are also degenerate. 00:10:33.810 --> 00:10:37.400 With respect to each other, they have the same energy. 00:10:37.400 --> 00:10:41.490 All right, so we have these now two sets of orbital types. 00:10:41.490 --> 00:10:44.460 Two orbitals that are destabilized, 00:10:44.460 --> 00:10:48.630 and three orbitals that are stabilized, compared to them. 00:10:48.630 --> 00:10:55.160 So now let's draw what's known as an Octahedral Crystal Field 00:10:55.160 --> 00:10:59.160 Splitting Diagram and think about what's happening. 00:10:59.160 --> 00:11:01.150 So, I have some over there. 00:11:01.150 --> 00:11:02.630 Ignore those for now. 00:11:02.630 --> 00:11:05.550 I'm going to draw one over here. 00:11:05.550 --> 00:11:09.080 So first, we have energy going up. 00:11:09.080 --> 00:11:13.070 And we have a situation we first want to think about. 00:11:13.070 --> 00:11:17.510 What would be the case, say, if you had ligands everywhere? 00:11:17.510 --> 00:11:21.230 Not just on the axis, not octahedral geometry, 00:11:21.230 --> 00:11:22.710 but just everywhere. 00:11:22.710 --> 00:11:25.160 So if you had ligands everywhere, 00:11:25.160 --> 00:11:28.440 you would have your 5 d orbitals, 00:11:28.440 --> 00:11:29.810 all would have the same energy. 00:11:29.810 --> 00:11:31.940 Because all of them-- there's ligands everywhere-- 00:11:31.940 --> 00:11:33.740 all of them would be experiencing 00:11:33.740 --> 00:11:36.320 the same amount of repulsion. 00:11:36.320 --> 00:11:42.060 So this would be the case for a Spherical Crystal Field. 00:11:47.180 --> 00:11:52.400 And I like to think about this with this prop. 00:11:52.400 --> 00:11:54.006 I had this before as an s orbital. 00:11:54.006 --> 00:11:55.380 It's convenient for that as well. 00:11:55.380 --> 00:11:59.540 But, really, what it is, is a Hypothetical Spherical Crystal 00:11:59.540 --> 00:12:00.890 Field. 00:12:00.890 --> 00:12:03.320 Because these are all little ligands. 00:12:03.320 --> 00:12:05.750 And you can see these little ligands are 00:12:05.750 --> 00:12:08.120 completely symmetric around. 00:12:08.120 --> 00:12:09.590 And if you feel sort of the inside, 00:12:09.590 --> 00:12:10.870 there's something in there. 00:12:10.870 --> 00:12:13.220 Well that, of course, is a metal ion. 00:12:13.220 --> 00:12:15.830 And these ligands are completely around. 00:12:15.830 --> 00:12:19.250 So all the d orbitals are equally 00:12:19.250 --> 00:12:22.340 feeling the repulsive effects of these ligands. 00:12:22.340 --> 00:12:25.190 And so they all have the same energy 00:12:25.190 --> 00:12:26.840 in this hypothetical case. 00:12:26.840 --> 00:12:29.312 I was so excited when I found this at CVS. 00:12:29.312 --> 00:12:30.770 And I went up and I was, like, wow, 00:12:30.770 --> 00:12:34.430 you sell hypothetical spherical crystal fields here. 00:12:34.430 --> 00:12:36.410 And the person was not amused. 00:12:36.410 --> 00:12:42.470 OK, so now what happens-- because this is not the case. 00:12:42.470 --> 00:12:43.267 This doesn't exist. 00:12:43.267 --> 00:12:44.350 This is just hypothetical. 00:12:44.350 --> 00:12:47.360 It looks like it exists, but it doesn't. 00:12:47.360 --> 00:12:49.410 This is what really exists. 00:12:49.410 --> 00:12:51.230 You have certain geometries. 00:12:51.230 --> 00:12:53.120 The ligands come together with the metal 00:12:53.120 --> 00:12:55.160 and form particular geometries. 00:12:55.160 --> 00:12:57.860 And we already talked about what those geometries are. 00:12:57.860 --> 00:12:59.750 There's not a whole lot of variation. 00:12:59.750 --> 00:13:01.580 We get the same kinds of geometries. 00:13:01.580 --> 00:13:04.700 And octahedral is the most common geometry 00:13:04.700 --> 00:13:06.650 for a transition metal complex. 00:13:06.650 --> 00:13:08.250 So what's going to happen here? 00:13:08.250 --> 00:13:12.860 So, the ligands will now split the energy of the d orbitals. 00:13:12.860 --> 00:13:16.460 And three of them are going to go down in energy. 00:13:16.460 --> 00:13:21.110 They're going to be stabilized compared to the two that 00:13:21.110 --> 00:13:24.560 go up in energy. 00:13:24.560 --> 00:13:28.360 So the three that go-- are stabilized again, 00:13:28.360 --> 00:13:36.195 are dxy, dyz, and dxz. 00:13:36.195 --> 00:13:38.570 If you can't read this, it all should be in your handout. 00:13:38.570 --> 00:13:41.020 So it's OK, you don't have to read my handwriting. 00:13:41.020 --> 00:13:44.810 And just kind of-- just follow along in your notes. 00:13:44.810 --> 00:13:47.730 And then the ones that have the most repulsion are 00:13:47.730 --> 00:13:54.770 dx2 minus y2 and dz2 up here. 00:13:54.770 --> 00:13:57.150 All right, so two go up and energy. 00:13:57.150 --> 00:13:58.670 There's more repulsion. 00:13:58.670 --> 00:14:01.010 Three go down in energy. 00:14:01.010 --> 00:14:04.110 And instead of writing all of those d's 00:14:04.110 --> 00:14:07.790 and x's and y's, they're little abbreviations that people use. 00:14:07.790 --> 00:14:14.850 So they call these two orbitals-- the eg orbitals. 00:14:14.850 --> 00:14:17.630 So those are the ones that are destabilized. 00:14:17.630 --> 00:14:19.760 And the ones that are stabilized are 00:14:19.760 --> 00:14:23.510 called t2g orbitals, which is going 00:14:23.510 --> 00:14:27.350 to make our nomenclature easier later on. 00:14:27.350 --> 00:14:29.180 OK, these two again. 00:14:29.180 --> 00:14:32.034 Same energy I tried to draw a straight line between them. 00:14:32.034 --> 00:14:33.950 They're degenerate with respect to each other. 00:14:33.950 --> 00:14:37.040 These three of the same energy, again, degenerate with respect 00:14:37.040 --> 00:14:38.180 to each other. 00:14:38.180 --> 00:14:43.400 And then the difference of how much it's being split. 00:14:43.400 --> 00:14:46.580 This energy difference has a special name. 00:14:46.580 --> 00:14:49.610 It's sort of this delta sub o. 00:14:49.610 --> 00:14:51.960 And this is the octahedral. 00:14:54.970 --> 00:14:56.390 And that's the o. 00:14:56.390 --> 00:14:58.730 The o is octahedral. 00:14:58.730 --> 00:15:10.370 Crystal field splitting energy because it's 00:15:10.370 --> 00:15:13.280 the energy that shows the splitting of the crystal field. 00:15:13.280 --> 00:15:16.620 So that's at least a good name for it. 00:15:16.620 --> 00:15:21.020 All right, now, overall this energy 00:15:21.020 --> 00:15:23.310 is going to be conserved. 00:15:23.310 --> 00:15:27.550 So the orbitals that go-- that are destabilized-- 00:15:27.550 --> 00:15:30.270 and two go up and three go down. 00:15:30.270 --> 00:15:38.420 So we can also put that the two that go up, go up by 3/5 times 00:15:38.420 --> 00:15:41.780 the octahedral splitting energy. 00:15:41.780 --> 00:15:45.670 And the three that go down-- are stabilized-- 00:15:45.670 --> 00:15:49.750 go down by minus 2/5 times the octahedral crystal 00:15:49.750 --> 00:15:51.010 field, splitting energy. 00:15:51.010 --> 00:15:52.330 So this is why I have it in your notes, 00:15:52.330 --> 00:15:54.413 because you can't really read my writing too well. 00:15:54.413 --> 00:15:59.020 So two go-- are destabilized, up by 3/5. 00:15:59.020 --> 00:16:03.910 Three, or stabilized, down by 2/5 in energy. 00:16:03.910 --> 00:16:08.770 All right, so now what controls the overall size 00:16:08.770 --> 00:16:10.744 of this splitting energy? 