WEBVTT 00:00:00.000 --> 00:00:00.272 The following content is provided under a Creative 00:00:00.272 --> 00:00:00.374 Commons license. 00:00:00.374 --> 00:00:00.646 Your support will help MIT OpenCourseWare continue to 00:00:00.646 --> 00:00:00.918 offer high quality educational resources for free. 00:00:00.918 --> 00:00:01.224 To make a donation or view additional materials from 00:00:01.224 --> 00:00:01.496 hundreds of MIT courses, visit MIT OpenCourseWare at 00:00:01.496 --> 00:00:01.540 ocw.mit.edu. 00:00:01.540 --> 00:00:22.230 PROFESSOR: OK. 00:00:22.230 --> 00:00:23.070 Let's get started. 00:00:23.070 --> 00:00:26.740 Can you go ahead and take 10 more seconds on this first 00:00:26.740 --> 00:00:46.430 clicker question here? 00:00:46.430 --> 00:00:46.880 OK. 00:00:46.880 --> 00:00:51.250 So it looks like most of you got that the electron 00:00:51.250 --> 00:00:53.860 configuration that we're writing here is for copper. 00:00:53.860 --> 00:00:56.450 So I'm actually going to give the benefit of the doubt that 00:00:56.450 --> 00:00:58.650 the people that didn't get it right were rushing to get out 00:00:58.650 --> 00:01:00.350 their clickers and didn't have time to think 00:01:00.350 --> 00:01:02.390 it all the way through. 00:01:02.390 --> 00:01:06.800 Remember that when we're talking about 4 s 1, 3 d 10, 00:01:06.800 --> 00:01:09.480 that's one of those exceptions where a completely filled d 00:01:09.480 --> 00:01:12.150 orbital is more stable than we would expect. 00:01:12.150 --> 00:01:15.190 So, that's actually the electron configuration we have 00:01:15.190 --> 00:01:17.180 when we're talking about copper and some other 00:01:17.180 --> 00:01:22.250 exceptions in the periodic table that you're going to be 00:01:22.250 --> 00:01:23.040 looking at. 00:01:23.040 --> 00:01:25.560 So, hopefully, if you were to go back and look you could see 00:01:25.560 --> 00:01:27.960 that this is, in fact, copper. 00:01:27.960 --> 00:01:30.660 We're actually going to do one more clicker question to get 00:01:30.660 --> 00:01:34.120 started with today, and as we do, I'll explain something 00:01:34.120 --> 00:01:36.180 we're going to be trying today, which is a little bit 00:01:36.180 --> 00:01:39.020 of a friendly competition in terms of answering the clicker 00:01:39.020 --> 00:01:40.900 questions correctly. 00:01:40.900 --> 00:01:44.070 So we've tagged each of your numbers to your actual 00:01:44.070 --> 00:01:47.630 recitation, so we can see today which recitation 00:01:47.630 --> 00:01:51.000 actually is going to be doing the best in terms of clicker 00:01:51.000 --> 00:01:54.870 questions, who's going to get the most correct today. 00:01:54.870 --> 00:01:58.670 So, you may or may not know this about your TAs, but this 00:01:58.670 --> 00:02:02.260 is a pretty competitive group of TAs we have this year, and 00:02:02.260 --> 00:02:05.440 they like to brag about how smart their recitation is, how 00:02:05.440 --> 00:02:09.220 good questions they're getting in the recitation section. 00:02:09.220 --> 00:02:13.290 So, do your TA proud today and see if you can be part of the 00:02:13.290 --> 00:02:16.300 recitation that gets the most correct in terms of a 00:02:16.300 --> 00:02:17.040 percentage. 00:02:17.040 --> 00:02:20.720 And at the end of class we'll announce which recitation that 00:02:20.720 --> 00:02:23.150 is, we'll also make sure to give you a little bit of a 00:02:23.150 --> 00:02:25.550 prize if you are, in fact, in that recitation. 00:02:25.550 --> 00:02:27.190 So we have extra incentive to get these 00:02:27.190 --> 00:02:28.260 clicker questions right. 00:02:28.260 --> 00:02:31.040 So, in this one we're selecting the correct 00:02:31.040 --> 00:02:33.470 electronic configuration for an ion. 00:02:33.470 --> 00:02:35.700 So, why don't you go ahead and take 10 more seconds on this 00:02:35.700 --> 00:02:47.770 second clicker question for our intro. 00:02:47.770 --> 00:02:49.430 OK. 00:02:49.430 --> 00:02:52.380 So, it looks like we have a little bit of a mixed 00:02:52.380 --> 00:02:53.360 consensus here. 00:02:53.360 --> 00:02:55.310 Let's go over this question. 00:02:55.310 --> 00:02:58.190 And I know there's a lot to talk about about this 00:02:58.190 --> 00:03:01.620 competition, but let's just get into listening mode here 00:03:01.620 --> 00:03:04.510 and talk about how we can figure out what the correct 00:03:04.510 --> 00:03:07.060 electron configuration is for this ion. 00:03:07.060 --> 00:03:08.760 Remember, ions are a little bit different. 00:03:08.760 --> 00:03:10.850 The first thing we need to do is write the electron 00:03:10.850 --> 00:03:13.720 configuration for the atom itself, and then we need to 00:03:13.720 --> 00:03:15.250 take an electron away. 00:03:15.250 --> 00:03:20.340 So here we're talking about v plus 1, so if we were to write 00:03:20.340 --> 00:03:25.040 it just for the neutral electron itself, we would find 00:03:25.040 --> 00:03:27.920 that the electron configuration is argon, that's 00:03:27.920 --> 00:03:29.940 the filled shell in front of it. 00:03:29.940 --> 00:03:35.380 Then 4 s 2 and 3 d 3. 00:03:35.380 --> 00:03:38.980 So this would be for the actual filled, the completely 00:03:38.980 --> 00:03:40.550 neutral atom. 00:03:40.550 --> 00:03:43.370 But remember what we said, which was when we talked 00:03:43.370 --> 00:03:46.040 about, this is at the end of class on Friday, we said that 00:03:46.040 --> 00:03:48.970 it turns out that even though 3 d is higher in energy when 00:03:48.970 --> 00:03:52.380 it's not filled, once we fill it with an electron, these 2 00:03:52.380 --> 00:03:55.620 orbitals actually switch place in terms of energy. 00:03:55.620 --> 00:03:57.850 So if we were to write this in terms of energy, we would 00:03:57.850 --> 00:04:03.080 actually have to rewrite it has 3 d 3, and then 4 s 2. 00:04:03.080 --> 00:04:05.530 So, which orbital would we take an electron out of if we 00:04:05.530 --> 00:04:09.550 were ionizing this atom here? 00:04:09.550 --> 00:04:09.790 The s. 00:04:09.790 --> 00:04:12.930 So, we would actually take an electron out of the s, which 00:04:12.930 --> 00:04:17.650 gives us 3 d 3 and then 4 s 1. 00:04:17.650 --> 00:04:20.110 So, it's a little bit of a trick when you're 00:04:20.110 --> 00:04:20.950 dealing with ions. 00:04:20.950 --> 00:04:23.820 The best suggestion is just to write it out completely for 00:04:23.820 --> 00:04:26.840 the neutral atom, and then you want to take an electron out 00:04:26.840 --> 00:04:27.900 of the highest orbital. 00:04:27.900 --> 00:04:30.380 It makes sense that it's going to come out of the highest 00:04:30.380 --> 00:04:32.570 occupied atomic orbital, because that's going to be the 00:04:32.570 --> 00:04:34.430 lowest amount of energy that's required to 00:04:34.430 --> 00:04:37.330 actually eject an electron. 00:04:37.330 --> 00:04:37.373 All right. 00:04:37.373 --> 00:04:39.860 So let's go to today's notes. 00:04:39.860 --> 00:04:43.670 And actually before we start into today's topics, I want to 00:04:43.670 --> 00:04:46.370 remind everyone and hopefully you all do remember that our 00:04:46.370 --> 00:04:49.140 first exam is coming up and it's coming up in exactly a 00:04:49.140 --> 00:04:53.260 week, so it'll be a week from today, next Wednesday. 00:04:53.260 --> 00:04:56.470 And on Friday in class, at the beginning of class, I'll go 00:04:56.470 --> 00:04:59.010 over just in all the detail you could possibly imagine 00:04:59.010 --> 00:05:01.670 everything you need to know logistically for the exam -- 00:05:01.670 --> 00:05:04.240 where it is, what you do, what kind of calculators you can 00:05:04.240 --> 00:05:06.400 bring, which by the way are any calculator. 00:05:06.400 --> 00:05:09.340 So you'll get all of that information on Friday. 00:05:09.340 --> 00:05:12.030 So don't worry if you have some questions right now. 00:05:12.030 --> 00:05:13.520 I just want to let you know that. 00:05:13.520 --> 00:05:16.120 The other thing I want to let you know is that instead of 00:05:16.120 --> 00:05:18.780 having a new problem-set that you'll be assigned this 00:05:18.780 --> 00:05:22.090 Friday, what we'll do instead is we'll give you some 00:05:22.090 --> 00:05:25.670 practice problems, and these will be just more of the same 00:05:25.670 --> 00:05:28.220 type of problems that you saw before but that's another 00:05:28.220 --> 00:05:30.020 chance to try them out more. 00:05:30.020 --> 00:05:32.140 These won't be graded, you don't have to turn them in, 00:05:32.140 --> 00:05:34.050 it's just to give you some extra practice if you want 00:05:34.050 --> 00:05:35.910 while you're studying for the exam. 00:05:35.910 --> 00:05:39.810 We'll also post an exam from a previous year so you can 00:05:39.810 --> 00:05:42.610 actually see exactly what the format's going to look like. 00:05:42.610 --> 00:05:45.900 So when you go into the exam a week from today, it'll all 00:05:45.900 --> 00:05:48.250 look really familiar, you'll be comfortable with the format 00:05:48.250 --> 00:05:50.250 and you can just dive right in and start 00:05:50.250 --> 00:05:51.320 answering the questions. 00:05:51.320 --> 00:05:53.200 So you'll have all that information and we'll get it 00:05:53.200 --> 00:05:54.880 to you on Friday. 00:05:54.880 --> 00:05:56.510 The other quick thing I want to say is that I do have 00:05:56.510 --> 00:06:00.650 office hours today from 3 to 5, so feel free to stop by if 00:06:00.650 --> 00:06:03.550 you have questions about problem-set 3 that you're 00:06:03.550 --> 00:06:04.750 finishing up. 00:06:04.750 --> 00:06:07.920 And also, for those of you that did sign up for the pizza 00:06:07.920 --> 00:06:10.540 forum tonight, that's going to be at 5 o'clock, it's in room 00:06:10.540 --> 00:06:16.380 56-502, so we'll see some of you tonight for that as well. 00:06:16.380 --> 00:06:16.690 All right. 00:06:16.690 --> 00:06:18.670 So, let's move on to what we're talking about today. 