WEBVTT 00:00:00.030 --> 00:00:02.400 The following content is provided under a Creative 00:00:02.400 --> 00:00:03.780 Commons license. 00:00:03.780 --> 00:00:06.020 Your support will help MIT OpenCourseWare 00:00:06.020 --> 00:00:10.090 continue to offer high quality educational resources for free. 00:00:10.090 --> 00:00:12.670 To make a donation or to view additional materials 00:00:12.670 --> 00:00:16.580 from hundreds of MIT courses, visit MIT OpenCourseWare 00:00:16.580 --> 00:00:18.710 at ocw.mit.edu. 00:00:37.982 --> 00:00:39.190 CATHERINE DRENNAN: All right. 00:00:39.190 --> 00:00:40.900 Let's just take 10 more seconds. 00:00:57.885 --> 00:00:58.385 OK. 00:01:01.280 --> 00:01:05.319 So let's look at this one. 00:01:05.319 --> 00:01:11.370 So first, you want to notice that you have a plus 1 here. 00:01:11.370 --> 00:01:13.790 So you've lost an electron. 00:01:13.790 --> 00:01:16.530 And then you want to think about what happens when you 00:01:16.530 --> 00:01:18.750 start filling the deorbitals. 00:01:18.750 --> 00:01:21.590 So when you start filling the deorbitals, 00:01:21.590 --> 00:01:27.910 then the energy changes and 4s and 3d switch an energy. 00:01:27.910 --> 00:01:30.110 And so we could write this one either way. 00:01:30.110 --> 00:01:33.980 We could have put the 3d first and the 4s second. 00:01:33.980 --> 00:01:38.220 But importantly now, because of that switch in energy, 00:01:38.220 --> 00:01:43.230 the electron that is lost is lost from the 4s over here. 00:01:43.230 --> 00:01:47.650 So this has to do with the fact that electron configuration 00:01:47.650 --> 00:01:51.340 of neutral atoms and ions are different and especially 00:01:51.340 --> 00:01:58.670 with this 4s-3d switch, that the 3d orbitals drop, change energy 00:01:58.670 --> 00:02:00.450 when you start to fill them. 00:02:00.450 --> 00:02:05.320 And there's really very similar energy between 4s and 3d. 00:02:05.320 --> 00:02:07.680 And that leads to some of the exceptions 00:02:07.680 --> 00:02:11.170 that you're responsible to know that there 00:02:11.170 --> 00:02:14.510 can be subtle things that switch the energy a little bit. 00:02:14.510 --> 00:02:17.050 So because they're so close in energy, 00:02:17.050 --> 00:02:19.640 you have this half-filled and full-filled thing 00:02:19.640 --> 00:02:22.330 where you can pull an electron from 4s 00:02:22.330 --> 00:02:26.520 and put it in 3d to make 3d5 or to make 3d10. 00:02:26.520 --> 00:02:29.220 So they're very close in energy. 00:02:29.220 --> 00:02:32.060 And that leads to some of these interesting features. 00:02:32.060 --> 00:02:32.720 OK. 00:02:32.720 --> 00:02:35.500 So today's lecture, we're moving on to the periodic table. 00:02:35.500 --> 00:02:38.110 But we're actually talking about a lot of the things 00:02:38.110 --> 00:02:39.510 that we just talked about. 00:02:39.510 --> 00:02:41.740 So today actually turns out to be 00:02:41.740 --> 00:02:45.170 an awesome review for some of the material that's 00:02:45.170 --> 00:02:45.815 on the exams. 00:02:45.815 --> 00:02:47.450 So that worked out really well. 00:02:47.450 --> 00:02:50.180 In past years, this material was on exam 1. 00:02:50.180 --> 00:02:51.670 Exam 1 was later. 00:02:51.670 --> 00:02:58.070 And so if you get old exams from other people, not the ones that 00:02:58.070 --> 00:02:59.620 are posted, the ones that are posted 00:02:59.620 --> 00:03:02.990 are mostly old exams, except we were placed questions 00:03:02.990 --> 00:03:06.350 for material not covered on this exam with material that 00:03:06.350 --> 00:03:07.340 is covered. 00:03:07.340 --> 00:03:10.990 So it's not 100% an old exam from this class 00:03:10.990 --> 00:03:13.650 because we've never had an exam this early before. 00:03:13.650 --> 00:03:15.210 So there were no good examples. 00:03:15.210 --> 00:03:17.570 So if you get old exams from other people, 00:03:17.570 --> 00:03:20.029 do not freak out when you look at it, 00:03:20.029 --> 00:03:21.070 and like, oh my goodness. 00:03:21.070 --> 00:03:23.210 Somehow I haven't learned this. 00:03:23.210 --> 00:03:25.810 There are today's lecture and also 00:03:25.810 --> 00:03:28.940 Friday's lecture we're typically on exam 1. 00:03:28.940 --> 00:03:30.930 So just keep that in mind. 00:03:30.930 --> 00:03:34.710 So use our practice exams and then you 00:03:34.710 --> 00:03:37.120 will not have that problem. 00:03:37.120 --> 00:03:37.620 All right. 00:03:37.620 --> 00:03:40.895 So moving on to the periodic table. 00:03:40.895 --> 00:03:43.890 This is very exciting for me. 00:03:43.890 --> 00:03:46.610 And so today, we're going to talk about trends 00:03:46.610 --> 00:03:48.070 in the periodic table. 00:03:48.070 --> 00:03:50.140 We're going to finish that up on Friday 00:03:50.140 --> 00:03:53.020 after the exam, which will be a clicker competition. 00:03:53.020 --> 00:03:56.310 And then we're going to go on to talk 00:03:56.310 --> 00:03:59.690 about bonding of the elements in the periodic table. 00:03:59.690 --> 00:04:02.170 So that's where we're headed. 00:04:02.170 --> 00:04:07.250 So the periodic table, here is one of them that's up here. 00:04:07.250 --> 00:04:10.680 So this was originally put together a while ago. 00:04:10.680 --> 00:04:13.380 And it turned out to be amazingly accurate. 00:04:13.380 --> 00:04:15.780 And this really describes all of the elements. 00:04:15.780 --> 00:04:21.019 So this is kind of like the artist's paintbox for a chemist 00:04:21.019 --> 00:04:22.860 or wordsmiths words. 00:04:22.860 --> 00:04:27.250 These are all the ingredients that go into making everything. 00:04:27.250 --> 00:04:29.830 Some of these elements are incredibly dangerous 00:04:29.830 --> 00:04:32.510 and they're used to make explosives. 00:04:32.510 --> 00:04:34.510 They're used to make bombs. 00:04:34.510 --> 00:04:37.300 Other elements here are found in the human body 00:04:37.300 --> 00:04:38.860 and allow us to live. 00:04:38.860 --> 00:04:42.060 All materials, whether it's a desk, a pointer, 00:04:42.060 --> 00:04:46.440 a bottle of water, everything is made up of elements. 