00:16:10.744 --> 00:16:11.410 How do you know? 00:16:11.410 --> 00:16:12.727 Is it a small splitting? 00:16:12.727 --> 00:16:14.560 Is this, you know, should I have drawn this, 00:16:14.560 --> 00:16:15.768 that they're just a tiny bit? 00:16:15.768 --> 00:16:18.760 Or is it, like, could it be a really large splitting? 00:16:18.760 --> 00:16:21.920 What determines the splitting? 00:16:21.920 --> 00:16:25.870 Or The magnitude of this splitting energy. 00:16:25.870 --> 00:16:29.920 So what determines that are the nature of ligands. 00:16:29.920 --> 00:16:34.330 So some ligands are really repulsive. 00:16:34.330 --> 00:16:35.740 Big splitting. 00:16:35.740 --> 00:16:38.740 Others-- eh-- you barely notice they're there. 00:16:38.740 --> 00:16:40.000 Very little splitting. 00:16:40.000 --> 00:16:42.550 There's always some splitting. 00:16:42.550 --> 00:16:44.590 But it can be different. 00:16:44.590 --> 00:16:47.470 So the relative ability of a ligand 00:16:47.470 --> 00:16:50.950 to split the crystal field gives rise 00:16:50.950 --> 00:16:54.610 to what's known as the Spectrochemical Series. 00:16:54.610 --> 00:16:57.760 So it's the relative ability of common ligands 00:16:57.760 --> 00:17:02.020 to split the energies of these d orbitals. 00:17:02.020 --> 00:17:04.869 And this is what gives rise to these beautiful colors. 00:17:04.869 --> 00:17:08.560 So all of those colors are possible from cobalt compounds. 00:17:08.560 --> 00:17:10.150 Every single one of them. 00:17:10.150 --> 00:17:12.520 Because different ligands will split the energy 00:17:12.520 --> 00:17:16.460 different amounts, giving rise to those different colors. 00:17:16.460 --> 00:17:19.750 So we have what's known as Strong field ligands. 00:17:19.750 --> 00:17:22.810 And as that name would suggest, Strong field ligands 00:17:22.810 --> 00:17:24.310 are going to have a large splitting. 00:17:24.310 --> 00:17:25.780 They're very strong. 00:17:25.780 --> 00:17:29.530 They split to a large degree. 00:17:29.530 --> 00:17:35.110 And we have Weak field ligands. 00:17:35.110 --> 00:17:37.090 Weak field don't cause much of a splitting. 00:17:37.090 --> 00:17:43.390 It's a small delta sub o, small octahedral crystal 00:17:43.390 --> 00:17:46.780 field splitting energy. 00:17:46.780 --> 00:17:48.970 All right, so which common ligands 00:17:48.970 --> 00:17:52.780 fall into which categories? 00:17:52.780 --> 00:17:55.750 Here is the list that we talk about pretty much 00:17:55.750 --> 00:17:56.540 in this class. 00:17:56.540 --> 00:17:58.630 I don't think there are any other ones. 00:17:58.630 --> 00:18:00.970 So what I will put on your equation sheet-- 00:18:00.970 --> 00:18:02.390 your equation sheet for exam four 00:18:02.390 --> 00:18:03.880 is lots of cool, interesting things 00:18:03.880 --> 00:18:06.310 that were not in the other equation sheets. 00:18:06.310 --> 00:18:08.220 And I will tell you which are weak field, 00:18:08.220 --> 00:18:09.970 and which are strong field, but I will not 00:18:09.970 --> 00:18:12.816 tell you that weak field means that it's a small splitting. 00:18:12.816 --> 00:18:14.440 That's something that you need to know. 00:18:14.440 --> 00:18:16.960 Or that strong field means it's a large splitting. 00:18:16.960 --> 00:18:19.360 But I will tell you that your halides down here 00:18:19.360 --> 00:18:21.520 are weak field ligands. 00:18:21.520 --> 00:18:24.370 Water and hydroxide are sort of in the middle. 00:18:24.370 --> 00:18:26.410 And they can have all sorts of different colors 00:18:26.410 --> 00:18:29.110 when they're bound to coordination complexes. 00:18:29.110 --> 00:18:30.640 So they're sort of intermediate. 00:18:30.640 --> 00:18:33.640 And then your strong field ligands-- with your strongest 00:18:33.640 --> 00:18:34.900 being cyanide. 00:18:34.900 --> 00:18:37.020 Very strong field ligand. 00:18:37.020 --> 00:18:41.890 All right, so, if your metal has a weak field, 00:18:41.890 --> 00:18:44.380 intermediate field, or strong field ligand, 00:18:44.380 --> 00:18:46.030 it can have very different properties. 00:18:46.030 --> 00:18:48.190 Especially very different colors. 00:18:48.190 --> 00:18:51.310 Also, it could be paramagnetic or diamagnetic, 00:18:51.310 --> 00:18:53.680 depending on this. 00:18:53.680 --> 00:18:56.980 So let's take a look at two different iron complexes. 00:18:56.980 --> 00:19:00.490 We have iron with six waters, with a plus 3 00:19:00.490 --> 00:19:04.500 charge, and iron with cyanide, with six cyanides 00:19:04.500 --> 00:19:05.860 and a minus 3. 00:19:05.860 --> 00:19:08.860 So the first thing we have to do is figure out 00:19:08.860 --> 00:19:11.980 the oxidation number of the iron and the d count. 00:19:11.980 --> 00:19:13.650 And that's our first clicker question. 00:19:34.619 --> 00:19:36.410 All right, let's just take 10 more seconds. 00:19:55.450 --> 00:19:58.110 OK. 00:19:58.110 --> 00:19:58.660 There you go. 00:19:58.660 --> 00:19:59.790 There's the right one. 00:19:59.790 --> 00:20:01.360 A little more people say that. 00:20:01.360 --> 00:20:02.100 All right. 00:20:02.100 --> 00:20:04.570 So, let's take a look at this. 00:20:04.570 --> 00:20:06.240 And you will get used to thinking 00:20:06.240 --> 00:20:09.210 about what the charges are on the various ligands. 00:20:09.210 --> 00:20:13.260 So here, we know that the overall charge 00:20:13.260 --> 00:20:17.460 has to be the same as the overall charge on the complex. 00:20:17.460 --> 00:20:19.180 Water is neutral. 00:20:19.180 --> 00:20:22.500 And so that means this iron has to be plus 3. 00:20:22.500 --> 00:20:24.840 Cyanide has a minus charge, and you 00:20:24.840 --> 00:20:27.720 may have noticed that in the list of ligands, 00:20:27.720 --> 00:20:30.390 that it was cn minus. 00:20:30.390 --> 00:20:33.090 That when I just showed you the strong field ligands. 00:20:33.090 --> 00:20:35.170 So there's six minus ones. 00:20:35.170 --> 00:20:37.410 And so it's also plus 3, to give you 00:20:37.410 --> 00:20:40.320 an overall charge of minus 3. 00:20:40.320 --> 00:20:43.370 And as you do these problems, and problem sets, 00:20:43.370 --> 00:20:45.150 you'll become very familiar with what 00:20:45.150 --> 00:20:47.280 the charges of the different ligands are. 00:20:47.280 --> 00:20:50.760 So overall, plus 3, 8 minus 3, is 5. 00:20:50.760 --> 00:20:51.915 Is a d5 system. 00:20:54.812 --> 00:20:56.270 So the next thing we're going to do 00:20:56.270 --> 00:20:58.790 is we're going to draw our octahedral crystal field 00:20:58.790 --> 00:21:01.680 splitting diagrams and place electrons. 00:21:01.680 --> 00:21:08.720 And I already have, over here, a starting place for those. 00:21:08.720 --> 00:21:13.160 So we're doing here our d5 system. 00:21:13.160 --> 00:21:17.720 And we have a diagram with a small splitting 00:21:17.720 --> 00:21:20.340 and one with a large splitting. 00:21:20.340 --> 00:21:22.260 So with the small splitting, is that 00:21:22.260 --> 00:21:25.617 going to be a weak field or a strong field? 00:21:25.617 --> 00:21:26.700 That will be a weak field. 00:21:29.240 --> 00:21:32.990 And when we have a large splitting, 00:21:32.990 --> 00:21:37.120 that is a strong field 00:21:37.120 --> 00:21:41.030 OK, so which of our two compounds 00:21:41.030 --> 00:21:43.860 is going to be the weak field compound? 00:21:43.860 --> 00:21:45.120 And which will be the strong? 