1 00:00:17,800 --> 00:00:21,904 We left off last Wednesday, last week Wednesday. 2 00:00:21,904 --> 00:00:22,738 So it's been awhile. 3 00:00:22,738 --> 00:00:25,274 So I wanted just to pick up where we left off. 4 00:00:25,274 --> 00:00:28,977 And then cover some new things today. 5 00:00:31,647 --> 00:00:35,751 But where we left off was with this diagram, OK? 6 00:00:35,751 --> 00:00:37,953 And, you know, I kind of went through it. 7 00:00:37,953 --> 00:00:38,787 And I went through it sort of quickly. 8 00:00:38,787 --> 00:00:40,956 But I want to make sure you understand it very well. 9 00:00:40,956 --> 00:00:43,859 Because this is such an important kind of diagram. 10 00:00:43,859 --> 00:00:45,294 And we'll see it again. 11 00:00:45,294 --> 00:00:47,062 And you may see it again in other classes. 12 00:00:47,062 --> 00:00:52,801 This is a diagram of attraction and repulsion 13 00:00:52,801 --> 00:00:57,239 coming together in a balance to form a bond. 14 00:00:57,239 --> 00:00:59,908 So, you know, last Wednesday, just to remind you, 15 00:00:59,908 --> 00:01:01,877 we made our first bond. 16 00:01:01,877 --> 00:01:04,745 All right, we made the ionic bond. 17 00:01:04,745 --> 00:01:06,782 And I showed you how that worked. 18 00:01:06,782 --> 00:01:09,585 Because, in this case, the attraction, 19 00:01:09,585 --> 00:01:13,188 the force of attraction is the Coulomb potential, right? 20 00:01:13,188 --> 00:01:18,994 Remember that goes as minus a constant times-- 21 00:01:18,994 --> 00:01:20,829 I'll just write it down because why not. 22 00:01:20,829 --> 00:01:23,398 You're using it in your goody bag. 23 00:01:23,398 --> 00:01:25,567 All right, so the Coulomb energy here 24 00:01:25,567 --> 00:01:31,106 goes as minus some constant times the charges, the two 25 00:01:31,106 --> 00:01:35,744 charges, divided by the distance between those charges. 26 00:01:35,744 --> 00:01:37,579 That's an energy. 27 00:01:37,579 --> 00:01:38,914 It's an energy of attraction. 28 00:01:38,914 --> 00:01:40,816 But, you know, so here's the thing though. 29 00:01:40,816 --> 00:01:43,619 All right, so if you have a plus and a minus charge, 30 00:01:43,619 --> 00:01:46,488 those are each 1, right, charge of electron. 31 00:01:46,488 --> 00:01:47,923 And then the distance between them, 32 00:01:47,923 --> 00:01:51,894 when it's really far this, energy is pretty weak. 33 00:01:51,894 --> 00:01:53,527 So that's this green curve here. 34 00:01:53,527 --> 00:01:55,163 But as it gets closer and closer, 35 00:01:55,163 --> 00:01:57,598 that energy gets lower and lower. 36 00:01:57,598 --> 00:02:00,535 And remember, happiness is lower energy. 37 00:02:00,535 --> 00:02:03,005 All right, these atoms want to find their happy place. 38 00:02:03,005 --> 00:02:04,139 And they see each other and they're like, well, 39 00:02:04,139 --> 00:02:05,974 we can be happier if we're closer, 40 00:02:05,974 --> 00:02:08,243 until a certain thing happens. 41 00:02:08,243 --> 00:02:12,047 Which is then, they've got similar charges 42 00:02:12,047 --> 00:02:14,182 like the electron shells, negative charge. 43 00:02:14,182 --> 00:02:16,685 Negative charge, so kind of coming too close. 44 00:02:16,685 --> 00:02:20,589 That's the forces of repulsion. 45 00:02:20,589 --> 00:02:24,493 And so that nets in a total energy curve, which 46 00:02:24,493 --> 00:02:27,062 is this white line here, the green and the red, 47 00:02:27,062 --> 00:02:29,164 and then you got the white line there, 48 00:02:29,164 --> 00:02:30,232 which is the total energy. 49 00:02:30,232 --> 00:02:32,567 Because if they came too close, then you're 50 00:02:32,567 --> 00:02:33,769 going to be on this thing. 51 00:02:33,769 --> 00:02:35,270 And you're just gonna be-- you know, 52 00:02:35,270 --> 00:02:38,507 all those electrons are going to be overlapping each other 53 00:02:38,507 --> 00:02:41,677 and very unhappy. 54 00:02:41,677 --> 00:02:42,778 So this is what we do. 55 00:02:42,778 --> 00:02:46,281 And we said, OK, this is the bond 56 00:02:46,281 --> 00:02:52,254 of an atom and another atom, an ion and another ion, a cation 57 00:02:52,254 --> 00:02:53,555 and an anion. 58 00:02:53,555 --> 00:02:54,623 We did all this Wednesday. 59 00:02:54,623 --> 00:02:56,158 I'm just getting us back in the mood. 60 00:02:58,493 --> 00:03:00,262 And what I told you is that that bond 61 00:03:00,262 --> 00:03:03,398 energy is related to the lattice energy, all right? 62 00:03:03,398 --> 00:03:08,236 I mean, now, technically, the lattice energy is-- 63 00:03:08,236 --> 00:03:11,106 and this is something you're playing around with-- 64 00:03:11,106 --> 00:03:14,376 the lattice energy would be the energy 65 00:03:14,376 --> 00:03:20,215 that it takes to go from those ions, sodium-plus in the gas 66 00:03:20,215 --> 00:03:20,882 phase, right? 67 00:03:20,882 --> 00:03:22,084 We put that little guy there. 68 00:03:22,084 --> 00:03:24,286 Now, that is something that's going keep coming, too. 69 00:03:24,286 --> 00:03:26,321 It's in a notation I've been sneaking in. 70 00:03:26,321 --> 00:03:31,893 Gas phase, all right, plus chlorine ion gas phase, 71 00:03:31,893 --> 00:03:37,031 and they came together to make NaCl-- 72 00:03:37,031 --> 00:03:38,466 ran out of room-- 73 00:03:38,466 --> 00:03:38,966 solid. 74 00:03:38,966 --> 00:03:42,471 But I put it underneath, solid sodium chloride. 75 00:03:42,471 --> 00:03:45,406 That's salt. Now, the lattice energy 76 00:03:45,406 --> 00:03:48,877 is the energy that it takes to go from these ions 77 00:03:48,877 --> 00:03:49,745 to the solid. 78 00:03:49,745 --> 00:03:53,915 And as you can see, well, here I just did two ions. 79 00:03:53,915 --> 00:03:56,317 But the lattice energy is going to be related 80 00:03:56,317 --> 00:03:59,087 to that bond energy, all right? 81 00:03:59,087 --> 00:04:00,022 OK? 82 00:04:00,022 --> 00:04:02,424 So the lattice energy of the solid that you make 83 00:04:02,424 --> 00:04:03,558 is going to be [INAUDIBLE]. 84 00:04:03,558 --> 00:04:07,329 And ionic solids, there's a whole bunch of materials 85 00:04:07,329 --> 00:04:08,630 that form solids this way. 86 00:04:08,630 --> 00:04:09,498 They're ionic solids. 87 00:04:09,498 --> 00:04:12,267 And they have properties that are general. 88 00:04:15,303 --> 00:04:16,805 They're not always these properties. 89 00:04:16,805 --> 00:04:18,440 But for the most part, these are the properties 90 00:04:18,440 --> 00:04:19,641 of our ionic solids, right? 91 00:04:19,641 --> 00:04:23,512 They tend to be solid at room temperature. 92 00:04:23,512 --> 00:04:26,248 They tend to have high melting and boiling points. 93 00:04:26,248 --> 00:04:28,817 They're often transparent in the visible. 94 00:04:28,817 --> 00:04:30,819 They're mostly electrical insulators. 95 00:04:30,819 --> 00:04:34,623 They're hard and brittle, soluble in water. 