1 00:00:16,000 --> 00:00:21,505 OK, this is the thing. 2 00:00:21,505 --> 00:00:25,809 We've done a lot of work on ionic bonds. 3 00:00:25,809 --> 00:00:29,680 And I drew the ionic bond energy again, on Monday. 4 00:00:29,680 --> 00:00:32,448 And remember, in an ironic bond-- 5 00:00:32,448 --> 00:00:34,785 so let's take sodium chloride-- 6 00:00:34,785 --> 00:00:37,688 we have, oh, we're going to go Lewis, right? 7 00:00:41,859 --> 00:00:44,261 And people say, well, why did I draw that dot there. 8 00:00:44,261 --> 00:00:46,463 I could have drawn two dots there and that dot there. 9 00:00:46,463 --> 00:00:47,097 Sure. 10 00:00:47,097 --> 00:00:47,598 Yeah. 11 00:00:47,598 --> 00:00:49,500 But they're kind of looking at each other. 12 00:00:49,500 --> 00:00:50,401 So, you know. 13 00:00:50,401 --> 00:00:50,901 [LAUGHTER] 14 00:00:50,901 --> 00:00:55,706 And remember in an iconic bond chlorine is like, give me! 15 00:00:55,706 --> 00:00:56,707 I want! 16 00:00:56,707 --> 00:00:59,676 And that's the kind of relationship they have, right? 17 00:00:59,676 --> 00:01:02,546 And so this went into something like this, where 18 00:01:02,546 --> 00:01:04,715 sodium was like, OK, fine. 19 00:01:04,715 --> 00:01:05,215 Take it. 20 00:01:05,215 --> 00:01:06,417 I'm a plus now. 21 00:01:06,417 --> 00:01:08,385 And chlorine was like, thank you very much. 22 00:01:08,385 --> 00:01:12,689 I'm fully octeted, right? 23 00:01:12,689 --> 00:01:13,590 Like that. 24 00:01:13,590 --> 00:01:14,958 And that's the ionic bond. 25 00:01:14,958 --> 00:01:16,560 So this is ionic. 26 00:01:16,560 --> 00:01:17,861 And we learned this. 27 00:01:17,861 --> 00:01:20,631 OK, but see, there is another kind of bond that can happen. 28 00:01:20,631 --> 00:01:24,201 It's not all about taking and one per-- no. 29 00:01:24,201 --> 00:01:27,137 It can also be about sharing. 30 00:01:27,137 --> 00:01:29,807 About sharing. 31 00:01:29,807 --> 00:01:31,742 So if I have hydrogen instead, let's 32 00:01:31,742 --> 00:01:33,644 suppose I have hydrogen like up there. 33 00:01:33,644 --> 00:01:35,979 And I've got hydrogen now. 34 00:01:35,979 --> 00:01:38,916 And here is hydrogen. Well, see when 35 00:01:38,916 --> 00:01:42,152 they see-- geshundheit-- each other, a very different thing 36 00:01:42,152 --> 00:01:43,620 happens. 37 00:01:43,620 --> 00:01:47,057 Because one of the hydrogens doesn't say, gimme. 38 00:01:47,057 --> 00:01:48,991 And the other one doesn't say, sure. 39 00:01:48,991 --> 00:01:51,228 Well, but something else happens. 40 00:01:51,228 --> 00:01:52,996 Because they get closer. 41 00:01:55,933 --> 00:01:58,402 They get closer, and closer. 42 00:01:58,402 --> 00:01:59,169 Oh! 43 00:01:59,169 --> 00:02:02,005 Let's look at this in terms of like, OK, so here's 44 00:02:02,005 --> 00:02:04,174 a plus and minus. 45 00:02:04,174 --> 00:02:05,843 Oh, yeah. 46 00:02:05,843 --> 00:02:08,612 It's not an orbit, it's an orbital! 47 00:02:08,612 --> 00:02:11,615 And here's another plus, and here's another minus. 48 00:02:11,615 --> 00:02:13,917 And these electrons-- you know, the thing is, 49 00:02:13,917 --> 00:02:17,554 the electrons are like, I don't like you other electron. 50 00:02:17,554 --> 00:02:18,956 You're repelling me. 51 00:02:18,956 --> 00:02:22,091 And the protons are like, I don't like you other proton. 52 00:02:22,091 --> 00:02:23,827 You're repelling me. 53 00:02:23,827 --> 00:02:25,896 But the electrons do like protons. 54 00:02:25,896 --> 00:02:31,034 And at a certain point, if you bring these together, 55 00:02:31,034 --> 00:02:34,271 one of them is like, hey, I got an idea! 56 00:02:34,271 --> 00:02:37,841 What if I'm attracted to you sometimes, over here, 57 00:02:37,841 --> 00:02:39,442 and I'm this electron. 58 00:02:39,442 --> 00:02:42,079 I'm like, I want to be attracted to you. 59 00:02:42,079 --> 00:02:45,449 And I'll tell you what, you can be attracted to my proton, 60 00:02:45,449 --> 00:02:46,817 and we'll share. 61 00:02:46,817 --> 00:02:49,119 We'll share. 62 00:02:49,119 --> 00:02:51,522 And so, when these come together, 63 00:02:51,522 --> 00:02:58,028 what you get is the protons are a certain distance apart, 64 00:02:58,028 --> 00:03:00,964 that's set by how far you can push them in without them 65 00:03:00,964 --> 00:03:03,000 feeling that repulsion. 66 00:03:03,000 --> 00:03:05,135 And the electrons-- as long as they don't get like, 67 00:03:05,135 --> 00:03:06,737 you know super on top of each other, 68 00:03:06,737 --> 00:03:08,505 because they're going to repel each other-- 69 00:03:08,505 --> 00:03:09,873 they're happier. 70 00:03:09,873 --> 00:03:12,309 They're happier because they got two positive charges 71 00:03:12,309 --> 00:03:15,746 that they can kind of go around and be near. 72 00:03:15,746 --> 00:03:21,084 That leads to happiness-- lower energy bond! 73 00:03:21,084 --> 00:03:24,121 But you can see right now, this is a very different kind 74 00:03:24,121 --> 00:03:25,622 of bond. 75 00:03:25,622 --> 00:03:26,123 Right? 76 00:03:26,123 --> 00:03:28,492 This is not ionic. 77 00:03:28,492 --> 00:03:29,860 This is covalent. 78 00:03:29,860 --> 00:03:31,161 This is covalent. 79 00:03:31,161 --> 00:03:37,935 When share electrons it's a covalent bond. 80 00:03:37,935 --> 00:03:38,602 OK? 81 00:03:38,602 --> 00:03:43,106 And that is something we write differently. 82 00:03:43,106 --> 00:03:45,542 We write it with a dash. 83 00:03:45,542 --> 00:03:48,111 Well, or you could've also written it-- 84 00:03:48,111 --> 00:03:50,914 or maybe you should say, well, let's just put those electrons 85 00:03:50,914 --> 00:03:54,017 in between them like that. 86 00:03:54,017 --> 00:03:54,518 Right? 87 00:03:54,518 --> 00:03:56,720 And it's showing that those electrons didn't 88 00:03:56,720 --> 00:03:59,256 go to one or the other, they're in between. 89 00:03:59,256 --> 00:04:02,492 They are what are making up the bond together, 90 00:04:02,492 --> 00:04:06,096 sharing those protons across the atoms. 91 00:04:06,096 --> 00:04:06,597 OK. 92 00:04:06,597 --> 00:04:08,465 So that's nice. 93 00:04:08,465 --> 00:04:11,602 That's hydrogen. What happens when 94 00:04:11,602 --> 00:04:15,706 we get to something a little bit more complicated, right? 95 00:04:15,706 --> 00:04:19,009 So let's go to water. 96 00:04:19,009 --> 00:04:21,245 Now, if I have something like water-- 97 00:04:21,245 --> 00:04:24,982 so now, I'm going to go through some examples. 98 00:04:24,982 --> 00:04:26,082 Let's suppose I have water. 99 00:04:26,082 --> 00:04:28,919 Well, I've got this here, and I've got this here. 100 00:04:28,919 --> 00:04:30,554 And now, remember, we're going to think 101 00:04:30,554 --> 00:04:32,856 about things in terms of Lewis dots, 102 00:04:32,856 --> 00:04:35,692 which I introduced to you on Monday. 103 00:04:35,692 --> 00:04:39,329 Those are the valence electrons in an atom, which are what 104 00:04:39,329 --> 00:04:41,031 do all of the chemical bonding. 105 00:04:41,031 --> 00:04:42,799 So those are the ones we're going to carry. 106 00:04:42,799 --> 00:04:46,236 Now, how many dots do I have for oxygen. I forget. 107 00:04:46,236 --> 00:04:47,070 Six! 108 00:04:47,070 --> 00:04:47,738 Six. 109 00:04:47,738 --> 00:04:51,008 And if you didn't know, you know where to look. 110 00:04:51,008 --> 00:04:54,177 Because you're always carrying your periodic table with you-- 111 00:04:54,177 --> 00:04:55,178 always! 112 00:04:55,178 --> 00:04:58,715 And so I might write six like that. 113 00:04:58,715 --> 00:04:59,249 OK. 114 00:04:59,249 --> 00:05:02,786 What lines do I draw where? 115 00:05:02,786 --> 00:05:05,122 How are these shared? 116 00:05:05,122 --> 00:05:17,200 So how are the electrons shared in covalent bonds? 117 00:05:17,200 --> 00:05:19,870 Covalent bonds. 