00:06:18.670 --> 00:06:21.560 What we're going to start with is discussing photoelectron 00:06:21.560 --> 00:06:24.480 spectroscopy, which is a spectroscopy technique that 00:06:24.480 --> 00:06:27.690 will give us some information about energy levels in 00:06:27.690 --> 00:06:31.510 multielectron atoms. We'll then take a turn to talking 00:06:31.510 --> 00:06:33.630 about the periodic table, we'll look at a bunch of 00:06:33.630 --> 00:06:37.200 periodic trends, including ionization energy, electron 00:06:37.200 --> 00:06:40.750 affinity, electronegativity and atomic radius. 00:06:40.750 --> 00:06:43.770 And then, if we have time at the end, we'll introduce one 00:06:43.770 --> 00:06:47.460 last topic, which is isoelectronic atoms and ions. 00:06:47.460 --> 00:06:51.370 I also want to note that the end of the material today, so 00:06:51.370 --> 00:06:54.520 this last topic here, that's the end of the material that's 00:06:54.520 --> 00:06:56.470 going to be on this first exam. 00:06:56.470 --> 00:06:59.260 So whether we finish it today, or more likely when we finish 00:06:59.260 --> 00:07:04.690 it up on Friday, once we get passed isoelectronic atoms, 00:07:04.690 --> 00:07:07.160 that's it, that's all you need to study for this first exam. 00:07:07.160 --> 00:07:10.120 So from that point on it'll be exam 2 material, so depending 00:07:10.120 --> 00:07:12.170 on how you like to come compartmentalize your 00:07:12.170 --> 00:07:15.360 information, you can separate that in your brain in terms of 00:07:15.360 --> 00:07:17.590 what you're trying to learn right now versus what you can 00:07:17.590 --> 00:07:20.500 put off until a little bit later. 00:07:20.500 --> 00:07:23.670 So, let's start with talking about photoelectron 00:07:23.670 --> 00:07:27.010 spectroscopy. 00:07:27.010 --> 00:07:29.820 This actually relates very closely to what we discussed 00:07:29.820 --> 00:07:33.510 in class on Friday before the long weekend, and what we were 00:07:33.510 --> 00:07:37.710 talking about is the energy levels of multielectron atoms. 00:07:37.710 --> 00:07:40.440 So what we'll start with today is talking about the technique 00:07:40.440 --> 00:07:43.570 that's primarily used to actually experimentally figure 00:07:43.570 --> 00:07:45.960 out what these different energy levels are. 00:07:45.960 --> 00:07:47.340 And this is called photoelectron spectroscopy, 00:07:47.340 --> 00:07:51.960 and essentially what it is is very similar conceptually to 00:07:51.960 --> 00:07:54.710 what we were talking about way back in the first couple 00:07:54.710 --> 00:07:56.120 lectures when we were talking about the 00:07:56.120 --> 00:07:57.640 photoelectric effect. 00:07:57.640 --> 00:08:01.270 Because here what we have is some atom that we're studying, 00:08:01.270 --> 00:08:04.900 in the case, it's going to be a gas, and we hit it with a 00:08:04.900 --> 00:08:07.550 photon that has some incident energy. 00:08:07.550 --> 00:08:11.590 So e sub i, some energy that the photon comes in with, and 00:08:11.590 --> 00:08:14.620 if it has sufficient energy to eject an electron, it will do 00:08:14.620 --> 00:08:18.210 that, and our electron will be ejected with a certain kinetic 00:08:18.210 --> 00:08:21.000 energy, which is going to be whatever energy is left over 00:08:21.000 --> 00:08:24.200 from the initial energy we put in minus what was taken up in 00:08:24.200 --> 00:08:27.370 order to actually ionize or eject the electron. 00:08:27.370 --> 00:08:29.670 So, you can see how this can directly give us different 00:08:29.670 --> 00:08:32.050 ionization energies for any atom that we're 00:08:32.050 --> 00:08:33.460 interested in studying. 00:08:33.460 --> 00:08:35.880 For example, with neon we can think about all of the 00:08:35.880 --> 00:08:38.490 different orbital energies we could be looking at. 00:08:38.490 --> 00:08:40.520 In the first case, so here is the electron 00:08:40.520 --> 00:08:42.390 configuration of neon. 00:08:42.390 --> 00:08:45.880 So we can think about what is our most loosely-bound 00:08:45.880 --> 00:08:49.065 electron, what's that highest energy orbital, and it's going 00:08:49.065 --> 00:08:51.500 to be the 2 p orbital, that's going to be 00:08:51.500 --> 00:08:52.610 what's highest in energy. 00:08:52.610 --> 00:08:55.570 So if we're going to eject an electron using a minimum 00:08:55.570 --> 00:08:58.130 amount of energy, that's where it's going to come from. 00:08:58.130 --> 00:09:00.470 So, you can imagine, that we'll actually probably have a 00:09:00.470 --> 00:09:03.890 lot of kinetic energy left over if we put a lot of energy 00:09:03.890 --> 00:09:04.790 in in the first place. 00:09:04.790 --> 00:09:07.340 We're only using up a little bit to eject the electron, 00:09:07.340 --> 00:09:09.480 then we'll have a lot left over. 00:09:09.480 --> 00:09:10.990 So, one difference between photoelectron spectroscopy 00:09:10.990 --> 00:09:14.760 and, for example, the photoelectric effect is that 00:09:14.760 --> 00:09:17.250 in this case, we're not just looking at one energy level, 00:09:17.250 --> 00:09:19.330 which is what we were looking at from the surface of a 00:09:19.330 --> 00:09:22.530 metal, now we're talking about this gaseous atom. 00:09:22.530 --> 00:09:26.470 So we can actually pop an electron or eject an electron 00:09:26.470 --> 00:09:29.720 from any single orbital that is occupied within the atom. 00:09:29.720 --> 00:09:33.180 So, for example, it's not just the 2 p that we could actually 00:09:33.180 --> 00:09:35.380 take an electron from, we could also think about 00:09:35.380 --> 00:09:38.190 ejecting an electron from the 2 s orbital. 00:09:38.190 --> 00:09:40.460 Now this, of course, is going to take more energy because a 00:09:40.460 --> 00:09:43.610 2 s is lower, it has has a more negative binding energy 00:09:43.610 --> 00:09:46.670 than the 2 p, but that's OK as long as we put in enough 00:09:46.670 --> 00:09:49.470 energy, but what we're going to find is the kinetic energy 00:09:49.470 --> 00:09:52.450 coming out with the electron is actually going to be a 00:09:52.450 --> 00:09:55.090 little bit less, right, because we had to use up more 00:09:55.090 --> 00:09:57.280 energy to eject the electron, so we don't have 00:09:57.280 --> 00:10:00.090 as much left over. 00:10:00.090 --> 00:10:02.540 There's actually one more orbital that we could talk 00:10:02.540 --> 00:10:05.430 about if we're talking about this sample case of neon, 00:10:05.430 --> 00:10:09.470 which is a 1 s orbital, and if we're talking about a 1 s 00:10:09.470 --> 00:10:13.030 orbital, now we're going to be even lower in energy still, so 00:10:13.030 --> 00:10:16.440 that means the minimum energy required to eject an electron 00:10:16.440 --> 00:10:19.320 is going to be at its highest, so that means the energy that 00:10:19.320 --> 00:10:22.200 we have left over that turns into kinetic energy for the 00:10:22.200 --> 00:10:26.000 electron, is now going to be really quite small. 00:10:26.000 --> 00:10:30.760 And what happens when you irradiate one of these atoms 00:10:30.760 --> 00:10:34.290 that you're studying with this light is in photoelectron 00:10:34.290 --> 00:10:36.350 spectroscopy, you want to make sure that you put in enough 00:10:36.350 --> 00:10:40.180 energy to actually ionize any single electron that you have 00:10:40.180 --> 00:10:41.000 in the atom. 00:10:41.000 --> 00:10:43.270 So the way that we really make sure this is done is that we 00:10:43.270 --> 00:10:44.710 use x-rays. 00:10:44.710 --> 00:10:48.200 So you know that x-rays are higher frequency than UV 00:10:48.200 --> 00:10:51.020 light, for example, that means it's also higher energy than 00:10:51.020 --> 00:10:54.880 UV light, and if you think back to our photoelectric 00:10:54.880 --> 00:10:57.465 effect experiments, do you remember what type of light we 00:10:57.465 --> 00:10:58.930 were usually using for those? 00:10:58.930 --> 00:11:01.490 Does anyone remember? 00:11:01.490 --> 00:11:02.620 Yeah. 00:11:02.620 --> 00:11:04.560 It was UV light that we used. 00:11:04.560 --> 00:11:06.850 Well, we can't guarantee with UV light we'll have enough 00:11:06.850 --> 00:11:09.450 energy to eject every single electron, so that's why when 00:11:09.450 --> 00:11:12.500 we use x-rays, they're higher energy, you can pretty much be 00:11:12.500 --> 00:11:14.000 guaranteed we're going to eject all of 00:11:14.000 --> 00:11:17.160 those electrons there. 00:11:17.160 --> 00:11:19.960 So I said that this technique was used to experimentally 00:11:19.960 --> 00:11:22.580 determine what the different binding energies or the 00:11:22.580 --> 00:11:25.730 different ionization energies are for the different states 00:11:25.730 --> 00:11:27.400 in a multielectron atom. 00:11:27.400 --> 00:11:29.140 Another way to say states is to talk 00:11:29.140 --> 00:11:30.650 about different orbitals. 00:11:30.650 --> 00:11:33.410 So we can do this directly as long as we have certain types 00:11:33.410 --> 00:11:34.140 of information. 00:11:34.140 --> 00:11:37.130 The first that we need to know the energy of the photon 00:11:37.130 --> 00:11:41.030 that's incident on our gaseous atom. 00:11:41.030 --> 00:11:43.590 The second piece of information we need to know is 00:11:43.590 --> 00:11:46.320 what actually the kinetic energy is of the ejected 00:11:46.320 --> 00:11:48.490 electron, and that's something we can just measure by 00:11:48.490 --> 00:11:50.470 measuring its velocity. 00:11:50.470 --> 00:11:53.980 So we can use an equation to relate the incident energy and 00:11:53.980 --> 00:11:56.570 the kinetic energy to the ionization energy, or the 00:11:56.570 --> 00:11:58.820 energy that's required to eject an electron. 00:11:58.820 --> 00:12:01.140 This should all sound incredibly familiar, like I'm 00:12:01.140 --> 00:12:03.780 just repeating myself in terms of photoelectric effect, 00:12:03.780 --> 00:12:06.010 because essentially that's what I'm doing, and that's one 00:12:06.010 --> 00:12:08.680 reason we spent so much time and did so many problem-set 00:12:08.680 --> 00:12:10.760 problems on the photoelectric effect. 00:12:10.760 --> 00:12:13.640 So what we're saying here is the incident energy, so the 00:12:13.640 --> 00:12:17.230 energy coming in, is just equal to the minimum energy 00:12:17.230 --> 00:12:19.420 that's required to a eject an electron. 00:12:19.420 --> 00:12:21.580 When we talked about the photoelectric effect, that was 00:12:21.580 --> 00:12:22.660 called the work function. 