96 00:04:34,623 --> 00:04:38,293 But in your goody bag, you're seeing that's not always true. 97 00:04:38,293 --> 00:04:41,763 Because sometimes, well, most of the time there, 98 00:04:41,763 --> 00:04:45,300 but if this lattice energy is too high, 99 00:04:45,300 --> 00:04:47,002 then it may not even dissolve. 100 00:04:47,002 --> 00:04:50,072 It may still be an-- it just may be some really, really 101 00:04:50,072 --> 00:04:51,339 strong ionic solid. 102 00:04:51,339 --> 00:04:55,177 But these are the general properties of ionic solids. 103 00:04:55,177 --> 00:04:57,412 We'll come back as we learn about other solids 104 00:04:57,412 --> 00:05:01,983 Wednesday to the differences in properties 105 00:05:01,983 --> 00:05:03,919 between different types of solids. 106 00:05:03,919 --> 00:05:06,154 OK, so that's where we ended. 107 00:05:06,154 --> 00:05:12,394 Now, to do this, to get to here, we had to make ions. 108 00:05:12,394 --> 00:05:14,162 And so we've been talking about ions. 109 00:05:14,162 --> 00:05:15,931 And we're going to keep talking about ions 110 00:05:15,931 --> 00:05:18,733 because that's a very important part of how atoms 111 00:05:18,733 --> 00:05:20,969 see each other, all right? 112 00:05:20,969 --> 00:05:24,339 Am I seeing you as a neutral atom with all your electrons 113 00:05:24,339 --> 00:05:28,043 in your shell or am I seeing you with a charge missing or not? 114 00:05:28,043 --> 00:05:30,345 That makes a big difference in how 115 00:05:30,345 --> 00:05:33,181 they approach each other and therefore how they bond, 116 00:05:33,181 --> 00:05:33,782 all right? 117 00:05:33,782 --> 00:05:39,387 This is a critical part of what we need to learn this semester. 118 00:05:39,387 --> 00:05:43,758 And so, you know, we showed this, which is sometimes 119 00:05:43,758 --> 00:05:48,330 atoms actually don't mind losing an electron, don't mind. 120 00:05:48,330 --> 00:05:50,899 Don't mind is like happiness level 121 00:05:50,899 --> 00:05:52,501 which has to do with energy. 122 00:05:52,501 --> 00:05:54,836 And so if we want to look at this more formally, 123 00:05:54,836 --> 00:05:57,305 we would look at, for example, this chart 124 00:05:57,305 --> 00:06:01,643 from [? Avril ?] which is the first ionization energy. 125 00:06:01,643 --> 00:06:05,247 Now, that's something that we talked about. 126 00:06:05,247 --> 00:06:08,083 So the first ionization energy, which 127 00:06:08,083 --> 00:06:11,820 is how much energy it takes to remove 128 00:06:11,820 --> 00:06:15,390 an electron from the outer shell, the most outer shell 129 00:06:15,390 --> 00:06:18,326 electron, the first one you would take away. 130 00:06:18,326 --> 00:06:20,395 That's the first ionization energy. 131 00:06:20,395 --> 00:06:27,736 All right, and we saw, again, getting us back in the mood. 132 00:06:27,736 --> 00:06:30,071 Oh, I've got colors there. 133 00:06:30,071 --> 00:06:33,742 So if you started, for example, let's just take a look at this. 134 00:06:33,742 --> 00:06:37,312 OK, so here we are at lithium. 135 00:06:37,312 --> 00:06:38,813 I'm going to start here. 136 00:06:38,813 --> 00:06:40,715 And that's first ionization energy. 137 00:06:40,715 --> 00:06:42,284 And this is just the atomic number. 138 00:06:42,284 --> 00:06:43,418 So there's lithium. 139 00:06:43,418 --> 00:06:45,854 And remember, we looked at this last week, lithium 140 00:06:45,854 --> 00:06:47,422 and beryllium. 141 00:06:47,422 --> 00:06:52,360 OK, so if you look at that, we said so for lithium, you had 142 00:06:52,360 --> 00:06:54,829 three electrons in the core. 143 00:06:54,829 --> 00:06:56,665 So there's lithium, right? 144 00:06:56,665 --> 00:06:59,401 And there's the lithium. 145 00:06:59,401 --> 00:07:02,938 Oh, this is so fun because now we know what to call this-- 146 00:07:02,938 --> 00:07:05,073 1s2. 147 00:07:05,073 --> 00:07:07,409 All right, and then we have another shell. 148 00:07:07,409 --> 00:07:09,010 These are just pictorial. 149 00:07:09,010 --> 00:07:14,115 The electron is not in an orbit, it's in an orbital. 150 00:07:14,115 --> 00:07:17,118 It's not moving around like this. 151 00:07:17,118 --> 00:07:21,456 That's our classical minds fighting. 152 00:07:21,456 --> 00:07:23,592 And it's got one more electron. 153 00:07:23,592 --> 00:07:24,526 Why did I draw a dash? 154 00:07:24,526 --> 00:07:28,597 It's got one more electron there in the 2s shell. 155 00:07:28,597 --> 00:07:30,398 And that's lithium. 156 00:07:30,398 --> 00:07:32,834 But now, we're going to go from lithium to beryllium 157 00:07:32,834 --> 00:07:34,269 and we talked about this. 158 00:07:34,269 --> 00:07:37,305 So beryllium now is going to add, OK, it's 159 00:07:37,305 --> 00:07:38,940 going to add another proton. 160 00:07:38,940 --> 00:07:39,808 It's got all of them. 161 00:07:39,808 --> 00:07:41,943 But I'm showing the one that was added. 162 00:07:41,943 --> 00:07:45,981 And it's also going to add an electron here. 163 00:07:45,981 --> 00:07:50,784 But see, for beryllium this electron 164 00:07:50,784 --> 00:07:59,694 is really not shielded any more, not shielded more 165 00:07:59,694 --> 00:08:00,795 for the most part. 166 00:08:00,795 --> 00:08:06,368 You know, it went into the same shell, the same N, all right, 167 00:08:06,368 --> 00:08:09,904 and the same L, same shape, same quantum number. 168 00:08:09,904 --> 00:08:11,973 So there's nothing else shielding it. 169 00:08:11,973 --> 00:08:14,376 And yet, there is a whole other proton. 170 00:08:14,376 --> 00:08:18,079 And that's why beryllium is smaller. 171 00:08:18,079 --> 00:08:20,148 This is all stuff we talked about Wednesday. 172 00:08:20,148 --> 00:08:25,287 But see, look, that's also why it's harder to pull the outer 173 00:08:25,287 --> 00:08:27,622 electron off of beryllium-- there it is-- 174 00:08:27,622 --> 00:08:28,790 than lithium. 175 00:08:28,790 --> 00:08:30,225 So those really go together. 176 00:08:30,225 --> 00:08:32,394 All right, all the radius stuff we 177 00:08:32,394 --> 00:08:35,897 talked about holds, you know, that same kind of logic 178 00:08:35,897 --> 00:08:37,832 in terms of how these electrons are 179 00:08:37,832 --> 00:08:42,003 with respect to their nucleus holds for ionization energy. 180 00:08:42,003 --> 00:08:45,974 Now, let's go to boron. 181 00:08:45,974 --> 00:08:50,879 So if we go to boron, now, we're going over, 182 00:08:50,879 --> 00:08:52,280 look at what happened. 183 00:08:52,280 --> 00:08:53,114 Look at that. 184 00:08:53,114 --> 00:08:55,517 We went from there to there. 185 00:08:55,517 --> 00:08:59,054 And the ionization energy got lower. 186 00:08:59,054 --> 00:09:01,122 Well, that's also something we can understand. 187 00:09:01,122 --> 00:09:06,561 Because now, we're putting it into the 2p. 188 00:09:06,561 --> 00:09:10,699 OK, so if I do that, it would be, 189 00:09:10,699 --> 00:09:14,402 I'm going to put it under here, 2s2, right? 190 00:09:14,402 --> 00:09:17,238 And now, if I go to boron, I'm going 191 00:09:17,238 --> 00:09:19,641 to put it here in a 2p shell. 