00:21:45.120 --> 00:21:46.800 Let's do strong first. 00:21:46.800 --> 00:21:50.660 Which one has a strong field ligand? 00:21:50.660 --> 00:21:52.220 Cyanide one. 00:21:52.220 --> 00:22:01.400 So this one is going to be our cyanide complex because it 00:22:01.400 --> 00:22:03.500 has the strong field. 00:22:03.500 --> 00:22:05.580 And so this one would be the water. 00:22:05.580 --> 00:22:06.750 Water's intermediate. 00:22:06.750 --> 00:22:09.600 So you kind of have to see what the comparison is first 00:22:09.600 --> 00:22:10.460 before you decide. 00:22:13.390 --> 00:22:17.370 Oops, six bracket 3 plus. 00:22:17.370 --> 00:22:19.080 OK, so here we have water. 00:22:19.080 --> 00:22:20.450 There, we have cyanide. 00:22:20.450 --> 00:22:24.050 So a weak, or intermediate field, versus a strong field. 00:22:24.050 --> 00:22:27.572 All right, now we need to put electrons in here. 00:22:27.572 --> 00:22:28.405 So I have to decide. 00:22:28.405 --> 00:22:31.050 I have five electrons I'm going to play with. 00:22:31.050 --> 00:22:33.600 And I could put them in here. 00:22:33.600 --> 00:22:34.600 Let's just start here. 00:22:34.600 --> 00:22:36.570 Do one, two, three. 00:22:36.570 --> 00:22:39.630 Now the question is, where am I going to put four? 00:22:39.630 --> 00:22:42.330 Am I going to put four down here? 00:22:42.330 --> 00:22:44.180 Or put it up here? 00:22:44.180 --> 00:22:50.480 And so, here, it depends on, if I put it down here on pairing-- 00:22:50.480 --> 00:22:52.926 and, you know, the seats on the bus-- people 00:22:52.926 --> 00:22:54.300 don't really want to sit together 00:22:54.300 --> 00:22:55.341 if there are empty seats. 00:22:55.341 --> 00:22:58.110 Now there are empty seats up here. 00:22:58.110 --> 00:23:03.020 So, the question is, is it going to take more energy to pair? 00:23:03.020 --> 00:23:05.030 Or more energy to put it up here? 00:23:05.030 --> 00:23:09.530 Now, if this is a weak field, which it is, 00:23:09.530 --> 00:23:11.940 then that's not all that far away. 00:23:11.940 --> 00:23:13.940 You get on a bus and you see a seat in the back. 00:23:13.940 --> 00:23:15.481 You'd rather sit up front, but you're 00:23:15.481 --> 00:23:18.230 like, than you have to sit with someone, so you go to the back. 00:23:18.230 --> 00:23:20.660 So that's what happens with a weak field. 00:23:20.660 --> 00:23:24.240 The other energy levels are just not that far away, 00:23:24.240 --> 00:23:26.300 so you go up there. 00:23:26.300 --> 00:23:30.270 And if I kind of put this up-- move it up 00:23:30.270 --> 00:23:34.590 for just a second-- and then I'll say, so this rule here, 00:23:34.590 --> 00:23:36.870 and I'm going to kind of cover this up again. 00:23:36.870 --> 00:23:38.820 But maybe I'll just put it down here. 00:23:38.820 --> 00:23:39.920 This is in your notes. 00:23:39.920 --> 00:23:44.340 So here, the octahedral crystal field splitting energy 00:23:44.340 --> 00:23:50.588 is less than we call PE, which is pairing energy. 00:23:53.900 --> 00:23:57.910 So, it's not that far away. 00:23:57.910 --> 00:24:00.230 Just put them singly, to the full extent 00:24:00.230 --> 00:24:04.590 possible, before you pair. 00:24:04.590 --> 00:24:07.550 So that's what happens with a weak field. 00:24:07.550 --> 00:24:10.110 And we also can think about how we're putting 00:24:10.110 --> 00:24:11.900 in our electrons parallel. 00:24:11.900 --> 00:24:15.410 We're not putting them in all sorts of different directions. 00:24:15.410 --> 00:24:18.037 And we're not-- if we do pair-- we're going to not pair-- 00:24:18.037 --> 00:24:18.870 we're going to pair. 00:24:18.870 --> 00:24:20.390 So one's up, one's down. 00:24:20.390 --> 00:24:22.400 So all the rules that we learned earlier 00:24:22.400 --> 00:24:23.400 are going to apply here. 00:24:23.400 --> 00:24:25.650 So this is good, good review. 00:24:25.650 --> 00:24:32.734 So now, in this case, we can put in our first three electrons. 00:24:32.734 --> 00:24:33.650 And what do you think? 00:24:33.650 --> 00:24:35.180 Do you think I'm going to pair? 00:24:35.180 --> 00:24:40.160 Or do you think I'm going to go up there? 00:24:40.160 --> 00:24:41.580 What do you think? 00:24:41.580 --> 00:24:42.270 I'm going pair. 00:24:42.270 --> 00:24:44.300 Yeah, I'm definitely going to pair. 00:24:44.300 --> 00:24:46.960 So I'm going to put my other two over here. 00:24:46.960 --> 00:24:51.500 So in this case, the pair-- the octahedral crystal field 00:24:51.500 --> 00:24:53.130 splitting energy-- it's so much fun 00:24:53.130 --> 00:24:55.430 to say that so many times-- is greater 00:24:55.430 --> 00:24:57.270 than the pairing energy. 00:24:57.270 --> 00:24:59.850 And, so, in this case, there might be empty seats. 00:24:59.850 --> 00:25:01.630 But maybe it's a long train. 00:25:01.630 --> 00:25:05.580 And there is-- you can sit in car one with someone else, 00:25:05.580 --> 00:25:07.050 or carry all your luggage. 00:25:07.050 --> 00:25:08.390 Why did you bring so much? 00:25:08.390 --> 00:25:10.160 You're just going home for Thanksgiving. 00:25:10.160 --> 00:25:13.590 All the way, 23 cars later, to an empty seat in the back. 00:25:13.590 --> 00:25:15.460 You're just not going to do it. 00:25:15.460 --> 00:25:17.300 You don't have enough energy. 00:25:17.300 --> 00:25:20.210 You'd rather sit with somebody up front. 00:25:20.210 --> 00:25:23.010 So how you put in electrons depends if it's 00:25:23.010 --> 00:25:24.600 a weak field or strong field. 00:25:24.600 --> 00:25:29.510 It depends on whether it takes just a little bit of energy, 00:25:29.510 --> 00:25:30.980 and it's worse to pair. 00:25:30.980 --> 00:25:32.850 Or takes a huge amount of energy. 00:25:32.850 --> 00:25:35.630 There's a big splitting, a really strong field. 00:25:35.630 --> 00:25:37.940 And in that case, you're going to pair first. 00:25:37.940 --> 00:25:40.590 And you're only going to put electrons up here when 00:25:40.590 --> 00:25:43.810 you're completely done here. 00:25:43.810 --> 00:25:48.250 All right, so now we have placed our electrons. 00:25:48.250 --> 00:25:50.380 We've talked about pairing energy. 00:25:50.380 --> 00:25:53.980 And we've talked about the weak and strong fields. 00:25:53.980 --> 00:25:56.560 And now we can talk about some notation. 00:25:56.560 --> 00:25:58.370 Because there's always notation. 00:25:58.370 --> 00:26:01.270 So this is what we've done already. 00:26:01.270 --> 00:26:07.450 And now we're going to do step E, which is to our d to the n 00:26:07.450 --> 00:26:09.400 electron configurations. 00:26:09.400 --> 00:26:13.630 Every diagram, there's different configurations every time. 00:26:13.630 --> 00:26:17.560 So this one we do using those little kind of cool terms 00:26:17.560 --> 00:26:19.400 I told you about. 00:26:19.400 --> 00:26:24.160 So instead of writing, I have one electron in dxy, 00:26:24.160 --> 00:26:28.900 one electron in dxz, and one electron in dyz, 00:26:28.900 --> 00:26:34.750 I can just say, I have three in the t2g set of orbitals 00:26:34.750 --> 00:26:36.800 that is a lot more convenient. 00:26:36.800 --> 00:26:39.760 So you would just say t2g3. 00:26:39.760 --> 00:26:41.420 And I have two up here. 00:26:41.420 --> 00:26:43.780 So EG2. 00:26:43.780 --> 00:26:45.310 And that's how you would do this. 00:26:45.310 --> 00:26:48.310 I think this is our last configuration for electrons 00:26:48.310 --> 00:26:53.390 in a diagram that you're going to be learning. 