00:12:22.660 --> 00:12:25.970 In this case, it's called the ionization energy, plus 00:12:25.970 --> 00:12:27.860 whatever kinetic energy we have 00:12:27.860 --> 00:12:29.810 left over in the electron. 00:12:29.810 --> 00:12:32.480 So if we want to solve for ionization energy, we can just 00:12:32.480 --> 00:12:33.980 rearrange this equation. 00:12:33.980 --> 00:12:36.700 Our ionization energy is going to be equal to the incident 00:12:36.700 --> 00:12:39.010 energy coming in, minus the kinetic 00:12:39.010 --> 00:12:40.060 energy of the electron. 00:12:40.060 --> 00:12:43.810 So, let's take a look at the different kinetic energies 00:12:43.810 --> 00:12:47.500 that would be observed in a spectrum for neon where we had 00:12:47.500 --> 00:12:49.330 this incident energy here. 00:12:49.330 --> 00:12:51.560 And it turns out that the first kinetic energy that we 00:12:51.560 --> 00:12:55.030 would see or the highest kinetic energy, would be 12 32 00:12:55.030 --> 00:12:56.800 electron volts. 00:12:56.800 --> 00:13:00.080 So if that's the case doing a quick little calculation, what 00:13:00.080 --> 00:13:03.800 would the ionization energy be for a 2 p electron in neon? 00:13:03.800 --> 00:13:07.650 Yup, 22. 00:13:07.650 --> 00:13:12.560 So, basically all we did was take 12 54, subtract 12 32, 00:13:12.560 --> 00:13:15.250 and we got 22 electron volts. 00:13:15.250 --> 00:13:17.050 We can do the same thing for the other 00:13:17.050 --> 00:13:18.010 observed kinetic energy. 00:13:18.010 --> 00:13:22.250 So, for example, in the second case, we say that we see 12 06 00:13:22.250 --> 00:13:24.140 in terms of the kinetic energy. 00:13:24.140 --> 00:13:26.430 Same sort of subtraction problem, what do we have for 00:13:26.430 --> 00:13:30.100 the ionization energy of the 2 s electron? 00:13:30.100 --> 00:13:30.980 Good, quick math. 00:13:30.980 --> 00:13:32.230 All right, so 48 electron volts. 00:13:32.230 --> 00:13:35.430 And let's look at the final kinetic energy that we'd 00:13:35.430 --> 00:13:38.720 observe in this spectrum, which is 384 electron volts, 00:13:38.720 --> 00:13:40.110 so what is that third 00:13:40.110 --> 00:13:44.810 corresponding ionization energy? 00:13:44.810 --> 00:13:47.260 I couldn't quite hear, but I have a feeling everyone said 00:13:47.260 --> 00:13:50.460 870 electron volts. 00:13:50.460 --> 00:13:54.150 So, we can actually kind of visualize what we would see if 00:13:54.150 --> 00:13:56.640 we were looking at a photoelectron spectrum. 00:13:56.640 --> 00:13:59.220 And what we would see if we were graphing, for example, 00:13:59.220 --> 00:14:02.600 increasing kinetic energy, is we would see 1 line 00:14:02.600 --> 00:14:06.570 corresponding to each of these energies of electrons that we 00:14:06.570 --> 00:14:07.680 see coming out. 00:14:07.680 --> 00:14:10.190 And, of course, each of those electrons correspond to an 00:14:10.190 --> 00:14:13.300 electron coming out of a particular orbital. 00:14:13.300 --> 00:14:18.180 So in the case of 12 32, that is our highest kinetic energy, 00:14:18.180 --> 00:14:21.040 that means it's our lowest ionization energy -- it's the 00:14:21.040 --> 00:14:24.140 smallest amount of energy it takes to pop an electron out 00:14:24.140 --> 00:14:25.100 of that orbital. 00:14:25.100 --> 00:14:29.770 So that's why we see the 2 p here, the 2 s is 12 06, and it 00:14:29.770 --> 00:14:33.130 makes sense that what we see as the greatest ionization 00:14:33.130 --> 00:14:36.350 energy, which is also the smallest kinetic energy is 00:14:36.350 --> 00:14:37.600 that 1 s orbital. 00:14:37.600 --> 00:14:40.130 Remember, because that 1 s orbital is all the way down in 00:14:40.130 --> 00:14:42.310 terms of if we're thinking about an energy diagram, we're 00:14:42.310 --> 00:14:45.210 all the way down here, so we have a huge amount of energy 00:14:45.210 --> 00:14:49.120 we have to put into the system in order to eject an electron. 00:14:49.120 --> 00:14:51.130 So what I want to point out when you're kind of looking at 00:14:51.130 --> 00:14:53.920 these numbers here, what the significance is, look at that 00:14:53.920 --> 00:14:56.850 huge difference between what the ionization energies are 00:14:56.850 --> 00:15:00.160 for what we call those valence electrons, those outer shell 00:15:00.160 --> 00:15:03.460 electrons, versus the ionization energy for the 1 s 00:15:03.460 --> 00:15:06.390 orbital -- those are core electrons there. 00:15:06.390 --> 00:15:08.620 So we can think about something I mentioned last 00:15:08.620 --> 00:15:10.560 time, which is when we're thinking about chemistry and 00:15:10.560 --> 00:15:13.560 what's really interesting in terms of chemical reactions, 00:15:13.560 --> 00:15:15.880 it's mostly valence electrons we're talking about, those are 00:15:15.880 --> 00:15:16.750 the ones that tend to be 00:15:16.750 --> 00:15:18.660 involved in chemical reactions. 00:15:18.660 --> 00:15:21.000 It makes a lot of sense when we look at it energetically, 00:15:21.000 --> 00:15:24.955 because if we think about a 1 s core electron, that's going 00:15:24.955 --> 00:15:27.060 to be held really, really tightly to the nucleus. 00:15:27.060 --> 00:15:29.440 We see that we have to put this huge energy in to 00:15:29.440 --> 00:15:33.410 actually get a 1 s electron ejected, so it makes a lot of 00:15:33.410 --> 00:15:35.640 sense that we wouldn't want to pay that energy cost in a 00:15:35.640 --> 00:15:37.190 normal chemical reaction. 00:15:37.190 --> 00:15:40.690 And we don't -- we very rarely would see these core electrons 00:15:40.690 --> 00:15:44.610 actually being involved in any type of a reaction. 00:15:44.610 --> 00:15:47.600 All right, so one thing that I want to point out, which I 00:15:47.600 --> 00:15:49.990 said many, many times on Friday, and this is perhaps 00:15:49.990 --> 00:15:52.990 the last time I'll say it, but one last time is we can think 00:15:52.990 --> 00:15:56.530 about why we only see a line for the 2 p orbital, versus we 00:15:56.530 --> 00:16:00.750 don't see separate lines for a 2 p x, a 2 p y, and a 2 p z. 00:16:00.750 --> 00:16:03.450 Remember, we need those three quantum numbers to completely 00:16:03.450 --> 00:16:04.620 describe the orbital. 00:16:04.620 --> 00:16:06.870 Why do we just see one for all the p's? 00:16:06.870 --> 00:16:09.650 And the reason is that the energy of the orbitals, depend 00:16:09.650 --> 00:16:12.520 on two quantum numbers, and that's quantum number n, and 00:16:12.520 --> 00:16:13.740 quantum number l. 00:16:13.740 --> 00:16:16.620 M does not actually have an effect, in this case, on the 00:16:16.620 --> 00:16:18.350 energy of the orbital. 00:16:18.350 --> 00:16:20.100 So that's why we're not seeing separate 00:16:20.100 --> 00:16:24.370 lines in this spectrum. 00:16:24.370 --> 00:16:24.600 All right. 00:16:24.600 --> 00:16:28.300 So let's go ahead and try an example here in thinking about 00:16:28.300 --> 00:16:29.770 photoelectron spectroscopy. 00:16:29.770 --> 00:16:33.120 So, let's say we're looking at an element and we have an 00:16:33.120 --> 00:16:35.950 emission spectra, and we know that it has five distinct 00:16:35.950 --> 00:16:38.860 different kinetic energies in that spectrum. 00:16:38.860 --> 00:16:42.600 We might be asked, for example, to determine what all 00:16:42.600 --> 00:16:44.740 of the different elements could be that would produce a 00:16:44.740 --> 00:16:47.410 spectrum that gave us 5 different lines. 00:16:47.410 --> 00:16:49.620 So the first thing that we want to do, if we're thinking 00:16:49.620 --> 00:16:56.210 about something like this, is just to determine exactly what 00:16:56.210 --> 00:16:58.990 orbitals are causing the five different lines that we're 00:16:58.990 --> 00:17:00.690 seeing in the spectrum. 00:17:00.690 --> 00:17:03.060 So, if we're talking about five different orbitals and 00:17:03.060 --> 00:17:05.420 we're talking about a ground state atom, we know that we 00:17:05.420 --> 00:17:06.880 just need to start at the bottom and 00:17:06.880 --> 00:17:08.220 work our way out up. 00:17:08.220 --> 00:17:10.840 So, our first orbital that an electron must be coming from 00:17:10.840 --> 00:17:11.900 is the 1 s. 00:17:11.900 --> 00:17:13.583 What comes after that? 00:17:13.583 --> 00:17:15.190 2 s. 00:17:15.190 --> 00:17:16.070 All right, then what? 00:17:16.070 --> 00:17:20.740 2 p. 00:17:20.740 --> 00:17:22.540 After that? 00:17:22.540 --> 00:17:23.990 3 s. 00:17:23.990 --> 00:17:25.530 Next? 00:17:25.530 --> 00:17:31.890 3 p, and that's 1, 2, 3, 4 -- that gives us five different 00:17:31.890 --> 00:17:34.200 options, five different orbitals, five different 00:17:34.200 --> 00:17:35.820 energies right there. 00:17:35.820 --> 00:17:38.950 So, then all we need to do to determine which elements that 00:17:38.950 --> 00:17:41.960 corresponds to is take a look at our periodic table. 00:17:41.960 --> 00:17:45.490 So we want to look at any element that has a 3 p orbital 00:17:45.490 --> 00:17:49.470 filled, but that does not then go on and have a 4 s, because 00:17:49.470 --> 00:17:51.880 if it had the 4 s filled then we would actually see six 00:17:51.880 --> 00:17:53.360 lines in the spectrum. 00:17:53.360 --> 00:17:58.230 So that is relevant for all of these atoms here, so we 00:17:58.230 --> 00:18:00.840 actually have several different possibilities. 00:18:00.840 --> 00:18:06.250 It could be aluminum, silicone, phosphorous, sulfur, 00:18:06.250 --> 00:18:09.530 chlorine or argon. 00:18:09.530 --> 00:18:12.000 Any one of these different elements could actually 00:18:12.000 --> 00:18:16.410 produce a photoelectron spectroscopy spectrum that has 00:18:16.410 --> 00:18:18.090 five distinct lines. 