1 00:00:00,030 --> 00:00:02,400 The following content is provided under a Creative 2 00:00:02,400 --> 00:00:03,780 Commons license. 3 00:00:03,780 --> 00:00:06,020 Your support will help MIT OpenCourseWare 4 00:00:06,020 --> 00:00:10,090 continue to offer high quality educational resources for free. 5 00:00:10,090 --> 00:00:12,670 To make a donation or to view additional materials 6 00:00:12,670 --> 00:00:16,580 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:16,580 --> 00:00:18,710 at ocw.mit.edu. 8 00:00:37,982 --> 00:00:39,190 CATHERINE DRENNAN: All right. 9 00:00:39,190 --> 00:00:40,900 Let's just take 10 more seconds. 10 00:00:57,885 --> 00:00:58,385 OK. 11 00:01:01,280 --> 00:01:05,319 So let's look at this one. 12 00:01:05,319 --> 00:01:11,370 So first, you want to notice that you have a plus 1 here. 13 00:01:11,370 --> 00:01:13,790 So you've lost an electron. 14 00:01:13,790 --> 00:01:16,530 And then you want to think about what happens when you 15 00:01:16,530 --> 00:01:18,750 start filling the deorbitals. 16 00:01:18,750 --> 00:01:21,590 So when you start filling the deorbitals, 17 00:01:21,590 --> 00:01:27,910 then the energy changes and 4s and 3d switch an energy. 18 00:01:27,910 --> 00:01:30,110 And so we could write this one either way. 19 00:01:30,110 --> 00:01:33,980 We could have put the 3d first and the 4s second. 20 00:01:33,980 --> 00:01:38,220 But importantly now, because of that switch in energy, 21 00:01:38,220 --> 00:01:43,230 the electron that is lost is lost from the 4s over here. 22 00:01:43,230 --> 00:01:47,650 So this has to do with the fact that electron configuration 23 00:01:47,650 --> 00:01:51,340 of neutral atoms and ions are different and especially 24 00:01:51,340 --> 00:01:58,670 with this 4s-3d switch, that the 3d orbitals drop, change energy 25 00:01:58,670 --> 00:02:00,450 when you start to fill them. 26 00:02:00,450 --> 00:02:05,320 And there's really very similar energy between 4s and 3d. 27 00:02:05,320 --> 00:02:07,680 And that leads to some of the exceptions 28 00:02:07,680 --> 00:02:11,170 that you're responsible to know that there 29 00:02:11,170 --> 00:02:14,510 can be subtle things that switch the energy a little bit. 30 00:02:14,510 --> 00:02:17,050 So because they're so close in energy, 31 00:02:17,050 --> 00:02:19,640 you have this half-filled and full-filled thing 32 00:02:19,640 --> 00:02:22,330 where you can pull an electron from 4s 33 00:02:22,330 --> 00:02:26,520 and put it in 3d to make 3d5 or to make 3d10. 34 00:02:26,520 --> 00:02:29,220 So they're very close in energy. 35 00:02:29,220 --> 00:02:32,060 And that leads to some of these interesting features. 36 00:02:32,060 --> 00:02:32,720 OK. 37 00:02:32,720 --> 00:02:35,500 So today's lecture, we're moving on to the periodic table. 38 00:02:35,500 --> 00:02:38,110 But we're actually talking about a lot of the things 39 00:02:38,110 --> 00:02:39,510 that we just talked about. 40 00:02:39,510 --> 00:02:41,740 So today actually turns out to be 41 00:02:41,740 --> 00:02:45,170 an awesome review for some of the material that's 42 00:02:45,170 --> 00:02:45,815 on the exams. 43 00:02:45,815 --> 00:02:47,450 So that worked out really well. 44 00:02:47,450 --> 00:02:50,180 In past years, this material was on exam 1. 45 00:02:50,180 --> 00:02:51,670 Exam 1 was later. 46 00:02:51,670 --> 00:02:58,070 And so if you get old exams from other people, not the ones that 47 00:02:58,070 --> 00:02:59,620 are posted, the ones that are posted 48 00:02:59,620 --> 00:03:02,990 are mostly old exams, except we were placed questions 49 00:03:02,990 --> 00:03:06,350 for material not covered on this exam with material that 50 00:03:06,350 --> 00:03:07,340 is covered. 51 00:03:07,340 --> 00:03:10,990 So it's not 100% an old exam from this class 52 00:03:10,990 --> 00:03:13,650 because we've never had an exam this early before. 53 00:03:13,650 --> 00:03:15,210 So there were no good examples. 54 00:03:15,210 --> 00:03:17,570 So if you get old exams from other people, 55 00:03:17,570 --> 00:03:20,029 do not freak out when you look at it, 56 00:03:20,029 --> 00:03:21,070 and like, oh my goodness. 57 00:03:21,070 --> 00:03:23,210 Somehow I haven't learned this. 58 00:03:23,210 --> 00:03:25,810 There are today's lecture and also 59 00:03:25,810 --> 00:03:28,940 Friday's lecture we're typically on exam 1. 60 00:03:28,940 --> 00:03:30,930 So just keep that in mind. 61 00:03:30,930 --> 00:03:34,710 So use our practice exams and then you 62 00:03:34,710 --> 00:03:37,120 will not have that problem. 63 00:03:37,120 --> 00:03:37,620 All right. 64 00:03:37,620 --> 00:03:40,895 So moving on to the periodic table. 65 00:03:40,895 --> 00:03:43,890 This is very exciting for me. 66 00:03:43,890 --> 00:03:46,610 And so today, we're going to talk about trends 67 00:03:46,610 --> 00:03:48,070 in the periodic table. 68 00:03:48,070 --> 00:03:50,140 We're going to finish that up on Friday 69 00:03:50,140 --> 00:03:53,020 after the exam, which will be a clicker competition. 70 00:03:53,020 --> 00:03:56,310 And then we're going to go on to talk 71 00:03:56,310 --> 00:03:59,690 about bonding of the elements in the periodic table. 72 00:03:59,690 --> 00:04:02,170 So that's where we're headed. 73 00:04:02,170 --> 00:04:07,250 So the periodic table, here is one of them that's up here. 74 00:04:07,250 --> 00:04:10,680 So this was originally put together a while ago. 75 00:04:10,680 --> 00:04:13,380 And it turned out to be amazingly accurate. 76 00:04:13,380 --> 00:04:15,780 And this really describes all of the elements. 77 00:04:15,780 --> 00:04:21,019 So this is kind of like the artist's paintbox for a chemist 78 00:04:21,019 --> 00:04:22,860 or wordsmiths words. 79 00:04:22,860 --> 00:04:27,250 These are all the ingredients that go into making everything. 80 00:04:27,250 --> 00:04:29,830 Some of these elements are incredibly dangerous 81 00:04:29,830 --> 00:04:32,510 and they're used to make explosives. 82 00:04:32,510 --> 00:04:34,510 They're used to make bombs. 83 00:04:34,510 --> 00:04:37,300 Other elements here are found in the human body 84 00:04:37,300 --> 00:04:38,860 and allow us to live. 85 00:04:38,860 --> 00:04:42,060 All materials, whether it's a desk, a pointer, 86 00:04:42,060 --> 00:04:46,440 a bottle of water, everything is made up of elements. 87 00:04:46,440 --> 00:04:49,280 So this is one of the reasons why 88 00:04:49,280 --> 00:04:52,100 chemistry is so cool because we think about the elements. 