00:04:46.440 --> 00:04:49.280 So this is one of the reasons why 00:04:49.280 --> 00:04:52.100 chemistry is so cool because we think about the elements. 00:04:52.100 --> 00:04:54.970 And elements are made of everything. 00:04:54.970 --> 00:04:58.580 So we think about everything that makes up everything. 00:04:58.580 --> 00:05:01.810 And that's pretty neat. 00:05:01.810 --> 00:05:05.070 So just to kind of give you a flavor 00:05:05.070 --> 00:05:09.280 of the joy of the periodic table and introduce you 00:05:09.280 --> 00:05:12.130 to the elements that make up this periodic table, 00:05:12.130 --> 00:05:15.980 I feel like we should think about this in music. 00:05:15.980 --> 00:05:20.780 [MUSIC - THEY MIGHT BE GIANTS, "MEET THE ELEMENTS"] 00:05:20.780 --> 00:05:23.300 [SINGING] Iron is a metal. 00:05:23.300 --> 00:05:25.910 You see it every day. 00:05:25.910 --> 00:05:31.190 Oxygen, eventually, will make it rust away. 00:05:31.190 --> 00:05:36.180 Carbon in its ordinary form is coal. 00:05:36.180 --> 00:05:41.010 Crush it together and diamonds are born. 00:05:41.010 --> 00:05:44.010 Come on, come on and meet the elements. 00:05:44.010 --> 00:05:48.628 May I introduce you to our friends, the elements? 00:05:48.628 --> 00:05:54.840 Like a box of paints that are mixed to make every shade, 00:05:54.840 --> 00:05:58.340 they either combine to make a chemical compound 00:05:58.340 --> 00:06:01.440 or stand alone as they are. 00:06:01.440 --> 00:06:05.798 Neon's a gas that lights up the sign for a pizza place. 00:06:05.798 --> 00:06:10.790 The coins that you pay with are copper, nickel, and zinc. 00:06:10.790 --> 00:06:15.452 Silicon and oxygen make concrete bricks and glass. 00:06:15.452 --> 00:06:21.270 Now add some gold and silver for some pizza place class. 00:06:21.270 --> 00:06:24.247 Come on, come on and meet the elements. 00:06:24.247 --> 00:06:28.540 I think you should check out the ones they call the elements. 00:06:28.540 --> 00:06:35.202 Like a box of paints that are mixed to make every shade, 00:06:35.202 --> 00:06:38.513 they either combine to make a chemical compound 00:06:38.513 --> 00:06:40.781 or stand alone as they are. 00:06:40.781 --> 00:06:41.280 OK. 00:06:41.280 --> 00:06:44.030 So you get the sense of this. 00:06:44.030 --> 00:06:45.440 The song is quite accurate. 00:06:45.440 --> 00:06:47.680 It has lots of information [INAUDIBLE] them. 00:06:47.680 --> 00:06:49.170 And it points out some other things 00:06:49.170 --> 00:06:51.420 like elephants are made of elements. 00:06:51.420 --> 00:06:55.590 And we're made of elephants-- oh no, wait-- elements. 00:06:55.590 --> 00:06:57.960 No, it's a really fun, fun song. 00:06:57.960 --> 00:07:01.030 And it really, I think, expresses 00:07:01.030 --> 00:07:03.730 why It's so important to learn about the properties 00:07:03.730 --> 00:07:05.520 of the elements and all the things 00:07:05.520 --> 00:07:07.000 that you can do with them. 00:07:07.000 --> 00:07:11.160 So when it was originally put together, 00:07:11.160 --> 00:07:14.770 it was put together based on sorting elements 00:07:14.770 --> 00:07:19.010 by their properties, such as ones over here in column 1 00:07:19.010 --> 00:07:21.370 are soft and reactive metals. 00:07:21.370 --> 00:07:24.930 And it was observed that the elements over here 00:07:24.930 --> 00:07:26.190 are pretty inert. 00:07:26.190 --> 00:07:28.070 So they were all grouped together. 00:07:28.070 --> 00:07:31.330 And later, we have pretty much kept this grouping. 00:07:31.330 --> 00:07:35.110 But now, it's really grouped by the electron configurations, 00:07:35.110 --> 00:07:38.090 which is one of the things you need to know for the exam, 00:07:38.090 --> 00:07:40.840 how to write these electron configurations. 00:07:40.840 --> 00:07:43.490 And these reactive metals, it turns out, 00:07:43.490 --> 00:07:45.690 they only have one valence electron. 00:07:45.690 --> 00:07:49.530 So they like to react because they want to have a noble gas 00:07:49.530 --> 00:07:53.880 configuration, so they're very reactive whereas these others 00:07:53.880 --> 00:07:57.980 that were not reactive, have filled electron configurations. 00:07:57.980 --> 00:07:59.896 So they don't want any extra electrons 00:07:59.896 --> 00:08:01.270 and they don't want to lose them. 00:08:01.270 --> 00:08:02.400 They don't want to get any. 00:08:02.400 --> 00:08:03.810 They're very happy as they are. 00:08:03.810 --> 00:08:04.930 So they're inert. 00:08:04.930 --> 00:08:07.340 So now these groupings make a lot of sense 00:08:07.340 --> 00:08:10.590 in terms of the electron configurations. 00:08:10.590 --> 00:08:12.770 Now, it doesn't tell you everything. 00:08:12.770 --> 00:08:17.990 So if you know one element is very safe to consume, 00:08:17.990 --> 00:08:20.630 that doesn't necessarily mean something right next 00:08:20.630 --> 00:08:22.990 to it is just as good. 00:08:22.990 --> 00:08:28.190 And if we consider over here, we consider lithium, sodium, 00:08:28.190 --> 00:08:31.280 and potassium, sodium and potassium 00:08:31.280 --> 00:08:34.840 are ions that are really important in the human body. 00:08:34.840 --> 00:08:37.870 And you have to make sure that if you're exercising a lot, 00:08:37.870 --> 00:08:41.730 that you keep up the amounts that you're getting. 00:08:41.730 --> 00:08:43.850 So they're very important ions. 00:08:43.850 --> 00:08:47.360 And they will often hang around and serve as counter-ions 00:08:47.360 --> 00:08:49.370 to other molecules in your body. 00:08:49.370 --> 00:08:50.830 You have citrate in your body. 00:08:50.830 --> 00:08:54.070 So you could have sodium citrate where the sodium is hanging out 00:08:54.070 --> 00:08:56.160 or potassium citrate. 00:08:56.160 --> 00:08:57.980 But that doesn't necessarily mean 00:08:57.980 --> 00:09:01.610 that other things will work as well, like lithium, 00:09:01.610 --> 00:09:02.670 for example. 00:09:02.670 --> 00:09:09.410 But a while ago when 7-Up soda was first put on the market, 00:09:09.410 --> 00:09:12.560 they thought well, sodium and potassium are a little boring. 00:09:12.560 --> 00:09:15.070 Let's sort of make things a little more exciting 00:09:15.070 --> 00:09:17.000 and use lithium citrate instead. 