00:18:18.090 --> 00:18:20.950 If I went on and told you what the different incident light 00:18:20.950 --> 00:18:24.830 was, and what the electrons were ejected with, and then 00:18:24.830 --> 00:18:26.910 you could look up the ionization energy for the 00:18:26.910 --> 00:18:29.780 particular different elements, you should be able to actually 00:18:29.780 --> 00:18:32.450 determine exactly which element it is, but just with 00:18:32.450 --> 00:18:34.830 the information given, we can only narrow it down to these 00:18:34.830 --> 00:18:36.880 choices here. 00:18:36.880 --> 00:18:41.350 So let's actually let you try another example of solving a 00:18:41.350 --> 00:18:43.540 problem that has to do with one of the spectrums. So, 00:18:43.540 --> 00:18:46.700 let's turn to another clicker question here. 00:18:46.700 --> 00:18:49.610 Remember, your answer holds great weight in terms of the 00:18:49.610 --> 00:18:52.950 state of the TA bragging for next week. 00:18:52.950 --> 00:18:55.640 So, how many distinct, so again, we're talking about 00:18:55.640 --> 00:18:58.380 distinct kinetic energies, would be displayed if you're 00:18:58.380 --> 00:19:01.990 talking about a spectrum for the element hafnium, and I'll 00:19:01.990 --> 00:19:04.620 tell you here that it has a z of 72, so you don't have to 00:19:04.620 --> 00:19:07.570 spend two minutes searching your periodic table. 00:19:07.570 --> 00:19:10.980 The period of table's on the back page of your notes if you 00:19:10.980 --> 00:19:46.270 don't see that there. 00:19:46.270 --> 00:19:46.490 All right. 00:19:46.490 --> 00:19:48.640 It looks like a lot of you are done, so let's take 10 more 00:19:48.640 --> 00:19:53.250 seconds here. 00:19:53.250 --> 00:19:56.220 Part of the challenge is speed, too, how quickly you 00:19:56.220 --> 00:19:59.680 can get these answers in terms of getting them in on time. 00:19:59.680 --> 00:20:02.120 So let's see what we say. 00:20:02.120 --> 00:20:02.730 All right. 00:20:02.730 --> 00:20:06.560 So I think I can safely say that most people had the right 00:20:06.560 --> 00:20:10.390 idea and were counting quickly, though I have a 00:20:10.390 --> 00:20:13.330 feeling that some people who wrote 13 might have forgotten 00:20:13.330 --> 00:20:16.960 about those 4 f, the 4 f electrons. 00:20:16.960 --> 00:20:19.340 So, remember when you're looking at your periodic 00:20:19.340 --> 00:20:22.180 table, don't forget about the lanthinides, sometimes they 00:20:22.180 --> 00:20:23.840 come into play. 00:20:23.840 --> 00:20:27.270 So it's actually 14, and the way that we got that answer 00:20:27.270 --> 00:20:29.990 was we just wrote out or just looked at your period table, 00:20:29.990 --> 00:20:32.590 figured out all of the different orbitals that you 00:20:32.590 --> 00:20:36.720 could have in terms of the principle quantum number, and 00:20:36.720 --> 00:20:39.110 then the l quantum number, and then write them all down -- it 00:20:39.110 --> 00:20:42.970 turns out to be 14, so that's what the answer is. 00:20:42.970 --> 00:20:45.040 So, it looks like this is good, because we'll have some 00:20:45.040 --> 00:20:48.520 separation in terms of not everyone's going to get 100% 00:20:48.520 --> 00:20:52.030 in terms of recitations here, which is what we're going for. 00:20:52.030 --> 00:20:52.870 All right. 00:20:52.870 --> 00:20:55.750 So let's turn our attention to a new topic, which is thinking 00:20:55.750 --> 00:20:58.300 a little bit about the periodic table, and also 00:20:58.300 --> 00:21:00.000 talking about periodic trends. 00:21:00.000 --> 00:21:03.140 And there's a lot we can explain by talking about what 00:21:03.140 --> 00:21:06.220 we see in the periodic table in terms of what different 00:21:06.220 --> 00:21:08.050 trends are in grouping different elements in 00:21:08.050 --> 00:21:10.860 different spots within the periodic table. 00:21:10.860 --> 00:21:13.840 So, here we have a picture of Dmitri Mendeleev, who is one 00:21:13.840 --> 00:21:17.220 of the scientists responsible for first compiling the 00:21:17.220 --> 00:21:18.560 periodic table. 00:21:18.560 --> 00:21:21.830 You'll notice I have what's a very flattering picture of him 00:21:21.830 --> 00:21:24.860 up here, and if you haven't done the reading yet you might 00:21:24.860 --> 00:21:27.130 not think this is particularly flattering, but if you look at 00:21:27.130 --> 00:21:31.130 the picture of him in the book, you'll notice I chose a 00:21:31.130 --> 00:21:34.820 very flattering picture of Dmitri up here, and here he's 00:21:34.820 --> 00:21:37.450 pondering putting these elements together in a 00:21:37.450 --> 00:21:38.690 periodic table. 00:21:38.690 --> 00:21:42.790 And he actually did this in the late 1800's, back before 00:21:42.790 --> 00:21:45.690 even all of the elements that we know today were discovered, 00:21:45.690 --> 00:21:49.740 really only about 60% or so, 70% were discovered then that 00:21:49.740 --> 00:21:51.040 we now know today. 00:21:51.040 --> 00:21:55.230 But still, he was able to put together a periodic table. 00:21:55.230 --> 00:21:57.870 And what he did what he actually grouped things in 00:21:57.870 --> 00:22:00.080 terms of their chemical properties. 00:22:00.080 --> 00:22:02.550 So the way that we like to think of things now is in 00:22:02.550 --> 00:22:04.660 terms of electron configurations, right, but at 00:22:04.660 --> 00:22:06.760 the time that wasn't really understood. 00:22:06.760 --> 00:22:09.240 So, instead, it was amazing he was able to group things in 00:22:09.240 --> 00:22:11.390 terms of the properties that he saw. 00:22:11.390 --> 00:22:15.050 So, for example, if he was talking about the group one 00:22:15.050 --> 00:22:18.040 metals, lithium, sodium, potassium -- he noticed these 00:22:18.040 --> 00:22:20.140 were all very soft reactive metals, those 00:22:20.140 --> 00:22:21.540 were grouped together. 00:22:21.540 --> 00:22:26.000 Versus looking at, for example, helium or neon or 00:22:26.000 --> 00:22:28.910 argon, these are all inert gases, inert meaning 00:22:28.910 --> 00:22:32.280 essentially do not react, those were grouped together in 00:22:32.280 --> 00:22:33.850 the periodic table. 00:22:33.850 --> 00:22:37.070 So basically, at the time he was just going on size and 00:22:37.070 --> 00:22:41.050 then traits, but what we actually know today is that we 00:22:41.050 --> 00:22:45.130 can also order things in the periodic table by electron 00:22:45.130 --> 00:22:45.750 configuration. 00:22:45.750 --> 00:22:48.130 In fact, that is the most logical way for us 00:22:48.130 --> 00:22:49.300 to look at it now. 00:22:49.300 --> 00:22:51.700 So, for example, if we're actually thinking about 00:22:51.700 --> 00:22:54.150 electron configuration and we look at lithium, sodium and 00:22:54.150 --> 00:22:58.060 potassium, these all have one valence electron. 00:22:58.060 --> 00:23:01.420 So basically, that means one electron in an s orbital in 00:23:01.420 --> 00:23:03.060 their outer-most most shell. 00:23:03.060 --> 00:23:05.740 So that explains why they're so reactive, they're all very 00:23:05.740 --> 00:23:08.510 willing to give up that 1 s orbital and then drop to a 00:23:08.510 --> 00:23:10.280 lower energy level. 00:23:10.280 --> 00:23:14.690 In contrast, helium, neon, and argon all have filled shells. 00:23:14.690 --> 00:23:17.140 That also explains why they're very stable. 00:23:17.140 --> 00:23:19.480 They're not going to want to add on another electron, 00:23:19.480 --> 00:23:21.950 because then it'll have to jump a very large energy level 00:23:21.950 --> 00:23:24.820 and start filling in another shell -- go from n equals 2, 00:23:24.820 --> 00:23:29.370 to n equals 3, and n equals 4, and so on. 00:23:29.370 --> 00:23:31.760 So it turns out that we can really know a lot just by 00:23:31.760 --> 00:23:34.430 looking at the periodic table. 00:23:34.430 --> 00:23:37.070 You will never in this class have to memorize anything 00:23:37.070 --> 00:23:38.070 about the periodic table. 00:23:38.070 --> 00:23:40.150 Depending on what kind of chemistry you go in to, you 00:23:40.150 --> 00:23:43.120 might accidentally memorize parts of the table, which is 00:23:43.120 --> 00:23:45.710 fine, but what you really want to know how to do is know how 00:23:45.710 --> 00:23:48.110 to use the periodic table. 00:23:48.110 --> 00:23:51.160 But you actually need to keep a few caveats in mind as you 00:23:51.160 --> 00:23:54.330 do this, which is the fact that trends predict a lot of 00:23:54.330 --> 00:23:57.490 chemical properties, but they can't predict everything in 00:23:57.490 --> 00:23:59.460 terms of biological properties. 00:23:59.460 --> 00:24:02.370 And after the periodic table was developed in the late 00:24:02.370 --> 00:24:04.760 1800's, people didn't understand this quite as well, 00:24:04.760 --> 00:24:06.170 they took things a little more literally. 00:24:06.170 --> 00:24:09.340 They thought, for example, if you could do something with 00:24:09.340 --> 00:24:12.250 one element, if you looked at an element very close to it, 00:24:12.250 --> 00:24:14.400 it would be similar enough that you could maybe replace 00:24:14.400 --> 00:24:15.400 it with that. 00:24:15.400 --> 00:24:18.120 Today we know, for example, if you can put one certain kind 00:24:18.120 --> 00:24:21.030 of element in your mouth or eat that, it doesn't 00:24:21.030 --> 00:24:23.160 necessarily mean you want to put the element next to it and 00:24:23.160 --> 00:24:25.740 your mouth as well, that might not be safe. 00:24:25.740 --> 00:24:29.390 But this is things we've learned as the years have gone 00:24:29.390 --> 00:24:30.370 past. 00:24:30.370 --> 00:24:33.840 So, let's just take a quick example to show how not 00:24:33.840 --> 00:24:36.050 completely you can use these periodic trends, that there 00:24:36.050 --> 00:24:36.970 are limits. 00:24:36.970 --> 00:24:39.540 So if we consider lithium, potassium, and sodium, they're 00:24:39.540 --> 00:24:42.690 all together in the same group on the periodic table, knowing 00:24:42.690 --> 00:24:45.640 what we do about biology we can immediately think of 00:24:45.640 --> 00:24:48.070 sodium and potassium, or even just knowing what you know 00:24:48.070 --> 00:24:52.160 about table salt, for example, that these are two elements 00:24:52.160 --> 00:24:55.250 that we find, and particularly in the ion form in very high 00:24:55.250 --> 00:24:57.030 concentrations in our body. 00:24:57.030 --> 00:24:59.910 For example, sodium in our blood plasma is almost to the 00:24:59.910 --> 00:25:03.130 point sometimes of 100 millimol or that's very, very 00:25:03.130 --> 00:25:04.630 concentrated. 00:25:04.630 --> 00:25:07.710 Similarly, we find it in table salt, we're taking it in all 00:25:07.710 --> 00:25:10.160 the time, the same with potassium, think of bananas, 00:25:10.160 --> 00:25:12.200 were always eating potassium. 