118 00:05:19,870 --> 00:05:27,110 And that is where Lewis will help. 119 00:05:27,110 --> 00:05:28,612 That is where Lewis will help. 120 00:05:28,612 --> 00:05:33,183 How do I take these valence configurations of electrons 121 00:05:33,183 --> 00:05:38,722 and make a molecule with these kinds of sharing bonds in it? 122 00:05:38,722 --> 00:05:42,826 And there's actually a fairly simple recipe 123 00:05:42,826 --> 00:05:44,728 that I want to teach you today, because that's 124 00:05:44,728 --> 00:05:46,063 how we're going to do it. 125 00:05:46,063 --> 00:05:47,731 And the recipe is written here. 126 00:05:47,731 --> 00:05:49,566 And don't worry, there's a lot of text here, 127 00:05:49,566 --> 00:05:53,170 but I'm going to go through it for three different examples. 128 00:05:53,170 --> 00:05:56,373 And if you haven't done Lewis-- 129 00:05:56,373 --> 00:05:58,909 I know some of you have in high school, some of you have not. 130 00:05:58,909 --> 00:05:59,743 That's OK. 131 00:05:59,743 --> 00:06:01,978 If you haven't, practice is really key. 132 00:06:01,978 --> 00:06:02,946 All right? 133 00:06:02,946 --> 00:06:05,916 We'll do three molecules, maybe four, today. 134 00:06:05,916 --> 00:06:09,252 And I encourage you to do a bunch more as practice. 135 00:06:09,252 --> 00:06:13,023 And this is the recipe for drawing Lewis structures. 136 00:06:13,023 --> 00:06:16,760 And Lewis structures is what tells us how electrons 137 00:06:16,760 --> 00:06:21,131 are bonded in these molecules. 138 00:06:21,131 --> 00:06:24,735 And so, let's follow this for the one I have up here. 139 00:06:24,735 --> 00:06:27,337 Let's follow this for water. 140 00:06:27,337 --> 00:06:27,838 OK? 141 00:06:27,838 --> 00:06:29,706 So we're going to go through this recipe. 142 00:06:29,706 --> 00:06:32,909 Now, the first-- so, one through six. 143 00:06:32,909 --> 00:06:35,679 I will write one through six for the example. 144 00:06:35,679 --> 00:06:37,547 I will parallel that recipe. 145 00:06:37,547 --> 00:06:40,217 So first, connect atom central. 146 00:06:40,217 --> 00:06:43,754 Central atom is often the least electronegative-- already 147 00:06:43,754 --> 00:06:45,021 I'm stuck! 148 00:06:45,021 --> 00:06:46,456 Because I didn't tell you anything 149 00:06:46,456 --> 00:06:47,957 about electronegativity. 150 00:06:47,957 --> 00:06:49,793 That's coming a little later. 151 00:06:49,793 --> 00:06:53,330 Today, I will tell you what electronegativity is. 152 00:06:53,330 --> 00:06:55,165 For now, trust me. 153 00:06:55,165 --> 00:06:56,700 So the first step is connect atoms. 154 00:06:56,700 --> 00:07:01,204 Central atom is often the least electronegative. 155 00:07:01,204 --> 00:07:01,705 OK. 156 00:07:01,705 --> 00:07:02,472 Well, so let's see. 157 00:07:02,472 --> 00:07:11,214 So for water, so step one, the H atoms are going to be terminal. 158 00:07:11,214 --> 00:07:13,950 That means that they're on the outside. 159 00:07:13,950 --> 00:07:14,885 Terminal. 160 00:07:14,885 --> 00:07:15,385 OK? 161 00:07:15,385 --> 00:07:16,286 Outside. 162 00:07:16,286 --> 00:07:19,756 They're also called terminal. 163 00:07:19,756 --> 00:07:25,996 And so, the arrangement should be something like H, O, and H. 164 00:07:25,996 --> 00:07:26,763 OK, good. 165 00:07:26,763 --> 00:07:28,532 So that's going to be my arrangement. 166 00:07:28,532 --> 00:07:29,032 OK. 167 00:07:29,032 --> 00:07:31,802 Step two-- determine the total number of valence electrons. 168 00:07:31,802 --> 00:07:33,103 OK, I can do that. 169 00:07:33,103 --> 00:07:34,538 So two. 170 00:07:34,538 --> 00:07:36,606 Well, I've got one, two , three-- 171 00:07:36,606 --> 00:07:37,107 OK. 172 00:07:37,107 --> 00:07:40,610 I've got eight valence electrons. 173 00:07:40,610 --> 00:07:41,945 Good. 174 00:07:41,945 --> 00:07:42,446 OK. 175 00:07:42,446 --> 00:07:47,350 Step three is where it gets really fun. 176 00:07:47,350 --> 00:07:50,487 Place bonding pair of electrons. 177 00:07:50,487 --> 00:07:52,155 Go all in, just like I did for-- 178 00:07:52,155 --> 00:07:54,124 So there's a bonding pair right there. 179 00:07:54,124 --> 00:07:55,258 There they are. 180 00:07:55,258 --> 00:07:57,260 Two electrons in a bonding pair. 181 00:07:57,260 --> 00:08:02,165 So place bonding pair between adjacent atoms. 182 00:08:02,165 --> 00:08:02,632 OK. 183 00:08:02,632 --> 00:08:03,300 I can do that. 184 00:08:03,300 --> 00:08:04,468 So let's see. 185 00:08:04,468 --> 00:08:05,836 Here we go. 186 00:08:05,836 --> 00:08:10,674 H, O, H. Right? 187 00:08:10,674 --> 00:08:11,608 OK. 188 00:08:11,608 --> 00:08:13,210 So there's my bonding pair. 189 00:08:13,210 --> 00:08:14,478 I put two electrons. 190 00:08:14,478 --> 00:08:19,483 But now, you see, OK, I only used up four electrons there. 191 00:08:19,483 --> 00:08:19,983 OK? 192 00:08:19,983 --> 00:08:24,221 Now, starting with that, now add enough electrons 193 00:08:24,221 --> 00:08:28,892 to each one to form an octet. 194 00:08:28,892 --> 00:08:32,028 Start with terminal atoms, add enough electrons 195 00:08:32,028 --> 00:08:33,496 to form an octet. 196 00:08:33,496 --> 00:08:34,063 OK? 197 00:08:34,063 --> 00:08:34,698 So let's see. 198 00:08:34,698 --> 00:08:38,835 But hydrogen is special, because hydrogen's octet is just two. 199 00:08:38,835 --> 00:08:40,604 Hydrogen doesn't want eight. 200 00:08:40,604 --> 00:08:42,371 Hydrogen just wants two. 201 00:08:42,371 --> 00:08:44,174 So we called it out here, in the recipe. 202 00:08:44,174 --> 00:08:46,209 Two for hydrogen. OK. 203 00:08:46,209 --> 00:08:49,112 So add enough electrons to form an octet. 204 00:08:49,112 --> 00:08:53,083 Well see, each H atom already has-- 205 00:08:53,083 --> 00:08:54,451 Remember they're sharing. 206 00:08:54,451 --> 00:08:55,352 They're sharing. 207 00:08:55,352 --> 00:08:55,952 OK? 208 00:08:55,952 --> 00:09:01,691 So each H atom already has the two electrons that it wants. 209 00:09:01,691 --> 00:09:05,095 And so, for four I've got that-- 210 00:09:05,095 --> 00:09:07,163 oh, I started with the terminal. 211 00:09:07,163 --> 00:09:07,664 Atoms. 212 00:09:07,664 --> 00:09:08,365 OK. 213 00:09:08,365 --> 00:09:16,940 And so for four, I've got each H is OK. 214 00:09:16,940 --> 00:09:18,174 It has two. 215 00:09:18,174 --> 00:09:18,875 All right? 216 00:09:18,875 --> 00:09:24,848 It has two electrons, which is what it wants in its valence. 217 00:09:24,848 --> 00:09:25,348 Next one. 218 00:09:25,348 --> 00:09:26,116 If-- oh! 219 00:09:26,116 --> 00:09:29,786 Now, it gets-- If there's electrons left over 220 00:09:29,786 --> 00:09:32,088 put them on the central atom. 221 00:09:32,088 --> 00:09:32,589 OK. 222 00:09:32,589 --> 00:09:34,224 So I went from the terminal in. 223 00:09:34,224 --> 00:09:35,592 I went from the outside in. 224 00:09:35,592 --> 00:09:36,626 H has two. 225 00:09:36,626 --> 00:09:37,193 H has two. 226 00:09:37,193 --> 00:09:38,862 That's good. 227 00:09:38,862 --> 00:09:39,362 Oh! 228 00:09:39,362 --> 00:09:41,131 But how do I know if I have any left over? 229 00:09:41,131 --> 00:09:43,400 Well, I did that in step two. 230 00:09:43,400 --> 00:09:45,669 I had a total number of electrons. 231 00:09:45,669 --> 00:09:47,404 Now, how many have I used? 232 00:09:47,404 --> 00:09:50,974 I've used two here, and I've used two here. 233 00:09:50,974 --> 00:09:54,277 I have four left over, because I started with eight. 234 00:09:54,277 --> 00:09:54,778 Right? 235 00:09:54,778 --> 00:09:57,180 And I was just told from step five 236 00:09:57,180 --> 00:09:58,682 to put those on the central atom. 237 00:09:58,682 --> 00:09:59,182 OK. 238 00:09:59,182 --> 00:10:03,253 So step five now, is going to make this look interesting. 239 00:10:03,253 --> 00:10:06,456 So H, O, H-- 240 00:10:06,456 --> 00:10:10,360 and now, I'm not going to put them in a bond. 241 00:10:10,360 --> 00:10:10,860 Right? 242 00:10:10,860 --> 00:10:12,262 I'm just going to put them on the atom. 243 00:10:12,262 --> 00:10:13,797 And those are called non-bonding. 244 00:10:16,800 --> 00:10:18,134 Well, OK. 245 00:10:18,134 --> 00:10:19,302 That's a genius name. 246 00:10:19,302 --> 00:10:20,003 Nonbinding. 