00:09:17.000 --> 00:09:21.790 It's right there in the same column of the periodic table. 00:09:21.790 --> 00:09:24.510 And citrate makes things taste lemony, 00:09:24.510 --> 00:09:26.220 which is a lovely taste. 00:09:26.220 --> 00:09:29.700 And we'll have lithium as the counter-ion to that. 00:09:29.700 --> 00:09:32.890 And so they said this dispels hangovers. 00:09:32.890 --> 00:09:35.320 It takes the ouch out of grouch. 00:09:35.320 --> 00:09:38.555 And does anyone know what lithium is used for today? 00:09:41.450 --> 00:09:43.120 So it's often used for people who 00:09:43.120 --> 00:09:45.860 have bipolar disorders or manic depressive. 00:09:45.860 --> 00:09:49.000 So it really did take the ouch out of grouch. 00:09:49.000 --> 00:09:52.130 But it's not something that you should just 00:09:52.130 --> 00:09:55.500 put in a consumable soda. 00:09:55.500 --> 00:09:59.020 So it has somewhat different properties, 00:09:59.020 --> 00:10:01.320 even though it's part of that same group. 00:10:01.320 --> 00:10:03.610 So this is a lesson that I feel like we 00:10:03.610 --> 00:10:06.220 keep learning over and over again with other things, 00:10:06.220 --> 00:10:08.860 that you have to be a little more careful. 00:10:08.860 --> 00:10:11.180 Just because it's hanging out near its friends, 00:10:11.180 --> 00:10:14.591 doesn't mean it's going to be exactly the same. 00:10:14.591 --> 00:10:15.090 All right. 00:10:15.090 --> 00:10:19.150 So the periodic table is an amazing thing. 00:10:19.150 --> 00:10:22.120 Let's think about the trends in the periodic table. 00:10:22.120 --> 00:10:24.570 So we're going to first do ionization energy. 00:10:24.570 --> 00:10:26.730 And we've already talked about ionization energy. 00:10:26.730 --> 00:10:29.040 So this is awesome because it turns out 00:10:29.040 --> 00:10:33.380 to be a really good review for the exam. 00:10:33.380 --> 00:10:36.570 So ionization energy, again, is the minimum energy 00:10:36.570 --> 00:10:41.360 it's going to take to remove an electron from an atom. 00:10:41.360 --> 00:10:46.250 And if we just talk about-- just say IE for ionization energy-- 00:10:46.250 --> 00:10:49.550 we're going to assume it's the first ionization 00:10:49.550 --> 00:10:53.180 energy unless it is specified. 00:10:53.180 --> 00:10:58.060 And we saw before that ionization energy is opposite 00:10:58.060 --> 00:11:00.800 in sign to the binding energy. 00:11:00.800 --> 00:11:04.040 And so here we have the binding energy of an electron. 00:11:04.040 --> 00:11:08.490 And we know that this is a multi-electron atom 00:11:08.490 --> 00:11:11.080 because it depends on n and l. 00:11:11.080 --> 00:11:14.700 If it was just hydrogen or one other one-electron atom, 00:11:14.700 --> 00:11:19.470 then anything with n, all those orbitals, are degenerate. 00:11:19.470 --> 00:11:21.460 But if you have putting in multi-electrons, 00:11:21.460 --> 00:11:24.320 then it matters whether you're talking about not just n, 00:11:24.320 --> 00:11:28.650 but l matters too, whether it's an s orbital or p orbital. 00:11:28.650 --> 00:11:30.220 So we've seen this before. 00:11:30.220 --> 00:11:34.800 But now let's talk more about different ionization energies. 00:11:34.800 --> 00:11:38.870 So let's look at boron and think about the first ionization 00:11:38.870 --> 00:11:39.670 energy. 00:11:39.670 --> 00:11:43.440 And this is the energy to move an electron from the highest 00:11:43.440 --> 00:11:45.494 occupied atomic orbital. 00:11:45.494 --> 00:11:46.660 That's what that stands for. 00:11:46.660 --> 00:11:48.440 And it's written out in your notes. 00:11:48.440 --> 00:11:55.530 And so what is the highest occupied orbital in this case? 00:11:55.530 --> 00:11:57.650 Just yell it out. 00:11:57.650 --> 00:11:59.340 2p. 00:11:59.340 --> 00:12:02.880 So let's look at removing an electron from 2p. 00:12:02.880 --> 00:12:05.980 If we do that, we go to boron plus. 00:12:05.980 --> 00:12:09.210 And we have 1s2, 2s2, an electron. 00:12:09.210 --> 00:12:12.610 And this process, the energy involved in this process, 00:12:12.610 --> 00:12:16.320 is the ionization energy-- the first ionization energy. 00:12:16.320 --> 00:12:21.360 It's also equal to the binding energy of the 2p electron. 00:12:21.360 --> 00:12:26.100 And again, the signs are opposite here. 00:12:26.100 --> 00:12:30.400 So now second ionization energy, we just keep going. 00:12:30.400 --> 00:12:35.860 The next highest occupied atomic orbital is 2s. 00:12:35.860 --> 00:12:41.670 So if we remove, we get boron plus 2 1s2, 2s1 00:12:41.670 --> 00:12:43.610 and an electron. 00:12:43.610 --> 00:12:48.130 And now the energy difference is due to these second ionization 00:12:48.130 --> 00:12:48.710 energies. 00:12:48.710 --> 00:12:50.910 So we say IE2. 00:12:50.910 --> 00:12:56.316 And that is equal to the binding energy of the 2s electron in B 00:12:56.316 --> 00:12:58.300 plus because that's what we're removing. 00:12:58.300 --> 00:13:03.980 We're moving a 2s electron from B plus here. 00:13:03.980 --> 00:13:05.200 So we can keep going. 00:13:05.200 --> 00:13:09.820 We can go to the third ionization energy. 00:13:09.820 --> 00:13:15.950 And now we're also going to be removing an electron from 2s. 00:13:15.950 --> 00:13:19.360 And when we remove the electron, it only had one. 00:13:19.360 --> 00:13:24.790 So now we have a boron plus 3 1s2 and an electron. 00:13:24.790 --> 00:13:28.540 The energy difference is the third ionization energy-- 00:13:28.540 --> 00:13:30.200 IE sub 3. 00:13:30.200 --> 00:13:33.650 And this is equal to the binding energy. 00:13:33.650 --> 00:13:36.930 Or the difference in sign is the binding energy of 2s 00:13:36.930 --> 00:13:39.624 in the plus 2 system. 00:13:42.460 --> 00:13:45.580 So now if we look at this little table over here that's 00:13:45.580 --> 00:13:49.120 in your handout or this little chart in your handout, 00:13:49.120 --> 00:13:53.110 you can see that there is quite a bit of difference 00:13:53.110 --> 00:13:55.920 between these different ionization energies. 00:13:55.920 --> 00:13:57.790 So we were talking about boron. 