00:25:12.200 --> 00:25:14.270 Not so with lithium. 00:25:14.270 --> 00:25:16.200 I don't think too many people and here are 00:25:16.200 --> 00:25:17.560 probably taking lithium. 00:25:17.560 --> 00:25:21.490 It turns out there's actually no natural function known in 00:25:21.490 --> 00:25:22.500 the body for lithium. 00:25:22.500 --> 00:25:25.310 So there's nothing naturally going on unless we were to 00:25:25.310 --> 00:25:27.992 introduce it ourselves in our body that we know of, at 00:25:27.992 --> 00:25:30.630 least, that involves lithium. 00:25:30.630 --> 00:25:33.410 But this did not stop people, for example, in the late 00:25:33.410 --> 00:25:39.910 1800's, early 1900's, and, in fact, in 1927 a new soft drink 00:25:39.910 --> 00:25:42.610 was put on to the market and they wanted to make a 00:25:42.610 --> 00:25:45.230 lemon-lime soft drink, these were very popular in the early 00:25:45.230 --> 00:25:48.880 1900's, and to get sort of that lemony flavor, they 00:25:48.880 --> 00:25:51.880 decided to use citric acid, so that's a good idea, that gives 00:25:51.880 --> 00:25:53.620 that soury taste. 00:25:53.620 --> 00:25:56.980 And they wanted to use a soluble salt of citric acid, 00:25:56.980 --> 00:25:58.740 so they could have used sodium, they 00:25:58.740 --> 00:25:59.310 could have used potassium. 00:25:59.310 --> 00:26:02.760 But, you know why not do something a little special, 00:26:02.760 --> 00:26:04.240 little different, and they decided 00:26:04.240 --> 00:26:06.370 instead to use lithium. 00:26:06.370 --> 00:26:09.160 So, here we have this soda with lithium citrate, some of 00:26:09.160 --> 00:26:14.580 you might be familiar with this, soda is called 7-Up. 00:26:14.580 --> 00:26:20.020 So, 7-Up no longer has lithium in it, but from 1927 to 1950 00:26:20.020 --> 00:26:24.220 it did, and, in fact, not only did they not try to hide the 00:26:24.220 --> 00:26:26.970 fact that there's lithium in the soda, this they used as a 00:26:26.970 --> 00:26:30.400 really special marketing technique, they really pointed 00:26:30.400 --> 00:26:32.670 out this is something that stands out about our soda, 00:26:32.670 --> 00:26:34.420 this is something special. 00:26:34.420 --> 00:26:36.510 There's a lot of good things about lithium. 00:26:36.510 --> 00:26:38.910 I don't know if you can see, probably not, what's written 00:26:38.910 --> 00:26:44.170 on here, so let me point out to you a few things. 00:26:44.170 --> 00:26:48.000 Lithium, slenderizing, that's great to see in a soda. 00:26:48.000 --> 00:26:50.140 Other nice things about lithium in your soda, it 00:26:50.140 --> 00:26:53.170 dispells hangovers, takes the ouch out of grouch. 00:26:53.170 --> 00:26:54.520 That's very nice. 00:26:54.520 --> 00:26:58.540 So basically, you get a lot of benefit supposedly from this 00:26:58.540 --> 00:27:02.960 7-Up soda from the 1920's or so. 00:27:02.960 --> 00:27:06.480 And this went on and was unregulated for some time, but 00:27:06.480 --> 00:27:09.910 at some point the Food and Drug Administration did take a 00:27:09.910 --> 00:27:12.930 step in, so here's a case where they did do something 00:27:12.930 --> 00:27:19.240 important -- that's not what I mean at all -- where they did 00:27:19.240 --> 00:27:21.380 take the step, they do many things that are important, 00:27:21.380 --> 00:27:23.400 often not quickly enough. 00:27:23.400 --> 00:27:26.810 Here's a -- actually here it did take 25 years, but they 00:27:26.810 --> 00:27:28.260 did, they did eventually step on before we 00:27:28.260 --> 00:27:30.220 started drinking 7-Up. 00:27:30.220 --> 00:27:33.060 And what they said was, look, you can't put this in, we're 00:27:33.060 --> 00:27:35.470 starting to notice it does some strange things. 00:27:35.470 --> 00:27:38.920 Because it was in the 1950's or so, maybe the late 1940's, 00:27:38.920 --> 00:27:41.520 that people started to discover lithium, even though 00:27:41.520 --> 00:27:43.250 it had no natural function, it did do 00:27:43.250 --> 00:27:45.080 something in our bodies. 00:27:45.080 --> 00:27:49.030 Does anyone know what was lithium's used for? 00:27:49.030 --> 00:27:52.040 Yeah, it's an anti-psychotic drug, so, for example, some 00:27:52.040 --> 00:27:55.180 people with bipolar disorder even today still take it, it 00:27:55.180 --> 00:27:57.260 works really well for some people, for other people it 00:27:57.260 --> 00:27:58.890 doesn't work so well. 00:27:58.890 --> 00:28:01.360 But anyway, this isn't really something you want to have in 00:28:01.360 --> 00:28:04.670 your soda, so they did take it out eventually. 00:28:04.670 --> 00:28:07.580 Another side effect if you take too much lithium is 00:28:07.580 --> 00:28:12.510 death, so that's no good to have in sodas either, and it 00:28:12.510 --> 00:28:15.260 might not have been as big a deal back in the 1920's, but 00:28:15.260 --> 00:28:17.930 you can imagine with supersizing today, this might 00:28:17.930 --> 00:28:19.470 be a bigger problem. 00:28:19.470 --> 00:28:23.580 So anyway, when we talk about periodic trends, it doesn't 00:28:23.580 --> 00:28:24.630 always match up. 00:28:24.630 --> 00:28:28.100 This was eventually taken out, and actually just for your 00:28:28.100 --> 00:28:31.450 interest, there was no overlap between the time when cocaine 00:28:31.450 --> 00:28:33.910 was in Coca Cola and lithium was in 7-Up, so there was a 00:28:33.910 --> 00:28:36.300 few years difference between those two times, but it's 00:28:36.300 --> 00:28:40.590 amazing to think about what does go into processed foods. 00:28:40.590 --> 00:28:43.200 And the other thing to point out, which I don't know if 00:28:43.200 --> 00:28:46.170 this is true or not, but does anyone know -- well that's 00:28:46.170 --> 00:28:48.300 part's true, does anyone know what the atomic mass of 00:28:48.300 --> 00:28:49.780 lithium is? 00:28:49.780 --> 00:28:50.790 Yes, it's 7. 00:28:50.790 --> 00:28:53.060 So, I don't know if this is true or not, but I wonder if 00:28:53.060 --> 00:28:55.030 that's where the actual name 7-Up came from. 00:28:55.030 --> 00:28:57.400 So, even though we don't have the lithium anymore, we still 00:28:57.400 --> 00:29:00.960 keep that atomic number 7 around. 00:29:00.960 --> 00:29:01.190 All right. 00:29:01.190 --> 00:29:05.210 So that is an anti-example of using periodic trends. 00:29:05.210 --> 00:29:09.000 So let's go to some actual real examples, which might 00:29:09.000 --> 00:29:10.750 come more in handy for this class. 00:29:10.750 --> 00:29:13.310 So it's going to keep in mind the limitations, so let's 00:29:13.310 --> 00:29:17.190 start off with talking about ionization energy. 00:29:17.190 --> 00:29:19.410 Now this is a good place to start, because we are very 00:29:19.410 --> 00:29:21.560 familiar with ionization energy, we've been talking 00:29:21.560 --> 00:29:24.250 about it in a lot of different forms for quite a while -- 00:29:24.250 --> 00:29:28.220 it's that minimum energy required to remove an electron 00:29:28.220 --> 00:29:29.310 from an atom. 00:29:29.310 --> 00:29:32.720 And specifically, when we talk about ionization energy, it's 00:29:32.720 --> 00:29:34.810 assumed that what we mean is actually the 00:29:34.810 --> 00:29:36.780 first ionization energy. 00:29:36.780 --> 00:29:39.310 So, you can imagine, we could talk about any of the 00:29:39.310 --> 00:29:41.860 different electrons, or we could talk about taking out an 00:29:41.860 --> 00:29:43.400 electron and taking out second electron. 00:29:43.400 --> 00:29:47.690 Whenever you hear the term ionization energy, make sure 00:29:47.690 --> 00:29:50.210 you keep in mind that unless we say otherwise, we're 00:29:50.210 --> 00:29:53.040 talking about that first ionization energy. 00:29:53.040 --> 00:29:55.490 And we know what that's equal to, this is something we've 00:29:55.490 --> 00:29:58.880 been over and over, ionization energy is simply equal to the 00:29:58.880 --> 00:30:00.840 negative of the binding energy. 00:30:00.840 --> 00:30:04.390 So negative e, which is sub n l, because it's a function of 00:30:04.390 --> 00:30:08.950 n and l in terms of quantum numbers. 00:30:08.950 --> 00:30:12.730 So, let's think about kind of differentiating, however, 00:30:12.730 --> 00:30:15.830 between first ionization energy or just ionization 00:30:15.830 --> 00:30:18.960 energy, and other types such as second or third ionization 00:30:18.960 --> 00:30:22.100 energy, and let's take boron as an example here. 00:30:22.100 --> 00:30:24.510 So, if we want to think about what the first ionization 00:30:24.510 --> 00:30:27.360 energy is of boron, what you want to do is write out the 00:30:27.360 --> 00:30:29.490 electron configuration, because then you can think 00:30:29.490 --> 00:30:32.070 about where it is that the electron's coming out of. 00:30:32.070 --> 00:30:34.900 The electron's going to come out of that highest occupied 00:30:34.900 --> 00:30:37.340 atomic orbital, that one that's the highest in energy, 00:30:37.340 --> 00:30:39.730 because that's going to be the at least amount of energy it 00:30:39.730 --> 00:30:41.120 needs to eject something. 00:30:41.120 --> 00:30:45.750 So what we'll end up with is boron plus, 1 s 2, 2 s 2, and 00:30:45.750 --> 00:30:49.450 what we say is the delta energy or the change in energy 00:30:49.450 --> 00:30:52.570 as the same thing as saying the energy of the products 00:30:52.570 --> 00:30:55.210 minus the energy of our reactant here, and we just 00:30:55.210 --> 00:30:57.310 call that the ionization energy -- that's how much 00:30:57.310 --> 00:31:00.660 energy we have to put into the system to eject an electron. 00:31:00.660 --> 00:31:03.560 And again, this is just the negative, the binding energy, 00:31:03.560 --> 00:31:07.920 when we're talking about the 2 p orbital. 00:31:07.920 --> 00:31:11.200 So, this is first ionization energy, let's think about 00:31:11.200 --> 00:31:13.310 second ionization energy. 