192 00:09:19,641 --> 00:09:23,978 So I'm starting a new L. Now, remember, 193 00:09:23,978 --> 00:09:26,414 that means the quantum number is still 2, 194 00:09:26,414 --> 00:09:28,483 but the shape of the orbital is different. 195 00:09:28,483 --> 00:09:30,485 And now, we know also from something 196 00:09:30,485 --> 00:09:33,388 we learned last week that because of orbital penetration, 197 00:09:33,388 --> 00:09:37,192 the energies of the 2p and 2s orbitals are not the same. 198 00:09:37,192 --> 00:09:40,128 All right, the s-energies are a little lower. 199 00:09:40,128 --> 00:09:42,797 And it lets those electrons get a little bit closer 200 00:09:42,797 --> 00:09:46,634 to that positive charge that they want so badly. 201 00:09:46,634 --> 00:09:49,838 So we know that this is going to be a little further out. 202 00:09:49,838 --> 00:09:55,009 And so there's a little bit of shielding, a little shielding 203 00:09:55,009 --> 00:09:59,447 that you get for this, plus orbital penetration 204 00:09:59,447 --> 00:10:00,882 that we talked about. 205 00:10:00,882 --> 00:10:05,987 And that puts it further out, all right? 206 00:10:05,987 --> 00:10:09,190 And therefore, the attraction is a little less. 207 00:10:09,190 --> 00:10:12,994 And therefore, the ionization energy went down. 208 00:10:12,994 --> 00:10:14,562 And now, we're going to fill those up. 209 00:10:14,562 --> 00:10:16,297 But it's the same thing as before. 210 00:10:16,297 --> 00:10:20,101 Now, you're not going further out, you're just adding 211 00:10:20,101 --> 00:10:23,271 and you're not really screening while you add. 212 00:10:23,271 --> 00:10:25,774 And so you're adding electrons into this 2p orbital. 213 00:10:25,774 --> 00:10:27,742 But you're also adding all the positive charge. 214 00:10:27,742 --> 00:10:29,544 Salute. 215 00:10:29,544 --> 00:10:31,780 And so, the ionization energy is going 216 00:10:31,780 --> 00:10:36,117 to go up, except look at that, half filling, right there, 217 00:10:36,117 --> 00:10:38,253 half filling, a little extra stability. 218 00:10:38,253 --> 00:10:40,288 Remember, we talked about exceptions, right? 219 00:10:40,288 --> 00:10:42,557 Half filling. 220 00:10:42,557 --> 00:10:43,191 Half filling. 221 00:10:43,191 --> 00:10:44,926 And so, you see, now you can see, 222 00:10:44,926 --> 00:10:48,096 we can understand these trends that were being measured. 223 00:10:48,096 --> 00:10:50,198 All right, and at the time, these ionization 224 00:10:50,198 --> 00:10:53,668 potentials, but now we really can understand them. 225 00:10:53,668 --> 00:10:54,702 And you can group them. 226 00:10:54,702 --> 00:10:57,639 And you can see if you group them, remember, we also grouped 227 00:10:57,639 --> 00:11:00,408 the periodic table a little bit by electron filling, quantum 228 00:11:00,408 --> 00:11:00,909 numbers. 229 00:11:00,909 --> 00:11:03,511 All right, you had the s and p blocks. 230 00:11:03,511 --> 00:11:06,648 Those are also often called the main group elements. 231 00:11:06,648 --> 00:11:08,783 They're in the first couple of rows of those. 232 00:11:08,783 --> 00:11:10,919 They're the most abundant elements. 233 00:11:15,690 --> 00:11:17,792 But those trends, now, you fully understand 234 00:11:17,792 --> 00:11:21,729 from the quantum mechanical solution 235 00:11:21,729 --> 00:11:23,832 to the atom, all right, and the electron 236 00:11:23,832 --> 00:11:25,767 filling of those orbitals. 237 00:11:25,767 --> 00:11:27,569 We can actually really understand it all. 238 00:11:30,305 --> 00:11:32,106 And then the same thing happens with the d. 239 00:11:32,106 --> 00:11:33,575 But it's a little more complicated. 240 00:11:33,575 --> 00:11:36,644 By the way, these are often called transition metals. 241 00:11:36,644 --> 00:11:38,913 The d-block, I told you about the d-block last week. 242 00:11:38,913 --> 00:11:41,049 They're also called transition metals. 243 00:11:41,049 --> 00:11:42,584 And the word metal is something we'll 244 00:11:42,584 --> 00:11:45,887 talk a lot about in a few weeks when we make metals. 245 00:11:45,887 --> 00:11:49,023 But they're called transitions because, literally, they 246 00:11:49,023 --> 00:11:51,593 transition in the filling. 247 00:11:51,593 --> 00:11:53,228 They transition. 248 00:11:53,228 --> 00:11:57,599 You're filling d-orbitals, all right, transitioning. 249 00:11:57,599 --> 00:11:59,367 And that makes it a little more complex 250 00:11:59,367 --> 00:12:00,869 in terms of what happens. 251 00:12:00,869 --> 00:12:03,037 But the same trends hold. 252 00:12:03,037 --> 00:12:04,806 The same trend holds. 253 00:12:04,806 --> 00:12:07,742 As you add more d-electrons, the ionization energy 254 00:12:07,742 --> 00:12:08,476 keeps going up. 255 00:12:08,476 --> 00:12:13,481 OK, now, this is extremely important, this ionization 256 00:12:13,481 --> 00:12:14,115 energy. 257 00:12:14,115 --> 00:12:16,017 The first ionization energy is very important 258 00:12:16,017 --> 00:12:19,153 because it tells you so much about the outer electron, 259 00:12:19,153 --> 00:12:23,091 whether an atom is going to be an anion or a cation. 260 00:12:23,091 --> 00:12:25,393 But all of the ionization, you could 261 00:12:25,393 --> 00:12:27,629 throw a whole lot of energy at these atoms 262 00:12:27,629 --> 00:12:30,198 and they'll all come off, all right. 263 00:12:30,198 --> 00:12:33,268 And, you know, so we played with this kind of energy. 264 00:12:33,268 --> 00:12:34,235 This is visible light. 265 00:12:34,235 --> 00:12:35,904 You had your goody bag, too. 266 00:12:35,904 --> 00:12:37,171 You got a spectrometer. 267 00:12:37,171 --> 00:12:38,473 You can see lines in here. 268 00:12:38,473 --> 00:12:39,841 This is a continuous spectrum. 269 00:12:39,841 --> 00:12:41,643 But you see, you've got this whole, 270 00:12:41,643 --> 00:12:44,746 all these different wavelengths, right? 271 00:12:44,746 --> 00:12:47,849 And now you see this and you don't just think about colors, 272 00:12:47,849 --> 00:12:51,019 you think about energies, all right? 273 00:12:51,019 --> 00:12:56,591 And so if you think that way, because I want to know 274 00:12:56,591 --> 00:12:58,059 how can I measure these things? 275 00:12:58,059 --> 00:13:01,329 Ah, stop, better. 276 00:13:01,329 --> 00:13:09,637 All right, and so, you know, if I look at energies, energies, 277 00:13:09,637 --> 00:13:14,742 I've got like the visible, which is around, oh, I don't know, 278 00:13:14,742 --> 00:13:18,279 say 2 to 6 EV. 279 00:13:18,279 --> 00:13:19,714 That's pretty high energy. 280 00:13:19,714 --> 00:13:23,351 And then you've got, well-- now, can I shine visible light 281 00:13:23,351 --> 00:13:27,355 and kick out, you know, a lithium electron? 282 00:13:27,355 --> 00:13:30,425 Well, the answer is roughly yes. 283 00:13:30,425 --> 00:13:33,661 You know, the lithium energy ionization, well, let's just 284 00:13:33,661 --> 00:13:34,796 go back and look. 285 00:13:34,796 --> 00:13:38,600 That first ionization energy, 520 kilojoules per mole, 286 00:13:38,600 --> 00:13:41,369 I know that's 5.4 EV-ish. 287 00:13:41,369 --> 00:13:43,605 Because I don't mind going back and forth, right? 