89 00:04:52,100 --> 00:04:54,970 And elements are made of everything. 90 00:04:54,970 --> 00:04:58,580 So we think about everything that makes up everything. 91 00:04:58,580 --> 00:05:01,810 And that's pretty neat. 92 00:05:01,810 --> 00:05:05,070 So just to kind of give you a flavor 93 00:05:05,070 --> 00:05:09,280 of the joy of the periodic table and introduce you 94 00:05:09,280 --> 00:05:12,130 to the elements that make up this periodic table, 95 00:05:12,130 --> 00:05:15,980 I feel like we should think about this in music. 96 00:05:15,980 --> 00:05:20,780 [MUSIC - THEY MIGHT BE GIANTS, "MEET THE ELEMENTS"] 97 00:05:20,780 --> 00:05:23,300 [SINGING] Iron is a metal. 98 00:05:23,300 --> 00:05:25,910 You see it every day. 99 00:05:25,910 --> 00:05:31,190 Oxygen, eventually, will make it rust away. 100 00:05:31,190 --> 00:05:36,180 Carbon in its ordinary form is coal. 101 00:05:36,180 --> 00:05:41,010 Crush it together and diamonds are born. 102 00:05:41,010 --> 00:05:44,010 Come on, come on and meet the elements. 103 00:05:44,010 --> 00:05:48,628 May I introduce you to our friends, the elements? 104 00:05:48,628 --> 00:05:54,840 Like a box of paints that are mixed to make every shade, 105 00:05:54,840 --> 00:05:58,340 they either combine to make a chemical compound 106 00:05:58,340 --> 00:06:01,440 or stand alone as they are. 107 00:06:01,440 --> 00:06:05,798 Neon's a gas that lights up the sign for a pizza place. 108 00:06:05,798 --> 00:06:10,790 The coins that you pay with are copper, nickel, and zinc. 109 00:06:10,790 --> 00:06:15,452 Silicon and oxygen make concrete bricks and glass. 110 00:06:15,452 --> 00:06:21,270 Now add some gold and silver for some pizza place class. 111 00:06:21,270 --> 00:06:24,247 Come on, come on and meet the elements. 112 00:06:24,247 --> 00:06:28,540 I think you should check out the ones they call the elements. 113 00:06:28,540 --> 00:06:35,202 Like a box of paints that are mixed to make every shade, 114 00:06:35,202 --> 00:06:38,513 they either combine to make a chemical compound 115 00:06:38,513 --> 00:06:40,781 or stand alone as they are. 116 00:06:40,781 --> 00:06:41,280 OK. 117 00:06:41,280 --> 00:06:44,030 So you get the sense of this. 118 00:06:44,030 --> 00:06:45,440 The song is quite accurate. 119 00:06:45,440 --> 00:06:47,680 It has lots of information [INAUDIBLE] them. 120 00:06:47,680 --> 00:06:49,170 And it points out some other things 121 00:06:49,170 --> 00:06:51,420 like elephants are made of elements. 122 00:06:51,420 --> 00:06:55,590 And we're made of elephants-- oh no, wait-- elements. 123 00:06:55,590 --> 00:06:57,960 No, it's a really fun, fun song. 124 00:06:57,960 --> 00:07:01,030 And it really, I think, expresses 125 00:07:01,030 --> 00:07:03,730 why It's so important to learn about the properties 126 00:07:03,730 --> 00:07:05,520 of the elements and all the things 127 00:07:05,520 --> 00:07:07,000 that you can do with them. 128 00:07:07,000 --> 00:07:11,160 So when it was originally put together, 129 00:07:11,160 --> 00:07:14,770 it was put together based on sorting elements 130 00:07:14,770 --> 00:07:19,010 by their properties, such as ones over here in column 1 131 00:07:19,010 --> 00:07:21,370 are soft and reactive metals. 132 00:07:21,370 --> 00:07:24,930 And it was observed that the elements over here 133 00:07:24,930 --> 00:07:26,190 are pretty inert. 134 00:07:26,190 --> 00:07:28,070 So they were all grouped together. 135 00:07:28,070 --> 00:07:31,330 And later, we have pretty much kept this grouping. 136 00:07:31,330 --> 00:07:35,110 But now, it's really grouped by the electron configurations, 137 00:07:35,110 --> 00:07:38,090 which is one of the things you need to know for the exam, 138 00:07:38,090 --> 00:07:40,840 how to write these electron configurations. 139 00:07:40,840 --> 00:07:43,490 And these reactive metals, it turns out, 140 00:07:43,490 --> 00:07:45,690 they only have one valence electron. 141 00:07:45,690 --> 00:07:49,530 So they like to react because they want to have a noble gas 142 00:07:49,530 --> 00:07:53,880 configuration, so they're very reactive whereas these others 143 00:07:53,880 --> 00:07:57,980 that were not reactive, have filled electron configurations. 144 00:07:57,980 --> 00:07:59,896 So they don't want any extra electrons 145 00:07:59,896 --> 00:08:01,270 and they don't want to lose them. 146 00:08:01,270 --> 00:08:02,400 They don't want to get any. 147 00:08:02,400 --> 00:08:03,810 They're very happy as they are. 148 00:08:03,810 --> 00:08:04,930 So they're inert. 149 00:08:04,930 --> 00:08:07,340 So now these groupings make a lot of sense 150 00:08:07,340 --> 00:08:10,590 in terms of the electron configurations. 151 00:08:10,590 --> 00:08:12,770 Now, it doesn't tell you everything. 152 00:08:12,770 --> 00:08:17,990 So if you know one element is very safe to consume, 153 00:08:17,990 --> 00:08:20,630 that doesn't necessarily mean something right next 154 00:08:20,630 --> 00:08:22,990 to it is just as good. 155 00:08:22,990 --> 00:08:28,190 And if we consider over here, we consider lithium, sodium, 156 00:08:28,190 --> 00:08:31,280 and potassium, sodium and potassium 157 00:08:31,280 --> 00:08:34,840 are ions that are really important in the human body. 158 00:08:34,840 --> 00:08:37,870 And you have to make sure that if you're exercising a lot, 159 00:08:37,870 --> 00:08:41,730 that you keep up the amounts that you're getting. 160 00:08:41,730 --> 00:08:43,850 So they're very important ions. 161 00:08:43,850 --> 00:08:47,360 And they will often hang around and serve as counter-ions 162 00:08:47,360 --> 00:08:49,370 to other molecules in your body. 163 00:08:49,370 --> 00:08:50,830 You have citrate in your body. 164 00:08:50,830 --> 00:08:54,070 So you could have sodium citrate where the sodium is hanging out 165 00:08:54,070 --> 00:08:56,160 or potassium citrate. 166 00:08:56,160 --> 00:08:57,980 But that doesn't necessarily mean 167 00:08:57,980 --> 00:09:01,610 that other things will work as well, like lithium, 168 00:09:01,610 --> 00:09:02,670 for example. 169 00:09:02,670 --> 00:09:09,410 But a while ago when 7-Up soda was first put on the market, 170 00:09:09,410 --> 00:09:12,560 they thought well, sodium and potassium are a little boring. 171 00:09:12,560 --> 00:09:15,070 Let's sort of make things a little more exciting 172 00:09:15,070 --> 00:09:17,000 and use lithium citrate instead. 173 00:09:17,000 --> 00:09:21,790 It's right there in the same column of the periodic table. 