00:31:13.310 --> 00:31:16.040 So, second ionization energy simply means you've already 00:31:16.040 --> 00:31:19.110 taken one electron out, now how much energy does it take 00:31:19.110 --> 00:31:21.180 for you to take a second electron out. 00:31:21.180 --> 00:31:24.210 So in the case of boron here, what we're starting with is 00:31:24.210 --> 00:31:29.080 the ion, boron 1 s 2, 2 s 2, and now we're going to pull 00:31:29.080 --> 00:31:30.850 one more electron out. 00:31:30.850 --> 00:31:34.570 The highest occupied orbital is now the 2 s orbital, so 00:31:34.570 --> 00:31:39.470 we're going to end up with boron 2 plus 1 s 2, 2 s 1, 00:31:39.470 --> 00:31:42.410 plus the electron coming out of there. 00:31:42.410 --> 00:31:45.490 And what we say when we talk about the delta energy is that 00:31:45.490 --> 00:31:49.840 this is going to be equal to i e 2, or the second ionization 00:31:49.840 --> 00:31:53.510 energy, or we could say the negative of the binding energy 00:31:53.510 --> 00:31:58.400 of a 2 s electron in b plus. so it's important to note that 00:31:58.400 --> 00:32:01.190 it's not in b, now we're talking about b plus, because 00:32:01.190 --> 00:32:04.130 we've already taken an electron out here. 00:32:04.130 --> 00:32:06.340 So, similarly if we start talking about our third 00:32:06.340 --> 00:32:09.930 ionization energy, this is going to be going from b plus 00:32:09.930 --> 00:32:12.690 2, to 1 s 2, 2 s 1. 00:32:12.690 --> 00:32:15.320 Now we're going to pull that second electron out of the 2 00:32:15.320 --> 00:32:19.160 s, so we end up with boron plus 3, and then the 00:32:19.160 --> 00:32:24.670 configuration is just 1 s 2, plus our extra electron here. 00:32:24.670 --> 00:32:28.040 So, what we call this is the third ionization energy, or 00:32:28.040 --> 00:32:30.770 the negative of the binding energy, again of the 2 s 00:32:30.770 --> 00:32:35.850 orbital, but now it's in boron plus 2 to we're starting with. 00:32:35.850 --> 00:32:38.830 So, this raises kind of an interesting question in terms 00:32:38.830 --> 00:32:41.800 of what the difference is between these two cases, and 00:32:41.800 --> 00:32:45.150 we're talking about numbers of energy. 00:32:45.150 --> 00:32:48.930 So let's address this by considering another example, 00:32:48.930 --> 00:32:51.830 which should clarify what the difference is between these 00:32:51.830 --> 00:32:52.820 ionization energies. 00:32:52.820 --> 00:32:55.730 So let's think about the energy required now to remove 00:32:55.730 --> 00:32:58.920 a 2 s electron, let's say we're removing it from boron 00:32:58.920 --> 00:33:01.340 plus 1 versus neutral boron. 00:33:01.340 --> 00:33:06.050 So, in the case of boron plus 1, what we are starting with 00:33:06.050 --> 00:33:10.700 is the ion, so we're starting with a 2 s electron, and then 00:33:10.700 --> 00:33:13.160 we're going to 2 s 1 here. 00:33:13.160 --> 00:33:16.800 And what we call the binding energy is negative 2 s in b 00:33:16.800 --> 00:33:19.670 plus -- this is what we saw on the last slide. 00:33:19.670 --> 00:33:22.695 And the second case here looks a lot more like what we saw 00:33:22.695 --> 00:33:25.780 when we were talking about photoelectron spectroscopy, 00:33:25.780 --> 00:33:28.610 because here we want to remove a 2 s electron, but it's 00:33:28.610 --> 00:33:32.070 actually not the highest occupied orbital, so that's 00:33:32.070 --> 00:33:34.140 not the one that would naturally come out first, but 00:33:34.140 --> 00:33:36.160 let's say we're hitting it with high energy light 00:33:36.160 --> 00:33:38.800 sufficient to knock out all the different electrons, and 00:33:38.800 --> 00:33:41.810 one that we end up knocking out is this 2 s here. 00:33:41.810 --> 00:33:45.160 So if we think about what that delta energy is, we call that 00:33:45.160 --> 00:33:48.490 the ionization of the 2 s, that's different from saying 00:33:48.490 --> 00:33:50.290 second ionization energy. 00:33:50.290 --> 00:33:52.580 And that's going to be equal to the negative the binding 00:33:52.580 --> 00:33:57.020 energy of 2 s in b, in neutral boron. 00:33:57.020 --> 00:34:01.100 So, my question to you is are these two energies equal? 00:34:01.100 --> 00:34:02.290 No. 00:34:02.290 --> 00:34:03.730 All right, good answer. 00:34:03.730 --> 00:34:06.660 So, we can think about why is it that these are not equal. 00:34:06.660 --> 00:34:08.580 In both cases we're taking an electron 00:34:08.580 --> 00:34:11.130 out of the 2 s orbital. 00:34:11.130 --> 00:34:14.210 And it turns out that if we're talking about a 2 s orbital in 00:34:14.210 --> 00:34:18.310 an ion, that means it doesn't have as many electrons in it, 00:34:18.310 --> 00:34:20.410 so what we're going to see is less sheilding. 00:34:20.410 --> 00:34:23.550 There are fewer electrons around to shield some of that 00:34:23.550 --> 00:34:24.700 nuclear charge. 00:34:24.700 --> 00:34:27.660 So what we're going to see is less sheilding, which means 00:34:27.660 --> 00:34:31.680 that it will actually feel a higher z effective. 00:34:31.680 --> 00:34:35.410 So even though they're both 2 s electrons, in one case it's 00:34:35.410 --> 00:34:38.300 going to think its feeling more pull from the nucleus, 00:34:38.300 --> 00:34:41.430 and it, in fact, will be, than in the other case, and if its 00:34:41.430 --> 00:34:44.090 feeling a higher z effective, then it's actually going to 00:34:44.090 --> 00:34:46.820 require more energy to remove that electron, right, it's 00:34:46.820 --> 00:34:49.480 being pulled in closer and more tightly to the nucleus, 00:34:49.480 --> 00:34:52.310 you have to put in more energy to rip it away from that very 00:34:52.310 --> 00:34:54.730 close interaction. 00:34:54.730 --> 00:34:57.380 So, that's the difference in thinking about different types 00:34:57.380 --> 00:35:00.550 of ionization energy, so it can get a little bit confusing 00:35:00.550 --> 00:35:02.620 with terminology if you're just looking at something 00:35:02.620 --> 00:35:04.670 quickly, so make sure you look really carefully about what 00:35:04.670 --> 00:35:05.460 we're discussing here. 00:35:05.460 --> 00:35:08.560 If you see a problem that asks you, for example, the third 00:35:08.560 --> 00:35:11.710 ionization energy versus taking a second electron out 00:35:11.710 --> 00:35:14.740 of the 2 s in a photoelectron spectroscopy experiment, those 00:35:14.740 --> 00:35:17.480 are two very different things. 00:35:17.480 --> 00:35:20.200 So, let's make sure everyone kind of has this down, let's 00:35:20.200 --> 00:35:25.030 do another clicker question here. 00:35:25.030 --> 00:35:27.540 And in this case we're going to look at silicone, and we'll 00:35:27.540 --> 00:35:31.120 say if you can point out to me which requires the least 00:35:31.120 --> 00:35:32.310 amount of energy. 00:35:32.310 --> 00:35:35.380 So, which has the smallest energy that you have to put in 00:35:35.380 --> 00:35:37.290 in order to eject this electron? 00:35:37.290 --> 00:35:40.970 Will it be if you take a 3 s electron from neutral 00:35:40.970 --> 00:35:44.390 silicone, if you take a 3 p electron from the neutral 00:35:44.390 --> 00:35:48.590 atom, or if you take a 3 p from the ion? 00:35:48.590 --> 00:35:51.070 So this you should be able to know pretty quickly, so let's 00:35:51.070 --> 00:36:05.280 just take 10 seconds here. 00:36:05.280 --> 00:36:05.950 All right, great. 00:36:05.950 --> 00:36:10.580 So most of you see that, in fact, the energy that's going 00:36:10.580 --> 00:36:14.080 to be the least that we need to put in is in case 2 here. 00:36:14.080 --> 00:36:16.950 Let's compare case 2 and 3, since this where some people 00:36:16.950 --> 00:36:18.750 seem to have gotten confused. 00:36:18.750 --> 00:36:22.390 In case 2, we're taking it out of -- oh, it's kind of hard to 00:36:22.390 --> 00:36:26.010 compare case 2 and 3 when we can't see it anymore. 00:36:26.010 --> 00:36:32.140 In case 2, we're taking the 3 p out of the neutral atom, 00:36:32.140 --> 00:36:35.180 whereas in case 3, we're taking it out of the ion. 00:36:35.180 --> 00:36:38.260 Remember in the ion, we're going to have less electrons 00:36:38.260 --> 00:36:42.400 around to counteract the pull from the nucleus. 00:36:42.400 --> 00:36:46.100 So we're going to feel a higher z effective in the case 00:36:46.100 --> 00:36:48.860 of the ion compared to the neutral atom. 00:36:48.860 --> 00:36:50.800 If we have a higher z effective, it's pulled in 00:36:50.800 --> 00:36:53.670 tighter, we have to put in more energy in order to eject 00:36:53.670 --> 00:36:56.220 an electron, so it turns out that that's why case 2 is 00:36:56.220 --> 00:36:59.000 actually the lowest energy that we need to put in. 00:36:59.000 --> 00:37:03.600 The z effective is lower, so we have to put less energy in 00:37:03.600 --> 00:37:07.030 to get an ion out. 00:37:07.030 --> 00:37:10.990 So, let's take a look at this in terms of periodic trends -- 00:37:10.990 --> 00:37:14.150 that's our topic here, we're talking about periodic trends. 00:37:14.150 --> 00:37:17.100 So as we go across the row, and this is my beautiful 00:37:17.100 --> 00:37:19.050 picture of a periodic table here. 00:37:19.050 --> 00:37:21.850 As we go across the row what happens is that the ionization 00:37:21.850 --> 00:37:25.240 energy actually increases, and we can think about logically 00:37:25.240 --> 00:37:27.540 why it is that that's happening. 00:37:27.540 --> 00:37:31.020 As we go across the row, what we have happening is that the 00:37:31.020 --> 00:37:32.710 z or the atomic charge -- 00:37:32.710 --> 00:37:34.300 I'm not talking about z effective here, I'm just 00:37:34.300 --> 00:37:37.960 talking about z -- the z is increasing as we go across a 00:37:37.960 --> 00:37:39.800 row, that's easy to see. 00:37:39.800 --> 00:37:42.330 But we're still in the same shell, so we still have the 00:37:42.330 --> 00:37:45.920 same n value as we go all the way across a row in the 00:37:45.920 --> 00:37:47.260 periodic table. 00:37:47.260 --> 00:37:50.380 So, in general what we're going to see is that what 00:37:50.380 --> 00:37:53.660 happens to z effective if we have z increasing but we're in 00:37:53.660 --> 00:37:56.150 the same shell here. 00:37:56.150 --> 00:38:01.220 Would it increase or decrease z effective? 00:38:01.220 --> 00:38:01.570 All right. 