00:13:57.790 --> 00:14:02.020 So here we have the first ionization energy, 00:14:02.020 --> 00:14:05.190 second ionization energy, third ionization energy, 00:14:05.190 --> 00:14:07.520 and fourth ionization energy. 00:14:07.520 --> 00:14:09.930 And so there can be quite a bit of difference 00:14:09.930 --> 00:14:13.610 in the magnitude of these ionization energies 00:14:13.610 --> 00:14:17.700 or how hard it is to pull off successive electrons. 00:14:17.700 --> 00:14:21.590 And so here are some of the other ones you see when you're 00:14:21.590 --> 00:14:25.300 going here with boron, you remove the first one here, 00:14:25.300 --> 00:14:28.220 the second one is about three times harder. 00:14:28.220 --> 00:14:31.050 We're jumping from p to s. 00:14:31.050 --> 00:14:33.990 Not too much difference within 2s. 00:14:33.990 --> 00:14:39.270 But once we get to helium here, 1s2, that's 00:14:39.270 --> 00:14:41.510 really hard to pull off another electron here. 00:14:41.510 --> 00:14:44.000 So this fourth one is really big. 00:14:44.000 --> 00:14:46.520 And then we can look at these other trends. 00:14:46.520 --> 00:14:51.440 Beryllium here, we have the 2s and then we go to a 1s. 00:14:51.440 --> 00:14:57.200 And then we have just the one electron over here for lithium. 00:14:57.200 --> 00:15:00.330 And then when we come up here, it's a lot harder. 00:15:00.330 --> 00:15:03.140 So we can look at these tables and realize 00:15:03.140 --> 00:15:05.390 these are not going to be necessarily the same. 00:15:05.390 --> 00:15:07.860 There can be big jumps in ionization energy. 00:15:07.860 --> 00:15:10.300 And I'm going to come back to all of this and sodium 00:15:10.300 --> 00:15:12.040 and potassium in a little bit. 00:15:12.040 --> 00:15:14.670 But first, let's just stick with boron for a minute 00:15:14.670 --> 00:15:17.980 and think more about the different kinds of ionization 00:15:17.980 --> 00:15:20.260 there. 00:15:20.260 --> 00:15:24.840 So now let's just consider taking a 2s electron, 00:15:24.840 --> 00:15:27.540 but from two different types of boron-- boron 00:15:27.540 --> 00:15:31.010 plus and regular boron. 00:15:31.010 --> 00:15:33.530 So in this first case here, we're 00:15:33.530 --> 00:15:37.390 going to take one of these two s electrons. 00:15:37.390 --> 00:15:39.270 And now we have a difference in energy. 00:15:39.270 --> 00:15:41.440 This is the second ionization energy. 00:15:41.440 --> 00:15:43.800 The first one removed the electron from p. 00:15:43.800 --> 00:15:44.795 So we saw this before. 00:15:44.795 --> 00:15:49.240 We're moving one of the electrons from 2s. 00:15:49.240 --> 00:15:51.650 And so this is the second ionization energy. 00:15:51.650 --> 00:15:55.270 It's also equal to the binding energy of the 2s electron 00:15:55.270 --> 00:15:57.240 in boron plus. 00:15:57.240 --> 00:16:00.690 Now we're going to take a 2s electron. 00:16:00.690 --> 00:16:02.300 But we're going to do it from boron. 00:16:02.300 --> 00:16:05.210 So the p electron is still there. 00:16:05.210 --> 00:16:09.740 So we go from 2s2 to 2s1 over here. 00:16:09.740 --> 00:16:13.620 And this energy difference is an ionization energy 00:16:13.620 --> 00:16:16.430 for a 2s electron. 00:16:16.430 --> 00:16:18.430 And that's equal to the binding energy 00:16:18.430 --> 00:16:21.890 of the 2s electron in boron. 00:16:21.890 --> 00:16:25.920 So do you think these energies are going 00:16:25.920 --> 00:16:30.020 to be the same or different? 00:16:30.020 --> 00:16:31.770 Are they equal? 00:16:31.770 --> 00:16:32.820 No. 00:16:32.820 --> 00:16:34.759 So I showed you that little chart and that 00:16:34.759 --> 00:16:36.300 made you probably think that there is 00:16:36.300 --> 00:16:37.810 going to be some differences. 00:16:37.810 --> 00:16:40.470 No, they're not equal. 00:16:40.470 --> 00:16:43.560 So why are they not equal? 00:16:43.560 --> 00:16:48.700 Well, when you have boron plus, you have lost an electron. 00:16:48.700 --> 00:16:52.430 So you have less electrons available to shield. 00:16:52.430 --> 00:16:57.880 So you have less shielding in boron plus than in boron. 00:16:57.880 --> 00:17:01.090 And if there's less shielding, you're 00:17:01.090 --> 00:17:05.480 going to have a higher Z effective, less shielding. 00:17:05.480 --> 00:17:09.819 They'll feel more of the force of the positive charge 00:17:09.819 --> 00:17:11.569 of the nucleus. 00:17:11.569 --> 00:17:14.329 And therefore, it's going to take more energy 00:17:14.329 --> 00:17:15.089 to pull it off. 00:17:15.089 --> 00:17:16.780 So it's going to be more tightly bound. 00:17:16.780 --> 00:17:19.920 It's going to be held in because of this less shielding, higher 00:17:19.920 --> 00:17:22.410 Z effective. 00:17:22.410 --> 00:17:23.390 All right. 00:17:23.390 --> 00:17:25.885 So now let's try a clicker question. 00:18:11.290 --> 00:18:12.068 10 more seconds. 00:18:28.240 --> 00:18:29.020 OK. 00:18:29.020 --> 00:18:32.410 So most of you did not like answer 1. 00:18:32.410 --> 00:18:35.450 But does someone want to explain this? 00:18:35.450 --> 00:18:38.500 And do you want to just walk up? 00:18:38.500 --> 00:18:44.170 Someone want to give an answer why? 00:18:44.170 --> 00:18:45.490 OK, over there. 00:18:48.939 --> 00:18:49.480 AUDIENCE: OK. 00:18:49.480 --> 00:18:58.440 So if we're choosing between 2 and 3, the answer for number 2, 00:18:58.440 --> 00:19:01.470 the 3p orbital has two electrons in it. 00:19:01.470 --> 00:19:03.820 And so the electrons, by nature, kind of repulse 00:19:03.820 --> 00:19:04.750 each other, right? 00:19:04.750 --> 00:19:07.890 So it's a little easier to pop one of those two 00:19:07.890 --> 00:19:12.020 out than if there was only one electron in there by itself 00:19:12.020 --> 00:19:14.640 and you're trying to pull it out. 00:19:14.640 --> 00:19:17.570 So yeah, you'd pick 2 over 3. 00:19:17.570 --> 00:19:18.960 CATHERINE DRENNAN: OK, yeah. 00:19:18.960 --> 00:19:22.140 So actually, I don't know if you can take the answer. 00:19:22.140 --> 00:19:26.460 It's a little hard to read it with the colors on top of it. 00:19:26.460 --> 00:19:31.870 But here, you have this plus system here. 00:19:31.870 --> 00:19:34.440 So you've removed this extra electron. 