174 00:09:21,790 --> 00:09:24,510 And citrate makes things taste lemony, 175 00:09:24,510 --> 00:09:26,220 which is a lovely taste. 176 00:09:26,220 --> 00:09:29,700 And we'll have lithium as the counter-ion to that. 177 00:09:29,700 --> 00:09:32,890 And so they said this dispels hangovers. 178 00:09:32,890 --> 00:09:35,320 It takes the ouch out of grouch. 179 00:09:35,320 --> 00:09:38,555 And does anyone know what lithium is used for today? 180 00:09:41,450 --> 00:09:43,120 So it's often used for people who 181 00:09:43,120 --> 00:09:45,860 have bipolar disorders or manic depressive. 182 00:09:45,860 --> 00:09:49,000 So it really did take the ouch out of grouch. 183 00:09:49,000 --> 00:09:52,130 But it's not something that you should just 184 00:09:52,130 --> 00:09:55,500 put in a consumable soda. 185 00:09:55,500 --> 00:09:59,020 So it has somewhat different properties, 186 00:09:59,020 --> 00:10:01,320 even though it's part of that same group. 187 00:10:01,320 --> 00:10:03,610 So this is a lesson that I feel like we 188 00:10:03,610 --> 00:10:06,220 keep learning over and over again with other things, 189 00:10:06,220 --> 00:10:08,860 that you have to be a little more careful. 190 00:10:08,860 --> 00:10:11,180 Just because it's hanging out near its friends, 191 00:10:11,180 --> 00:10:14,591 doesn't mean it's going to be exactly the same. 192 00:10:14,591 --> 00:10:15,090 All right. 193 00:10:15,090 --> 00:10:19,150 So the periodic table is an amazing thing. 194 00:10:19,150 --> 00:10:22,120 Let's think about the trends in the periodic table. 195 00:10:22,120 --> 00:10:24,570 So we're going to first do ionization energy. 196 00:10:24,570 --> 00:10:26,730 And we've already talked about ionization energy. 197 00:10:26,730 --> 00:10:29,040 So this is awesome because it turns out 198 00:10:29,040 --> 00:10:33,380 to be a really good review for the exam. 199 00:10:33,380 --> 00:10:36,570 So ionization energy, again, is the minimum energy 200 00:10:36,570 --> 00:10:41,360 it's going to take to remove an electron from an atom. 201 00:10:41,360 --> 00:10:46,250 And if we just talk about-- just say IE for ionization energy-- 202 00:10:46,250 --> 00:10:49,550 we're going to assume it's the first ionization 203 00:10:49,550 --> 00:10:53,180 energy unless it is specified. 204 00:10:53,180 --> 00:10:58,060 And we saw before that ionization energy is opposite 205 00:10:58,060 --> 00:11:00,800 in sign to the binding energy. 206 00:11:00,800 --> 00:11:04,040 And so here we have the binding energy of an electron. 207 00:11:04,040 --> 00:11:08,490 And we know that this is a multi-electron atom 208 00:11:08,490 --> 00:11:11,080 because it depends on n and l. 209 00:11:11,080 --> 00:11:14,700 If it was just hydrogen or one other one-electron atom, 210 00:11:14,700 --> 00:11:19,470 then anything with n, all those orbitals, are degenerate. 211 00:11:19,470 --> 00:11:21,460 But if you have putting in multi-electrons, 212 00:11:21,460 --> 00:11:24,320 then it matters whether you're talking about not just n, 213 00:11:24,320 --> 00:11:28,650 but l matters too, whether it's an s orbital or p orbital. 214 00:11:28,650 --> 00:11:30,220 So we've seen this before. 215 00:11:30,220 --> 00:11:34,800 But now let's talk more about different ionization energies. 216 00:11:34,800 --> 00:11:38,870 So let's look at boron and think about the first ionization 217 00:11:38,870 --> 00:11:39,670 energy. 218 00:11:39,670 --> 00:11:43,440 And this is the energy to move an electron from the highest 219 00:11:43,440 --> 00:11:45,494 occupied atomic orbital. 220 00:11:45,494 --> 00:11:46,660 That's what that stands for. 221 00:11:46,660 --> 00:11:48,440 And it's written out in your notes. 222 00:11:48,440 --> 00:11:55,530 And so what is the highest occupied orbital in this case? 223 00:11:55,530 --> 00:11:57,650 Just yell it out. 224 00:11:57,650 --> 00:11:59,340 2p. 225 00:11:59,340 --> 00:12:02,880 So let's look at removing an electron from 2p. 226 00:12:02,880 --> 00:12:05,980 If we do that, we go to boron plus. 227 00:12:05,980 --> 00:12:09,210 And we have 1s2, 2s2, an electron. 228 00:12:09,210 --> 00:12:12,610 And this process, the energy involved in this process, 229 00:12:12,610 --> 00:12:16,320 is the ionization energy-- the first ionization energy. 230 00:12:16,320 --> 00:12:21,360 It's also equal to the binding energy of the 2p electron. 231 00:12:21,360 --> 00:12:26,100 And again, the signs are opposite here. 232 00:12:26,100 --> 00:12:30,400 So now second ionization energy, we just keep going. 233 00:12:30,400 --> 00:12:35,860 The next highest occupied atomic orbital is 2s. 234 00:12:35,860 --> 00:12:41,670 So if we remove, we get boron plus 2 1s2, 2s1 235 00:12:41,670 --> 00:12:43,610 and an electron. 236 00:12:43,610 --> 00:12:48,130 And now the energy difference is due to these second ionization 237 00:12:48,130 --> 00:12:48,710 energies. 238 00:12:48,710 --> 00:12:50,910 So we say IE2. 239 00:12:50,910 --> 00:12:56,316 And that is equal to the binding energy of the 2s electron in B 240 00:12:56,316 --> 00:12:58,300 plus because that's what we're removing. 241 00:12:58,300 --> 00:13:03,980 We're moving a 2s electron from B plus here. 242 00:13:03,980 --> 00:13:05,200 So we can keep going. 243 00:13:05,200 --> 00:13:09,820 We can go to the third ionization energy. 244 00:13:09,820 --> 00:13:15,950 And now we're also going to be removing an electron from 2s. 245 00:13:15,950 --> 00:13:19,360 And when we remove the electron, it only had one. 246 00:13:19,360 --> 00:13:24,790 So now we have a boron plus 3 1s2 and an electron. 247 00:13:24,790 --> 00:13:28,540 The energy difference is the third ionization energy-- 248 00:13:28,540 --> 00:13:30,200 IE sub 3. 249 00:13:30,200 --> 00:13:33,650 And this is equal to the binding energy. 250 00:13:33,650 --> 00:13:36,930 Or the difference in sign is the binding energy of 2s 251 00:13:36,930 --> 00:13:39,624 in the plus 2 system. 252 00:13:42,460 --> 00:13:45,580 So now if we look at this little table over here that's 253 00:13:45,580 --> 00:13:49,120 in your handout or this little chart in your handout, 254 00:13:49,120 --> 00:13:53,110 you can see that there is quite a bit of difference 255 00:13:53,110 --> 00:13:55,920 between these different ionization energies. 256 00:13:55,920 --> 00:13:57,790 So we were talking about boron. 