00:38:01.570 --> 00:38:04.140 Kind of mixed thoughts here. 00:38:04.140 --> 00:38:07.020 So it turns out that it increases, and the reason is 00:38:07.020 --> 00:38:10.230 because the predominant thing that's going on here is that z 00:38:10.230 --> 00:38:11.330 is increasing. 00:38:11.330 --> 00:38:13.970 So the z is increasing, and what goes along with it is 00:38:13.970 --> 00:38:16.840 that the z effective is increasing, because it turns 00:38:16.840 --> 00:38:19.430 out that while we're in the same n, even though we know 00:38:19.430 --> 00:38:22.420 that energy depends on both the n and the l in terms of 00:38:22.420 --> 00:38:25.390 quantum numbers, while we're in the same n, the distance 00:38:25.390 --> 00:38:27.280 from the nucleus, it's pretty close, 00:38:27.280 --> 00:38:28.850 it's not hugely different. 00:38:28.850 --> 00:38:30.850 So the factor that predominates is that we're 00:38:30.850 --> 00:38:32.300 actually increasing z. 00:38:32.300 --> 00:38:34.680 That's why we see z effective increase, and that's why we 00:38:34.680 --> 00:38:37.160 see ionization energy increase. 00:38:37.160 --> 00:38:40.770 As we go down a column, what happens is that the ionization 00:38:40.770 --> 00:38:42.040 energy decreases. 00:38:42.040 --> 00:38:45.220 We can also think about this in terms of z effective. 00:38:45.220 --> 00:38:48.450 This is because even though z, the atomic number is still 00:38:48.450 --> 00:38:51.300 increasing, we are also getting further 00:38:51.300 --> 00:38:52.160 away from the nucleus. 00:38:52.160 --> 00:38:55.030 So, remember when we talk about Coulomb force, what's 00:38:55.030 --> 00:38:57.750 holding the nucleus and the electron together, there's 2 00:38:57.750 --> 00:38:58.890 things we need to think about. 00:38:58.890 --> 00:39:02.110 The first is this the z effective, or how much charge 00:39:02.110 --> 00:39:05.130 is actually in the nucleus that's felt, or the I guess we 00:39:05.130 --> 00:39:08.510 would say the z, how much the charge is on the nucleus that 00:39:08.510 --> 00:39:09.870 holds it close together. 00:39:09.870 --> 00:39:11.970 But the second factor is how far away we 00:39:11.970 --> 00:39:12.810 are from the nucleus. 00:39:12.810 --> 00:39:15.500 So, if we're really close to the nucleus, that's when z 00:39:15.500 --> 00:39:18.410 effective is high, but if we get really far away, then z 00:39:18.410 --> 00:39:20.590 effective is going to get low, because even though we have 00:39:20.590 --> 00:39:22.640 the same charge in the nucleus, the z 00:39:22.640 --> 00:39:23.670 effective gets lower. 00:39:23.670 --> 00:39:26.460 So this is not even thinking about the other electron 00:39:26.460 --> 00:39:29.540 shielding, just if we think of the fact, all we need to think 00:39:29.540 --> 00:39:33.030 about is that the effect of going to a further away n 00:39:33.030 --> 00:39:36.170 actually dominates as we go down the table. 00:39:36.170 --> 00:39:38.980 We're getting further away from the nucleus because we're 00:39:38.980 --> 00:39:42.070 jumping, for example, from the n equals 2 to the n equals 3 00:39:42.070 --> 00:39:45.030 shell, or from the n equals 3 to the n equals 4 shell. 00:39:45.030 --> 00:39:47.270 And when you're switching n's, you're actually getting quite 00:39:47.270 --> 00:39:48.520 a bit farther away. 00:39:48.520 --> 00:39:50.980 That's why in the earlier models of the atom, they're 00:39:50.980 --> 00:39:54.080 not horrible to sometimes think about just each n value 00:39:54.080 --> 00:39:55.600 as a little ring around. 00:39:55.600 --> 00:39:58.530 It's not complete and it's not accurate, but it's OK to kind 00:39:58.530 --> 00:40:00.840 of think of it in terms of how far we're getting away from 00:40:00.840 --> 00:40:01.890 the nucleus. 00:40:01.890 --> 00:40:04.600 So, as we go down a column, we see ionization energy's going 00:40:04.600 --> 00:40:06.850 to decrease. 00:40:06.850 --> 00:40:09.440 So, this means we have the general trends down, so we 00:40:09.440 --> 00:40:12.950 should be able to look at actual atoms in our periodic 00:40:12.950 --> 00:40:14.580 table and graph them and see that they 00:40:14.580 --> 00:40:16.040 match up with our trends. 00:40:16.040 --> 00:40:19.840 So here we have that graphed here, we have atomic number z 00:40:19.840 --> 00:40:23.720 graphed against ionization energy, so, let's fill in what 00:40:23.720 --> 00:40:27.080 the actual atoms are here, and we can see in general, yes, 00:40:27.080 --> 00:40:28.260 we're following the trend. 00:40:28.260 --> 00:40:32.350 For row one, we're increasing, as we should, across the row. 00:40:32.350 --> 00:40:34.550 Let's look at row two also. 00:40:34.550 --> 00:40:36.800 Well, we're generally increasing here, we'll talk 00:40:36.800 --> 00:40:38.180 about that more in a minute. 00:40:38.180 --> 00:40:41.630 And also in a row three, yeah, we're generally increasing, 00:40:41.630 --> 00:40:43.190 there's some glitches here, but the 00:40:43.190 --> 00:40:45.320 general trend holds true. 00:40:45.320 --> 00:40:48.710 Similarly we see as we go down the table, so as we're going 00:40:48.710 --> 00:40:52.780 from one row to the next row, so, for example, between 00:40:52.780 --> 00:40:56.300 helium and lithium, we see a drop; the same with neon to 00:40:56.300 --> 00:40:58.270 sodium, we see a drop here. 00:40:58.270 --> 00:41:00.660 So it looks like we're generally following our trend, 00:41:00.660 --> 00:41:02.150 that's a good thing. 00:41:02.150 --> 00:41:05.720 But hopefully, you will not be satisfied to just make a 00:41:05.720 --> 00:41:09.280 general statement here when we do have these glitches. 00:41:09.280 --> 00:41:11.930 So you can see, for example, we have several places where 00:41:11.930 --> 00:41:15.220 instead of going up as we go across the row, we actually go 00:41:15.220 --> 00:41:17.460 down in ionization energy a little bit. 00:41:17.460 --> 00:41:21.620 So between b e, and b, between n and o, magesium and 00:41:21.620 --> 00:41:25.170 aluminum, and then phosphorous and sulfur, what we see here 00:41:25.170 --> 00:41:27.700 is that we're kind of going down, or quite specifically, 00:41:27.700 --> 00:41:29.250 we are going down. 00:41:29.250 --> 00:41:31.780 So, let's take a look at one of these rows in more detail 00:41:31.780 --> 00:41:34.810 to think about why this might be happening, and it turns out 00:41:34.810 --> 00:41:38.680 the reason that these glitches occur are because the sub 00:41:38.680 --> 00:41:42.660 shell structure predominates in certain instances, and 00:41:42.660 --> 00:41:44.930 that's where these glitches take place. 00:41:44.930 --> 00:41:48.600 So I've sort of just spread out what we have as the second 00:41:48.600 --> 00:41:52.800 row here, graphed against the ionization energy. 00:41:52.800 --> 00:41:54.170 So, let's consider specifically where these 00:41:54.170 --> 00:41:55.540 glitches are taking place. 00:41:55.540 --> 00:41:58.300 So, let's look at the first one between beryllium and 00:41:58.300 --> 00:42:00.900 boron here. 00:42:00.900 --> 00:42:04.600 And the glitch that doesn't make sense just through 00:42:04.600 --> 00:42:07.500 periodic trends, is that it turns out that the ionization 00:42:07.500 --> 00:42:11.100 energy of boron is actually less than the ionization 00:42:11.100 --> 00:42:12.680 energy up beryllium. 00:42:12.680 --> 00:42:15.060 So I put the electron configurations and actually 00:42:15.060 --> 00:42:18.080 drew it on an energy diagram here, so we can actually think 00:42:18.080 --> 00:42:19.880 about why this might be happening. 00:42:19.880 --> 00:42:23.910 So what is this, which element did I chart here? 00:42:23.910 --> 00:42:28.930 Which one is that, the boron or the beryllium? 00:42:28.930 --> 00:42:30.730 I couldn't tell what you said, sorry. 00:42:30.730 --> 00:42:34.530 So, I'm going to assume that was beryllium, and then it 00:42:34.530 --> 00:42:36.210 turns out that if that's beryllium, the 00:42:36.210 --> 00:42:37.930 other one must be boron. 00:42:37.930 --> 00:42:41.360 So, we have beryllium in the first case here, it has four 00:42:41.360 --> 00:42:43.630 electrons, that's how we know it's beryllium, 00:42:43.630 --> 00:42:45.500 boron has five electrons. 00:42:45.500 --> 00:42:49.370 So, just looking at putting in the electrons, filling up the 00:42:49.370 --> 00:42:53.190 energy diagram here, we should be able to see a little bit 00:42:53.190 --> 00:42:54.430 why this is happening. 00:42:54.430 --> 00:42:57.780 And the reason is simply because the energy that we 00:42:57.780 --> 00:43:02.510 gain in terms of moving up in z, so from going to z equals 4 00:43:02.510 --> 00:43:06.160 to z equals 5, is actually outweighed by the energy it 00:43:06.160 --> 00:43:09.250 takes to go into this new shell, to go into 00:43:09.250 --> 00:43:10.410 this new sub shell. 00:43:10.410 --> 00:43:14.330 So to jump from the 2 s to the 2 p, takes more energy than we 00:43:14.330 --> 00:43:17.580 can actually compensate with by increasing the pull from 00:43:17.580 --> 00:43:18.560 the nucleus. 00:43:18.560 --> 00:43:23.020 So, it turns out that in this case, and any time that we see 00:43:23.020 --> 00:43:27.960 we're going from a 2 s to 2 p, filling in of electrons, we 00:43:27.960 --> 00:43:29.350 actually see that little bit of glitch 00:43:29.350 --> 00:43:31.030 in ionization energy. 00:43:31.030 --> 00:43:33.350 So it's shown here for the second row, but it's actually 00:43:33.350 --> 00:43:35.280 also going to be true for the third row. 00:43:35.280 --> 00:43:38.080 The same thing when you're going from filling in the 2 s 00:43:38.080 --> 00:43:40.380 to putting that first electron into the 2 p. 00:43:40.380 --> 00:43:42.850 So that explains one of our glitches here, but we have 00:43:42.850 --> 00:43:46.120 another glitch, and that second glitch comes between 00:43:46.120 --> 00:43:48.400 nitrogen and oxygen. 00:43:48.400 --> 00:43:50.010 So, these sound more different, so I think I'll be 00:43:50.010 --> 00:43:51.000 able to distinguish. 00:43:51.000 --> 00:43:56.630 Which element is shown here? 00:43:56.630 --> 00:43:57.290 Yeah, nitrogen. 00:43:57.290 --> 00:44:00.220 So, nitrogen is shown here, we know that 00:44:00.220 --> 00:44:01.950 because it has 7 electrons. 