00:19:34.440 --> 00:19:39.040 So there should be, you feel, a higher Z effective here, 00:19:39.040 --> 00:19:44.230 which will mean that it's harder to sort of pull things off. 00:19:44.230 --> 00:19:48.300 And let's see this one. 00:19:48.300 --> 00:19:51.740 There's no way to take the answer down, right? 00:19:51.740 --> 00:19:53.670 So this one-- oh yeah. 00:19:53.670 --> 00:19:56.060 OK there, that's better. 00:19:56.060 --> 00:19:57.160 I can see this more. 00:19:57.160 --> 00:20:01.730 So this one here, you're pulling one from the s orbitals here. 00:20:01.730 --> 00:20:03.840 The p orbital's easier to pull it off. 00:20:03.840 --> 00:20:07.790 It takes less energy from p than from s. 00:20:07.790 --> 00:20:08.290 OK. 00:20:11.720 --> 00:20:12.980 So let's continue. 00:20:12.980 --> 00:20:14.710 We'll come back to some of these ideas 00:20:14.710 --> 00:20:16.990 as we go along because now, we're 00:20:16.990 --> 00:20:19.330 going to think about how these trends go 00:20:19.330 --> 00:20:21.880 across the periodic table. 00:20:21.880 --> 00:20:28.310 So across a row, ionization energy is going to increase. 00:20:28.310 --> 00:20:33.740 And the reason for this is that Z is increasing. 00:20:33.740 --> 00:20:38.620 So we're having more and more protons, a bigger Z effective. 00:20:38.620 --> 00:20:41.780 You're also adding electrons though. 00:20:41.780 --> 00:20:46.640 But n, the shell, remains the same. 00:20:46.640 --> 00:20:51.450 So if Z is increasing, n is remaining the same, 00:20:51.450 --> 00:20:55.490 what do you predict about Z effective? 00:20:55.490 --> 00:21:00.040 Is it going to increase, decrease, or stay the same? 00:21:00.040 --> 00:21:01.780 It's going to increase. 00:21:01.780 --> 00:21:04.850 So Z effective will also increase. 00:21:04.850 --> 00:21:07.910 And if you had a case that every single time you 00:21:07.910 --> 00:21:11.550 had total shielding of that added electron, 00:21:11.550 --> 00:21:13.470 then it might stay the same. 00:21:13.470 --> 00:21:16.250 But you're not going to have this case, this extreme case 00:21:16.250 --> 00:21:17.720 of total shielding. 00:21:17.720 --> 00:21:20.530 So if Z increased, Z effective is also 00:21:20.530 --> 00:21:24.090 going to increase as you go across. 00:21:24.090 --> 00:21:26.970 And because n is staying the same, 00:21:26.970 --> 00:21:30.840 you have more or less the same amount of distance 00:21:30.840 --> 00:21:32.310 from the nucleus. 00:21:32.310 --> 00:21:35.830 So you just have this stronger Z effective 00:21:35.830 --> 00:21:39.970 and it's holding on to the electrons. 00:21:39.970 --> 00:21:44.730 Now, if you go down a column, the ionization energy 00:21:44.730 --> 00:21:46.470 decreases. 00:21:46.470 --> 00:21:51.020 So in this case, you're also increasing Z. 00:21:51.020 --> 00:21:54.150 But now you're increasing n as well. 00:21:54.150 --> 00:21:59.440 And so when you increase n, you have your 3s and you go 00:21:59.440 --> 00:22:01.800 to your 4's and your 5's. 00:22:01.800 --> 00:22:06.960 And so now, those other orbitals are way far away 00:22:06.960 --> 00:22:10.810 and you have a much bigger effective radius here. 00:22:10.810 --> 00:22:13.340 The Z is getting bigger. 00:22:13.340 --> 00:22:16.750 But it's not really reaching as strongly out. 00:22:16.750 --> 00:22:20.080 So here, the effect of increasing n 00:22:20.080 --> 00:22:24.110 is making a much bigger difference than increasing Z. 00:22:24.110 --> 00:22:28.310 So going across, we have this increase in ionization energy 00:22:28.310 --> 00:22:31.710 because Z effective is increasing 00:22:31.710 --> 00:22:34.644 while n is staying the same or Z is increasing 00:22:34.644 --> 00:22:36.310 while n is staying the same, which means 00:22:36.310 --> 00:22:38.300 the effective is increasing. 00:22:38.300 --> 00:22:43.130 And going down, it's really n that dominates that pattern. 00:22:43.130 --> 00:22:44.880 So you have a decrease because you're 00:22:44.880 --> 00:22:48.770 going to higher and higher n. 00:22:48.770 --> 00:22:50.510 So let's look at some of those. 00:22:50.510 --> 00:22:55.220 And we can go back and look at it what I showed you before. 00:22:55.220 --> 00:22:58.570 I said I'd get back to sodium and potassium here. 00:22:58.570 --> 00:23:04.210 So if we consider all these, if we remove one electron, 00:23:04.210 --> 00:23:07.240 then we're going to go to a noble gas configuration. 00:23:07.240 --> 00:23:13.940 So with our first ionization when we're over here, 00:23:13.940 --> 00:23:15.490 we're going to go. 00:23:15.490 --> 00:23:18.260 And so when we do that, then we say, 00:23:18.260 --> 00:23:22.000 why are these numbers different for the second ionization? 00:23:22.000 --> 00:23:24.670 We have a noble gas configuration after we've 00:23:24.670 --> 00:23:26.900 lost one electron in each case. 00:23:26.900 --> 00:23:30.220 But then we can say, OK, well helium is up here, 00:23:30.220 --> 00:23:32.760 then neon, then argon. 00:23:32.760 --> 00:23:37.670 So the ionization energy is decreasing 00:23:37.670 --> 00:23:41.210 as we go down here because n is increasing. 00:23:41.210 --> 00:23:46.480 So we see that trend in our plot over here. 00:23:46.480 --> 00:23:51.040 There's a couple other things that we can see in this plot. 00:23:51.040 --> 00:23:56.360 So we also see that for boron, this fourth ionization energy 00:23:56.360 --> 00:23:58.820 is really big. 00:23:58.820 --> 00:24:02.720 And it's bigger than beryllium's third, which is bigger 00:24:02.720 --> 00:24:04.650 than lithium's second. 00:24:04.650 --> 00:24:07.959 So let's think about why that's the case. 00:24:07.959 --> 00:24:09.500 And that is another clicker question. 00:25:01.050 --> 00:25:01.550 OK. 00:25:01.550 --> 00:25:02.930 Let's just do 10 more seconds. 00:25:19.170 --> 00:25:19.670 Oops. 00:25:22.420 --> 00:25:24.960 All right. 00:25:24.960 --> 00:25:27.920 I was actually expecting a lower number for this. 00:25:27.920 --> 00:25:29.580 That's awesome. 00:25:29.580 --> 00:25:30.080 Right. 