288 00:13:43,605 --> 00:13:46,608 Kilojoules per mole of electrons, Jules, EV, 289 00:13:46,608 --> 00:13:48,676 moles, you can go back and forth. 290 00:13:48,676 --> 00:13:51,145 But that's right around here. 291 00:13:51,145 --> 00:13:53,948 So I could shine visible light and potentially knock that out. 292 00:13:53,948 --> 00:13:59,387 But see if I wanted the 1s electron of lithium, 293 00:13:59,387 --> 00:14:00,955 well, it's much, much lower in energy. 294 00:14:00,955 --> 00:14:02,624 Because, remember, we talked about this. 295 00:14:02,624 --> 00:14:04,559 It goes in and in each time I add charge. 296 00:14:04,559 --> 00:14:07,095 And so it would take 122 electron volts 297 00:14:07,095 --> 00:14:09,097 to knock that out, right? 298 00:14:09,097 --> 00:14:13,568 So but we have that kind of light, all right. 299 00:14:13,568 --> 00:14:18,806 The UV would be something like, oh, 10 to 100. 300 00:14:18,806 --> 00:14:20,942 And then, if we really want to blast these, 301 00:14:20,942 --> 00:14:22,577 we could go x-rays. 302 00:14:22,577 --> 00:14:25,279 Oh, are we going to have fun with X-rays 303 00:14:25,279 --> 00:14:28,216 later in the semester. 304 00:14:28,216 --> 00:14:30,652 And this would go to something like 100,000. 305 00:14:30,652 --> 00:14:31,753 And so I got it. 306 00:14:31,753 --> 00:14:35,123 You know, if I wanted to, I could shine light and ionize 307 00:14:35,123 --> 00:14:36,491 the whole thing. 308 00:14:36,491 --> 00:14:39,827 And that is, in fact, one of the single most important 309 00:14:39,827 --> 00:14:42,030 experiments we do to characterize materials. 310 00:14:42,030 --> 00:14:44,532 And so I want you to know about it. 311 00:14:44,532 --> 00:14:47,301 It's called photoelectron spectroscopy, 312 00:14:47,301 --> 00:14:54,142 photoelectron spectroscopy. 313 00:14:57,779 --> 00:15:04,686 And, for short, we will not write that out ever again. 314 00:15:04,686 --> 00:15:07,689 I will write out PES, photoelectron spectroscopy. 315 00:15:07,689 --> 00:15:11,192 Now, this is a characterization tool. 316 00:15:11,192 --> 00:15:13,594 I'm basically saying, well, you know, I need energy. 317 00:15:13,594 --> 00:15:15,430 I'm going to get it from some photon source. 318 00:15:15,430 --> 00:15:16,998 But I'm going to get enough to just blast 319 00:15:16,998 --> 00:15:19,333 all the electrons out of this material, out of this atom. 320 00:15:19,333 --> 00:15:22,170 Because, for now, our material, they're just atoms. 321 00:15:22,170 --> 00:15:25,139 And I want to know about these atoms. 322 00:15:25,139 --> 00:15:26,007 So let's take a look. 323 00:15:26,007 --> 00:15:27,942 So what happens when I do this? 324 00:15:27,942 --> 00:15:29,877 Well, let's see, first of all, I've 325 00:15:29,877 --> 00:15:34,515 got some energy that we know is h nu. 326 00:15:34,515 --> 00:15:36,551 It's dependent on the frequency. 327 00:15:36,551 --> 00:15:37,852 There are the frequencies. 328 00:15:37,852 --> 00:15:38,486 There they are. 329 00:15:38,486 --> 00:15:39,721 No, there they are. 330 00:15:39,721 --> 00:15:44,926 OK, so now, I've got some atom here. 331 00:15:44,926 --> 00:15:47,095 And what do I do? 332 00:15:47,095 --> 00:15:48,763 Well, I look, did anything happen? 333 00:15:48,763 --> 00:15:49,497 No. 334 00:15:49,497 --> 00:15:50,565 What about now? 335 00:15:50,565 --> 00:15:51,099 I don't know. 336 00:15:51,099 --> 00:15:51,999 OK, what about now? 337 00:15:51,999 --> 00:15:56,504 Oh, all of a sudden, they come flying out, electrons. 338 00:15:56,504 --> 00:15:58,439 All right? 339 00:15:58,439 --> 00:16:02,610 And I measure their energy. 340 00:16:02,610 --> 00:16:05,379 It goes right back to the photoelectric effect 341 00:16:05,379 --> 00:16:06,447 that Einstein was doing. 342 00:16:06,447 --> 00:16:11,385 He was shining visible-ish light onto metals 343 00:16:11,385 --> 00:16:13,121 and seeing what electron-- but now I'm 344 00:16:13,121 --> 00:16:15,256 shining all sorts of light onto an atom 345 00:16:15,256 --> 00:16:18,359 and I want them all to come out, not just the outer one. 346 00:16:18,359 --> 00:16:19,794 And so we will. 347 00:16:19,794 --> 00:16:23,097 You can see if I measure, so now I'm 348 00:16:23,097 --> 00:16:28,269 going to measure the kinetic energy of these. 349 00:16:28,269 --> 00:16:33,407 And the ionization energy of that electron 350 00:16:33,407 --> 00:16:37,278 is going to equal whatever the energy of the incident photon 351 00:16:37,278 --> 00:16:41,915 was minus the kinetic energy of the electron. 352 00:16:41,915 --> 00:16:43,618 That's what I want. 353 00:16:43,618 --> 00:16:46,087 I want that ionization energy. 354 00:16:46,087 --> 00:16:52,627 This is, just to be clear, ionization energy. 355 00:16:52,627 --> 00:16:54,929 And like I said, I want it all. 356 00:16:54,929 --> 00:16:57,765 Not just the first, I want the second and the third. 357 00:16:57,765 --> 00:16:58,699 So now, you see. 358 00:16:58,699 --> 00:17:01,335 So this is the experiment that you do. 359 00:17:01,335 --> 00:17:02,203 What are the results? 360 00:17:04,771 --> 00:17:07,541 Well, the results are really just what we've been doing. 361 00:17:07,541 --> 00:17:09,143 But you turn it over. 362 00:17:09,143 --> 00:17:11,779 So let's look at hydrogen, OK? 363 00:17:11,779 --> 00:17:13,013 Now, what have we been doing? 364 00:17:13,013 --> 00:17:13,948 What do I mean by that? 365 00:17:13,948 --> 00:17:16,349 Well, what we've been doing is we've been going like this. 366 00:17:16,349 --> 00:17:16,884 What's that? 367 00:17:16,884 --> 00:17:19,686 OK, this is hydrogen 1s1. 368 00:17:19,686 --> 00:17:22,022 I could do that or I could just label it the 1s and then 369 00:17:22,022 --> 00:17:25,425 you see the one electron right there. 370 00:17:25,425 --> 00:17:29,564 Now, if I shine light on this and I measure, 371 00:17:29,564 --> 00:17:34,836 the way that you do a PES for hydrogen is you 372 00:17:34,836 --> 00:17:39,674 would look at the ionization energy on the x-axis. 373 00:17:39,674 --> 00:17:45,646 And this would be the relative electron count on the y-axis. 374 00:17:45,646 --> 00:17:48,983 So you're just counting, all right? 375 00:17:48,983 --> 00:17:50,518 And what you would see in hydrogen 376 00:17:50,518 --> 00:17:51,719 is there would be a peak. 377 00:17:51,719 --> 00:17:54,222 It would look like this. 378 00:17:54,222 --> 00:17:54,956 That's it. 379 00:17:54,956 --> 00:17:58,426 If all the electrons in hydrogen, 1, 380 00:17:58,426 --> 00:18:02,163 are in their ground state, 1s, then you would see a peak 381 00:18:02,163 --> 00:18:05,900 and this would be, you know that it would be at minus 13.6, 382 00:18:05,900 --> 00:18:06,400 right? 383 00:18:06,400 --> 00:18:08,669 That would be the energy that it takes to ionize it. 384 00:18:08,669 --> 00:18:12,940 And this would be the 1s peak. 385 00:18:12,940 --> 00:18:14,108 And that's what you measure. 