257 00:13:57,790 --> 00:14:02,020 So here we have the first ionization energy, 258 00:14:02,020 --> 00:14:05,190 second ionization energy, third ionization energy, 259 00:14:05,190 --> 00:14:07,520 and fourth ionization energy. 260 00:14:07,520 --> 00:14:09,930 And so there can be quite a bit of difference 261 00:14:09,930 --> 00:14:13,610 in the magnitude of these ionization energies 262 00:14:13,610 --> 00:14:17,700 or how hard it is to pull off successive electrons. 263 00:14:17,700 --> 00:14:21,590 And so here are some of the other ones you see when you're 264 00:14:21,590 --> 00:14:25,300 going here with boron, you remove the first one here, 265 00:14:25,300 --> 00:14:28,220 the second one is about three times harder. 266 00:14:28,220 --> 00:14:31,050 We're jumping from p to s. 267 00:14:31,050 --> 00:14:33,990 Not too much difference within 2s. 268 00:14:33,990 --> 00:14:39,270 But once we get to helium here, 1s2, that's 269 00:14:39,270 --> 00:14:41,510 really hard to pull off another electron here. 270 00:14:41,510 --> 00:14:44,000 So this fourth one is really big. 271 00:14:44,000 --> 00:14:46,520 And then we can look at these other trends. 272 00:14:46,520 --> 00:14:51,440 Beryllium here, we have the 2s and then we go to a 1s. 273 00:14:51,440 --> 00:14:57,200 And then we have just the one electron over here for lithium. 274 00:14:57,200 --> 00:15:00,330 And then when we come up here, it's a lot harder. 275 00:15:00,330 --> 00:15:03,140 So we can look at these tables and realize 276 00:15:03,140 --> 00:15:05,390 these are not going to be necessarily the same. 277 00:15:05,390 --> 00:15:07,860 There can be big jumps in ionization energy. 278 00:15:07,860 --> 00:15:10,300 And I'm going to come back to all of this and sodium 279 00:15:10,300 --> 00:15:12,040 and potassium in a little bit. 280 00:15:12,040 --> 00:15:14,670 But first, let's just stick with boron for a minute 281 00:15:14,670 --> 00:15:17,980 and think more about the different kinds of ionization 282 00:15:17,980 --> 00:15:20,260 there. 283 00:15:20,260 --> 00:15:24,840 So now let's just consider taking a 2s electron, 284 00:15:24,840 --> 00:15:27,540 but from two different types of boron-- boron 285 00:15:27,540 --> 00:15:31,010 plus and regular boron. 286 00:15:31,010 --> 00:15:33,530 So in this first case here, we're 287 00:15:33,530 --> 00:15:37,390 going to take one of these two s electrons. 288 00:15:37,390 --> 00:15:39,270 And now we have a difference in energy. 289 00:15:39,270 --> 00:15:41,440 This is the second ionization energy. 290 00:15:41,440 --> 00:15:43,800 The first one removed the electron from p. 291 00:15:43,800 --> 00:15:44,795 So we saw this before. 292 00:15:44,795 --> 00:15:49,240 We're moving one of the electrons from 2s. 293 00:15:49,240 --> 00:15:51,650 And so this is the second ionization energy. 294 00:15:51,650 --> 00:15:55,270 It's also equal to the binding energy of the 2s electron 295 00:15:55,270 --> 00:15:57,240 in boron plus. 296 00:15:57,240 --> 00:16:00,690 Now we're going to take a 2s electron. 297 00:16:00,690 --> 00:16:02,300 But we're going to do it from boron. 298 00:16:02,300 --> 00:16:05,210 So the p electron is still there. 299 00:16:05,210 --> 00:16:09,740 So we go from 2s2 to 2s1 over here. 300 00:16:09,740 --> 00:16:13,620 And this energy difference is an ionization energy 301 00:16:13,620 --> 00:16:16,430 for a 2s electron. 302 00:16:16,430 --> 00:16:18,430 And that's equal to the binding energy 303 00:16:18,430 --> 00:16:21,890 of the 2s electron in boron. 304 00:16:21,890 --> 00:16:25,920 So do you think these energies are going 305 00:16:25,920 --> 00:16:30,020 to be the same or different? 306 00:16:30,020 --> 00:16:31,770 Are they equal? 307 00:16:31,770 --> 00:16:32,820 No. 308 00:16:32,820 --> 00:16:34,759 So I showed you that little chart and that 309 00:16:34,759 --> 00:16:36,300 made you probably think that there is 310 00:16:36,300 --> 00:16:37,810 going to be some differences. 311 00:16:37,810 --> 00:16:40,470 No, they're not equal. 312 00:16:40,470 --> 00:16:43,560 So why are they not equal? 313 00:16:43,560 --> 00:16:48,700 Well, when you have boron plus, you have lost an electron. 314 00:16:48,700 --> 00:16:52,430 So you have less electrons available to shield. 315 00:16:52,430 --> 00:16:57,880 So you have less shielding in boron plus than in boron. 316 00:16:57,880 --> 00:17:01,090 And if there's less shielding, you're 317 00:17:01,090 --> 00:17:05,480 going to have a higher Z effective, less shielding. 318 00:17:05,480 --> 00:17:09,819 They'll feel more of the force of the positive charge 319 00:17:09,819 --> 00:17:11,569 of the nucleus. 320 00:17:11,569 --> 00:17:14,329 And therefore, it's going to take more energy 321 00:17:14,329 --> 00:17:15,089 to pull it off. 322 00:17:15,089 --> 00:17:16,780 So it's going to be more tightly bound. 323 00:17:16,780 --> 00:17:19,920 It's going to be held in because of this less shielding, higher 324 00:17:19,920 --> 00:17:22,410 Z effective. 325 00:17:22,410 --> 00:17:23,390 All right. 326 00:17:23,390 --> 00:17:25,885 So now let's try a clicker question. 327 00:18:11,290 --> 00:18:12,068 10 more seconds. 328 00:18:28,240 --> 00:18:29,020 OK. 329 00:18:29,020 --> 00:18:32,410 So most of you did not like answer 1. 330 00:18:32,410 --> 00:18:35,450 But does someone want to explain this? 331 00:18:35,450 --> 00:18:38,500 And do you want to just walk up? 332 00:18:38,500 --> 00:18:44,170 Someone want to give an answer why? 333 00:18:44,170 --> 00:18:45,490 OK, over there. 334 00:18:48,939 --> 00:18:49,480 AUDIENCE: OK. 335 00:18:49,480 --> 00:18:58,440 So if we're choosing between 2 and 3, the answer for number 2, 336 00:18:58,440 --> 00:19:01,470 the 3p orbital has two electrons in it. 337 00:19:01,470 --> 00:19:03,820 And so the electrons, by nature, kind of repulse 338 00:19:03,820 --> 00:19:04,750 each other, right? 339 00:19:04,750 --> 00:19:07,890 So it's a little easier to pop one of those two 340 00:19:07,890 --> 00:19:12,020 out than if there was only one electron in there by itself 341 00:19:12,020 --> 00:19:14,640 and you're trying to pull it out. 342 00:19:14,640 --> 00:19:17,570 So yeah, you'd pick 2 over 3. 343 00:19:17,570 --> 00:19:18,960 CATHERINE DRENNAN: OK, yeah. 344 00:19:18,960 --> 00:19:22,140 So actually, I don't know if you can take the answer. 345 00:19:22,140 --> 00:19:26,460 It's a little hard to read it with the colors on top of it. 346 00:19:26,460 --> 00:19:31,870 But here, you have this plus system here. 347 00:19:31,870 --> 00:19:34,440 So you've removed this extra electron. 