00:26:53.390 --> 00:26:54.510 There's a lot of them. 00:26:54.510 --> 00:26:57.130 OK, so then over here, we would just 00:26:57.130 --> 00:27:00.310 say we have five, all in the lower energy 00:27:00.310 --> 00:27:03.360 set, all in our t2g. 00:27:03.360 --> 00:27:08.740 All right, one other thing, part F that you can be asked about. 00:27:08.740 --> 00:27:14.830 Which is the crystal field stabilization energy. 00:27:14.830 --> 00:27:21.100 Not to be confused with the crystal field splitting energy. 00:27:21.100 --> 00:27:22.780 They both start with an s. 00:27:22.780 --> 00:27:25.660 So I don't know why you wouldn't be confused by that. 00:27:25.660 --> 00:27:29.440 But if you can try to remember it, that would be awesome. 00:27:29.440 --> 00:27:33.820 It's often abbreviated, CFSE. 00:27:33.820 --> 00:27:37.420 And this is the energy change that's 00:27:37.420 --> 00:27:41.050 due to going from this hypothetical spherical crystal 00:27:41.050 --> 00:27:44.560 field, where all the d orbitals have the same energy. 00:27:44.560 --> 00:27:46.330 And if you put your electrons in here, 00:27:46.330 --> 00:27:50.590 where they'd all have the same energy, to the diff energy 00:27:50.590 --> 00:27:53.290 difference, when you're placing energies-- when you're placing 00:27:53.290 --> 00:27:56.830 the electrons in lower energy orbitals or higher energy 00:27:56.830 --> 00:27:57.550 orbitals. 00:27:57.550 --> 00:28:00.750 So you're thinking about how much more stabilized 00:28:00.750 --> 00:28:04.370 is the system if all of the electrons are down here. 00:28:04.370 --> 00:28:06.010 That's going to be stabilized compared 00:28:06.010 --> 00:28:07.330 to where they were here. 00:28:07.330 --> 00:28:09.610 But if a lot of them are up here, 00:28:09.610 --> 00:28:11.980 then there'd be less stabilization due 00:28:11.980 --> 00:28:13.660 to this splitting. 00:28:13.660 --> 00:28:18.250 All right, so let's look at how we would write that. 00:28:18.250 --> 00:28:23.350 So we have three electrons that are down in energy. 00:28:23.350 --> 00:28:27.250 And they are down in energy by minus 2/5 times 00:28:27.250 --> 00:28:31.490 the octahedral crystal field splitting energy. 00:28:31.490 --> 00:28:34.150 And that's because the overall energy is maintained. 00:28:34.150 --> 00:28:37.060 Three go down in energy, so that's minus 2. 00:28:37.060 --> 00:28:39.580 Two go up in energy, again, plus 3. 00:28:39.580 --> 00:28:42.880 And then we have two electrons up here. 00:28:42.880 --> 00:28:47.890 So 2 times plus 3/5, again times the octahedral crystal field 00:28:47.890 --> 00:28:49.430 splitting energy. 00:28:49.430 --> 00:28:52.930 And so overall, our stabilization is zero. 00:28:52.930 --> 00:28:55.240 There's no stabilization of this system, 00:28:55.240 --> 00:28:58.570 compared to the system here, because three electrons are 00:28:58.570 --> 00:29:01.030 down in energy, and two are up. 00:29:01.030 --> 00:29:03.730 All right, so now you might imagine 00:29:03.730 --> 00:29:06.820 that this is going to have some extra stabilization. 00:29:06.820 --> 00:29:08.500 And you would be right. 00:29:08.500 --> 00:29:10.160 So we would write this like this. 00:29:10.160 --> 00:29:12.880 We'd say there are five electrons down. 00:29:12.880 --> 00:29:16.070 Stabilized in the lower energy orbitals. 00:29:16.070 --> 00:29:20.320 So five times minus 2/5, times the optic single crystal field 00:29:20.320 --> 00:29:24.610 splitting energy, minus 10/5 times the octahedral crystal 00:29:24.610 --> 00:29:26.200 field splitting energy. 00:29:26.200 --> 00:29:29.470 And sometimes you'll also see, kind of a little truth, 00:29:29.470 --> 00:29:34.570 that there's also some energy kind of due to this pairing. 00:29:34.570 --> 00:29:39.910 So you might see an indication that there's pairing energy 00:29:39.910 --> 00:29:41.500 for two sets of electrons. 00:29:41.500 --> 00:29:42.880 So sometimes that's included. 00:29:42.880 --> 00:29:43.720 Sometimes it's not. 00:29:43.720 --> 00:29:45.880 The questions were asked to indicate, you know, 00:29:45.880 --> 00:29:48.130 how many of sets of electrons ended up 00:29:48.130 --> 00:29:51.970 being paired for that stabilization? 00:29:51.970 --> 00:29:55.630 All right, so we can think about, 00:29:55.630 --> 00:29:58.632 again, we have this nomenclature here. 00:29:58.632 --> 00:30:00.340 And we can think about the stabilization. 00:30:00.340 --> 00:30:03.100 So there's a big difference between these iron compounds. 00:30:03.100 --> 00:30:05.705 One, there's no stabilization due to the splitting. 00:30:05.705 --> 00:30:07.330 And the other one, there's quite a bit, 00:30:07.330 --> 00:30:09.430 because all the electrons ended down 00:30:09.430 --> 00:30:10.994 in the lower energy orbitals. 00:30:13.900 --> 00:30:16.780 So now it's time to try some of these on your own. 00:30:16.780 --> 00:30:19.510 See if you got the rules down. 00:30:19.510 --> 00:30:24.460 And let's try some clicker questions. 00:30:24.460 --> 00:30:25.690 Clicker question one. 00:30:48.520 --> 00:30:49.500 OK, 10 more seconds. 00:31:04.000 --> 00:31:05.810 All right, yes. 00:31:05.810 --> 00:31:11.150 So the trick here is to remind yourself what weak field meant. 00:31:11.150 --> 00:31:13.730 And in this case, if it's a weak field, that 00:31:13.730 --> 00:31:16.790 meant that you place all the electrons singly-- 00:31:16.790 --> 00:31:19.580 there are seven of them-- to the fullest extent possible 00:31:19.580 --> 00:31:20.390 before you pair. 00:31:20.390 --> 00:31:23.180 You still have to pair. 00:31:23.180 --> 00:31:25.580 But here you put more-- you filled these up 00:31:25.580 --> 00:31:26.870 before you paired. 00:31:26.870 --> 00:31:29.210 And this is a strong field diagram 00:31:29.210 --> 00:31:31.040 where you put-- you paired all of them 00:31:31.040 --> 00:31:33.500 possible before you put any of them up here. 00:31:33.500 --> 00:31:36.260 And to make it harder, I made-- drew them the same. 00:31:36.260 --> 00:31:37.790 So you have to really pay attention 00:31:37.790 --> 00:31:39.500 to what weak field meant. 00:31:39.500 --> 00:31:41.840 But this would be the version of the strong field. 00:31:41.840 --> 00:31:44.640 And this is just wrong. 00:31:44.640 --> 00:31:47.270 So, you wouldn't have more electrons 00:31:47.270 --> 00:31:50.120 up in the higher energy orbitals for really any reason 00:31:50.120 --> 00:31:51.250 whatsoever. 00:31:51.250 --> 00:31:54.324 OK, so let's try the next one. 00:32:12.960 --> 00:32:15.030 All right, let's just take 10 more seconds 00:32:15.030 --> 00:32:17.636 and we'll mention high spin and we'll do this problem. 00:32:29.140 --> 00:32:29.830 Yeah. 00:32:29.830 --> 00:32:31.121 People did very well with that. 00:32:31.121 --> 00:32:34.910 OK, so I forgot to mention that I ran out of room to draw. 00:32:34.910 --> 00:32:37.030 So I decided that was enough. 00:32:37.030 --> 00:32:39.940 So it's in your notes though, for here. 00:32:39.940 --> 00:32:44.620 And when you have a very small, weak field, 00:32:44.620 --> 00:32:48.640 and you end up putting all the electrons in singly, 00:32:48.640 --> 00:32:51.490 that is also known-- and I'll move this up a little 00:32:51.490 --> 00:32:57.080 bit-- as a high spin. 00:32:57.080 --> 00:33:00.730 And so you have a lot of unpaired electrons 00:33:00.730 --> 00:33:01.960 in this case. 00:33:01.960 --> 00:33:11.185 So that is the maximum number of unpaired electrons. 