386 00:18:14,108 --> 00:18:17,278 Now, it gets more fun, because now I can also 387 00:18:17,278 --> 00:18:18,980 look at other elements. 388 00:18:18,980 --> 00:18:21,115 So let's draw helium underneath it. 389 00:18:21,115 --> 00:18:23,951 I'm gonna try to squeeze it in. 390 00:18:23,951 --> 00:18:30,224 If I look at helium, well, helium is also 1s. 391 00:18:30,224 --> 00:18:34,161 And its PES would be-- 392 00:18:34,161 --> 00:18:36,864 so this is now ionization energy. 393 00:18:36,864 --> 00:18:39,066 This is the PES plot. 394 00:18:39,066 --> 00:18:43,905 And the PES for helium would be also the 1s. 395 00:18:43,905 --> 00:18:47,241 But the relative counts would be twice as high. 396 00:18:47,241 --> 00:18:50,344 So the peak of helium would be twice as high 397 00:18:50,344 --> 00:18:51,979 as the peak of hydrogen. 398 00:18:51,979 --> 00:18:55,449 Because, you know, for the same number of photons in, 399 00:18:55,449 --> 00:18:56,817 I'm getting that many more. 400 00:18:56,817 --> 00:19:01,055 I've got both these electrons coming out. 401 00:19:01,055 --> 00:19:07,495 So the relative peaks, I've got two more that can come out. 402 00:19:07,495 --> 00:19:09,397 Now, if I go to-- 403 00:19:09,397 --> 00:19:11,165 OK, now, it gets really interesting, 404 00:19:11,165 --> 00:19:16,404 because now, oh, I even have room, 405 00:19:16,404 --> 00:19:18,506 which is making me very happy. 406 00:19:18,506 --> 00:19:21,776 Because now I can do lithium right here. 407 00:19:21,776 --> 00:19:27,748 And if you look at lithium, lithium 408 00:19:27,748 --> 00:19:31,953 goes like this, all right? 409 00:19:31,953 --> 00:19:35,289 And if I look at a PES plot of lithium, the ionization 410 00:19:35,289 --> 00:19:40,328 energy and the relative electron count, 411 00:19:40,328 --> 00:19:46,067 OK, I'm going to have those 1s electrons filled. 412 00:19:46,067 --> 00:19:48,836 And there's going to be another energy where 413 00:19:48,836 --> 00:19:50,037 the 2s electrons are. 414 00:19:50,037 --> 00:19:51,706 So this is energy here. 415 00:19:51,706 --> 00:19:52,873 These are the orbitals. 416 00:19:52,873 --> 00:19:55,910 And somewhere over here is going to be a peak that's 417 00:19:55,910 --> 00:19:59,313 exactly half as high, exactly. 418 00:19:59,313 --> 00:20:00,915 I mean, that's makes a lot of sense 419 00:20:00,915 --> 00:20:04,385 because there's twice as many electrons. 420 00:20:04,385 --> 00:20:06,520 It's the relative electron count in the atom. 421 00:20:06,520 --> 00:20:09,323 There's twice as many electrons coming out 422 00:20:09,323 --> 00:20:10,925 of that 1s orbital and the 2s. 423 00:20:10,925 --> 00:20:13,894 So I'm going to get a half as high peak here, all right. 424 00:20:13,894 --> 00:20:19,533 And I just told you, the lithium atom, this electron is 5 point 425 00:20:19,533 --> 00:20:22,570 something, 4-ish electron volts to remove. 426 00:20:22,570 --> 00:20:24,338 This is 122. 427 00:20:24,338 --> 00:20:27,541 So literally, for lithium, this would be 122. 428 00:20:27,541 --> 00:20:29,377 This would be 5.4. 429 00:20:29,377 --> 00:20:32,480 And you know, that's the ionization energy in EV. 430 00:20:32,480 --> 00:20:35,716 And what you would do is you would draw the axis like that. 431 00:20:35,716 --> 00:20:40,087 So you don't have to put this all the way over here, 432 00:20:40,087 --> 00:20:41,622 all right? 433 00:20:41,622 --> 00:20:44,925 And all this means is I've broken up the axis 434 00:20:44,925 --> 00:20:46,627 and it's continuing to count here 435 00:20:46,627 --> 00:20:49,964 in a different scale, all right? 436 00:20:49,964 --> 00:20:55,870 These PES plots are absolutely essential in understanding 437 00:20:55,870 --> 00:20:57,605 atoms and materials. 438 00:20:57,605 --> 00:20:58,906 Because look at what you get. 439 00:20:58,906 --> 00:21:04,845 You get, literally, the electron filling plot turned over. 440 00:21:04,845 --> 00:21:06,414 It's incredible. 441 00:21:06,414 --> 00:21:09,917 You get it turned over. 442 00:21:09,917 --> 00:21:12,486 And you can write this as, oh, let's just do this. 443 00:21:12,486 --> 00:21:14,588 You know, I could write this as 1s2. 444 00:21:14,588 --> 00:21:17,224 We have so many options now, 2s1. 445 00:21:17,224 --> 00:21:23,397 All right, I could write this as helium 2s1. 446 00:21:23,397 --> 00:21:25,099 That would be like using the noble gas. 447 00:21:28,369 --> 00:21:31,005 I could make what people, you know, there are so many-- 448 00:21:31,005 --> 00:21:34,475 I can make box plots, oh, box plots. 449 00:21:34,475 --> 00:21:35,676 You can do this. 450 00:21:35,676 --> 00:21:37,645 Some people really like putting things 451 00:21:37,645 --> 00:21:42,616 in boxes, 1s, 2s, box plots. 452 00:21:47,488 --> 00:21:52,560 So these are all meaning, these all say the same thing-- 453 00:21:52,560 --> 00:21:54,028 Lithium. 454 00:21:54,028 --> 00:21:58,632 They all say lithium, all right? 455 00:21:58,632 --> 00:22:00,134 Photoelectron spectra. 456 00:22:00,134 --> 00:22:01,769 So I could ask you questions like this. 457 00:22:01,769 --> 00:22:03,037 There's one. 458 00:22:03,037 --> 00:22:07,775 Ionization energy, megajoules per mole, relative number 459 00:22:07,775 --> 00:22:10,978 of electrons, this element has a charge of 2-plus 460 00:22:10,978 --> 00:22:12,246 and the PES shown below. 461 00:22:12,246 --> 00:22:13,681 What is it? 462 00:22:13,681 --> 00:22:20,121 So, OK, I know, 1s2, 2s2, and since this is going up 463 00:22:20,121 --> 00:22:24,191 three times as high, that sure looks like 2p6, doesn't it? 464 00:22:24,191 --> 00:22:25,726 That looks like 2p6. 465 00:22:25,726 --> 00:22:28,329 Remember, it's this turned over on its side, 466 00:22:28,329 --> 00:22:31,665 all right, where the peak height corresponds to the filling. 467 00:22:31,665 --> 00:22:34,368 That's what that experiment gives you, 2p6. 468 00:22:34,368 --> 00:22:35,202 Well, then it must-- 469 00:22:35,202 --> 00:22:41,175 But then you have your periodic table, ah-ha. 470 00:22:41,175 --> 00:22:42,376 Gesundheit. 471 00:22:42,376 --> 00:22:45,646 Neon, it must be neon. 472 00:22:45,646 --> 00:22:47,281 No, who said no? 473 00:22:47,281 --> 00:22:48,382 No. 474 00:22:48,382 --> 00:22:52,786 Don't just-- Yes, it can't be neon because of the question. 475 00:22:52,786 --> 00:22:56,123 It's got a charge of 2-plus. 476 00:22:56,123 --> 00:23:00,394 Oh, tricky, tricky, tricky. 477 00:23:00,394 --> 00:23:03,564 Magnesium, it must be magnesium. 478 00:23:03,564 --> 00:23:05,633 That is the PES, right? 479 00:23:05,633 --> 00:23:08,068 But it's magnesium 2-plus because I said it had a charge. 480 00:23:08,068 --> 00:23:11,972 Thank you, shout out, I appreciate that. 481 00:23:11,972 --> 00:23:16,277 OK, so that's the power of the photoelectron spectra. 482 00:23:16,277 --> 00:23:18,712 And we'll be using it in the class. 483 00:23:18,712 --> 00:23:22,683 And this tells us about how electrons leave atoms. 