348 00:19:34,440 --> 00:19:39,040 So there should be, you feel, a higher Z effective here, 349 00:19:39,040 --> 00:19:44,230 which will mean that it's harder to sort of pull things off. 350 00:19:44,230 --> 00:19:48,300 And let's see this one. 351 00:19:48,300 --> 00:19:51,740 There's no way to take the answer down, right? 352 00:19:51,740 --> 00:19:53,670 So this one-- oh yeah. 353 00:19:53,670 --> 00:19:56,060 OK there, that's better. 354 00:19:56,060 --> 00:19:57,160 I can see this more. 355 00:19:57,160 --> 00:20:01,730 So this one here, you're pulling one from the s orbitals here. 356 00:20:01,730 --> 00:20:03,840 The p orbital's easier to pull it off. 357 00:20:03,840 --> 00:20:07,790 It takes less energy from p than from s. 358 00:20:07,790 --> 00:20:08,290 OK. 359 00:20:11,720 --> 00:20:12,980 So let's continue. 360 00:20:12,980 --> 00:20:14,710 We'll come back to some of these ideas 361 00:20:14,710 --> 00:20:16,990 as we go along because now, we're 362 00:20:16,990 --> 00:20:19,330 going to think about how these trends go 363 00:20:19,330 --> 00:20:21,880 across the periodic table. 364 00:20:21,880 --> 00:20:28,310 So across a row, ionization energy is going to increase. 365 00:20:28,310 --> 00:20:33,740 And the reason for this is that Z is increasing. 366 00:20:33,740 --> 00:20:38,620 So we're having more and more protons, a bigger Z effective. 367 00:20:38,620 --> 00:20:41,780 You're also adding electrons though. 368 00:20:41,780 --> 00:20:46,640 But n, the shell, remains the same. 369 00:20:46,640 --> 00:20:51,450 So if Z is increasing, n is remaining the same, 370 00:20:51,450 --> 00:20:55,490 what do you predict about Z effective? 371 00:20:55,490 --> 00:21:00,040 Is it going to increase, decrease, or stay the same? 372 00:21:00,040 --> 00:21:01,780 It's going to increase. 373 00:21:01,780 --> 00:21:04,850 So Z effective will also increase. 374 00:21:04,850 --> 00:21:07,910 And if you had a case that every single time you 375 00:21:07,910 --> 00:21:11,550 had total shielding of that added electron, 376 00:21:11,550 --> 00:21:13,470 then it might stay the same. 377 00:21:13,470 --> 00:21:16,250 But you're not going to have this case, this extreme case 378 00:21:16,250 --> 00:21:17,720 of total shielding. 379 00:21:17,720 --> 00:21:20,530 So if Z increased, Z effective is also 380 00:21:20,530 --> 00:21:24,090 going to increase as you go across. 381 00:21:24,090 --> 00:21:26,970 And because n is staying the same, 382 00:21:26,970 --> 00:21:30,840 you have more or less the same amount of distance 383 00:21:30,840 --> 00:21:32,310 from the nucleus. 384 00:21:32,310 --> 00:21:35,830 So you just have this stronger Z effective 385 00:21:35,830 --> 00:21:39,970 and it's holding on to the electrons. 386 00:21:39,970 --> 00:21:44,730 Now, if you go down a column, the ionization energy 387 00:21:44,730 --> 00:21:46,470 decreases. 388 00:21:46,470 --> 00:21:51,020 So in this case, you're also increasing Z. 389 00:21:51,020 --> 00:21:54,150 But now you're increasing n as well. 390 00:21:54,150 --> 00:21:59,440 And so when you increase n, you have your 3s and you go 391 00:21:59,440 --> 00:22:01,800 to your 4's and your 5's. 392 00:22:01,800 --> 00:22:06,960 And so now, those other orbitals are way far away 393 00:22:06,960 --> 00:22:10,810 and you have a much bigger effective radius here. 394 00:22:10,810 --> 00:22:13,340 The Z is getting bigger. 395 00:22:13,340 --> 00:22:16,750 But it's not really reaching as strongly out. 396 00:22:16,750 --> 00:22:20,080 So here, the effect of increasing n 397 00:22:20,080 --> 00:22:24,110 is making a much bigger difference than increasing Z. 398 00:22:24,110 --> 00:22:28,310 So going across, we have this increase in ionization energy 399 00:22:28,310 --> 00:22:31,710 because Z effective is increasing 400 00:22:31,710 --> 00:22:34,644 while n is staying the same or Z is increasing 401 00:22:34,644 --> 00:22:36,310 while n is staying the same, which means 402 00:22:36,310 --> 00:22:38,300 the effective is increasing. 403 00:22:38,300 --> 00:22:43,130 And going down, it's really n that dominates that pattern. 404 00:22:43,130 --> 00:22:44,880 So you have a decrease because you're 405 00:22:44,880 --> 00:22:48,770 going to higher and higher n. 406 00:22:48,770 --> 00:22:50,510 So let's look at some of those. 407 00:22:50,510 --> 00:22:55,220 And we can go back and look at it what I showed you before. 408 00:22:55,220 --> 00:22:58,570 I said I'd get back to sodium and potassium here. 409 00:22:58,570 --> 00:23:04,210 So if we consider all these, if we remove one electron, 410 00:23:04,210 --> 00:23:07,240 then we're going to go to a noble gas configuration. 411 00:23:07,240 --> 00:23:13,940 So with our first ionization when we're over here, 412 00:23:13,940 --> 00:23:15,490 we're going to go. 413 00:23:15,490 --> 00:23:18,260 And so when we do that, then we say, 414 00:23:18,260 --> 00:23:22,000 why are these numbers different for the second ionization? 415 00:23:22,000 --> 00:23:24,670 We have a noble gas configuration after we've 416 00:23:24,670 --> 00:23:26,900 lost one electron in each case. 417 00:23:26,900 --> 00:23:30,220 But then we can say, OK, well helium is up here, 418 00:23:30,220 --> 00:23:32,760 then neon, then argon. 419 00:23:32,760 --> 00:23:37,670 So the ionization energy is decreasing 420 00:23:37,670 --> 00:23:41,210 as we go down here because n is increasing. 421 00:23:41,210 --> 00:23:46,480 So we see that trend in our plot over here. 422 00:23:46,480 --> 00:23:51,040 There's a couple other things that we can see in this plot. 423 00:23:51,040 --> 00:23:56,360 So we also see that for boron, this fourth ionization energy 424 00:23:56,360 --> 00:23:58,820 is really big. 425 00:23:58,820 --> 00:24:02,720 And it's bigger than beryllium's third, which is bigger 426 00:24:02,720 --> 00:24:04,650 than lithium's second. 427 00:24:04,650 --> 00:24:07,959 So let's think about why that's the case. 428 00:24:07,959 --> 00:24:09,500 And that is another clicker question. 429 00:25:01,050 --> 00:25:01,550 OK. 430 00:25:01,550 --> 00:25:02,930 Let's just do 10 more seconds. 431 00:25:19,170 --> 00:25:19,670 Oops. 432 00:25:22,420 --> 00:25:24,960 All right. 433 00:25:24,960 --> 00:25:27,920 I was actually expecting a lower number for this. 434 00:25:27,920 --> 00:25:29,580 That's awesome. 435 00:25:29,580 --> 00:25:30,080 Right. 