00:33:14.804 --> 00:33:16.720 And it's easier to remember because, you know, 00:33:16.720 --> 00:33:17.594 you have these spins. 00:33:17.594 --> 00:33:18.640 There's a lot of spins. 00:33:18.640 --> 00:33:22.540 There are a lot of single spins and they're also high up. 00:33:22.540 --> 00:33:26.410 And this is a low spin case. 00:33:26.410 --> 00:33:28.810 When you have a strong field. 00:33:28.810 --> 00:33:32.770 Because you like to pair first before putting them singly. 00:33:32.770 --> 00:33:36.970 So this is going to give you the minimum number 00:33:36.970 --> 00:33:41.462 of unpaired electrons. 00:33:47.080 --> 00:33:49.840 So high spin, weak field. 00:33:49.840 --> 00:33:53.380 Low spin often comes from a strong field. 00:33:53.380 --> 00:33:55.540 So it's about whether you have maximum number 00:33:55.540 --> 00:33:57.400 of unpaired electrons, which you do 00:33:57.400 --> 00:34:00.340 with weak field, high spin, minimum number. 00:34:00.340 --> 00:34:02.440 All right, so let's look at this one then. 00:34:02.440 --> 00:34:06.340 So it's a high field one. 00:34:06.340 --> 00:34:08.830 So that means that you're going to have the maximum number 00:34:08.830 --> 00:34:11.659 of unpaired electrons. 00:34:11.659 --> 00:34:14.620 So this would be diagram here. 00:34:14.620 --> 00:34:19.420 And I can put that over here. 00:34:19.420 --> 00:34:23.050 And so then you have to figure out how to write that. 00:34:23.050 --> 00:34:30.340 And so you would have three ones down in energy, minus 2/5 times 00:34:30.340 --> 00:34:34.030 the octahedral crystal field splitting energy. 00:34:34.030 --> 00:34:40.270 And you would have one electron, up by 3/5 times 00:34:40.270 --> 00:34:44.080 the octahedral crystal field splitting energy. 00:34:44.080 --> 00:34:50.710 So minus 6 plus 3 is minus 3/5 times the octahedral crystal 00:34:50.710 --> 00:34:52.480 field splitting energy. 00:34:52.480 --> 00:34:56.350 So this problem required you to know what high spin was, 00:34:56.350 --> 00:35:00.490 then correctly identify the weak field diagram, 00:35:00.490 --> 00:35:04.420 and then figure out the crystal field stabilization energy. 00:35:04.420 --> 00:35:06.820 So that was actually quite good. 00:35:06.820 --> 00:35:12.250 And maybe you'll remember the high spin, low spin definitions 00:35:12.250 --> 00:35:13.630 as well. 00:35:13.630 --> 00:35:23.140 OK, so let's just do one more thing and then 00:35:23.140 --> 00:35:27.010 we'll-- because we've just been talking about high spin. 00:35:27.010 --> 00:35:31.180 So back to our compounds, we're going to talk about magnetism. 00:35:31.180 --> 00:35:33.910 And then we're going to come back next time 00:35:33.910 --> 00:35:34.840 and talk about color. 00:35:34.840 --> 00:35:38.240 And we have some cool demos for color which we'll do next time. 00:35:38.240 --> 00:35:41.440 But before we leave from this, our iron compounds, 00:35:41.440 --> 00:35:44.470 we want to think about whether they're paramagnetic, which is 00:35:44.470 --> 00:35:45.970 attracted by a magnetic field. 00:35:45.970 --> 00:35:48.330 Or diamagnetic, repelled by a magnetic field. 00:35:48.330 --> 00:35:50.740 And we've already talked about this in this class. 00:35:50.740 --> 00:35:54.310 So, based-- and here are our iron diagrams again. 00:35:54.310 --> 00:35:56.200 Based on these diagrams, would you 00:35:56.200 --> 00:36:00.770 expect these to be paramagnetic, or diamagnetic? 00:36:00.770 --> 00:36:01.860 Paramedic. 00:36:01.860 --> 00:36:05.550 And that was because it has what kind of electrons? 00:36:05.550 --> 00:36:06.700 Paired, right. 00:36:06.700 --> 00:36:09.370 So here you just have to remember your definition 00:36:09.370 --> 00:36:10.860 of paramagnetic. 00:36:10.860 --> 00:36:12.760 It has unpaired electrons. 00:36:12.760 --> 00:36:16.390 Now, normally, things with a weak field, and a high spin, 00:36:16.390 --> 00:36:18.610 are going to be more likely to be paramagnetic, 00:36:18.610 --> 00:36:20.530 have unpaired electrons. 00:36:20.530 --> 00:36:23.500 Things that have a very strong field. 00:36:23.500 --> 00:36:26.230 And so you pair first, before you fill up. 00:36:26.230 --> 00:36:28.570 Minimum number-- low spin, minimum number 00:36:28.570 --> 00:36:32.050 of unpaired electrons are more likely to be diamagnetic. 00:36:32.050 --> 00:36:34.240 But in this case, we didn't have enough electrons, 00:36:34.240 --> 00:36:36.849 so they're still both paramagnetic. 00:36:36.849 --> 00:36:38.140 All right, so we'll stop there. 00:36:38.140 --> 00:36:41.620 We'll come back and talk about the colors of those iron 00:36:41.620 --> 00:36:42.700 compounds. 00:36:42.700 --> 00:36:45.850 And more colors and cool demos on Friday. 00:36:45.850 --> 00:36:46.660 Don't miss Friday. 00:36:46.660 --> 00:36:50.290 Remember, Friday, double clicker competition. 00:36:50.290 --> 00:36:54.820 The team that comes in second is automatically in the playoffs. 00:37:02.070 --> 00:37:02.653 Are you-- 00:37:02.653 --> 00:37:04.990 AUDIENCE: We're at 166, but it stopped. 00:37:04.990 --> 00:37:07.290 PROFESSOR: OK, let's just take 10 more a seconds 00:37:07.290 --> 00:37:08.700 on the clicker question. 00:37:22.900 --> 00:37:25.812 All right, let's quiet down. 00:37:28.410 --> 00:37:31.440 I'd like to see the 85% that's good. 00:37:31.440 --> 00:37:34.140 Of course it doesn't distinguish all that much for the clicker 00:37:34.140 --> 00:37:35.060 competition today. 00:37:37.830 --> 00:37:40.190 So if we can quiet down a little bit. 00:37:43.890 --> 00:37:46.710 People can just yell out. 00:37:46.710 --> 00:37:49.410 What would this have been the correct answer to? 00:37:49.410 --> 00:37:51.390 What should the question have said for that 00:37:51.390 --> 00:37:53.840 to be the correct answer? 00:37:53.840 --> 00:37:55.290 Low spin, right. 00:37:55.290 --> 00:37:59.520 So low spin-- shh-- is the minimum number 00:37:59.520 --> 00:38:01.900 of unpaired electrons. 00:38:01.900 --> 00:38:04.320 And so this is the low spin. 00:38:04.320 --> 00:38:07.900 High spin is the maximum number of unpaired electrons. 00:38:07.900 --> 00:38:09.930 So this is the correct diagram. 00:38:09.930 --> 00:38:12.820 And C is wrong. 00:38:12.820 --> 00:38:15.570 It's not correct for either high or low spin. 00:38:15.570 --> 00:38:18.600 Because we have two electrons here 00:38:18.600 --> 00:38:20.430 that would have the same four quantum 00:38:20.430 --> 00:38:22.710 numbers, which is not allowed. 00:38:22.710 --> 00:38:27.070 OK, so let's continue on with the lecture. 00:38:27.070 --> 00:38:30.330 And we are talking about colors. 00:38:30.330 --> 00:38:32.370 So, we're talking-- we're talking 00:38:32.370 --> 00:38:34.740 about the colors of the two iron compounds 00:38:34.740 --> 00:38:36.630 that we had described before. 00:38:36.630 --> 00:38:38.010 And so let's continue. 00:38:38.010 --> 00:38:41.460 And when we talk about colors, we need to do a little review 00:38:41.460 --> 00:38:45.210 and think about what's happening when a substance gives off 00:38:45.210 --> 00:38:47.370 a color. 