247 00:10:20,003 --> 00:10:22,138 Because they're not bonding. 248 00:10:22,138 --> 00:10:23,039 [LAUGHS] 249 00:10:23,039 --> 00:10:26,810 That's a good name for those electrons. 250 00:10:26,810 --> 00:10:30,847 You can also call those lone pairs, because they're lone. 251 00:10:30,847 --> 00:10:32,282 They're not involved in a bond. 252 00:10:32,282 --> 00:10:32,782 All right? 253 00:10:32,782 --> 00:10:35,218 So those are my four extra electrons. 254 00:10:35,218 --> 00:10:41,324 And then finally, if the central atom is less than an octet, 255 00:10:41,324 --> 00:10:43,026 used the lone pairs from terminal atoms-- 256 00:10:43,026 --> 00:10:44,260 Oh, this looks complicated. 257 00:10:44,260 --> 00:10:45,362 I don't want to deal with it. 258 00:10:45,362 --> 00:10:45,862 Why? 259 00:10:45,862 --> 00:10:50,400 Because I've got an octet here already. 260 00:10:50,400 --> 00:10:54,070 So six is not needed. 261 00:10:54,070 --> 00:10:59,376 Because everything since the oxygen-- 262 00:10:59,376 --> 00:11:04,214 since O is happy. 263 00:11:04,214 --> 00:11:06,216 It's got its octet. 264 00:11:06,216 --> 00:11:10,353 So that is a very slow-- 265 00:11:10,353 --> 00:11:11,187 we went slow. 266 00:11:11,187 --> 00:11:12,522 We'll go faster now. 267 00:11:12,522 --> 00:11:13,023 Right? 268 00:11:13,023 --> 00:11:14,624 So that is a very slow introduction 269 00:11:14,624 --> 00:11:18,428 to how to do a Lewis dot diagram for a molecule. 270 00:11:18,428 --> 00:11:19,896 In this case, H2O. 271 00:11:19,896 --> 00:11:24,067 Now, you may notice I drew it linear. 272 00:11:24,067 --> 00:11:27,771 Some of us know that is not the shape of this molecule. 273 00:11:27,771 --> 00:11:29,005 But shapes come later. 274 00:11:29,005 --> 00:11:31,207 Shapes come next week, right? 275 00:11:31,207 --> 00:11:33,343 Right now we're not thinking about shapes. 276 00:11:33,343 --> 00:11:34,377 Let's do another example. 277 00:11:34,377 --> 00:11:42,719 So my next example is O, Cl. 278 00:11:42,719 --> 00:11:45,588 I'm taking this and I'm putting a charge on it. 279 00:11:45,588 --> 00:11:48,858 So here's my next example. 280 00:11:48,858 --> 00:11:51,161 Well, anyway, that's my example. 281 00:11:51,161 --> 00:11:52,996 I'm going to go through the numbers again. 282 00:11:52,996 --> 00:11:54,431 We're going to go a little faster. 283 00:11:54,431 --> 00:11:57,300 So I want to know how this looks in a Lewis. 284 00:11:57,300 --> 00:12:00,136 Structure well, OK. 285 00:12:00,136 --> 00:12:03,173 So there's only two atoms, so-- 286 00:12:03,173 --> 00:12:06,776 Maybe I should have called this example B, because now I 287 00:12:06,776 --> 00:12:08,178 have point 1, all right? 288 00:12:08,178 --> 00:12:09,279 So there's only two atoms. 289 00:12:09,279 --> 00:12:10,747 So there's no central atom. 290 00:12:10,747 --> 00:12:14,150 OK, that sounds like that might be easy. 291 00:12:14,150 --> 00:12:17,554 And then step two is, how many valence electrons are there? 292 00:12:17,554 --> 00:12:21,124 Well, there's six, plus seven, plus one, right? 293 00:12:21,124 --> 00:12:23,460 So oxygen is six. 294 00:12:23,460 --> 00:12:30,133 Chlorine is seven, plus one, equals 14 electrons. 295 00:12:30,133 --> 00:12:31,334 Where did the one come from? 296 00:12:31,334 --> 00:12:33,937 That's because it's got a negative charge here. 297 00:12:33,937 --> 00:12:35,605 It's a negatively charged molecule. 298 00:12:35,605 --> 00:12:36,106 OK. 299 00:12:36,106 --> 00:12:36,606 Good. 300 00:12:36,606 --> 00:12:38,441 Now-- OK, now it gets interesting. 301 00:12:38,441 --> 00:12:41,511 Place bonding pair of electrons between adjacent atoms. 302 00:12:41,511 --> 00:12:44,347 So my adjacent atoms are these two atoms, 303 00:12:44,347 --> 00:12:49,652 which I could write like this, or I could also 304 00:12:49,652 --> 00:12:52,255 have written it like this. 305 00:12:52,255 --> 00:12:54,790 OK? 306 00:12:54,790 --> 00:12:56,960 Those are equivalent. 307 00:12:56,960 --> 00:12:57,894 Now step four. 308 00:12:57,894 --> 00:12:58,394 OK. 309 00:12:58,394 --> 00:13:00,063 Now, starting with the terminal atoms, 310 00:13:00,063 --> 00:13:02,599 add enough electrons to each one to form an octet. 311 00:13:02,599 --> 00:13:04,067 So let's go through this. 312 00:13:04,067 --> 00:13:06,503 So now step four. 313 00:13:06,503 --> 00:13:07,003 OK. 314 00:13:11,141 --> 00:13:16,513 Now, this can count the two electrons. 315 00:13:16,513 --> 00:13:17,981 This can count those two electrons. 316 00:13:17,981 --> 00:13:18,948 You see how this works? 317 00:13:18,948 --> 00:13:20,984 Because we're sharing now. 318 00:13:20,984 --> 00:13:22,252 No one took. 319 00:13:22,252 --> 00:13:22,852 We're sharing. 320 00:13:22,852 --> 00:13:25,555 So they can each count those, because 321 00:13:25,555 --> 00:13:28,358 of what I drew up there in terms of how a convenient bond works. 322 00:13:28,358 --> 00:13:32,428 But now, they need another six to form an octet. 323 00:13:32,428 --> 00:13:33,563 So how many? 324 00:13:33,563 --> 00:13:34,964 I used two. 325 00:13:34,964 --> 00:13:35,965 How many do I have left? 326 00:13:35,965 --> 00:13:37,867 I've got 12 left. 327 00:13:37,867 --> 00:13:39,102 It's perfect. 328 00:13:39,102 --> 00:13:39,602 Right? 329 00:13:39,602 --> 00:13:40,470 It's perfect. 330 00:13:40,470 --> 00:13:42,772 So I've got exactly as many as I want. 331 00:13:42,772 --> 00:13:46,776 And I can write O has all of those. 332 00:13:46,776 --> 00:13:49,212 Cl has all of these. 333 00:13:49,212 --> 00:13:51,414 And if we want to be careful about it, 334 00:13:51,414 --> 00:13:54,951 we will emphasize that this molecule is not neutral. 335 00:13:54,951 --> 00:13:56,419 It got an extra electron. 336 00:13:56,419 --> 00:13:58,688 That's why we put the minus sign up there. 337 00:13:58,688 --> 00:13:59,189 Right? 338 00:13:59,189 --> 00:14:01,424 It's charged. 339 00:14:01,424 --> 00:14:03,760 And this molecule, OK. 340 00:14:03,760 --> 00:14:05,328 Each atom-- let's see, OK. 341 00:14:05,328 --> 00:14:07,030 I used the extra electrons. 342 00:14:07,030 --> 00:14:08,331 If electrons are left over-- 343 00:14:08,331 --> 00:14:10,700 No electrons left over. 344 00:14:10,700 --> 00:14:15,038 If central atoms-- no, they're already octets. 345 00:14:15,038 --> 00:14:19,108 So five and six are not needed. 346 00:14:19,108 --> 00:14:21,978 Oh, but you know the last example 347 00:14:21,978 --> 00:14:23,913 is going to be more interesting. 348 00:14:23,913 --> 00:14:26,249 So let's do that. 349 00:14:26,249 --> 00:14:27,784 Last example. 350 00:14:27,784 --> 00:14:31,754 O-- C, example C. O-- 351 00:14:31,754 --> 00:14:35,191 so I've got H, OK. 352 00:14:35,191 --> 00:14:36,793 I'm just going to write the atoms here, 353 00:14:36,793 --> 00:14:39,963 because I'm starting where I don't even know 354 00:14:39,963 --> 00:14:41,164 what it's going to look like. 355 00:14:41,164 --> 00:14:42,732 I don't even want to hint at it. 356 00:14:42,732 --> 00:14:43,499 Those are my atoms. 357 00:14:43,499 --> 00:14:47,503 I've got two hydrogens, an oxygen, and a chlorine. 358 00:14:47,503 --> 00:14:48,004 OK. 359 00:14:48,004 --> 00:14:49,339 I'm sorry, a carbon. 360 00:14:49,339 --> 00:14:50,406 Oh, yeah. 361 00:14:50,406 --> 00:14:52,842 I meant this to be a carbon. 362 00:14:52,842 --> 00:14:55,211 There we go. 363 00:14:55,211 --> 00:14:57,614 Two hydrogens, an oxygen, and carbon. 364 00:14:57,614 --> 00:14:58,147 OK. 365 00:14:58,147 --> 00:15:01,851 Now, as we will see when I tell you what electronegativity is, 366 00:15:01,851 --> 00:15:04,387 carbon has the lowest electronegativity. 367 00:15:04,387 --> 00:15:05,154 OK? 368 00:15:05,154 --> 00:15:09,425 And so, I'm going to put that in the center. 369 00:15:09,425 --> 00:15:14,364 That's going to tell me that if I answer point 1, 370 00:15:14,364 --> 00:15:16,900 it might look something like this. 371 00:15:16,900 --> 00:15:20,169 Oh, now it's taking some form, right? 