436 00:25:30,080 --> 00:25:34,260 So it turns out 1 is true. 437 00:25:34,260 --> 00:25:37,640 But all of these other ones are also 438 00:25:37,640 --> 00:25:39,450 going to be the same because they've just 439 00:25:39,450 --> 00:25:40,740 lost more electrons. 440 00:25:40,740 --> 00:25:43,460 So all of them have the same configuration. 441 00:25:43,460 --> 00:25:46,820 So that doesn't explain what's going on here. 442 00:25:46,820 --> 00:25:49,570 And this is also true. 443 00:25:49,570 --> 00:25:51,930 But binding energies are always negative. 444 00:25:51,930 --> 00:25:53,970 That does not explain anything. 445 00:25:53,970 --> 00:25:56,950 So the thing that explains the trend is this one. 446 00:25:56,950 --> 00:26:00,840 Even though they all now have the same configuration, 447 00:26:00,840 --> 00:26:03,620 it's going to be a lot harder to pull off 448 00:26:03,620 --> 00:26:07,220 the electron from the one that has the biggest Z effective 449 00:26:07,220 --> 00:26:09,630 because that's going to be bound more tightly. 450 00:26:09,630 --> 00:26:10,130 Great. 451 00:26:10,130 --> 00:26:13,800 So you're getting the hang of these types of questions. 452 00:26:13,800 --> 00:26:14,790 All right. 453 00:26:14,790 --> 00:26:16,450 So those are some of the trends. 454 00:26:16,450 --> 00:26:18,600 And, of course, when there are trends, 455 00:26:18,600 --> 00:26:20,430 there is always glitches. 456 00:26:20,430 --> 00:26:22,860 These aren't really exceptions. 457 00:26:22,860 --> 00:26:24,890 They are more glitches. 458 00:26:24,890 --> 00:26:27,810 And we can rationalize them pretty easily. 459 00:26:27,810 --> 00:26:32,580 So again the trend, increasing ionization energy across, 460 00:26:32,580 --> 00:26:37,180 decreasing iron energy down, the increase 461 00:26:37,180 --> 00:26:40,400 across as the Z effective increase, and down 462 00:26:40,400 --> 00:26:42,590 is the increase in n. 463 00:26:42,590 --> 00:26:45,930 But when you actually look at ionization energies, which 464 00:26:45,930 --> 00:26:50,860 are often reported in kilojoules per mole, versus Z, 465 00:26:50,860 --> 00:26:56,260 you see that it's not just kind of a straight line here. 466 00:26:56,260 --> 00:27:00,290 And if we put the elements on here that these correspond to, 467 00:27:00,290 --> 00:27:05,890 we see 1s1, 1s2, a drop to 2s, and then 468 00:27:05,890 --> 00:27:09,560 we're doing another 2s, a drop to 2p, 469 00:27:09,560 --> 00:27:12,420 and then so on as you go up along. 470 00:27:12,420 --> 00:27:15,230 So let's look at some of these little glitches. 471 00:27:15,230 --> 00:27:19,170 Why isn't this a straighter line here? 472 00:27:19,170 --> 00:27:24,300 So I'm now going to blow up this region on this slide here. 473 00:27:24,300 --> 00:27:28,510 And I can just put up this diagram again. 474 00:27:28,510 --> 00:27:30,430 And you can see that it's true. 475 00:27:30,430 --> 00:27:33,600 So we're talking about the first ionization energies here. 476 00:27:33,600 --> 00:27:36,180 We see lithium is lower then it goes higher then 477 00:27:36,180 --> 00:27:37,650 it goes down again. 478 00:27:37,650 --> 00:27:40,110 So that's that little trend over here. 479 00:27:40,110 --> 00:27:42,070 So why is this the case? 480 00:27:42,070 --> 00:27:45,060 So the ionization energy for beryllium 481 00:27:45,060 --> 00:27:49,400 is a bit higher than the ionization energy for boron. 482 00:27:49,400 --> 00:27:52,490 And so it turns out that this glitch then 483 00:27:52,490 --> 00:27:56,241 is we're going from the 2s to the 2p. 484 00:27:56,241 --> 00:28:00,480 And 2p, It's easier to pull off that electron. 485 00:28:00,480 --> 00:28:06,360 So that's why you have this lower ionization energy. 486 00:28:06,360 --> 00:28:08,920 We have another glitch over here. 487 00:28:08,920 --> 00:28:12,280 Now we're just within p. 488 00:28:12,280 --> 00:28:14,540 So what's going on there? 489 00:28:14,540 --> 00:28:15,980 And it's very small. 490 00:28:15,980 --> 00:28:18,120 It's a very small little difference. 491 00:28:18,120 --> 00:28:21,280 But here, the ionization energy for nitrogen 492 00:28:21,280 --> 00:28:24,080 is bigger than for oxygen. So it's easier 493 00:28:24,080 --> 00:28:26,900 to pull off an electron from oxygen. 494 00:28:26,900 --> 00:28:30,360 And if you draw out your diagram here, 495 00:28:30,360 --> 00:28:34,070 is nitrogen where we have obeyed Hund's rules 496 00:28:34,070 --> 00:28:36,530 and we put everything in parallel. 497 00:28:36,530 --> 00:28:38,630 But for oxygen, we have one extra. 498 00:28:38,630 --> 00:28:40,820 So we had to pair the electron. 499 00:28:40,820 --> 00:28:42,650 So it turns out it's a little easier 500 00:28:42,650 --> 00:28:45,910 to steal this 2p electron because it's 501 00:28:45,910 --> 00:28:47,690 the first one paired. 502 00:28:47,690 --> 00:28:50,120 And I kind of think about that as, again, sort 503 00:28:50,120 --> 00:28:52,650 of the bus where everyone sits. 504 00:28:52,650 --> 00:28:54,490 You can sit two people per seat. 505 00:28:54,490 --> 00:28:57,740 One person sits down, no one else wants to sit next to them 506 00:28:57,740 --> 00:28:59,650 until all the seats are taken. 507 00:28:59,650 --> 00:29:01,940 And sometimes when you're sitting in the seat, 508 00:29:01,940 --> 00:29:04,660 you're really, really, happy when that person gets up 509 00:29:04,660 --> 00:29:06,040 who's sitting next to you. 510 00:29:06,040 --> 00:29:07,660 Maybe there's another seat available. 511 00:29:07,660 --> 00:29:09,530 They move over to another seat. 512 00:29:09,530 --> 00:29:13,040 So it's often easier to eject the second person 513 00:29:13,040 --> 00:29:13,790 from the seat. 514 00:29:13,790 --> 00:29:16,070 There's a little bit of repulsion going on there. 515 00:29:16,070 --> 00:29:17,010 Everyone's working. 516 00:29:17,010 --> 00:29:18,730 They're moving their arms as they're 517 00:29:18,730 --> 00:29:20,520 doing their chemistry homework, at least 518 00:29:20,520 --> 00:29:21,825 the buses I'm on anyway. 519 00:29:21,825 --> 00:29:22,670 [LAUGHTER] 520 00:29:22,670 --> 00:29:28,710 So that's why there's a glitch there. 521 00:29:28,710 --> 00:29:30,390 All right. 522 00:29:30,390 --> 00:29:32,410 So this is all well and good. 523 00:29:32,410 --> 00:29:33,800 We have our trends. 524 00:29:33,800 --> 00:29:37,390 But I always like to think about how do we know any of this 525 00:29:37,390 --> 00:29:39,330 is really true? 526 00:29:39,330 --> 00:29:43,080 How do you actually measure these ionization energies? 