484 00:23:22,683 --> 00:23:25,419 It tells us about ionization energies, not just 485 00:23:25,419 --> 00:23:27,388 the first, which is the one all the way 486 00:23:27,388 --> 00:23:30,391 out here to the right on the PES plot, but all of them. 487 00:23:30,391 --> 00:23:34,495 Because I shine enough energy light to get them all out. 488 00:23:34,495 --> 00:23:35,896 Now, you can also-- 489 00:23:35,896 --> 00:23:37,765 so that's about losing electrons-- 490 00:23:37,765 --> 00:23:40,067 you can also gain them. 491 00:23:40,067 --> 00:23:44,705 And so I mentioned this a little bit, but just for completeness, 492 00:23:44,705 --> 00:23:46,707 I want to come back to this. 493 00:23:46,707 --> 00:23:50,044 You have ionization energy, which 494 00:23:50,044 --> 00:23:52,213 is how much energy it takes to pull an electron out. 495 00:23:52,213 --> 00:23:55,416 You also have electron affinity. 496 00:23:55,416 --> 00:23:59,820 Because some atoms also might want electrons. 497 00:23:59,820 --> 00:24:01,322 And so when you look at those plots, 498 00:24:01,322 --> 00:24:03,290 it actually all makes sense again. 499 00:24:03,290 --> 00:24:05,659 Look at this, some atoms like chlorine-- 500 00:24:05,659 --> 00:24:07,695 this is electron affinity by atom number-- 501 00:24:07,695 --> 00:24:10,130 some atoms like chlorine really want another electron. 502 00:24:10,130 --> 00:24:12,032 Why? 503 00:24:12,032 --> 00:24:16,337 Because it's got an incomplete shell. 504 00:24:16,337 --> 00:24:17,771 It's so close. 505 00:24:17,771 --> 00:24:23,010 It just needs one more electron to fill that outer shell. 506 00:24:23,010 --> 00:24:24,178 And it wants it. 507 00:24:24,178 --> 00:24:26,880 And that's the electron affinity is how much does it want it. 508 00:24:26,880 --> 00:24:30,751 Now, want-- happiness, happiness-- lower energy. 509 00:24:30,751 --> 00:24:31,585 That's what this is. 510 00:24:31,585 --> 00:24:34,255 So if you're not going to lower your energy 511 00:24:34,255 --> 00:24:36,924 with another electron, then you're just saying no. 512 00:24:36,924 --> 00:24:38,759 You just say no, 0. 513 00:24:38,759 --> 00:24:41,962 I will not take an electron because if you give me one, 514 00:24:41,962 --> 00:24:43,130 my energy is going to go up. 515 00:24:43,130 --> 00:24:44,765 And I will be a less happy atom. 516 00:24:44,765 --> 00:24:46,367 Now, that makes sense, too, right? 517 00:24:46,367 --> 00:24:47,901 Filled shells. 518 00:24:47,901 --> 00:24:52,640 Nitrogen, nitrogen has got a half-filled shell. 519 00:24:52,640 --> 00:24:55,342 "No" to that electron, I like my half-filled shell. 520 00:24:55,342 --> 00:24:58,812 It gives me a little added stability, a little extra kick. 521 00:24:58,812 --> 00:25:01,282 If you give me that electron, you know, 522 00:25:01,282 --> 00:25:03,651 I'm gonna not have that added stability. 523 00:25:03,651 --> 00:25:05,319 I don't want it, 0. 524 00:25:05,319 --> 00:25:08,555 All right, 0. 525 00:25:08,555 --> 00:25:12,126 Losing electrons, gaining electrons, losing electrons, 526 00:25:12,126 --> 00:25:15,996 gaining electrons, why does it matter? 527 00:25:15,996 --> 00:25:17,798 Why does it matter? 528 00:25:17,798 --> 00:25:19,300 Well, we made a solid last week. 529 00:25:19,300 --> 00:25:21,935 Today, the answer is obvious. 530 00:25:21,935 --> 00:25:27,875 It matters because of Danish wind, obviously. 531 00:25:27,875 --> 00:25:32,379 43%, in 2014, 43% of all the electrical energy in Denmark 532 00:25:32,379 --> 00:25:33,347 came from wind. 533 00:25:33,347 --> 00:25:35,015 It's higher now. 534 00:25:35,015 --> 00:25:39,420 But see, now, this is a quarter of the Danish wind. 535 00:25:39,420 --> 00:25:41,889 I only gave you a two minute hemodialysis 536 00:25:41,889 --> 00:25:43,357 why this matters on Wednesday. 537 00:25:43,357 --> 00:25:47,261 So I'm going extended today just a little bit. 538 00:25:47,261 --> 00:25:51,298 Danish wind, people are very dependable. 539 00:25:51,298 --> 00:25:54,335 So over a three-month period, this is how much we need, 540 00:25:54,335 --> 00:25:56,670 energy, electricity. 541 00:25:56,670 --> 00:25:59,940 But look at the wind supply. 542 00:25:59,940 --> 00:26:02,242 Sometimes it's really there for us. 543 00:26:02,242 --> 00:26:03,677 Sometimes it's not at all there. 544 00:26:03,677 --> 00:26:05,079 Sometimes it's predictable. 545 00:26:05,079 --> 00:26:08,982 Sometimes it's not at all predictable. 546 00:26:08,982 --> 00:26:10,651 With that much of your electricity 547 00:26:10,651 --> 00:26:14,188 coming from this type of unreliable resource, 548 00:26:14,188 --> 00:26:16,290 that is a huge challenge. 549 00:26:16,290 --> 00:26:18,125 I mean, even if you go out to Arizona 550 00:26:18,125 --> 00:26:19,593 and you talk about solar subsidies, 551 00:26:19,593 --> 00:26:21,061 Arizona is sunny all the time. 552 00:26:21,061 --> 00:26:27,201 No, not sunny all the time, most of the time, more than Boston. 553 00:26:27,201 --> 00:26:29,470 But this is the sun in Arizona. 554 00:26:29,470 --> 00:26:31,605 That's the power you're getting from it. 555 00:26:31,605 --> 00:26:34,241 And look at this, these are just clouds. 556 00:26:34,241 --> 00:26:36,810 Because Arizona does have clouds. 557 00:26:36,810 --> 00:26:38,779 And they passed by and they blocked the sun. 558 00:26:38,779 --> 00:26:42,416 Do you know what a nightmare this is for a grid operator? 559 00:26:42,416 --> 00:26:47,588 If a lot of your customers get their energy in this way, 560 00:26:47,588 --> 00:26:52,025 you know, and all of a sudden, half of the your supply 561 00:26:52,025 --> 00:26:56,830 of energy just turns off, I mean, that's a huge problem. 562 00:26:56,830 --> 00:27:00,501 And this is one of the most limiting factors 563 00:27:00,501 --> 00:27:02,970 for increasing, to a large extent, 564 00:27:02,970 --> 00:27:05,939 the amount of renewables we have on our grid. 565 00:27:05,939 --> 00:27:07,541 And so, of course, I know a lot of you 566 00:27:07,541 --> 00:27:08,976 are thinking, well, just store it. 567 00:27:08,976 --> 00:27:11,612 And that's what we need to do. 568 00:27:11,612 --> 00:27:13,647 But it turns out that really one of the only ways 569 00:27:13,647 --> 00:27:17,518 we have to store energy at this large scale is pumped hydro. 570 00:27:17,518 --> 00:27:20,220 And you see, we're pumping water up a hill. 571 00:27:20,220 --> 00:27:23,524 When I have access, I pump water up a hill. 572 00:27:23,524 --> 00:27:25,559 And then when I need, I roll it back down 573 00:27:25,559 --> 00:27:27,027 and I turn a turbine with it. 574 00:27:27,027 --> 00:27:31,031 I'm literally just trading energy, potential energy. 575 00:27:31,031 --> 00:27:32,699 And then I bring it back, kinetic energy. 576 00:27:32,699 --> 00:27:35,269 And then I make electricity. 577 00:27:35,269 --> 00:27:37,971 The problem is that, you know, well, as you can see, 578 00:27:37,971 --> 00:27:39,873 pumped hydro is going to be good where there's 579 00:27:39,873 --> 00:27:41,909 hydro, where there's water. 580 00:27:41,909 --> 00:27:43,811 So that's limiting. 