372 00:15:20,169 --> 00:15:20,670 OK? 373 00:15:20,670 --> 00:15:22,472 So the hydrogens are going to go like that. 374 00:15:22,472 --> 00:15:26,976 Their terminally oxygen is outside, carbons in the middle. 375 00:15:26,976 --> 00:15:28,378 And how many electrons do I have? 376 00:15:28,378 --> 00:15:29,846 OK, so now, let's see. 377 00:15:29,846 --> 00:15:37,654 Answering step two, I've got 12 valence electrons. 378 00:15:37,654 --> 00:15:38,521 OK. 379 00:15:38,521 --> 00:15:43,459 Because I've got six, four, five, right? 380 00:15:43,459 --> 00:15:44,794 So 12. 381 00:15:44,794 --> 00:15:45,295 OK? 382 00:15:45,295 --> 00:15:46,863 Good. 383 00:15:46,863 --> 00:15:49,032 And now, I'm going to put the bonding pair in there. 384 00:15:49,032 --> 00:15:50,500 So let's do that. 385 00:15:50,500 --> 00:15:52,035 So step three-- 386 00:15:52,035 --> 00:15:59,242 OK, so now I've got C, H, H, O. So I've done step three. 387 00:15:59,242 --> 00:15:59,742 OK. 388 00:15:59,742 --> 00:16:01,544 So I've got two, four, six. 389 00:16:01,544 --> 00:16:07,850 I've used up six electrons in this sharing covalent bond 390 00:16:07,850 --> 00:16:11,454 situation, and I started with 12. 391 00:16:11,454 --> 00:16:14,657 So that means I've got six left. 392 00:16:14,657 --> 00:16:15,158 OK. 393 00:16:15,158 --> 00:16:16,659 So I'm going to go to step four. 394 00:16:16,659 --> 00:16:19,195 Now, starting with the terminal atoms, add enough to each one 395 00:16:19,195 --> 00:16:20,029 to form an octet. 396 00:16:20,029 --> 00:16:21,965 Now hydrogen is good, right? 397 00:16:21,965 --> 00:16:24,267 Because hydrogen, remember, it's octet is a doublet. 398 00:16:24,267 --> 00:16:25,301 It's two. 399 00:16:25,301 --> 00:16:25,902 So that's good. 400 00:16:25,902 --> 00:16:27,136 But what about oxygen? 401 00:16:27,136 --> 00:16:27,637 OK. 402 00:16:27,637 --> 00:16:29,772 It looks like oxygen needs some. 403 00:16:29,772 --> 00:16:33,609 So now, we're going to write this structure like this. 404 00:16:33,609 --> 00:16:38,982 I've got to add six more electrons to oxygen in order 405 00:16:38,982 --> 00:16:40,450 to fulfill its octet, right? 406 00:16:40,450 --> 00:16:46,656 And oxygen is happy. 407 00:16:46,656 --> 00:16:47,156 All right? 408 00:16:47,156 --> 00:16:50,293 Yeah, it is. 409 00:16:50,293 --> 00:16:51,861 Just like that. 410 00:16:51,861 --> 00:16:54,397 But if electrons are left over-- but are 411 00:16:54,397 --> 00:16:57,467 there any electrons left over? 412 00:16:57,467 --> 00:16:58,601 No. 413 00:16:58,601 --> 00:17:00,503 So I can't place electrons on the center atom, 414 00:17:00,503 --> 00:17:04,173 yet now we invoke number six. 415 00:17:04,173 --> 00:17:06,041 If central less than an octet-- 416 00:17:06,041 --> 00:17:10,012 it is two, two, two-- 417 00:17:10,012 --> 00:17:12,214 then use lone pairs from terminal atoms 418 00:17:12,214 --> 00:17:14,617 to form multiple bonds to the central atom. 419 00:17:14,617 --> 00:17:15,885 Oh, yeah. 420 00:17:15,885 --> 00:17:17,319 Now we're there. 421 00:17:17,319 --> 00:17:17,987 Now we're there. 422 00:17:17,987 --> 00:17:19,589 So now we jump to step six. 423 00:17:22,759 --> 00:17:23,760 Because look. 424 00:17:23,760 --> 00:17:24,560 Let's continue. 425 00:17:24,560 --> 00:17:28,031 Because look, if I add all these up and I go to carbon, 426 00:17:28,031 --> 00:17:28,931 it's not happy. 427 00:17:31,601 --> 00:17:35,405 But let's make it happy, because that's what Lewis lets us do. 428 00:17:35,405 --> 00:17:39,008 And I'm going to go down to here-- 429 00:17:39,008 --> 00:17:40,910 six continued. 430 00:17:40,910 --> 00:17:44,680 And all I need to do to do that is 431 00:17:44,680 --> 00:17:49,752 to follow the instructions, which is, taking one lone pair 432 00:17:49,752 --> 00:17:51,287 and put it here. 433 00:17:51,287 --> 00:17:55,124 So I'm going to draw these explicitly now as dots, right? 434 00:17:55,124 --> 00:17:58,127 So I took one of those lone pairs and I moved it here. 435 00:17:58,127 --> 00:18:01,197 And I created a stronger sharing bond. 436 00:18:04,400 --> 00:18:08,404 I wrote down the guidelines of Lewis, remember, on Monday. 437 00:18:08,404 --> 00:18:10,840 And the third point was octet! 438 00:18:10,840 --> 00:18:11,340 Right? 439 00:18:11,340 --> 00:18:13,609 Atoms want to achieve their nearest octet. 440 00:18:13,609 --> 00:18:17,013 And this this tells us then, by following 441 00:18:17,013 --> 00:18:22,151 these steps to implement Lewis' dream and vision, 442 00:18:22,151 --> 00:18:25,788 we get nothing less than the nature of bonding itself 443 00:18:25,788 --> 00:18:27,156 in molecules. 444 00:18:27,156 --> 00:18:28,858 That's cool. 445 00:18:28,858 --> 00:18:32,662 And so you could write this with sticks if you want. 446 00:18:32,662 --> 00:18:37,867 C, H-- that's a double bond with those electrons up there. 447 00:18:37,867 --> 00:18:39,202 It's the same thing. 448 00:18:39,202 --> 00:18:41,938 And now, if you count-- 449 00:18:41,938 --> 00:18:45,041 happy, happy, happy, happy. 450 00:18:45,041 --> 00:18:47,443 Everybody's happy. 451 00:18:47,443 --> 00:18:49,378 Caring is sharing. 452 00:18:49,378 --> 00:18:50,213 They're all sharing. 453 00:18:52,815 --> 00:18:56,853 So this is the general idea of Lewis. 454 00:18:56,853 --> 00:19:00,323 Following the Lewis prescription tells us about covalent bonds, 455 00:19:00,323 --> 00:19:02,358 and it tells us how many electrons 456 00:19:02,358 --> 00:19:03,326 are going to be shared. 457 00:19:03,326 --> 00:19:06,162 Now, it also tells us something else that's very important, 458 00:19:06,162 --> 00:19:08,397 and it's through this concept called formal charge. 459 00:19:08,397 --> 00:19:12,602 So that's the next thing that we need to learn. 460 00:19:12,602 --> 00:19:14,570 Because now, I go to another molecule. 461 00:19:14,570 --> 00:19:16,506 In this case, it's formaldehyde. 462 00:19:16,506 --> 00:19:17,039 OK. 463 00:19:17,039 --> 00:19:18,641 CH2O. 464 00:19:18,641 --> 00:19:21,911 But look, now, neither of these is done. 465 00:19:21,911 --> 00:19:23,012 These are not done. 466 00:19:23,012 --> 00:19:25,248 But it's like my starting place. 467 00:19:25,248 --> 00:19:25,748 OK. 468 00:19:25,748 --> 00:19:26,816 Carbon central here. 469 00:19:26,816 --> 00:19:29,152 It's kind of central-ish there. 470 00:19:29,152 --> 00:19:32,421 Can I start with either of these? 471 00:19:32,421 --> 00:19:34,757 And the answer is yes, you can. 472 00:19:34,757 --> 00:19:36,259 And you can draw-- 473 00:19:36,259 --> 00:19:38,895 and let's do that-- you can actually 474 00:19:38,895 --> 00:19:42,231 draw correct Lewis structures. 475 00:19:42,231 --> 00:19:43,533 Let me use the board over here. 476 00:19:50,206 --> 00:19:51,207 All right? 477 00:19:51,207 --> 00:19:54,410 So I could draw this like this. 478 00:19:54,410 --> 00:19:57,980 H-- Let me see here. 479 00:19:57,980 --> 00:20:06,255 H, C, double bond, O, hydrogen. And I could put that there 480 00:20:06,255 --> 00:20:07,690 and that there. 481 00:20:07,690 --> 00:20:10,326 Or I could draw it like this. 482 00:20:10,326 --> 00:20:11,460 Do I have it this way? 483 00:20:11,460 --> 00:20:12,228 Yes. 484 00:20:12,228 --> 00:20:12,795 All right? 485 00:20:12,795 --> 00:20:13,863 Like this. 486 00:20:13,863 --> 00:20:17,300 And carbon double bond O. 487 00:20:17,300 --> 00:20:22,572 And when I look at this, and I look at the electron count, 488 00:20:22,572 --> 00:20:23,806 it all works out. 489 00:20:23,806 --> 00:20:25,841 All right? 490 00:20:25,841 --> 00:20:28,110 I got to add my lone pairs to the oxygen. 491 00:20:28,110 --> 00:20:30,446 Don't let me forget those. 492 00:20:30,446 --> 00:20:32,415 It all works out. 493 00:20:32,415 --> 00:20:36,052 The total number of valence electrons is 12 in both cases, 494 00:20:36,052 --> 00:20:40,656 and everybody's obeying the octet rule. 495 00:20:40,656 --> 00:20:43,259 But the concept of formal charge allows 496 00:20:43,259 --> 00:20:45,962 us to distinguish between which one 497 00:20:45,962 --> 00:20:48,564 is likely to be more stable. 