527 00:29:43,080 --> 00:29:46,850 And so we're just going to talk about one method for measuring 528 00:29:46,850 --> 00:29:48,580 these for a minute. 529 00:29:48,580 --> 00:29:52,890 So photoelectron spectroscopy, PES, 530 00:29:52,890 --> 00:29:56,710 is used to determine ionization values. 531 00:29:56,710 --> 00:30:00,700 And so you can have some energy that you 532 00:30:00,700 --> 00:30:03,200 will use to excite something like neon, which 533 00:30:03,200 --> 00:30:06,490 is gas which lights up a sign for a pizza place, 534 00:30:06,490 --> 00:30:09,060 and you can inject an electron from it 535 00:30:09,060 --> 00:30:12,440 that has a certain amount of kinetic energy. 536 00:30:12,440 --> 00:30:14,810 And what you actually measure in this technique 537 00:30:14,810 --> 00:30:16,940 is the velocity of the electron. 538 00:30:16,940 --> 00:30:20,860 But from velocity, as you know, you can get kinetic energy. 539 00:30:20,860 --> 00:30:24,700 And from kinetic energy, we can get ionization energy. 540 00:30:24,700 --> 00:30:28,660 So let's look at this experiment and think about the electrons 541 00:30:28,660 --> 00:30:29,890 being ejected. 542 00:30:29,890 --> 00:30:34,720 So we have, again, our neon configuration. 543 00:30:34,720 --> 00:30:39,450 And we'll lose one electron from p here. 544 00:30:39,450 --> 00:30:42,810 And it will have a velocity and a kinetic energy. 545 00:30:42,810 --> 00:30:46,580 We can also think about losing an electron from s. 546 00:30:46,580 --> 00:30:51,550 And we're just going to lose one electron per shell here. 547 00:30:51,550 --> 00:30:56,050 And we can lose an electron from the 2s and the 1s. 548 00:30:56,050 --> 00:30:59,720 And all of those should have distinct velocities 549 00:30:59,720 --> 00:31:03,350 and distinct kinetic energies. 550 00:31:03,350 --> 00:31:08,840 So if we measure velocity, calculate kinetic energy, 551 00:31:08,840 --> 00:31:13,180 then we can find the ionization energy 552 00:31:13,180 --> 00:31:17,240 if we knew the energy that we used to excite the neon. 553 00:31:17,240 --> 00:31:21,000 So the incident energy equals ionization energy 554 00:31:21,000 --> 00:31:22,560 plus kinetic energy. 555 00:31:22,560 --> 00:31:25,910 Or rewritten, ionization energy equals 556 00:31:25,910 --> 00:31:28,390 the incident energy or initial energy 557 00:31:28,390 --> 00:31:30,700 minus the kinetic energy. 558 00:31:30,700 --> 00:31:34,090 So we can use this to calculate ionization energies. 559 00:31:34,090 --> 00:31:36,730 And this should look awfully familiar to you. 560 00:31:36,730 --> 00:31:39,090 It's very similar to something that 561 00:31:39,090 --> 00:31:43,430 will be an exam 1 where we're talking about using photons 562 00:31:43,430 --> 00:31:46,880 and shooting them at metal surfaces 563 00:31:46,880 --> 00:31:50,260 and ejecting electrons that have kinetic energy 564 00:31:50,260 --> 00:31:55,780 if the energy used to hit the metal is greater in energy 565 00:31:55,780 --> 00:31:57,500 than the work function and the extra 566 00:31:57,500 --> 00:31:59,380 comes off in kinetic energy. 567 00:31:59,380 --> 00:32:04,341 This is basically all the same idea here. 568 00:32:04,341 --> 00:32:04,840 All right. 569 00:32:04,840 --> 00:32:07,260 So in this particular case, you would 570 00:32:07,260 --> 00:32:11,110 measure three different velocities or three 571 00:32:11,110 --> 00:32:13,000 different kinetic energies. 572 00:32:13,000 --> 00:32:17,870 And now we can think about what those should probably 573 00:32:17,870 --> 00:32:21,630 correspond to using our chemistry knowledge. 574 00:32:21,630 --> 00:32:23,580 And some calculations here. 575 00:32:23,580 --> 00:32:27,480 So we have these three different kinetic energies. 576 00:32:27,480 --> 00:32:30,130 We know the energy of the incident. 577 00:32:30,130 --> 00:32:31,990 So we can do some math. 578 00:32:31,990 --> 00:32:40,210 And when we subtract those, we get one energy of 22. 579 00:32:40,210 --> 00:32:44,360 And then this kinetic energy is less. 580 00:32:44,360 --> 00:32:49,620 So we're going to get a higher ionization energy of 48. 581 00:32:49,620 --> 00:32:51,740 And this is really small. 582 00:32:51,740 --> 00:32:57,710 And so now we get an ionization energy of 870. 583 00:32:57,710 --> 00:33:00,770 And so we might not necessarily know which 584 00:33:00,770 --> 00:33:02,480 orbitals these correspond to. 585 00:33:02,480 --> 00:33:05,170 But if we think about it, you should 586 00:33:05,170 --> 00:33:08,490 have the lowest ionization energy to take an electron out 587 00:33:08,490 --> 00:33:11,890 of 2p, next would be to 2s, and then 588 00:33:11,890 --> 00:33:15,650 the hardest electron to eject would be from the 1s. 589 00:33:15,650 --> 00:33:18,420 And these are pretty similar to each other. 590 00:33:18,420 --> 00:33:21,130 But this is a much bigger number over here. 591 00:33:21,130 --> 00:33:25,860 And so that's kind of consistent with what we know. 592 00:33:25,860 --> 00:33:26,360 All right. 593 00:33:26,360 --> 00:33:27,850 So this is how you measure it. 594 00:33:27,850 --> 00:33:31,980 And again, this is a multi-electron system. 595 00:33:31,980 --> 00:33:34,930 And so then the energy is going to depend on the two quantum 596 00:33:34,930 --> 00:33:35,750 numbers. 597 00:33:35,750 --> 00:33:38,360 It depends on l and n. 598 00:33:38,360 --> 00:33:42,078 It matters what specific orbital you're talking about. 599 00:33:45,670 --> 00:33:49,510 So let's just think about another problem here. 600 00:33:49,510 --> 00:33:54,350 Suppose you had five really distinct kinetic energies. 601 00:33:54,350 --> 00:33:57,950 Assume that a very distinct kinetic energy 602 00:33:57,950 --> 00:34:00,220 means a different subshell. 603 00:34:00,220 --> 00:34:04,240 And so then we want to think about what 604 00:34:04,240 --> 00:34:09,060 are the possible elements in the periodic table that 605 00:34:09,060 --> 00:34:11,469 could produce a spectrum with these five very, 606 00:34:11,469 --> 00:34:13,620 very distinct kinetic energies? 607 00:34:13,620 --> 00:34:15,830 And so the way you think about this 608 00:34:15,830 --> 00:34:20,460 is you want to find what elements are going to have five 609 00:34:20,460 --> 00:34:22,929 different kinds of orbitals. 