581 00:27:43,811 --> 00:27:48,315 But it also is a very low areal density. 582 00:27:48,315 --> 00:27:51,251 And there are also a lot of environmental challenges 583 00:27:51,251 --> 00:27:52,719 with making this work in a way that 584 00:27:52,719 --> 00:27:54,788 doesn't harm the environment. 585 00:27:54,788 --> 00:27:56,490 So there are a lot of issues with scaling 586 00:27:56,490 --> 00:27:58,826 up pumped hydro, a lot of issues as a storage. 587 00:27:58,826 --> 00:28:02,396 And so I ask, well, what else can we pump up hills? 588 00:28:02,396 --> 00:28:04,298 And we know what the answer is because it's 589 00:28:04,298 --> 00:28:05,399 what we're talking about-- 590 00:28:08,368 --> 00:28:09,036 ions. 591 00:28:09,036 --> 00:28:09,670 Where are they? 592 00:28:09,670 --> 00:28:14,041 Ions, we can pump ions up hills. 593 00:28:14,041 --> 00:28:15,509 There's my picture. 594 00:28:15,509 --> 00:28:17,878 Look at that. 595 00:28:17,878 --> 00:28:21,582 Ions, and you know what this is, it's a battery. 596 00:28:21,582 --> 00:28:24,184 A battery is two different materials, 597 00:28:24,184 --> 00:28:28,455 two different metals, a and b, where one of them has an ion, 598 00:28:28,455 --> 00:28:35,229 I don't know, like lithium, for example, 599 00:28:35,229 --> 00:28:36,997 that can go back and forth. 600 00:28:36,997 --> 00:28:39,199 And the electrolyte is this thing in between 601 00:28:39,199 --> 00:28:42,569 that only allows that ion through, OK? 602 00:28:42,569 --> 00:28:43,570 Now, here's the thing. 603 00:28:43,570 --> 00:28:50,377 So if I'm a metal and I lose a positively charged atom, 604 00:28:50,377 --> 00:28:53,180 well, then I got to stay neutral. 605 00:28:53,180 --> 00:28:56,483 And the only way to stay neutral is to pump an electron out, 606 00:28:56,483 --> 00:28:58,585 all right? 607 00:28:58,585 --> 00:29:01,088 So if I want to draw electrons out of this, 608 00:29:01,088 --> 00:29:03,924 that's fine as long as I draw ions out of it. 609 00:29:03,924 --> 00:29:05,692 And then both of them can do work. 610 00:29:05,692 --> 00:29:09,496 And then they come back and they roll down an energy hill. 611 00:29:09,496 --> 00:29:11,632 That's what they're doing and going back and forth, 612 00:29:11,632 --> 00:29:13,800 shuttling back and forth, back and forth. 613 00:29:13,800 --> 00:29:17,271 They're rolling down a hill, literally, of energy. 614 00:29:17,271 --> 00:29:21,074 You know, when it's in one metal, it's higher in energy. 615 00:29:21,074 --> 00:29:24,177 And then, when I, you know, plug my phone in, 616 00:29:24,177 --> 00:29:28,549 it rolls down that energy hill. 617 00:29:28,549 --> 00:29:31,218 And as it does, it travels across to the other metal, 618 00:29:31,218 --> 00:29:32,819 gets lower in energy, and the electron 619 00:29:32,819 --> 00:29:34,621 has got to come around and do work for me. 620 00:29:34,621 --> 00:29:36,990 Because otherwise, it wouldn't stay neutral. 621 00:29:36,990 --> 00:29:38,325 That's what a battery is. 622 00:29:38,325 --> 00:29:40,561 It's all about ions, all right? 623 00:29:40,561 --> 00:29:41,395 It's all about ions. 624 00:29:41,395 --> 00:29:42,462 It's like a ski lift. 625 00:29:42,462 --> 00:29:43,764 I like to think of it, you know, it's 626 00:29:43,764 --> 00:29:45,499 like these ions are getting into a ski lift 627 00:29:45,499 --> 00:29:47,467 and they're just getting pumped up the mountain. 628 00:29:47,467 --> 00:29:49,803 And then when you plug it in, they're ready to ski down 629 00:29:49,803 --> 00:29:50,504 and they go down. 630 00:29:50,504 --> 00:29:53,807 And that's just cruising across this electrolyte. 631 00:29:53,807 --> 00:29:56,343 And I don't know what the electron is in this analogy. 632 00:29:56,343 --> 00:29:57,578 But that's all a battery is. 633 00:29:57,578 --> 00:30:01,982 You plug it in and the ski lift takes it up when you charge it. 634 00:30:01,982 --> 00:30:05,385 And now, you power your phone on and it rolls back down. 635 00:30:05,385 --> 00:30:08,522 Well, see the thing is that batteries have seen 636 00:30:08,522 --> 00:30:11,792 a Moore's law of themselves. 637 00:30:11,792 --> 00:30:16,263 If you look at the Moore's law for batteries, it doubles. 638 00:30:16,263 --> 00:30:18,999 So this is the energy storage of batteries 639 00:30:18,999 --> 00:30:20,801 over the last 150-ish years. 640 00:30:20,801 --> 00:30:23,370 It doubles every 60 years. 641 00:30:23,370 --> 00:30:25,105 That's not a very good Moore's law. 642 00:30:25,105 --> 00:30:27,074 But that's completely changed. 643 00:30:27,074 --> 00:30:28,508 That's completely changed recently. 644 00:30:28,508 --> 00:30:33,780 And the reason is all about ion shuttling materials and ion 645 00:30:33,780 --> 00:30:35,482 storing materials. 646 00:30:35,482 --> 00:30:37,150 This is why this has happened. 647 00:30:37,150 --> 00:30:39,186 This is why we've had a revolution 648 00:30:39,186 --> 00:30:41,855 in electrochemical energy storage, all right. 649 00:30:41,855 --> 00:30:44,691 Because 150 years ago, we only made batteries out 650 00:30:44,691 --> 00:30:46,193 of about 10 different materials. 651 00:30:46,193 --> 00:30:50,330 And today, there's well over 80 that are commercialized. 652 00:30:50,330 --> 00:30:53,467 There's many hundreds in research labs. 653 00:30:53,467 --> 00:30:57,104 What is making the difference is that those materials now 654 00:30:57,104 --> 00:30:59,940 allow the shuttling to happen. 655 00:30:59,940 --> 00:31:02,676 It allows the shuttling to happen more easily, maybe 656 00:31:02,676 --> 00:31:04,011 faster. 657 00:31:04,011 --> 00:31:06,947 And it allows more of them to be stored per volume. 658 00:31:06,947 --> 00:31:09,983 It's all about the chemistry that houses those ions. 659 00:31:09,983 --> 00:31:12,252 It's all about the chemistry of the ions. 660 00:31:12,252 --> 00:31:13,387 So that's why this matters. 661 00:31:13,387 --> 00:31:19,960 Now, we roll things down hills to power our world. 662 00:31:19,960 --> 00:31:22,362 I told you this already in the first or second lecture. 663 00:31:22,362 --> 00:31:26,199 We roll things down hills all the time, all right? 664 00:31:26,199 --> 00:31:30,871 So like methane is the core ingredient in natural gas. 665 00:31:30,871 --> 00:31:33,774 And what we do-- and we talked about combustion already-- 666 00:31:33,774 --> 00:31:35,642 is we light that methane on fire. 667 00:31:35,642 --> 00:31:39,312 But see, the thing is that what nature has done 668 00:31:39,312 --> 00:31:44,017 is it has put all this stuff up the hill for us. 669 00:31:44,017 --> 00:31:46,486 So over tens of millions of years, 670 00:31:46,486 --> 00:31:50,490 nature has pushed the chemistry up a hill. 671 00:31:50,490 --> 00:31:53,694 That is literally what it's done in energy. 672 00:31:53,694 --> 00:31:55,662 Because, you know, it's made it so 673 00:31:55,662 --> 00:31:59,332 that if I light this on fire, it will go down the hill. 674 00:31:59,332 --> 00:32:04,805 It will roll down the hill and give off energy. 