498 00:20:48,564 --> 00:20:51,601 And so, what formal charge is-- and I've got it written out 499 00:20:51,601 --> 00:20:53,069 here-- 500 00:20:53,069 --> 00:20:54,203 OK? 501 00:20:54,203 --> 00:20:56,339 So formal charge-- non-binding electrons 502 00:20:56,339 --> 00:20:57,473 count for the given atom. 503 00:20:57,473 --> 00:20:59,775 Bonding electrons are divided equally. 504 00:20:59,775 --> 00:21:04,013 And so formal charge is the total valence of an atom-- 505 00:21:04,013 --> 00:21:07,149 so I can take atom here and say, what's it's total valence? 506 00:21:07,149 --> 00:21:08,017 Carbon, four. 507 00:21:08,017 --> 00:21:09,485 Oxygen, six. 508 00:21:09,485 --> 00:21:11,554 All right? 509 00:21:11,554 --> 00:21:13,923 So that's the total balance of the free atom. 510 00:21:13,923 --> 00:21:16,459 And then I subtract from that how many 511 00:21:16,459 --> 00:21:22,265 nonbinding electrons it has, plus the bonding ones over two. 512 00:21:22,265 --> 00:21:22,765 Right? 513 00:21:22,765 --> 00:21:25,067 And so, if I do that-- 514 00:21:25,067 --> 00:21:26,936 let's write that. 515 00:21:26,936 --> 00:21:29,739 So if I think about that-- 516 00:21:29,739 --> 00:21:44,920 gesundheit-- from my pictures, the formal charge 517 00:21:44,920 --> 00:21:54,263 is equal to the number of valence electrons 518 00:21:54,263 --> 00:21:55,231 of the free atom. 519 00:21:55,231 --> 00:21:58,668 That means the atom, before it ever 520 00:21:58,668 --> 00:22:05,908 participated in a bond, minus the number of dots, 521 00:22:05,908 --> 00:22:08,077 minus the number of lines. 522 00:22:11,414 --> 00:22:16,485 Because that is really the same definition, right? 523 00:22:16,485 --> 00:22:19,722 That's the same definition. 524 00:22:19,722 --> 00:22:21,991 So let's go up to this one. 525 00:22:21,991 --> 00:22:28,831 So now, if I look at carbon in this configuration, 526 00:22:28,831 --> 00:22:30,833 and I calculate the formal charge of carbon, 527 00:22:30,833 --> 00:22:32,902 it's going to be 4-- 528 00:22:32,902 --> 00:22:36,038 the valence electron of the free atom-- 529 00:22:36,038 --> 00:22:42,411 minus 2-- because it's got the two dots there, right? 530 00:22:42,411 --> 00:22:45,114 Minus 3-- 1, 2, 3. 531 00:22:45,114 --> 00:22:47,750 Or the total number of electrons involved in bonds 532 00:22:47,750 --> 00:22:48,617 divided by two-- 533 00:22:48,617 --> 00:22:49,652 6 over 2. 534 00:22:49,652 --> 00:22:52,254 3, right? 535 00:22:52,254 --> 00:22:53,489 So those are equivalent. 536 00:22:53,489 --> 00:22:59,061 But that means that the formal charge on this is-- 537 00:22:59,061 --> 00:23:05,868 just spell it out here for now-- formal charge is equal to -1. 538 00:23:05,868 --> 00:23:10,339 And if I do the same thing here, then it's +1. 539 00:23:10,339 --> 00:23:13,843 But you see, if I look at this structure, 540 00:23:13,843 --> 00:23:16,245 and I think about the formal charge on the carbon, atom-- 541 00:23:16,245 --> 00:23:23,753 Again, I'm basically counting a change from the free atom. 542 00:23:23,753 --> 00:23:24,820 OK? 543 00:23:24,820 --> 00:23:26,055 And so carbon had four. 544 00:23:28,758 --> 00:23:31,327 What did this new bonding environment 545 00:23:31,327 --> 00:23:34,930 do to the valence chemistry? 546 00:23:34,930 --> 00:23:36,999 And in this case, the formal charge on carbon 547 00:23:36,999 --> 00:23:39,168 is going to be 4-- 548 00:23:39,168 --> 00:23:41,704 starting with the number of free valence electrons-- 549 00:23:41,704 --> 00:23:48,177 minus no dots, but it's got one, two, three, four bonds. 550 00:23:48,177 --> 00:23:49,879 So that's zero. 551 00:23:49,879 --> 00:23:51,814 And the formal charge on the oxygen 552 00:23:51,814 --> 00:23:56,051 is going to be 6 minus 1, 2, 3, 4, 5, 6. 553 00:23:56,051 --> 00:23:58,020 So that's also zero. 554 00:23:58,020 --> 00:23:59,455 And you get a sense-- how much did 555 00:23:59,455 --> 00:24:05,394 I push this atom away from where it normally thinks 556 00:24:05,394 --> 00:24:08,063 about its charge balance? 557 00:24:08,063 --> 00:24:10,032 And you get a sense for why this might be true. 558 00:24:10,032 --> 00:24:13,669 Lewis structure with a set of formal charges closest to 0 559 00:24:13,669 --> 00:24:15,471 is usually the most stable. 560 00:24:15,471 --> 00:24:16,906 And that's our guideline. 561 00:24:16,906 --> 00:24:22,044 And so, this one not very happy. 562 00:24:22,044 --> 00:24:25,714 That one happy. 563 00:24:25,714 --> 00:24:29,218 And so you can calculate the formal charge on any atom 564 00:24:29,218 --> 00:24:32,054 in any Lewis structure-- gesundheit-- 565 00:24:32,054 --> 00:24:35,391 by following this very simple procedure. 566 00:24:35,391 --> 00:24:39,795 You take any atom and you look at how you've drawn it's Lewis 567 00:24:39,795 --> 00:24:41,464 structure, right? 568 00:24:41,464 --> 00:24:43,632 And you just count. 569 00:24:43,632 --> 00:24:47,903 So for example, if I take CO2, and I think, 570 00:24:47,903 --> 00:24:49,805 well, I can do the same thing here. 571 00:24:49,805 --> 00:24:53,642 I've got two Lewis structures and they look like 572 00:24:53,642 --> 00:24:55,911 they both satisfy the recipe. 573 00:24:55,911 --> 00:24:58,180 The recipe is satisfied. 574 00:24:58,180 --> 00:25:00,282 But which one is more stable? 575 00:25:00,282 --> 00:25:04,086 Well, if I look at this, it's the same idea. 576 00:25:04,086 --> 00:25:08,190 And I won't go through it in detail, 577 00:25:08,190 --> 00:25:10,359 but if I look at this then-- 578 00:25:10,359 --> 00:25:17,733 C, O, O, with lone pairs on the Os, like that. 579 00:25:17,733 --> 00:25:18,300 All right? 580 00:25:18,300 --> 00:25:25,174 This is going to give me formal charges of 0, 0, and 0. 581 00:25:25,174 --> 00:25:29,211 Whereas, if I do the one on the right and I put a triple bond-- 582 00:25:29,211 --> 00:25:31,947 so I put too many electrons sharing-- 583 00:25:31,947 --> 00:25:35,651 then yeah, I satisfied the octets, 584 00:25:35,651 --> 00:25:39,355 but no, I'm not as stable, because the formal charges 585 00:25:39,355 --> 00:25:40,689 aren't as close to zero. 586 00:25:43,592 --> 00:25:47,897 So this gives me to my brief, why this matters for take. 587 00:25:47,897 --> 00:25:52,535 Why would I care which one of these CO2 takes? 588 00:25:52,535 --> 00:25:53,135 All right? 589 00:25:53,135 --> 00:25:53,636 OK. 590 00:25:53,636 --> 00:25:59,808 Well, it turns out that as long as we're not at absolute zero, 591 00:25:59,808 --> 00:26:03,078 this molecule is moving. 592 00:26:03,078 --> 00:26:08,651 And so, obviously, that's related to this. 593 00:26:08,651 --> 00:26:09,552 It's not obvious. 594 00:26:09,552 --> 00:26:16,458 But cars in the US are now the number one emitter of CO2. 595 00:26:16,458 --> 00:26:16,959 OK? 596 00:26:16,959 --> 00:26:21,096 They're the number one cause of CO2 emissions. 597 00:26:21,096 --> 00:26:24,867 And here's a nice little corner somewhere. 598 00:26:24,867 --> 00:26:28,804 And so, this is coming out now from the transportation sector. 599 00:26:31,941 --> 00:26:35,144 More of the CO2 comes from that than any other sector. 600 00:26:35,144 --> 00:26:36,011 Why does it matter? 601 00:26:36,011 --> 00:26:39,848 Well, why does this Lewis structure matter? 602 00:26:39,848 --> 00:26:41,717 Well, it has to do with how it moves. 603 00:26:41,717 --> 00:26:46,755 Because, you see, I showed you this before. 604 00:26:46,755 --> 00:26:50,225 And I didn't complete it because we were talking about electron 605 00:26:50,225 --> 00:26:53,062 transitions, and then I gave you the example 606 00:26:53,062 --> 00:26:56,832 of ozone being really important for absorbing in the UV. 607 00:26:56,832 --> 00:26:59,902 And I showed you the chemistry of ozone degradation with CFCs. 608 00:26:59,902 --> 00:27:02,371 You see, look at this absorption out here. 609 00:27:02,371 --> 00:27:04,373 There's CO2, right? 