00:44:01.950 --> 00:44:03.460 In this case, we're talking about 8 00:44:03.460 --> 00:44:06.470 electrons, which is oxygen. 00:44:06.470 --> 00:44:08.690 So if we're comparing the difference between these 2 00:44:08.690 --> 00:44:11.950 now, what you'll notice is that in nitrogen we have all 00:44:11.950 --> 00:44:16.700 half-filled 2 p orbitals, and now, once we move into oxygen, 00:44:16.700 --> 00:44:19.340 we actually have to add 1 more electron into 00:44:19.340 --> 00:44:20.760 1 of the 2 p orbitals. 00:44:20.760 --> 00:44:23.050 There's no more 2 p orbitals to put it into, so we're going 00:44:23.050 --> 00:44:24.540 to actually have to double up. 00:44:24.540 --> 00:44:27.570 So now we're putting 2 electrons into the same p 00:44:27.570 --> 00:44:29.670 orbital, that's not a problem, we can do it, it's not a huge 00:44:29.670 --> 00:44:30.980 energy cost to do that. 00:44:30.980 --> 00:44:33.900 But actually there is a little bit of an energy cost into 00:44:33.900 --> 00:44:36.670 doubling up into a single orbital, because, of course, 00:44:36.670 --> 00:44:40.380 it takes energy when you create more electron 00:44:40.380 --> 00:44:42.820 repulsion, that's not something we want to do, but 00:44:42.820 --> 00:44:45.810 we have to do it here, and it turns out that that effect 00:44:45.810 --> 00:44:48.640 predominates over, again, the energy that we gain by 00:44:48.640 --> 00:44:51.160 increasing the atomic number by one. 00:44:51.160 --> 00:44:54.480 So, our two glitches we see when we go from the 2 p, or 00:44:54.480 --> 00:44:57.500 from 2 s to start filling the 2 p, and then we also get 00:44:57.500 --> 00:45:00.380 another glitch when we've half-filled the 2 p, and now 00:45:00.380 --> 00:45:02.170 we're adding and having to double up in 00:45:02.170 --> 00:45:03.550 one of those p orbitals. 00:45:03.550 --> 00:45:05.510 Again, we see the same effect as we go into 00:45:05.510 --> 00:45:09.410 different rows as well. 00:45:09.410 --> 00:45:13.440 So let's talk about another periodic trend, this one is 00:45:13.440 --> 00:45:14.660 called electron affinity. 00:45:14.660 --> 00:45:19.140 Electron affinity is actually the ability of an atom, or we 00:45:19.140 --> 00:45:21.880 could also talk about an ion to gain electrons. 00:45:21.880 --> 00:45:24.590 So it's the affinity it has for electrons, it's how much 00:45:24.590 --> 00:45:26.370 it likes to get an electron. 00:45:26.370 --> 00:45:30.320 We can write out what it is for any certain atom or ion x, 00:45:30.320 --> 00:45:33.550 so it's just x plus an electron gives us x minus. 00:45:33.550 --> 00:45:35.970 We have the minus because we're adding a negative charge 00:45:35.970 --> 00:45:37.550 from the electron. 00:45:37.550 --> 00:45:40.780 So, basically any time we have a really high positive number 00:45:40.780 --> 00:45:44.110 of electron affinity, it means that that atom or ion really 00:45:44.110 --> 00:45:46.620 wants to gain another electron, and it will be very 00:45:46.620 --> 00:45:48.690 stable and happy if it does so. 00:45:48.690 --> 00:45:51.800 So let's look at an example of chlorine here. 00:45:51.800 --> 00:45:54.950 So chlorine, if we talk about it in terms of electron 00:45:54.950 --> 00:45:58.010 affinity, we would be writing that we're actually gaining an 00:45:58.010 --> 00:46:01.230 electron here, and getting the ion, c l minus. 00:46:01.230 --> 00:46:04.760 And the change in energy for this reaction is negative 349 00:46:04.760 --> 00:46:07.490 kilojoules per mole. 00:46:07.490 --> 00:46:10.110 So if we have a negative change in energy for any 00:46:10.110 --> 00:46:12.960 reaction as it's written, what that actually means is we're 00:46:12.960 --> 00:46:15.990 giving off energy as the reaction proceeds. 00:46:15.990 --> 00:46:19.640 So, in other words, this c l minus is actually lower in 00:46:19.640 --> 00:46:21.500 energy than the reactants were. 00:46:21.500 --> 00:46:23.500 So that's why we're giving off extra energy. 00:46:23.500 --> 00:46:25.940 We saw a similar thing as we saw electrons move from 00:46:25.940 --> 00:46:26.770 different levels. 00:46:26.770 --> 00:46:29.350 We can think of it in the same type of way when we're talking 00:46:29.350 --> 00:46:31.720 about actual reactions happening. 00:46:31.720 --> 00:46:34.930 So, if we have energy that's released, would you say that 00:46:34.930 --> 00:46:38.270 the chlorine ion is more or less stable than 00:46:38.270 --> 00:46:38.830 the chlorine atom? 00:46:38.830 --> 00:46:42.300 Who thinks it's more stable, show of hands? 00:46:42.300 --> 00:46:45.260 All right, who thinks it's less stable? 00:46:45.260 --> 00:46:46.450 Very good. 00:46:46.450 --> 00:46:48.660 So it turns out it is, in fact, more stable. 00:46:48.660 --> 00:46:51.370 It's more stable because you actually -- this happens 00:46:51.370 --> 00:46:54.610 spontaneously, you actually get energy out of the reaction 00:46:54.610 --> 00:46:55.410 as this happens. 00:46:55.410 --> 00:46:57.510 And we haven't talked about reactions at all yet, so you 00:46:57.510 --> 00:47:01.400 don't need to worry about the specifics of that exactly, but 00:47:01.400 --> 00:47:03.830 just that if you have this negative change in energy, you 00:47:03.830 --> 00:47:07.430 have a more stable product than you do reactant. 00:47:07.430 --> 00:47:11.150 So, we were talking, however, about energy in terms of 00:47:11.150 --> 00:47:14.040 electron affinity, so we can actually relate electron 00:47:14.040 --> 00:47:17.470 affinity to any reaction by saying if we have this 00:47:17.470 --> 00:47:20.310 reaction written as here where we're gaining an electron, we 00:47:20.310 --> 00:47:23.110 say that electron affinity is just equal to the negative of 00:47:23.110 --> 00:47:24.780 that change in energy. 00:47:24.780 --> 00:47:28.240 So, for example, for the chlorine case, we would say 00:47:28.240 --> 00:47:32.090 that the electron affinity for chlorine is actually positive 00:47:32.090 --> 00:47:35.120 349 kilojoules per mole. 00:47:35.120 --> 00:47:37.980 That's a very large number, it's all relative, so you 00:47:37.980 --> 00:47:39.990 don't necessarily know it's large without me telling you 00:47:39.990 --> 00:47:43.690 or giving you other ions to compare to, but chlorine does 00:47:43.690 --> 00:47:46.670 have a very large affinity, meaning it's really likes 00:47:46.670 --> 00:47:50.170 getting an electron and becoming a chlorine ion. 00:47:50.170 --> 00:47:53.020 One major difference between electron affinity and 00:47:53.020 --> 00:47:56.010 ionization energy is that when we talked about ionization 00:47:56.010 --> 00:47:58.230 energy, remember ionization energy 00:47:58.230 --> 00:47:59.790 always has to be positive. 00:47:59.790 --> 00:48:01.230 We will never have a case where 00:48:01.230 --> 00:48:03.410 ionization energy is negative. 00:48:03.410 --> 00:48:06.200 Electron affinity, however, can be either negative or it 00:48:06.200 --> 00:48:07.540 can be positive. 00:48:07.540 --> 00:48:09.160 So let's look at a case where it's 00:48:09.160 --> 00:48:10.350 actually going to be negative. 00:48:10.350 --> 00:48:12.610 So, if we took the case of nitrogen, if we add an 00:48:12.610 --> 00:48:15.750 electron to nitrogen and go to n minus, we find that the 00:48:15.750 --> 00:48:18.600 change in energy is 7 kilojoules per mole. 00:48:18.600 --> 00:48:22.310 This means in order to do that we actually have to put 7 00:48:22.310 --> 00:48:24.320 kilojoules per mole of energy into the 00:48:24.320 --> 00:48:26.000 reaction to make it happen. 00:48:26.000 --> 00:48:28.450 So this is not going to be a favorable process, we're going 00:48:28.450 --> 00:48:31.620 to find that the electron affinity is actually a 00:48:31.620 --> 00:48:34.590 negative 7 kilojoules per mole for nitrogen. 00:48:34.590 --> 00:48:38.240 So this means nitrogen has low electron affinity, it doesn't 00:48:38.240 --> 00:48:41.710 actually want to gain an electron. 00:48:41.710 --> 00:48:45.440 So, that also tells us that the n minus ion is less stable 00:48:45.440 --> 00:48:47.950 than the neutral atom itself. 00:48:47.950 --> 00:48:50.930 So, we can think about trends in electron affinity just like 00:48:50.930 --> 00:48:53.180 we did for ionization energy, and what we see 00:48:53.180 --> 00:48:54.510 is a similar trend. 00:48:54.510 --> 00:48:57.760 Electron affinity increases as we go across a row in the 00:48:57.760 --> 00:49:00.500 periodic table, and it decreases as 00:49:00.500 --> 00:49:02.320 we go down a column. 00:49:02.320 --> 00:49:05.090 I left out the noble gases here because they do something 00:49:05.090 --> 00:49:07.240 a little bit special, and actually, I'm going to give 00:49:07.240 --> 00:49:10.320 you one last clicker question today to see if you can tell 00:49:10.320 --> 00:49:12.480 me what you think noble gases do. 00:49:12.480 --> 00:49:14.300 To answer this question you just really want to think 00:49:14.300 --> 00:49:16.020 about what does electron affinity means. 00:49:16.020 --> 00:49:18.600 It means how much a certain atom actually 00:49:18.600 --> 00:49:21.370 wants to get an electron. 00:49:21.370 --> 00:49:23.880 So do you think noble gases would have a high positive 00:49:23.880 --> 00:49:25.910 electron affinity, a low positive, or 00:49:25.910 --> 00:49:26.700 negative electron affinity? 00:49:26.700 --> 00:49:40.160 So, let's take 10 seconds on that. 00:49:40.160 --> 00:49:40.480 All right. 00:49:40.480 --> 00:49:40.850 Great. 00:49:40.850 --> 00:49:43.800 So most of you recognize, if we switch back to the notes, 00:49:43.800 --> 00:49:46.150 that they do have a negative electron affinity. 00:49:46.150 --> 00:49:48.430 This should make sense to you, because they don't, in fact, 00:49:48.430 --> 00:49:51.450 want to gain another electron, because that would mean that 00:49:51.450 --> 00:49:54.750 electron would have to go into a new value of n, a new shell, 00:49:54.750 --> 00:49:56.350 and that's really going to increase the 00:49:56.350 --> 00:49:58.220 energy of the system. 00:49:58.220 --> 00:50:00.910 So they'd much rather just stay the way they are and not 00:50:00.910 --> 00:50:04.400 have another electron come on, and it turns out that halogens 00:50:04.400 --> 00:50:06.570 have the highest electron affinities.