00:38:47.370 --> 00:38:50.340 And so, when a substance-- whether a substance is going 00:38:50.340 --> 00:38:54.750 to absorb a photon or not, to excite an electron to a higher 00:38:54.750 --> 00:38:57.180 energy level that then, when it falls back, 00:38:57.180 --> 00:38:59.314 will emit a beautiful light. 00:38:59.314 --> 00:39:01.230 We can talk about whether a substance is going 00:39:01.230 --> 00:39:02.790 to absorb a photon or not. 00:39:02.790 --> 00:39:06.600 And it will if the energy of that photon 00:39:06.600 --> 00:39:09.850 is equal to the difference in that energy level. 00:39:09.850 --> 00:39:11.470 So we talked about this before. 00:39:11.470 --> 00:39:14.700 Exam one, exam two, somewhere around there. 00:39:14.700 --> 00:39:17.820 And so, we saw this equation a lot. 00:39:17.820 --> 00:39:20.760 That the energy equals Planck's constant, times the frequency 00:39:20.760 --> 00:39:21.780 of the light. 00:39:21.780 --> 00:39:24.750 And now we can take that same gorgeous equation 00:39:24.750 --> 00:39:26.610 and add a little thing to it. 00:39:26.610 --> 00:39:28.320 So we can add that that energy is 00:39:28.320 --> 00:39:32.130 going to be equal to the octahedral crystal field 00:39:32.130 --> 00:39:34.240 splitting energy. 00:39:34.240 --> 00:39:37.380 And so, a substance, one of these transition metal 00:39:37.380 --> 00:39:41.010 complexes, will absorb a photon of light 00:39:41.010 --> 00:39:44.550 if the energy of that photon is equal to this splitting 00:39:44.550 --> 00:39:45.510 difference. 00:39:45.510 --> 00:39:49.800 And if it is, it can promote an electron between a lower 00:39:49.800 --> 00:39:51.630 and a higher state. 00:39:51.630 --> 00:39:53.192 So this is all the same kind of thing 00:39:53.192 --> 00:39:55.650 that we talked about before, but now we're just applying it 00:39:55.650 --> 00:39:58.020 to transition metals. 00:39:58.020 --> 00:40:01.770 So, let's think about what's happening with our iron 00:40:01.770 --> 00:40:03.150 complex. 00:40:03.150 --> 00:40:06.270 And if we say, had a low frequency 00:40:06.270 --> 00:40:08.550 of light that was absorbed, what would 00:40:08.550 --> 00:40:10.080 be true about the wavelength? 00:40:10.080 --> 00:40:12.420 Would it be long or short? 00:40:12.420 --> 00:40:13.500 It would be long. 00:40:13.500 --> 00:40:15.880 And how do we know this? 00:40:15.880 --> 00:40:19.820 We know this from the fact that if you're talking about light, 00:40:19.820 --> 00:40:23.650 the speed of light equals the wavelength times the frequency. 00:40:23.650 --> 00:40:26.100 So if you have a low frequency, then you're 00:40:26.100 --> 00:40:28.610 going to have a long wavelength. 00:40:28.610 --> 00:40:32.190 So our long wavelengths, then, are on this 00:40:32.190 --> 00:40:36.600 and over here, sort of our yellow, orange, red, with red 00:40:36.600 --> 00:40:39.670 being our longest wavelength. 00:40:39.670 --> 00:40:42.960 So if, then, we have a high frequency of light absorbed, 00:40:42.960 --> 00:40:45.240 then the wavelength would be short. 00:40:45.240 --> 00:40:47.280 So it'll be short wavelength absorbed. 00:40:47.280 --> 00:40:49.020 And so, again, our short wavelengths 00:40:49.020 --> 00:40:52.820 are down here, with our shortest being the violet wavelength. 00:40:52.820 --> 00:40:56.910 All right, and now, the color that you actually see 00:40:56.910 --> 00:41:01.020 is the one that is complimentary to the color that 00:41:01.020 --> 00:41:03.270 is of the absorbed light. 00:41:03.270 --> 00:41:07.170 So we're going to think about how big those energy 00:41:07.170 --> 00:41:09.420 differences are, whether that translates 00:41:09.420 --> 00:41:12.720 to high frequency, low frequency, long wavelength, 00:41:12.720 --> 00:41:15.660 short length-- wavelength for the absorb light. 00:41:15.660 --> 00:41:18.570 And then, the complimentary of the absorb light 00:41:18.570 --> 00:41:21.810 is the light that we see, the transmitted light. 00:41:21.810 --> 00:41:24.180 All right, so let's think about the iron complexes 00:41:24.180 --> 00:41:26.040 that we talked about. 00:41:26.040 --> 00:41:30.330 And we had a high spin, or a higher spin, iron water 00:41:30.330 --> 00:41:30.920 complex. 00:41:30.920 --> 00:41:36.650 Water is actually kind of an intermediate field ligand. 00:41:36.650 --> 00:41:41.760 And it absorbs low frequency, or a longer wavelength of light. 00:41:41.760 --> 00:41:45.230 And so it's going to transmit on the shorter end of things. 00:41:45.230 --> 00:41:48.140 Again, water sort of an intermediate field. 00:41:48.140 --> 00:41:53.340 But in this case, it was less strong than our other one, 00:41:53.340 --> 00:41:55.410 which was cyanide, which is very strong. 00:41:55.410 --> 00:41:58.330 And, actually, these iron water complexes 00:41:58.330 --> 00:42:00.311 can appear actually a variety of colors. 00:42:00.311 --> 00:42:02.435 If they're solid, they're more of this pale violet. 00:42:02.435 --> 00:42:05.960 So definitely a very short color wavelength that we're seeing. 00:42:05.960 --> 00:42:07.940 But in solution, and depending on the pH, 00:42:07.940 --> 00:42:11.540 they can be sort of yellowish, brownish color. 00:42:11.540 --> 00:42:14.460 But the strong field ligand, remember the other compound 00:42:14.460 --> 00:42:15.580 had cyanide on it. 00:42:15.580 --> 00:42:17.810 That's a very strong field ligand. 00:42:17.810 --> 00:42:20.920 And so that's going to absorb, then, a high frequency. 00:42:20.920 --> 00:42:23.720 So a strong field, so you have a big energy difference. 00:42:23.720 --> 00:42:26.710 So you have a big energy, high frequency, and therefore short 00:42:26.710 --> 00:42:27.560 wavelength. 00:42:27.560 --> 00:42:32.100 So it will transmit on the longer end of things. 00:42:32.100 --> 00:42:35.810 And this is actually a bright orange red color. 00:42:35.810 --> 00:42:39.650 So you have a very long, long wavelength 00:42:39.650 --> 00:42:41.020 that you're observing here. 00:42:41.020 --> 00:42:42.860 This beautiful red orange. 00:42:42.860 --> 00:42:44.390 It's a really brilliant color. 00:42:44.390 --> 00:42:47.730 Now interestingly, I mentioned in terms of applications, 00:42:47.730 --> 00:42:50.690 as some transition metal complexes were used to color 00:42:50.690 --> 00:42:53.630 things-- and I mentioned the blue in blueprint-- 00:42:53.630 --> 00:42:57.350 and if you take this compound and actually add iron 00:42:57.350 --> 00:42:59.330 in a different oxidation state to it, 00:42:59.330 --> 00:43:02.600 and, form this complex that has iron plus 3, 00:43:02.600 --> 00:43:05.390 and iron plus true with cyanide, you actually 00:43:05.390 --> 00:43:07.160 get the blueprint blue. 00:43:07.160 --> 00:43:10.000 So the colors can be just dramatically different 00:43:10.000 --> 00:43:14.120 depending on what gets added to the system. 00:43:14.120 --> 00:43:17.160 All right, so now let's think about-- it's a little sad-- 00:43:17.160 --> 00:43:19.210 but things without color. 00:43:19.210 --> 00:43:23.230 So what coordination complexes would be colorless? 00:43:23.230 --> 00:43:26.910 What would be true about the d orbitals 00:43:26.910 --> 00:43:29.960 If you had a colorless thing? 00:43:29.960 --> 00:43:31.743 Yeah, what would be true? 00:43:31.743 --> 00:43:33.774 AUDIENCE: [INAUDIBLE] 00:43:33.774 --> 00:43:35.690 PROFESSOR: Yeah, they could all be degenerate, 00:43:35.690 --> 00:43:37.979 so there's no splitting at all. 00:43:37.979 --> 00:43:40.520 Which usually doesn't happen if there are any ligands around. 