610 00:27:04,373 --> 00:27:06,442 And so, there's the sunlight above the atmosphere. 611 00:27:06,442 --> 00:27:07,810 Here it is on Earth. 612 00:27:07,810 --> 00:27:09,979 And you could see CO2 there. 613 00:27:09,979 --> 00:27:13,716 But see, the reason CO2 absorbs there 614 00:27:13,716 --> 00:27:15,884 has to do with how it moves. 615 00:27:15,884 --> 00:27:19,088 It has to do with its vibrations. 616 00:27:19,088 --> 00:27:20,522 Now, that's not something that you 617 00:27:20,522 --> 00:27:23,892 need to know for like a test or something, 618 00:27:23,892 --> 00:27:26,328 but I wanted to tell you about it because it is directly 619 00:27:26,328 --> 00:27:28,464 related to what we just did. 620 00:27:28,464 --> 00:27:30,232 Those vibrations-- and by the way, 621 00:27:30,232 --> 00:27:34,970 that first mode is the one out here doing all the IR 622 00:27:34,970 --> 00:27:36,105 absorption. 623 00:27:36,105 --> 00:27:36,605 Right? 624 00:27:36,605 --> 00:27:37,673 This one. 625 00:27:37,673 --> 00:27:41,777 And you can see right away, if this thing is wiggling, 626 00:27:41,777 --> 00:27:43,812 it's going to wiggle very differently. 627 00:27:43,812 --> 00:27:44,313 Right? 628 00:27:44,313 --> 00:27:46,682 It's going to wiggle very differently whether it 629 00:27:46,682 --> 00:27:49,685 has two double bonds on either side of the carbon, 630 00:27:49,685 --> 00:27:51,053 or a triple and a single. 631 00:27:51,053 --> 00:27:51,553 Right? 632 00:27:51,553 --> 00:27:53,188 And so that, alone, tells you something 633 00:27:53,188 --> 00:27:55,324 really important about how it interacts 634 00:27:55,324 --> 00:27:59,595 in our atmosphere with radiant heat, right? 635 00:27:59,595 --> 00:28:02,197 With IR radiation. 636 00:28:02,197 --> 00:28:03,098 OK. 637 00:28:03,098 --> 00:28:05,100 That's my 'why this matters.' 638 00:28:05,100 --> 00:28:13,075 Now, I've been talking about all these things in absolutes. 639 00:28:13,075 --> 00:28:18,247 But you see, the world is not so absolute. 640 00:28:18,247 --> 00:28:22,217 And in fact, we're missing a really important part 641 00:28:22,217 --> 00:28:24,019 of the picture here. 642 00:28:24,019 --> 00:28:27,322 So this is H2, right? 643 00:28:27,322 --> 00:28:31,427 There is an iconic bond where, remember, it's like, I'm picky! 644 00:28:31,427 --> 00:28:31,994 OK. 645 00:28:31,994 --> 00:28:34,029 And then it's like a Coulomb interaction. 646 00:28:34,029 --> 00:28:35,798 And here it's a sharing. 647 00:28:35,798 --> 00:28:38,701 Each electron sees both of those protons. 648 00:28:38,701 --> 00:28:42,805 But there's a whole bunch of room in between, right? 649 00:28:42,805 --> 00:28:44,506 There's a whole bunch of room in between. 650 00:28:44,506 --> 00:28:49,411 And so what we need next, as we talk about covalent bonds, 651 00:28:49,411 --> 00:28:53,515 is we need a way to think about how ionic they are. 652 00:28:53,515 --> 00:28:54,349 Right? 653 00:28:54,349 --> 00:28:57,252 Because there's only a certain kind of covalent bond 654 00:28:57,252 --> 00:29:00,856 that's purely covalent. 655 00:29:00,856 --> 00:29:01,990 As it's written here-- 656 00:29:01,990 --> 00:29:03,926 non-polar covalent. 657 00:29:03,926 --> 00:29:07,229 So let's talk about that next. 658 00:29:07,229 --> 00:29:09,164 And what we're going to do is use this term 659 00:29:09,164 --> 00:29:10,899 that I alluded to in the beginning, which 660 00:29:10,899 --> 00:29:15,003 is point number one in your recipe, 661 00:29:15,003 --> 00:29:18,574 and that is electronegativity. 662 00:29:18,574 --> 00:29:19,074 OK? 663 00:29:19,074 --> 00:29:21,543 So I'm going to get it done. 664 00:29:25,514 --> 00:29:27,483 Almost. 665 00:29:27,483 --> 00:29:29,084 Practice makes perfect. 666 00:29:29,084 --> 00:29:29,585 OK. 667 00:29:32,788 --> 00:29:33,555 All right. 668 00:29:33,555 --> 00:29:38,527 So there is a symbol kai, that we 669 00:29:38,527 --> 00:29:44,767 use for this concept of electronegativity. 670 00:29:44,767 --> 00:29:48,170 Electronegativity. 671 00:29:48,170 --> 00:29:49,605 OK? 672 00:29:49,605 --> 00:30:02,518 Now, this is the tendency of an atom 673 00:30:02,518 --> 00:30:19,067 to attract shared pair of electrons to itself. 674 00:30:19,067 --> 00:30:19,568 OK? 675 00:30:23,672 --> 00:30:26,508 Let's write "in a bond," just to be sure. 676 00:30:26,508 --> 00:30:27,176 All right? 677 00:30:27,176 --> 00:30:27,676 In a bond. 678 00:30:27,676 --> 00:30:33,649 So if an electron in a bond, the question is, 679 00:30:33,649 --> 00:30:38,053 how much was it able to pull those bonding electrons to it? 680 00:30:38,053 --> 00:30:38,987 All right? 681 00:30:38,987 --> 00:30:46,461 And you can already think about this in terms of concepts 682 00:30:46,461 --> 00:30:48,063 that we've learned already. 683 00:30:48,063 --> 00:30:48,564 Right? 684 00:30:48,564 --> 00:30:50,432 Like the size of an atom. 685 00:30:50,432 --> 00:30:52,067 How far out electrons are? 686 00:30:52,067 --> 00:30:52,568 Right? 687 00:30:52,568 --> 00:30:53,735 The radius of an atom. 688 00:30:53,735 --> 00:30:56,205 Whether there's shielding going on. 689 00:30:56,205 --> 00:30:56,839 Right? 690 00:30:56,839 --> 00:31:00,175 This kind of leads you-- how many protons there are. 691 00:31:00,175 --> 00:31:00,776 All right? 692 00:31:00,776 --> 00:31:03,345 This leads you already to be able to think about this. 693 00:31:03,345 --> 00:31:07,983 Which atom is going to want a pair of electrons in a bond, 694 00:31:07,983 --> 00:31:08,483 right? 695 00:31:08,483 --> 00:31:10,686 Which one is going to want it more, and how much? 696 00:31:10,686 --> 00:31:13,822 But it was Pauling who said, no, I want to go further that. 697 00:31:13,822 --> 00:31:15,858 I want to write down-- 698 00:31:15,858 --> 00:31:16,925 even if it's empirical-- 699 00:31:16,925 --> 00:31:19,728 I want to write down some way, some number. 700 00:31:19,728 --> 00:31:22,164 I want to quantify this. 701 00:31:22,164 --> 00:31:26,468 And so he came up with a scale for electronegativity. 702 00:31:26,468 --> 00:31:28,403 The term and concept of electronegativity 703 00:31:28,403 --> 00:31:32,574 goes back long before Pauling, to, I think, [INAUDIBLE].. 704 00:31:32,574 --> 00:31:35,577 But Pauling is the one who said, I want to quantify this. 705 00:31:35,577 --> 00:31:37,145 And the way we're going to do is we're 706 00:31:37,145 --> 00:31:40,515 going to measure bonding energies between all sorts 707 00:31:40,515 --> 00:31:42,351 of different atoms. 708 00:31:42,351 --> 00:31:45,287 And what he found is that, if a bonds to a, 709 00:31:45,287 --> 00:31:49,725 and b bonds to b, a to b is not just a simple sum of the two. 710 00:31:49,725 --> 00:31:52,327 And that clued him in for how to think 711 00:31:52,327 --> 00:31:57,532 about this partially covalent or polar covalent nature. 712 00:31:57,532 --> 00:31:59,368 I'll tell you why that word "polar" is there 713 00:31:59,368 --> 00:32:01,303 in a few minutes. 714 00:32:01,303 --> 00:32:03,538 And so Pauling developed this scale-- 715 00:32:03,538 --> 00:32:06,208 the electronegativity scale-- to tell us this. 716 00:32:06,208 --> 00:32:10,879 And he arbitrarily set fluorine to four and hydrogen 717 00:32:10,879 --> 00:32:15,350 at first 2.1, now it's 2.2. 718 00:32:15,350 --> 00:32:17,586 But basically, this is just some of the elements 719 00:32:17,586 --> 00:32:20,255 of the periodic table, and these are their electronegativities. 720 00:32:20,255 --> 00:32:21,256 OK? 721 00:32:21,256 --> 00:32:24,927 And you don't need to worry about how this scale was 722 00:32:24,927 --> 00:32:26,094 developed quantitatively. 723 00:32:26,094 --> 00:32:29,197 There are actually many electronegativity scales. 