00:25:30.080 --> 00:25:34.260 So it turns out 1 is true. 00:25:34.260 --> 00:25:37.640 But all of these other ones are also 00:25:37.640 --> 00:25:39.450 going to be the same because they've just 00:25:39.450 --> 00:25:40.740 lost more electrons. 00:25:40.740 --> 00:25:43.460 So all of them have the same configuration. 00:25:43.460 --> 00:25:46.820 So that doesn't explain what's going on here. 00:25:46.820 --> 00:25:49.570 And this is also true. 00:25:49.570 --> 00:25:51.930 But binding energies are always negative. 00:25:51.930 --> 00:25:53.970 That does not explain anything. 00:25:53.970 --> 00:25:56.950 So the thing that explains the trend is this one. 00:25:56.950 --> 00:26:00.840 Even though they all now have the same configuration, 00:26:00.840 --> 00:26:03.620 it's going to be a lot harder to pull off 00:26:03.620 --> 00:26:07.220 the electron from the one that has the biggest Z effective 00:26:07.220 --> 00:26:09.630 because that's going to be bound more tightly. 00:26:09.630 --> 00:26:10.130 Great. 00:26:10.130 --> 00:26:13.800 So you're getting the hang of these types of questions. 00:26:13.800 --> 00:26:14.790 All right. 00:26:14.790 --> 00:26:16.450 So those are some of the trends. 00:26:16.450 --> 00:26:18.600 And, of course, when there are trends, 00:26:18.600 --> 00:26:20.430 there is always glitches. 00:26:20.430 --> 00:26:22.860 These aren't really exceptions. 00:26:22.860 --> 00:26:24.890 They are more glitches. 00:26:24.890 --> 00:26:27.810 And we can rationalize them pretty easily. 00:26:27.810 --> 00:26:32.580 So again the trend, increasing ionization energy across, 00:26:32.580 --> 00:26:37.180 decreasing iron energy down, the increase 00:26:37.180 --> 00:26:40.400 across as the Z effective increase, and down 00:26:40.400 --> 00:26:42.590 is the increase in n. 00:26:42.590 --> 00:26:45.930 But when you actually look at ionization energies, which 00:26:45.930 --> 00:26:50.860 are often reported in kilojoules per mole, versus Z, 00:26:50.860 --> 00:26:56.260 you see that it's not just kind of a straight line here. 00:26:56.260 --> 00:27:00.290 And if we put the elements on here that these correspond to, 00:27:00.290 --> 00:27:05.890 we see 1s1, 1s2, a drop to 2s, and then 00:27:05.890 --> 00:27:09.560 we're doing another 2s, a drop to 2p, 00:27:09.560 --> 00:27:12.420 and then so on as you go up along. 00:27:12.420 --> 00:27:15.230 So let's look at some of these little glitches. 00:27:15.230 --> 00:27:19.170 Why isn't this a straighter line here? 00:27:19.170 --> 00:27:24.300 So I'm now going to blow up this region on this slide here. 00:27:24.300 --> 00:27:28.510 And I can just put up this diagram again. 00:27:28.510 --> 00:27:30.430 And you can see that it's true. 00:27:30.430 --> 00:27:33.600 So we're talking about the first ionization energies here. 00:27:33.600 --> 00:27:36.180 We see lithium is lower then it goes higher then 00:27:36.180 --> 00:27:37.650 it goes down again. 00:27:37.650 --> 00:27:40.110 So that's that little trend over here. 00:27:40.110 --> 00:27:42.070 So why is this the case? 00:27:42.070 --> 00:27:45.060 So the ionization energy for beryllium 00:27:45.060 --> 00:27:49.400 is a bit higher than the ionization energy for boron. 00:27:49.400 --> 00:27:52.490 And so it turns out that this glitch then 00:27:52.490 --> 00:27:56.241 is we're going from the 2s to the 2p. 00:27:56.241 --> 00:28:00.480 And 2p, It's easier to pull off that electron. 00:28:00.480 --> 00:28:06.360 So that's why you have this lower ionization energy. 00:28:06.360 --> 00:28:08.920 We have another glitch over here. 00:28:08.920 --> 00:28:12.280 Now we're just within p. 00:28:12.280 --> 00:28:14.540 So what's going on there? 00:28:14.540 --> 00:28:15.980 And it's very small. 00:28:15.980 --> 00:28:18.120 It's a very small little difference. 00:28:18.120 --> 00:28:21.280 But here, the ionization energy for nitrogen 00:28:21.280 --> 00:28:24.080 is bigger than for oxygen. So it's easier 00:28:24.080 --> 00:28:26.900 to pull off an electron from oxygen. 00:28:26.900 --> 00:28:30.360 And if you draw out your diagram here, 00:28:30.360 --> 00:28:34.070 is nitrogen where we have obeyed Hund's rules 00:28:34.070 --> 00:28:36.530 and we put everything in parallel. 00:28:36.530 --> 00:28:38.630 But for oxygen, we have one extra. 00:28:38.630 --> 00:28:40.820 So we had to pair the electron. 00:28:40.820 --> 00:28:42.650 So it turns out it's a little easier 00:28:42.650 --> 00:28:45.910 to steal this 2p electron because it's 00:28:45.910 --> 00:28:47.690 the first one paired. 00:28:47.690 --> 00:28:50.120 And I kind of think about that as, again, sort 00:28:50.120 --> 00:28:52.650 of the bus where everyone sits. 00:28:52.650 --> 00:28:54.490 You can sit two people per seat. 00:28:54.490 --> 00:28:57.740 One person sits down, no one else wants to sit next to them 00:28:57.740 --> 00:28:59.650 until all the seats are taken. 00:28:59.650 --> 00:29:01.940 And sometimes when you're sitting in the seat, 00:29:01.940 --> 00:29:04.660 you're really, really, happy when that person gets up 00:29:04.660 --> 00:29:06.040 who's sitting next to you. 00:29:06.040 --> 00:29:07.660 Maybe there's another seat available. 00:29:07.660 --> 00:29:09.530 They move over to another seat. 00:29:09.530 --> 00:29:13.040 So it's often easier to eject the second person 00:29:13.040 --> 00:29:13.790 from the seat. 00:29:13.790 --> 00:29:16.070 There's a little bit of repulsion going on there. 00:29:16.070 --> 00:29:17.010 Everyone's working. 00:29:17.010 --> 00:29:18.730 They're moving their arms as they're 00:29:18.730 --> 00:29:20.520 doing their chemistry homework, at least 00:29:20.520 --> 00:29:21.825 the buses I'm on anyway. 00:29:21.825 --> 00:29:22.670 [LAUGHTER] 00:29:22.670 --> 00:29:28.710 So that's why there's a glitch there. 00:29:28.710 --> 00:29:30.390 All right. 00:29:30.390 --> 00:29:32.410 So this is all well and good. 00:29:32.410 --> 00:29:33.800 We have our trends. 00:29:33.800 --> 00:29:37.390 But I always like to think about how do we know any of this 00:29:37.390 --> 00:29:39.330 is really true? 00:29:39.330 --> 00:29:43.080 How do you actually measure these ionization energies? 