00:43:40.520 --> 00:43:43.040 That's their hypothetical spherical crystal field, 00:43:43.040 --> 00:43:44.290 which I brought with me again. 00:43:44.290 --> 00:43:45.664 Because I just love carrying this 00:43:45.664 --> 00:43:49.250 through the infinite corridor and have people look at me. 00:43:49.250 --> 00:43:52.400 But, if you do have the ligands around, it will happen. 00:43:52.400 --> 00:43:54.830 If all of your d orbitals are filled, 00:43:54.830 --> 00:43:57.140 or if the energy levels are basically 00:43:57.140 --> 00:43:58.940 out of the visible range. 00:43:58.940 --> 00:44:01.910 So the transitions are not in the visible range at all. 00:44:01.910 --> 00:44:04.000 So, if they're all filled-- so, there's 00:44:04.000 --> 00:44:07.580 no way that you can move an electron. 00:44:07.580 --> 00:44:09.020 Or, if you can. 00:44:09.020 --> 00:44:12.250 But it's outside the visible region 00:44:12.250 --> 00:44:14.690 All right, so now let's think about some examples 00:44:14.690 --> 00:44:18.710 of what transition metals would fit into this. 00:44:18.710 --> 00:44:20.459 And I'll bring up my periodic table. 00:44:20.459 --> 00:44:22.250 And we'll also bring up a clicker question. 00:44:33.230 --> 00:44:36.530 All right, let's just take 10 more seconds on this. 00:44:51.900 --> 00:44:53.230 All right. 00:44:53.230 --> 00:44:55.144 So we can take a look at this. 00:44:58.640 --> 00:45:03.220 And with our periodic table, we have nickel and palladium, 00:45:03.220 --> 00:45:06.350 group 10 minus 2 is 8. 00:45:06.350 --> 00:45:11.020 Copper plus 2, gold plus 2, 11 minus 2 is 9. 00:45:11.020 --> 00:45:15.560 Zinc plus 2, cadmium plus 2, twelve minus 2 is 10. 00:45:15.560 --> 00:45:18.770 And so 10 would be the correct number for our field d 00:45:18.770 --> 00:45:19.310 orbitals. 00:45:19.310 --> 00:45:23.310 They can hold 10 electrons. 00:45:23.310 --> 00:45:27.920 S if we, then, go and fill this in, examples would include: 00:45:27.920 --> 00:45:32.830 zinc plus 2, and cadmium plus 2, with our d10 system. 00:45:32.830 --> 00:45:38.560 And in fact, zinc plus 2 is a very common oxidation state 00:45:38.560 --> 00:45:39.560 for zinc. 00:45:39.560 --> 00:45:41.630 Many proteins require zinc. 00:45:41.630 --> 00:45:44.120 Many of you have zinc in vitamin tablets. 00:45:44.120 --> 00:45:46.460 Some people take extra zinc to make 00:45:46.460 --> 00:45:49.690 sure you have enough zinc plus 2 in your body. 00:45:49.690 --> 00:45:52.820 And a lot of times people who are studying proteins 00:45:52.820 --> 00:45:55.790 do not realize it's a zinc containing protein because they 00:45:55.790 --> 00:45:57.147 isolate the protein. 00:45:57.147 --> 00:45:58.730 And it's clear, so they don't think it 00:45:58.730 --> 00:46:00.370 has a transition metal in it. 00:46:00.370 --> 00:46:02.290 But zinc is hiding in that protein 00:46:02.290 --> 00:46:04.850 because it's colorless so you don't know it's there. 00:46:04.850 --> 00:46:08.330 If you purify a protein with color with other metals, 00:46:08.330 --> 00:46:10.400 it's really obvious that the metal is there. 00:46:10.400 --> 00:46:13.040 But zinc can be sneaky. 00:46:13.040 --> 00:46:14.810 Cadmium can also be sneaky. 00:46:14.810 --> 00:46:18.110 Cadmium, for the most part, is a poison to us. 00:46:18.110 --> 00:46:21.590 And they used to use it to coat barbecue grills. 00:46:21.590 --> 00:46:23.090 Which is not-- you don't want to put 00:46:23.090 --> 00:46:25.830 a poisonous substance on a barbecue grill 00:46:25.830 --> 00:46:26.710 and then heat it up. 00:46:26.710 --> 00:46:28.870 That's a really bad idea. 00:46:28.870 --> 00:46:31.270 So if you go to a barbecue and you think, 00:46:31.270 --> 00:46:35.362 wow, that grill looks like it's, like, 70 or 80 years old, 00:46:35.362 --> 00:46:36.320 or something like that. 00:46:36.320 --> 00:46:37.460 It looks ancient. 00:46:37.460 --> 00:46:40.190 Maybe you don't want to eat from that barbecue grill. 00:46:40.190 --> 00:46:42.790 They don't do this anymore, but old barbecue grills 00:46:42.790 --> 00:46:43.960 had cadmium on it. 00:46:43.960 --> 00:46:47.390 And I know someone who actually had cadmium poisoning. 00:46:47.390 --> 00:46:49.730 And it was a really pretty terrible thing because it's 00:46:49.730 --> 00:46:50.980 hard to diagnose that. 00:46:50.980 --> 00:46:53.270 But they finally got the right diagnosis. 00:46:53.270 --> 00:46:55.400 All right, so again, colorless things, 00:46:55.400 --> 00:46:58.610 you don't know that they're there, but they sometimes are. 00:46:58.610 --> 00:47:01.376 All right, so what about cobalt plus 3? 00:47:01.376 --> 00:47:02.500 You can just yell this out. 00:47:02.500 --> 00:47:06.910 Would this be a colorless compound? 00:47:06.910 --> 00:47:07.750 No. 00:47:07.750 --> 00:47:13.550 So we have in our group 9, minus 3 would be sync -- would be 6. 00:47:13.550 --> 00:47:14.770 So it's not. 00:47:14.770 --> 00:47:17.390 Which vitamin contains cobalt? 00:47:17.390 --> 00:47:19.030 And you probably all know because we've 00:47:19.030 --> 00:47:20.350 been talking about it. 00:47:20.350 --> 00:47:22.030 Vitamin B-12. 00:47:22.030 --> 00:47:24.490 And I just thought I would share with you 00:47:24.490 --> 00:47:27.790 the colors of vitamin B-12. 00:47:27.790 --> 00:47:31.720 And so this is crystals that contain vitamin B-12. 00:47:31.720 --> 00:47:34.570 And these are their actual colors of the crystals. 00:47:34.570 --> 00:47:37.210 So it's really fun to work with vitamin B12. 00:47:37.210 --> 00:47:39.160 It's absolutely brilliant. 00:47:39.160 --> 00:47:41.030 Except that it's also light sensitive. 00:47:41.030 --> 00:47:43.660 So you have to work in the dark, under red light. 00:47:43.660 --> 00:47:46.420 So everything, then, is red because you're under red light. 00:47:46.420 --> 00:47:48.910 But if you bring them out, and you expose them to light, 00:47:48.910 --> 00:47:50.320 they're really, really pretty. 00:47:50.320 --> 00:47:52.778 All right, so we're going to continue on this cobalt theme. 00:47:52.778 --> 00:47:56.080 Because cobalt is one of the most spectacular transition 00:47:56.080 --> 00:47:58.160 metals when it comes to color. 00:47:58.160 --> 00:48:01.156 And I'm going to get you ready for a little demo. 00:48:01.156 --> 00:48:02.530 And you're going to help me first 00:48:02.530 --> 00:48:05.770 figure out what colors you should observe in this demo. 00:48:05.770 --> 00:48:10.640 All right, so, we're going to have a cobalt compound that 00:48:10.640 --> 00:48:12.940 has six waters with it. 00:48:12.940 --> 00:48:17.780 And you're given the octahedral crystal field splitting energy. 00:48:17.780 --> 00:48:19.840 So now we want to predict the color. 00:48:19.840 --> 00:48:21.790 And when we predict the color, we're 00:48:21.790 --> 00:48:23.740 asking about what sort of wavelength 00:48:23.740 --> 00:48:24.750 is going to be absorbed. 00:48:24.750 --> 00:48:26.249 So we can think about the wavelength 00:48:26.249 --> 00:48:27.410 that will be transmitted. 00:48:27.410 --> 00:48:29.830 So we need to think about our equations. 00:48:29.830 --> 00:48:33.250 And we can combine these just like we did in many problems 00:48:33.250 --> 00:48:35.110 in the earlier part of the course. 00:48:35.110 --> 00:48:37.930 And so wavelength equals Planck's constant times 00:48:37.930 --> 00:48:38.950 the speed of light. 