724 00:32:29,197 --> 00:32:29,898 OK? 725 00:32:29,898 --> 00:32:34,169 What I want you to know is what it means conceptually, 726 00:32:34,169 --> 00:32:36,972 and then how to use it to think about 727 00:32:36,972 --> 00:32:41,276 whether a bond is going to be ionic, or covalent, 728 00:32:41,276 --> 00:32:43,312 or somewhere in between. 729 00:32:43,312 --> 00:32:45,847 And so, you can see already here, OK, the extremes of this 730 00:32:45,847 --> 00:32:47,416 are fluorine and caesium. 731 00:32:47,416 --> 00:32:50,852 These are the most electronegative, 732 00:32:50,852 --> 00:32:55,524 least electronegative, or if you want to be positive about it, 733 00:32:55,524 --> 00:32:56,825 most electropositive. 734 00:32:56,825 --> 00:32:58,527 When you're talking to these elements 735 00:32:58,527 --> 00:33:01,296 you want them to feel good. 736 00:33:01,296 --> 00:33:02,264 They're not the least. 737 00:33:02,264 --> 00:33:03,598 They're very important. 738 00:33:03,598 --> 00:33:05,233 So they're electropositive. 739 00:33:05,233 --> 00:33:06,201 Right? 740 00:33:06,201 --> 00:33:07,569 And now you know conceptually. 741 00:33:07,569 --> 00:33:11,773 But look, now we also can think about differences. 742 00:33:11,773 --> 00:33:16,411 Because, if the difference between this concept, 743 00:33:16,411 --> 00:33:20,849 from one atom to another is zero, 744 00:33:20,849 --> 00:33:24,319 well then, that must be a pure covalent bond. 745 00:33:24,319 --> 00:33:29,891 Because neither one could bring in the electron pair 746 00:33:29,891 --> 00:33:32,728 more than the other, right? 747 00:33:32,728 --> 00:33:35,163 So like chlorine two-- 748 00:33:35,163 --> 00:33:39,901 the chlorine dimer-- then the change in electronegativity 749 00:33:39,901 --> 00:33:45,340 between one chlorine and another is zero, it's a pure covalent. 750 00:33:45,340 --> 00:33:47,409 I mean, just think about that conceptually, right? 751 00:33:47,409 --> 00:33:52,748 So that's what electronegativity means. 752 00:33:52,748 --> 00:33:56,952 So if I have two that are the same, neither one can draw in. 753 00:33:56,952 --> 00:33:58,520 They have the same kai. 754 00:33:58,520 --> 00:34:01,356 Neither one can draw the pair towards them more. 755 00:34:01,356 --> 00:34:01,857 Right? 756 00:34:01,857 --> 00:34:04,693 So the same is true for any dimer like this, 757 00:34:04,693 --> 00:34:06,128 where it's the same atom. 758 00:34:06,128 --> 00:34:10,264 The H2 dimer that we started with, also has delta kai of 0. 759 00:34:10,264 --> 00:34:14,436 Those are called pure covalent, because it's just pure sharing. 760 00:34:14,436 --> 00:34:16,071 Nobody took more charge than the other. 761 00:34:16,071 --> 00:34:19,708 But see, if I go to something like sodium chloride, 762 00:34:19,708 --> 00:34:26,081 well now, from this table I can calculate 763 00:34:26,081 --> 00:34:27,516 the difference in electronegativity 764 00:34:27,516 --> 00:34:29,384 between sodium and chlorine. 765 00:34:29,384 --> 00:34:37,259 And it's 2.23, which is pretty high. 766 00:34:37,259 --> 00:34:40,996 And it's ionic. 767 00:34:40,996 --> 00:34:45,434 So if that difference is high, then it means one of the atoms 768 00:34:45,434 --> 00:34:48,670 grabbed the electrons. 769 00:34:48,670 --> 00:34:52,841 And if it's kind of 0, it's pure covalent. 770 00:34:52,841 --> 00:34:54,476 And if it's somewhere in between, 771 00:34:54,476 --> 00:34:55,911 it's this polar covalent. 772 00:34:55,911 --> 00:34:58,013 So, for example, HCL. 773 00:34:58,013 --> 00:35:00,615 So these are all with the same atom-- chlorine. 774 00:35:00,615 --> 00:35:07,255 But here delta kai is equal to 0.96. 775 00:35:07,255 --> 00:35:11,393 So this is called polar covalent. 776 00:35:15,130 --> 00:35:17,165 OK? 777 00:35:17,165 --> 00:35:21,069 So this is also partially ionic, right? 778 00:35:21,069 --> 00:35:22,704 These mean the same things. 779 00:35:22,704 --> 00:35:27,008 There's ionic character-- is another way that we say it. 780 00:35:27,008 --> 00:35:31,613 This bond is not purely covalent because one of them 781 00:35:31,613 --> 00:35:34,716 took a little more charge, because it's electronegativity 782 00:35:34,716 --> 00:35:36,118 was higher. 783 00:35:36,118 --> 00:35:38,086 And therefore, there's a little bit 784 00:35:38,086 --> 00:35:40,021 of that kind of ionic thing going on, 785 00:35:40,021 --> 00:35:43,091 because you got a little plus over here, and a little minus 786 00:35:43,091 --> 00:35:44,392 over there. 787 00:35:44,392 --> 00:35:46,161 Right? 788 00:35:46,161 --> 00:35:59,007 And that is something that can be 789 00:35:59,007 --> 00:36:03,011 looked at for a whole bunch of different bonds. 790 00:36:03,011 --> 00:36:06,314 And so here, this is what Pauling was trying to fit. 791 00:36:06,314 --> 00:36:08,984 So he came up with these empirical fits. 792 00:36:08,984 --> 00:36:10,018 Right? 793 00:36:10,018 --> 00:36:15,624 OK, things kind of tend to lie on this line, which 794 00:36:15,624 --> 00:36:18,226 is the plot of the electronegativity difference 795 00:36:18,226 --> 00:36:24,032 between two different atoms the percent ionic character. 796 00:36:24,032 --> 00:36:25,667 Is it really fully ionic? 797 00:36:25,667 --> 00:36:27,002 Is it is it fully covalent? 798 00:36:27,002 --> 00:36:30,205 And you can see, over here, it's kind of not interesting, right? 799 00:36:30,205 --> 00:36:32,707 It's just anything with itself is zero. 800 00:36:32,707 --> 00:36:36,311 And over here, you've got some of the same ionic bonds 801 00:36:36,311 --> 00:36:38,547 that we've already talked about, right? 802 00:36:38,547 --> 00:36:40,849 And then you've got all this stuff in between. 803 00:36:40,849 --> 00:36:44,252 And what this says is, as you've now seen, right? 804 00:36:44,252 --> 00:36:47,389 [INAUDIBLE] is a suggestion of a rule, 805 00:36:47,389 --> 00:36:50,158 and then it gets broken 20% of the time. 806 00:36:50,158 --> 00:36:53,828 This is also a way of qualitatively classifying 807 00:36:53,828 --> 00:36:57,832 bonds and thinking about the ionic character in a bond, 808 00:36:57,832 --> 00:37:00,802 but it is not always quantitative. 809 00:37:00,802 --> 00:37:03,672 But in general, what you'll see is 810 00:37:03,672 --> 00:37:09,010 that if delta kai is greater than 2, then 811 00:37:09,010 --> 00:37:11,613 it tends to be an ionic bond. 812 00:37:11,613 --> 00:37:17,752 And if delta kai is less than, let's say, 1.6, 813 00:37:17,752 --> 00:37:22,257 it tends to be covalent or polar covalent. 814 00:37:27,429 --> 00:37:31,066 And in-between it depends. 815 00:37:31,066 --> 00:37:32,000 How do I know? 816 00:37:32,000 --> 00:37:32,500 Right? 817 00:37:32,500 --> 00:37:35,203 I'll show you an example. 818 00:37:35,203 --> 00:37:36,037 Where's my example? 819 00:37:36,037 --> 00:37:37,772 I've got an example here. 820 00:37:37,772 --> 00:37:38,707 Sodium bromide. 821 00:37:38,707 --> 00:37:39,841 It's not on there. 822 00:37:39,841 --> 00:37:47,582 But if I take sodium bromide and I take HF, 823 00:37:47,582 --> 00:37:53,822 they both have delta kai equal 1.9. 824 00:37:53,822 --> 00:37:57,359 Now, some textbooks will simply say 1.7. 825 00:37:57,359 --> 00:37:59,594 You will see that in some textbooks, 826 00:37:59,594 --> 00:38:01,863 because they just want it to be all or nothing. 827 00:38:01,863 --> 00:38:03,131 It's always ionic, or it's-- 828 00:38:03,131 --> 00:38:04,532 But the fact of the matter is that 829 00:38:04,532 --> 00:38:08,837 in this intermediate regime you get variations 830 00:38:08,837 --> 00:38:10,472 that depend on other things. 831 00:38:10,472 --> 00:38:15,810 And so, for example, HF is a gas at room temperature. 832 00:38:15,810 --> 00:38:17,979 So these have the same electronegativity difference, 833 00:38:17,979 --> 00:38:22,584 but this really behaves like a polar covalent molecule. 834 00:38:22,584 --> 00:38:25,820 And this really behaves like an ionic solid-- 835 00:38:25,820 --> 00:38:26,755 an ionic bond. 836 00:38:26,755 --> 00:38:28,056 How do you know? 837 00:38:28,056 --> 00:38:29,658 It's the properties. 