610 00:34:22,929 --> 00:34:31,130 And so we can list the first set here-- 1s, 2s, 2p, 3s, 3p, 611 00:34:31,130 --> 00:34:32,960 that's five. 612 00:34:32,960 --> 00:34:36,480 And then you need to know from the periodic table 613 00:34:36,480 --> 00:34:40,276 where are the elements where you're filling the 3p. 614 00:34:43,510 --> 00:34:46,210 And those are over here. 615 00:34:46,210 --> 00:34:50,560 So again, we talked and these problems aren't on the exam. 616 00:34:50,560 --> 00:34:52,620 But on the exam, you need to know 617 00:34:52,620 --> 00:34:56,870 that this is 1s-- you're filling 1s, you're filling 2s, 618 00:34:56,870 --> 00:34:59,410 you're filling 2p, you're filling 3s, 619 00:34:59,410 --> 00:35:02,380 you're filling 3p-- that you need to interpret. 620 00:35:02,380 --> 00:35:03,980 You'll be given a periodic table. 621 00:35:03,980 --> 00:35:06,640 But you need to be able to know what orbitals 622 00:35:06,640 --> 00:35:08,420 are being filled in the different parts 623 00:35:08,420 --> 00:35:10,550 of the periodic table. 624 00:35:10,550 --> 00:35:13,543 So let's just try a practice with that. 625 00:36:08,490 --> 00:36:08,990 All right. 626 00:36:08,990 --> 00:36:10,480 Let's just take 10 more seconds. 627 00:36:28,392 --> 00:36:29,870 All right. 628 00:36:29,870 --> 00:36:32,764 So we might need to work on the sort of counting. 629 00:36:35,490 --> 00:36:42,290 So again, you want to think about you have 1s, 2s, 2p, 3s, 630 00:36:42,290 --> 00:36:50,070 3p, 4s, 3d, and 4p. 631 00:36:50,070 --> 00:36:53,550 So I think if we get the counting down we'll be good. 632 00:36:53,550 --> 00:36:56,000 But again, you need to look at the periodic table 633 00:36:56,000 --> 00:36:58,840 and know what's getting filled. 634 00:36:58,840 --> 00:36:59,820 All right. 635 00:36:59,820 --> 00:37:04,010 So let's move on and talk about electron affinity. 636 00:37:04,010 --> 00:37:09,200 And maybe we can squeeze in some electronegativity at the end. 637 00:37:09,200 --> 00:37:14,420 These are very related topics and pretty fast. 638 00:37:14,420 --> 00:37:14,920 All right. 639 00:37:14,920 --> 00:37:21,720 So electron affinity-- the ability to gain electrons. 640 00:37:21,720 --> 00:37:23,610 So what we're talking about here is 641 00:37:23,610 --> 00:37:30,145 how likely atom X is to grab an electron and become X minus. 642 00:37:33,210 --> 00:37:35,630 So we often think about halogens when 643 00:37:35,630 --> 00:37:38,960 we're talking about this like chlorine. 644 00:37:38,960 --> 00:37:44,190 So we have Cl plus an electron, Cl minus. 645 00:37:44,190 --> 00:37:47,100 And here the change in energy associated 646 00:37:47,100 --> 00:37:52,160 with gaining that electron is minus 349 kilojoules per mole. 647 00:37:52,160 --> 00:37:54,800 Energy is released. 648 00:37:54,800 --> 00:37:58,870 And that means that the ion is more stable than the parent. 649 00:37:58,870 --> 00:38:03,070 So chloride is very happy to become Cl minus. 650 00:38:03,070 --> 00:38:06,540 And so you think about energy being released, 651 00:38:06,540 --> 00:38:10,169 if you think about a kid-- my husband's out of town, 652 00:38:10,169 --> 00:38:11,960 so I was watching our six-year-old daughter 653 00:38:11,960 --> 00:38:13,000 this weekend. 654 00:38:13,000 --> 00:38:15,310 And she was racing around like a crazy person 655 00:38:15,310 --> 00:38:17,900 until she collapsed in a heap. 656 00:38:17,900 --> 00:38:19,280 So energy is released. 657 00:38:19,280 --> 00:38:22,930 And she became a more stable six-year-old. 658 00:38:22,930 --> 00:38:25,660 So that's what's happening with chloride as well-- more 659 00:38:25,660 --> 00:38:27,260 or less. 660 00:38:27,260 --> 00:38:35,130 So here, the electron affinity is minus the change in energy. 661 00:38:35,130 --> 00:38:39,240 So if we talked about the electron affinity of chloride 662 00:38:39,240 --> 00:38:42,330 for the electron to become Cl minus, 663 00:38:42,330 --> 00:38:49,670 you would say that was plus 349 kilojoules per mole. 664 00:38:49,670 --> 00:38:55,450 So unlike ionization energy, which is always what? 665 00:38:55,450 --> 00:38:59,250 Positive or negative-- ionization energy? 666 00:38:59,250 --> 00:39:02,910 Always positive. 667 00:39:02,910 --> 00:39:06,090 Electron affinity can be positive or negative. 668 00:39:06,090 --> 00:39:08,310 And that tells you something about how much 669 00:39:08,310 --> 00:39:10,870 it wants to gain electrons. 670 00:39:10,870 --> 00:39:14,590 So nitrogen plus an electron, going to N minus, 671 00:39:14,590 --> 00:39:19,970 has a positive energy value here and has a negative electron 672 00:39:19,970 --> 00:39:21,100 affinity. 673 00:39:21,100 --> 00:39:28,750 So N minus-- the minus one ion is less stable than its parent. 674 00:39:28,750 --> 00:39:33,680 So it is not as happy as chloride to do this. 675 00:39:33,680 --> 00:39:37,210 So trends in ionization. 676 00:39:37,210 --> 00:39:40,640 Usually you have an increase going across 677 00:39:40,640 --> 00:39:44,310 and a decrease going down. 678 00:39:44,310 --> 00:39:49,140 And let's just consider noble gases 679 00:39:49,140 --> 00:39:51,050 and what you think about them. 680 00:39:51,050 --> 00:39:53,596 So we'll do one final clicker question. 681 00:40:05,930 --> 00:40:07,090 It should be pretty fast. 682 00:40:15,760 --> 00:40:17,125 OK, ten seconds. 683 00:40:31,910 --> 00:40:33,650 OK, yup. 684 00:40:33,650 --> 00:40:36,370 They are, in fact, negative. 685 00:40:36,370 --> 00:40:38,450 And so we can think about this over here. 686 00:40:38,450 --> 00:40:42,010 Noble gases have negative electron affinities. 687 00:40:42,010 --> 00:40:46,220 Noble gases are very happy the way they are. 688 00:40:46,220 --> 00:40:49,430 If you had to add another electron to them, 689 00:40:49,430 --> 00:40:52,830 you would need to make a new subshell there, 690 00:40:52,830 --> 00:40:55,200 which they don't want to do. 691 00:40:55,200 --> 00:40:58,770 And so halogens, on the other hand, 692 00:40:58,770 --> 00:41:04,750 which are right next door, have highest electron affinity. 693 00:41:04,750 --> 00:41:08,000 So if you're over here, they want to gain an electron 694 00:41:08,000 --> 00:41:09,530 and become a noble gas. 695 00:41:09,530 --> 00:41:11,900 Noble gases want to stay the way they are. 696 00:41:11,900 --> 00:41:15,600 So the increase trend ends right before you 697 00:41:15,600 --> 00:41:17,170 get to the noble gases. 698 00:41:17,170 --> 00:41:19,030 They're in their own category. 699 00:41:19,030 --> 00:41:19,530 OK. 700 00:41:19,530 --> 00:41:21,120 So we're going to end with that. 701 00:41:21,120 --> 00:41:26,370 And we'll continue with electronegativity on Friday.