00:48:38.950 --> 00:48:41.200 Now, instead of just divided by any energy, 00:48:41.200 --> 00:48:44.050 we're dividing by the energy that's the octahedral crystal 00:48:44.050 --> 00:48:46.130 field splitting energy. 00:48:46.130 --> 00:48:48.010 And so we can put in our Planck's constant 00:48:48.010 --> 00:48:49.430 and our speed of light. 00:48:49.430 --> 00:48:52.360 And we can put in the octahedral crystal field splitting energy 00:48:52.360 --> 00:48:53.560 that we were given. 00:48:53.560 --> 00:48:57.250 But we want units in meters. 00:48:57.250 --> 00:49:00.920 And so we need our joules to cancel out. 00:49:00.920 --> 00:49:03.220 And in the bottom we're given the splitting energy 00:49:03.220 --> 00:49:04.220 in kilojoules. 00:49:04.220 --> 00:49:06.220 So we need to do some conversions. 00:49:06.220 --> 00:49:08.450 So first we need to get rid of this kilojoules. 00:49:08.450 --> 00:49:10.540 So we're going to convert it to joules. 00:49:10.540 --> 00:49:13.330 Then we can get rid of our joules. 00:49:13.330 --> 00:49:14.440 We also have seconds. 00:49:14.440 --> 00:49:16.420 We don't want seconds in our wavelength. 00:49:16.420 --> 00:49:19.790 But that is going to cancel out here and here, so we're good. 00:49:19.790 --> 00:49:22.550 But now our answer, we have meters at the top, 00:49:22.550 --> 00:49:24.550 but we have moles on the bottom. 00:49:24.550 --> 00:49:27.917 So we need to use Avogadro's number to cancel out our moles. 00:49:27.917 --> 00:49:29.500 And if you don't do that, you're going 00:49:29.500 --> 00:49:33.190 to get a really weird number for your wavelength that's 00:49:33.190 --> 00:49:34.380 not going to make sense. 00:49:34.380 --> 00:49:35.796 It's going to be off by something, 00:49:35.796 --> 00:49:38.320 like, a factor of 10 to the 23. 00:49:38.320 --> 00:49:41.410 That should remind you, you want to use Avogadro's number here 00:49:41.410 --> 00:49:43.540 to get rid of your per mole. 00:49:43.540 --> 00:49:47.230 All right, so now we have a wavelength. 00:49:47.230 --> 00:49:50.470 And yes, on your equation sheet, we will give you this. 00:49:50.470 --> 00:49:52.270 We will give you the color spectrums. 00:49:52.270 --> 00:49:54.410 You don't have to memorize this. 00:49:54.410 --> 00:49:59.500 So about 500 nanometers is in our green region over here. 00:49:59.500 --> 00:50:02.530 So the color that should be absorbed, 00:50:02.530 --> 00:50:06.680 given this octahedral crystal field splitting energy, 00:50:06.680 --> 00:50:07.990 is green. 00:50:07.990 --> 00:50:15.740 So now, for green, what is the complementary color of green? 00:50:15.740 --> 00:50:17.690 Yup, so it's going to be reddish. 00:50:17.690 --> 00:50:19.780 We have our little drawing over here. 00:50:19.780 --> 00:50:22.940 So the predicted color would be red. 00:50:22.940 --> 00:50:25.742 So let me just now tell you about this demo. 00:50:25.742 --> 00:50:27.700 And we're actually going to see some red color. 00:50:27.700 --> 00:50:31.400 But we're also going to see another color which is blue. 00:50:31.400 --> 00:50:37.000 So, in this demo, if you have, start with some copper chloride 00:50:37.000 --> 00:50:38.500 and add a lot of water. 00:50:38.500 --> 00:50:39.460 A lot, a lot of water. 00:50:39.460 --> 00:50:40.870 Hydrate it really well. 00:50:40.870 --> 00:50:44.290 You'll get this octahedral system 00:50:44.290 --> 00:50:46.330 that you just told me was red. 00:50:46.330 --> 00:50:48.310 But if you don't add a lot of water, 00:50:48.310 --> 00:50:49.780 just a little bit of water, you'll 00:50:49.780 --> 00:50:52.270 only display some of the chlorides. 00:50:52.270 --> 00:50:54.560 And then you're going to have a blue system. 00:50:54.560 --> 00:50:56.950 So if you have a lot of water, red. 00:50:56.950 --> 00:50:58.840 And you're hydrated, red. 00:50:58.840 --> 00:51:01.490 If you're more dehydrated, you get blue. 00:51:01.490 --> 00:51:04.680 So we're going to now try this out and see if it works. 00:51:10.190 --> 00:51:11.190 GUEST SPEAKER: Is it on? 00:51:11.190 --> 00:51:11.773 Yeah, it's on. 00:51:11.773 --> 00:51:12.600 Great. 00:51:12.600 --> 00:51:15.426 OK, so that's the cobalt flower. 00:51:15.426 --> 00:51:17.800 And as Cathy said, it's-- oh, we're going to put it under 00:51:17.800 --> 00:51:18.850 there. 00:51:18.850 --> 00:51:23.230 As Cathy said, it's got some cobalt. 00:51:23.230 --> 00:51:25.376 And it's got water ligands. 00:51:25.376 --> 00:51:26.500 And it's also got chlorine. 00:51:26.500 --> 00:51:29.034 And Eric's going to sprinkle it with water now. 00:51:29.034 --> 00:51:30.700 PROFESSOR: So we're going to hydrate it. 00:51:30.700 --> 00:51:32.740 GUEST SPEAKER: Hydrate it, as you do, 00:51:32.740 --> 00:51:34.210 when you have to water a flower. 00:51:34.210 --> 00:51:40.680 And it's turned, like, it's a pinkish, reddish color, right? 00:51:40.680 --> 00:51:42.220 Can they see that up there? 00:51:42.220 --> 00:51:42.760 Yeah. 00:51:42.760 --> 00:51:44.218 PROFESSOR: It looks better with it. 00:51:44.218 --> 00:51:45.800 Hold it against this, too, I think. 00:51:45.800 --> 00:51:46.675 GUEST SPEAKER: Right. 00:51:49.060 --> 00:51:52.720 So to show you that it was, in fact, the water 00:51:52.720 --> 00:51:56.390 that led to this color change, we're 00:51:56.390 --> 00:52:01.460 going to try to dry out the flower. 00:52:01.460 --> 00:52:02.550 Is it working? 00:52:02.550 --> 00:52:03.190 Am I on hot? 00:52:03.190 --> 00:52:04.231 Yes, I am. 00:52:04.231 --> 00:52:05.230 I know it's really slow. 00:52:05.230 --> 00:52:06.438 I'd just rather it go faster. 00:52:09.530 --> 00:52:12.930 And, well-- 00:52:12.930 --> 00:52:14.621 PROFESSOR: Yeah. 00:52:14.621 --> 00:52:16.620 Why don't you hold it under the document camera? 00:52:16.620 --> 00:52:18.520 I think you can kind of see it happening. 00:52:27.050 --> 00:52:29.610 GUEST SPEAKER: So as-- there we go. 00:52:29.610 --> 00:52:30.360 That's working. 00:52:30.360 --> 00:52:32.760 As Eric continues to warm this thing up, 00:52:32.760 --> 00:52:35.070 the water is evaporating. 00:52:35.070 --> 00:52:39.150 And as that happens, it starts forming that hydrous chloride 00:52:39.150 --> 00:52:41.190 complex instead of up here, hydrous complex, 00:52:41.190 --> 00:52:45.420 and it's going back to emitting blue color instead of red. 00:52:45.420 --> 00:52:49.200 And hopefully we can see. 00:52:49.200 --> 00:52:50.060 Oh, there. 00:52:50.060 --> 00:52:50.773 It's working. 00:52:50.773 --> 00:52:52.560 Yea. 00:52:52.560 --> 00:52:54.890 PROFESSOR: So some people give each other roses. 00:52:54.890 --> 00:52:59.100 But if your significant other is a geek, what's 00:52:59.100 --> 00:53:02.410 better than a flower that changes color on hydration? 00:53:02.410 --> 00:53:03.130 I don't know. 00:53:03.130 --> 00:53:05.940 I think this is a pretty good gift. 00:53:05.940 --> 00:53:07.890 Valentine's Day isn't quite coming up, 00:53:07.890 --> 00:53:08.990 but just keep it in mind. 00:53:11.630 --> 00:53:14.760 All right, so we'll leave the flower here 00:53:14.760 --> 00:53:19.560 and we'll keep an eye on it as we go along. 00:53:19.560 --> 00:53:21.460 It will change back eventually. 00:53:21.460 --> 00:53:24.060 It depends a lot on the weather, but it's pretty dry right now 00:53:24.060 --> 00:53:26.220 in this time of year.