838 00:38:29,658 --> 00:38:30,191 Right? 839 00:38:30,191 --> 00:38:32,360 Remember, I showed you the properties 840 00:38:32,360 --> 00:38:35,997 of ionic solids on Monday. 841 00:38:35,997 --> 00:38:37,999 And so, I can look at those and check them off-- 842 00:38:37,999 --> 00:38:39,801 solid at room temperature, et cetera. 843 00:38:39,801 --> 00:38:41,870 And I can see, well, does this fit the bill? 844 00:38:41,870 --> 00:38:43,471 Does it look like an iconic solid? 845 00:38:43,471 --> 00:38:45,273 It absolutely does not. 846 00:38:45,273 --> 00:38:47,542 So even though this is the same, you 847 00:38:47,542 --> 00:38:50,945 got to be careful in this intermediate regime. 848 00:38:50,945 --> 00:38:53,715 Now, you can also go even further, 849 00:38:53,715 --> 00:38:56,351 and you can get quantitative. 850 00:38:56,351 --> 00:39:00,355 Because, you see, what we're really talking about here 851 00:39:00,355 --> 00:39:03,858 is something called a dipole. 852 00:39:03,858 --> 00:39:06,361 That is why it's called polar covalent. 853 00:39:08,930 --> 00:39:09,764 OK? 854 00:39:09,764 --> 00:39:13,568 It's called polar covalent because we made a dipole. 855 00:39:13,568 --> 00:39:19,174 And as far as I know, from my electricity and magnetism 856 00:39:19,174 --> 00:39:21,743 training, the dipole moment-- 857 00:39:21,743 --> 00:39:23,778 mu, it's written as mu-- 858 00:39:23,778 --> 00:39:25,880 is the charge times the distance. 859 00:39:25,880 --> 00:39:28,616 Where Q is that the charge. 860 00:39:28,616 --> 00:39:31,753 In this case, it's literally the charge that was pulled. 861 00:39:31,753 --> 00:39:33,688 It's exactly that. 862 00:39:33,688 --> 00:39:34,756 There's the chart, right? 863 00:39:34,756 --> 00:39:37,359 Tendency to pull a shared electron. 864 00:39:39,961 --> 00:39:42,564 I pulled it over here, so I created 865 00:39:42,564 --> 00:39:45,900 a little more negative charge on me, 866 00:39:45,900 --> 00:39:48,436 and a little positive charge on there. 867 00:39:48,436 --> 00:39:51,473 And that meant that I've got a partial charge now, 868 00:39:51,473 --> 00:39:53,875 separated by a distance. 869 00:39:53,875 --> 00:39:54,376 Right? 870 00:39:54,376 --> 00:39:57,379 And so you can actually use this to get quantitative. 871 00:39:57,379 --> 00:40:00,215 So let's do sodium chloride, right? 872 00:40:00,215 --> 00:40:04,753 So for sodium chloride the dipole moment is nine to debye. 873 00:40:04,753 --> 00:40:07,055 And this is just one debye. 874 00:40:07,055 --> 00:40:12,293 This is charge times distance, so one debye is equal to 3.3. 875 00:40:12,293 --> 00:40:17,999 10 to the minus 30th coulomb meters. 876 00:40:17,999 --> 00:40:23,271 That's the units of a dipole moment-- charge times distance. 877 00:40:23,271 --> 00:40:25,373 So if I take sodium chloride and I tell you 878 00:40:25,373 --> 00:40:28,943 that its dipole moment is nine debye, 879 00:40:28,943 --> 00:40:34,349 then I also have to tell you that the distance between them, 880 00:40:34,349 --> 00:40:39,187 r, is equal to 2.36 angstroms. 881 00:40:39,187 --> 00:40:40,889 That is this distance here. 882 00:40:40,889 --> 00:40:45,059 I've made a bond between these two things, 883 00:40:45,059 --> 00:40:49,030 and that bond is some distance apart. 884 00:40:49,030 --> 00:40:50,698 Well, that's exactly the distance 885 00:40:50,698 --> 00:40:52,534 I need to think about the dipole, right? 886 00:40:52,534 --> 00:40:55,069 So remember, a dipole is because I've 887 00:40:55,069 --> 00:40:58,206 got positive charge and negative charge. 888 00:40:58,206 --> 00:41:01,409 And in fact, you might see it written like this. 889 00:41:01,409 --> 00:41:04,679 You might see there's a little positive charge here, 890 00:41:04,679 --> 00:41:06,581 and a little negative charge there, 891 00:41:06,581 --> 00:41:09,818 and the dipole moment goes like that. 892 00:41:09,818 --> 00:41:10,318 All right? 893 00:41:10,318 --> 00:41:11,186 There's a dipole. 894 00:41:15,490 --> 00:41:18,860 And now, those charges at this distance in the bond 895 00:41:18,860 --> 00:41:21,629 allow me to actually be quantitative, 896 00:41:21,629 --> 00:41:25,266 because Q is equal to mu over r. 897 00:41:25,266 --> 00:41:30,672 And if I plug that in, then it's 1.3 times 10 898 00:41:30,672 --> 00:41:32,807 to the minus 19th coulombs. 899 00:41:32,807 --> 00:41:34,809 So for sodium chloride-- 900 00:41:34,809 --> 00:41:38,713 because I was given the dipole moment in that molecule, 901 00:41:38,713 --> 00:41:40,882 and I can look up the bonds distance-- 902 00:41:40,882 --> 00:41:45,987 I can actually tell you how much charge are on those atoms 903 00:41:45,987 --> 00:41:48,923 if I know that information. 904 00:41:48,923 --> 00:41:54,529 But I also know what the charge of a full electron is. 905 00:41:54,529 --> 00:41:56,331 This is almost there. 906 00:41:56,331 --> 00:42:07,075 It's something like 80% of an electron. 907 00:42:07,075 --> 00:42:12,013 And so that's a pretty strong ionic bond. 908 00:42:12,013 --> 00:42:14,716 But it's not 100%, right? 909 00:42:14,716 --> 00:42:17,285 So this is the message I want to tell you. 910 00:42:17,285 --> 00:42:20,455 In reality, we've been talking about absolutes. 911 00:42:20,455 --> 00:42:22,957 I fully took a charge. 912 00:42:22,957 --> 00:42:23,725 Right? 913 00:42:23,725 --> 00:42:24,626 No! 914 00:42:24,626 --> 00:42:26,127 You didn't. 915 00:42:26,127 --> 00:42:28,062 You took 80%. 916 00:42:28,062 --> 00:42:30,298 And there's a little bit still over there. 917 00:42:30,298 --> 00:42:30,798 Right? 918 00:42:33,301 --> 00:42:36,838 But we do like to still categorize materials. 919 00:42:36,838 --> 00:42:38,506 And that's what this does really nicely, 920 00:42:38,506 --> 00:42:41,776 is it says, well, this is going to behave like an iconic solid. 921 00:42:41,776 --> 00:42:43,611 Meaning, it's going to have those properties 922 00:42:43,611 --> 00:42:45,280 that I showed you on Monday. 923 00:42:45,280 --> 00:42:45,847 Right? 924 00:42:45,847 --> 00:42:50,652 Even though it's not fully ionic, it's pretty darn ionic. 925 00:42:50,652 --> 00:42:51,452 Right? 926 00:42:51,452 --> 00:42:54,756 And now, even though these are not fully covalent, 927 00:42:54,756 --> 00:42:59,027 meaning, pure, non-polar covalent-- non-polar, 928 00:42:59,027 --> 00:43:02,230 no dipole in the bond. 929 00:43:02,230 --> 00:43:05,233 But these have some dipole, but that's OK. 930 00:43:05,233 --> 00:43:09,170 They're still acting like covalent molecules. 931 00:43:09,170 --> 00:43:10,238 Right? 932 00:43:10,238 --> 00:43:12,307 And so there's this spectrum in between. 933 00:43:12,307 --> 00:43:15,843 And you can use these concepts to think about the bonding, 934 00:43:15,843 --> 00:43:20,748 and to think about in particular this-- that so many bonds are 935 00:43:20,748 --> 00:43:21,549 actually like this. 936 00:43:21,549 --> 00:43:23,251 Even though we categorize them like this, 937 00:43:23,251 --> 00:43:25,820 and we think about them like that, 938 00:43:25,820 --> 00:43:27,622 they actually look like this. 939 00:43:27,622 --> 00:43:32,493 And electronegativity and dipoles 940 00:43:32,493 --> 00:43:37,398 are what help us characterize these differences. 941 00:43:37,398 --> 00:43:44,138 Now, there is more to Lewis that I will talk about on Friday. 942 00:43:44,138 --> 00:43:47,976 But there's something called resonant structures, 943 00:43:47,976 --> 00:43:50,044 and that's a very important part of Lewis. 944 00:43:50,044 --> 00:43:51,479 I'm going to talk about it Friday, 945 00:43:51,479 --> 00:43:53,648 and it will not be on the exam on Monday. 946 00:43:53,648 --> 00:43:54,148 OK? 947 00:43:54,148 --> 00:43:56,351 But on Friday, we'll talk about resonance structures, 948 00:43:56,351 --> 00:43:57,919 we'll do a few more Lewis examples, 949 00:43:57,919 --> 00:43:59,454 and then I'll talk about exam one.