00:29:43.080 --> 00:29:46.850 And so we're just going to talk about one method for measuring 00:29:46.850 --> 00:29:48.580 these for a minute. 00:29:48.580 --> 00:29:52.890 So photoelectron spectroscopy, PES, 00:29:52.890 --> 00:29:56.710 is used to determine ionization values. 00:29:56.710 --> 00:30:00.700 And so you can have some energy that you 00:30:00.700 --> 00:30:03.200 will use to excite something like neon, which 00:30:03.200 --> 00:30:06.490 is gas which lights up a sign for a pizza place, 00:30:06.490 --> 00:30:09.060 and you can inject an electron from it 00:30:09.060 --> 00:30:12.440 that has a certain amount of kinetic energy. 00:30:12.440 --> 00:30:14.810 And what you actually measure in this technique 00:30:14.810 --> 00:30:16.940 is the velocity of the electron. 00:30:16.940 --> 00:30:20.860 But from velocity, as you know, you can get kinetic energy. 00:30:20.860 --> 00:30:24.700 And from kinetic energy, we can get ionization energy. 00:30:24.700 --> 00:30:28.660 So let's look at this experiment and think about the electrons 00:30:28.660 --> 00:30:29.890 being ejected. 00:30:29.890 --> 00:30:34.720 So we have, again, our neon configuration. 00:30:34.720 --> 00:30:39.450 And we'll lose one electron from p here. 00:30:39.450 --> 00:30:42.810 And it will have a velocity and a kinetic energy. 00:30:42.810 --> 00:30:46.580 We can also think about losing an electron from s. 00:30:46.580 --> 00:30:51.550 And we're just going to lose one electron per shell here. 00:30:51.550 --> 00:30:56.050 And we can lose an electron from the 2s and the 1s. 00:30:56.050 --> 00:30:59.720 And all of those should have distinct velocities 00:30:59.720 --> 00:31:03.350 and distinct kinetic energies. 00:31:03.350 --> 00:31:08.840 So if we measure velocity, calculate kinetic energy, 00:31:08.840 --> 00:31:13.180 then we can find the ionization energy 00:31:13.180 --> 00:31:17.240 if we knew the energy that we used to excite the neon. 00:31:17.240 --> 00:31:21.000 So the incident energy equals ionization energy 00:31:21.000 --> 00:31:22.560 plus kinetic energy. 00:31:22.560 --> 00:31:25.910 Or rewritten, ionization energy equals 00:31:25.910 --> 00:31:28.390 the incident energy or initial energy 00:31:28.390 --> 00:31:30.700 minus the kinetic energy. 00:31:30.700 --> 00:31:34.090 So we can use this to calculate ionization energies. 00:31:34.090 --> 00:31:36.730 And this should look awfully familiar to you. 00:31:36.730 --> 00:31:39.090 It's very similar to something that 00:31:39.090 --> 00:31:43.430 will be an exam 1 where we're talking about using photons 00:31:43.430 --> 00:31:46.880 and shooting them at metal surfaces 00:31:46.880 --> 00:31:50.260 and ejecting electrons that have kinetic energy 00:31:50.260 --> 00:31:55.780 if the energy used to hit the metal is greater in energy 00:31:55.780 --> 00:31:57.500 than the work function and the extra 00:31:57.500 --> 00:31:59.380 comes off in kinetic energy. 00:31:59.380 --> 00:32:04.341 This is basically all the same idea here. 00:32:04.341 --> 00:32:04.840 All right. 00:32:04.840 --> 00:32:07.260 So in this particular case, you would 00:32:07.260 --> 00:32:11.110 measure three different velocities or three 00:32:11.110 --> 00:32:13.000 different kinetic energies. 00:32:13.000 --> 00:32:17.870 And now we can think about what those should probably 00:32:17.870 --> 00:32:21.630 correspond to using our chemistry knowledge. 00:32:21.630 --> 00:32:23.580 And some calculations here. 00:32:23.580 --> 00:32:27.480 So we have these three different kinetic energies. 00:32:27.480 --> 00:32:30.130 We know the energy of the incident. 00:32:30.130 --> 00:32:31.990 So we can do some math. 00:32:31.990 --> 00:32:40.210 And when we subtract those, we get one energy of 22. 00:32:40.210 --> 00:32:44.360 And then this kinetic energy is less. 00:32:44.360 --> 00:32:49.620 So we're going to get a higher ionization energy of 48. 00:32:49.620 --> 00:32:51.740 And this is really small. 00:32:51.740 --> 00:32:57.710 And so now we get an ionization energy of 870. 00:32:57.710 --> 00:33:00.770 And so we might not necessarily know which 00:33:00.770 --> 00:33:02.480 orbitals these correspond to. 00:33:02.480 --> 00:33:05.170 But if we think about it, you should 00:33:05.170 --> 00:33:08.490 have the lowest ionization energy to take an electron out 00:33:08.490 --> 00:33:11.890 of 2p, next would be to 2s, and then 00:33:11.890 --> 00:33:15.650 the hardest electron to eject would be from the 1s. 00:33:15.650 --> 00:33:18.420 And these are pretty similar to each other. 00:33:18.420 --> 00:33:21.130 But this is a much bigger number over here. 00:33:21.130 --> 00:33:25.860 And so that's kind of consistent with what we know. 00:33:25.860 --> 00:33:26.360 All right. 00:33:26.360 --> 00:33:27.850 So this is how you measure it. 00:33:27.850 --> 00:33:31.980 And again, this is a multi-electron system. 00:33:31.980 --> 00:33:34.930 And so then the energy is going to depend on the two quantum 00:33:34.930 --> 00:33:35.750 numbers. 00:33:35.750 --> 00:33:38.360 It depends on l and n. 00:33:38.360 --> 00:33:42.078 It matters what specific orbital you're talking about. 00:33:45.670 --> 00:33:49.510 So let's just think about another problem here. 00:33:49.510 --> 00:33:54.350 Suppose you had five really distinct kinetic energies. 00:33:54.350 --> 00:33:57.950 Assume that a very distinct kinetic energy 00:33:57.950 --> 00:34:00.220 means a different subshell. 00:34:00.220 --> 00:34:04.240 And so then we want to think about what 00:34:04.240 --> 00:34:09.060 are the possible elements in the periodic table that 00:34:09.060 --> 00:34:11.469 could produce a spectrum with these five very, 00:34:11.469 --> 00:34:13.620 very distinct kinetic energies? 00:34:13.620 --> 00:34:15.830 And so the way you think about this 00:34:15.830 --> 00:34:20.460 is you want to find what elements are going to have five 00:34:20.460 --> 00:34:22.929 different kinds of orbitals. 00:34:22.929 --> 00:34:31.130 And so we can list the first set here-- 1s, 2s, 2p, 3s, 3p, 00:34:31.130 --> 00:34:32.960 that's five. 00:34:32.960 --> 00:34:36.480 And then you need to know from the periodic table 00:34:36.480 --> 00:34:40.276 where are the elements where you're filling the 3p. 00:34:43.510 --> 00:34:46.210 And those are over here. 00:34:46.210 --> 00:34:50.560 So again, we talked and these problems aren't on the exam. 00:34:50.560 --> 00:34:52.620 But on the exam, you need to know 00:34:52.620 --> 00:34:56.870 that this is 1s-- you're filling 1s, you're filling 2s, 00:34:56.870 --> 00:34:59.410 you're filling 2p, you're filling 3s, 00:34:59.410 --> 00:35:02.380 you're filling 3p-- that you need to interpret. 00:35:02.380 --> 00:35:03.980 You'll be given a periodic table. 00:35:03.980 --> 00:35:06.640 But you need to be able to know what orbitals 00:35:06.640 --> 00:35:08.420 are being filled in the different parts 00:35:08.420 --> 00:35:10.550 of the periodic table. 00:35:10.550 --> 00:35:13.543 So let's just try a practice with that. 00:36:08.490 --> 00:36:08.990 All right. 00:36:08.990 --> 00:36:10.480 Let's just take 10 more seconds. 00:36:28.392 --> 00:36:29.870 All right. 00:36:29.870 --> 00:36:32.764 So we might need to work on the sort of counting. 00:36:35.490 --> 00:36:42.290 So again, you want to think about you have 1s, 2s, 2p, 3s, 00:36:42.290 --> 00:36:50.070 3p, 4s, 3d, and 4p. 00:36:50.070 --> 00:36:53.550 So I think if we get the counting down we'll be good. 00:36:53.550 --> 00:36:56.000 But again, you need to look at the periodic table 00:36:56.000 --> 00:36:58.840 and know what's getting filled. 00:36:58.840 --> 00:36:59.820 All right. 00:36:59.820 --> 00:37:04.010 So let's move on and talk about electron affinity. 00:37:04.010 --> 00:37:09.200 And maybe we can squeeze in some electronegativity at the end. 00:37:09.200 --> 00:37:14.420 These are very related topics and pretty fast. 00:37:14.420 --> 00:37:14.920 All right. 00:37:14.920 --> 00:37:21.720 So electron affinity-- the ability to gain electrons. 00:37:21.720 --> 00:37:23.610 So what we're talking about here is 00:37:23.610 --> 00:37:30.145 how likely atom X is to grab an electron and become X minus. 00:37:33.210 --> 00:37:35.630 So we often think about halogens when 00:37:35.630 --> 00:37:38.960 we're talking about this like chlorine. 00:37:38.960 --> 00:37:44.190 So we have Cl plus an electron, Cl minus. 00:37:44.190 --> 00:37:47.100 And here the change in energy associated 00:37:47.100 --> 00:37:52.160 with gaining that electron is minus 349 kilojoules per mole. 00:37:52.160 --> 00:37:54.800 Energy is released. 00:37:54.800 --> 00:37:58.870 And that means that the ion is more stable than the parent. 00:37:58.870 --> 00:38:03.070 So chloride is very happy to become Cl minus. 00:38:03.070 --> 00:38:06.540 And so you think about energy being released, 00:38:06.540 --> 00:38:10.169 if you think about a kid-- my husband's out of town, 00:38:10.169 --> 00:38:11.960 so I was watching our six-year-old daughter 00:38:11.960 --> 00:38:13.000 this weekend. 00:38:13.000 --> 00:38:15.310 And she was racing around like a crazy person 00:38:15.310 --> 00:38:17.900 until she collapsed in a heap. 00:38:17.900 --> 00:38:19.280 So energy is released. 00:38:19.280 --> 00:38:22.930 And she became a more stable six-year-old. 00:38:22.930 --> 00:38:25.660 So that's what's happening with chloride as well-- more 00:38:25.660 --> 00:38:27.260 or less. 00:38:27.260 --> 00:38:35.130 So here, the electron affinity is minus the change in energy. 00:38:35.130 --> 00:38:39.240 So if we talked about the electron affinity of chloride 00:38:39.240 --> 00:38:42.330 for the electron to become Cl minus, 00:38:42.330 --> 00:38:49.670 you would say that was plus 349 kilojoules per mole. 00:38:49.670 --> 00:38:55.450 So unlike ionization energy, which is always what? 00:38:55.450 --> 00:38:59.250 Positive or negative-- ionization energy? 00:38:59.250 --> 00:39:02.910 Always positive. 00:39:02.910 --> 00:39:06.090 Electron affinity can be positive or negative. 00:39:06.090 --> 00:39:08.310 And that tells you something about how much 00:39:08.310 --> 00:39:10.870 it wants to gain electrons. 00:39:10.870 --> 00:39:14.590 So nitrogen plus an electron, going to N minus, 00:39:14.590 --> 00:39:19.970 has a positive energy value here and has a negative electron 00:39:19.970 --> 00:39:21.100 affinity. 00:39:21.100 --> 00:39:28.750 So N minus-- the minus one ion is less stable than its parent. 00:39:28.750 --> 00:39:33.680 So it is not as happy as chloride to do this. 00:39:33.680 --> 00:39:37.210 So trends in ionization. 00:39:37.210 --> 00:39:40.640 Usually you have an increase going across 00:39:40.640 --> 00:39:44.310 and a decrease going down. 00:39:44.310 --> 00:39:49.140 And let's just consider noble gases 00:39:49.140 --> 00:39:51.050 and what you think about them. 00:39:51.050 --> 00:39:53.596 So we'll do one final clicker question. 00:40:05.930 --> 00:40:07.090 It should be pretty fast. 00:40:15.760 --> 00:40:17.125 OK, ten seconds. 00:40:31.910 --> 00:40:33.650 OK, yup. 00:40:33.650 --> 00:40:36.370 They are, in fact, negative. 00:40:36.370 --> 00:40:38.450 And so we can think about this over here. 00:40:38.450 --> 00:40:42.010 Noble gases have negative electron affinities. 00:40:42.010 --> 00:40:46.220 Noble gases are very happy the way they are. 00:40:46.220 --> 00:40:49.430 If you had to add another electron to them, 00:40:49.430 --> 00:40:52.830 you would need to make a new subshell there, 00:40:52.830 --> 00:40:55.200 which they don't want to do. 00:40:55.200 --> 00:40:58.770 And so halogens, on the other hand, 00:40:58.770 --> 00:41:04.750 which are right next door, have highest electron affinity. 00:41:04.750 --> 00:41:08.000 So if you're over here, they want to gain an electron 00:41:08.000 --> 00:41:09.530 and become a noble gas. 00:41:09.530 --> 00:41:11.900 Noble gases want to stay the way they are. 00:41:11.900 --> 00:41:15.600 So the increase trend ends right before you 00:41:15.600 --> 00:41:17.170 get to the noble gases. 00:41:17.170 --> 00:41:19.030 They're in their own category. 00:41:19.030 --> 00:41:19.530 OK. 00:41:19.530 --> 00:41:21.120 So we're going to end with that. 00:41:21.120 --> 00:41:26.370 And we'll continue with electronegativity on Friday.