675 00:32:04,805 --> 00:32:06,273 Nature has done that for us. 676 00:32:06,273 --> 00:32:10,277 But see, we need to be able to do this as well as nature. 677 00:32:10,277 --> 00:32:13,647 And so in the last minute of why this matters, 678 00:32:13,647 --> 00:32:16,783 I want to explain why this is so challenging. 679 00:32:16,783 --> 00:32:18,118 We need to be able to match. 680 00:32:18,118 --> 00:32:21,888 Because if you look at the energy per weight 681 00:32:21,888 --> 00:32:25,425 versus the energy per volume of a material, 682 00:32:25,425 --> 00:32:27,294 that's a very important metric. 683 00:32:27,294 --> 00:32:29,763 We plot this all the time if you work on energy materials-- 684 00:32:29,763 --> 00:32:35,102 the volumetric versus the gravimetric energy density. 685 00:32:35,102 --> 00:32:37,871 This is good, a lot of energy per weight and volume. 686 00:32:37,871 --> 00:32:39,906 Well, look at where gasoline is. 687 00:32:39,906 --> 00:32:42,375 I want to do some math here. 688 00:32:42,375 --> 00:32:44,211 Because I think this is very important. 689 00:32:44,211 --> 00:32:46,046 Because I want you to see, now, if I 690 00:32:46,046 --> 00:32:48,782 take one liter of gasoline, so if I 691 00:32:48,782 --> 00:33:03,029 take one liter of gasoline, now, the cost is around $1. 692 00:33:03,029 --> 00:33:04,998 Well, it fluctuates, but, you know, 693 00:33:04,998 --> 00:33:07,701 in this country right around now it's about $1. 694 00:33:07,701 --> 00:33:10,804 OK, now, if I look at how much energy 695 00:33:10,804 --> 00:33:17,978 is in that gasoline, the energy stored in those bonds 696 00:33:17,978 --> 00:33:20,981 that nature has pushed up a hill over millions of years, 697 00:33:20,981 --> 00:33:26,086 the energy stored is about 33 megajoules. 698 00:33:26,086 --> 00:33:26,987 OK, good. 699 00:33:26,987 --> 00:33:30,323 Now, I'm going to make a comparison. 700 00:33:30,323 --> 00:33:38,064 One MIT professor, one MIT professor 701 00:33:38,064 --> 00:33:43,203 operates at around 60 watts. 702 00:33:43,203 --> 00:33:45,739 Now, this is something like-- well, 703 00:33:45,739 --> 00:33:49,242 this is equal to 60 joules per second. 704 00:33:49,242 --> 00:33:50,710 Now, I know some professors who can 705 00:33:50,710 --> 00:33:52,813 operate a little higher than that and maybe some 706 00:33:52,813 --> 00:33:53,446 a little lower. 707 00:33:53,446 --> 00:33:55,749 But that's like the average-- 708 00:33:55,749 --> 00:33:56,950 60 joules per second. 709 00:33:56,950 --> 00:34:02,389 Now, the thing is, if I want to get 33 megajoules out 710 00:34:02,389 --> 00:34:06,893 of this professor, then I get, at this rate, 711 00:34:06,893 --> 00:34:17,170 33 megajoules takes the prof 153 hours. 712 00:34:17,170 --> 00:34:18,737 Now, here's why this matters. 713 00:34:18,737 --> 00:34:26,513 Because 153 hours will cost about $1,530 714 00:34:26,513 --> 00:34:40,393 at the MIT professor salary, which is around $10 per hour. 715 00:34:40,393 --> 00:34:43,897 And, OK, but look at this. 716 00:34:46,699 --> 00:34:48,068 I dug something out of the ground 717 00:34:48,068 --> 00:34:51,571 that nature spent 100 million years making, fine, OK. 718 00:34:51,571 --> 00:34:52,438 And I burned it. 719 00:34:52,438 --> 00:34:53,406 And I got it for a $1. 720 00:34:53,406 --> 00:34:55,041 I got the same amount of energy that it 721 00:34:55,041 --> 00:34:59,145 would have taken me literally $1,530 to pay for it. 722 00:34:59,145 --> 00:35:01,581 That's our challenge. 723 00:35:01,581 --> 00:35:03,083 Now, you can plot other things here. 724 00:35:03,083 --> 00:35:05,619 But look at this. ethanol, wood, OK, liquid hydrogen, 725 00:35:05,619 --> 00:35:07,053 we're still trying to compress it. 726 00:35:07,053 --> 00:35:10,257 But look at this, batteries are way down there. 727 00:35:10,257 --> 00:35:11,324 This is why this matters. 728 00:35:11,324 --> 00:35:13,593 Because we're not even close to being done. 729 00:35:13,593 --> 00:35:15,262 We're not even close. 730 00:35:15,262 --> 00:35:18,365 See that great uptick in electrochemical storage. 731 00:35:18,365 --> 00:35:21,101 We need another order or two of magnitude 732 00:35:21,101 --> 00:35:28,275 still in storing energy, efficiencies, costs, et cetera. 733 00:35:28,275 --> 00:35:31,811 So that's my "why this matters" for today. 734 00:35:31,811 --> 00:35:36,449 Now, back to ions and electrons and atoms. 735 00:35:36,449 --> 00:35:40,487 What I want to take the last 15 minutes of class 736 00:35:40,487 --> 00:35:43,957 is to introduce a new way of looking at this. 737 00:35:43,957 --> 00:35:46,660 And some of you may have seen the Lewis dots, OK? 738 00:35:49,429 --> 00:35:50,864 I'm going to introduce them today. 739 00:35:50,864 --> 00:35:52,599 And then we're going to make a whole bunch 740 00:35:52,599 --> 00:35:56,169 of molecular structures on Wednesday. 741 00:35:56,169 --> 00:35:58,838 And the reason this is so important 742 00:35:58,838 --> 00:36:03,810 is that it gives us a sense of these outer electrons. 743 00:36:03,810 --> 00:36:07,280 It gives us a sense of how those outer electrons 744 00:36:07,280 --> 00:36:11,818 look for the atoms, and then, very importantly, how 745 00:36:11,818 --> 00:36:13,920 they come together in bonds. 746 00:36:13,920 --> 00:36:17,190 OK, how they come together in bonds. 747 00:36:17,190 --> 00:36:24,564 So if I just very, very simply ask, 748 00:36:24,564 --> 00:36:29,569 you know, what does the Lewis dot structure look like? 749 00:36:29,569 --> 00:36:36,977 Well, first of all, the number of dots 750 00:36:36,977 --> 00:36:42,983 is equal to the number of valence electrons. 751 00:36:47,187 --> 00:36:55,061 And this is equal to the last digit of the group, so 752 00:36:55,061 --> 00:36:57,764 of the element group. 753 00:36:57,764 --> 00:36:59,699 I'll show you that in a second. 754 00:36:59,699 --> 00:37:00,867 OK, so there's Lewis. 755 00:37:00,867 --> 00:37:06,840 Now, Lewis, you know, so there's one of his drawings in one 756 00:37:06,840 --> 00:37:09,242 of his original papers in the early 1900s. 757 00:37:09,242 --> 00:37:13,346 He actually was a professor here, as well. 758 00:37:13,346 --> 00:37:16,383 And then he went and did a lot of this work out in Berkeley. 759 00:37:16,383 --> 00:37:19,152 And so they named a hall after him. 760 00:37:19,152 --> 00:37:22,789 And his contribution was absolutely profound 761 00:37:22,789 --> 00:37:27,827 because in thinking about atoms with dots 762 00:37:27,827 --> 00:37:31,831 to represent electrons in the outer valence, 763 00:37:31,831 --> 00:37:37,670 it gave us a way to so easily think about bonding. 764 00:37:37,670 --> 00:37:40,173 Now, we can think about ionic bonding for sure, 765 00:37:40,173 --> 00:37:41,207 which is what we've done. 766 00:37:41,207 --> 00:37:43,443 But more importantly, what Lewis helps 767 00:37:43,443 --> 00:37:45,979 us with is to think about covalent bonding. 768 00:37:45,979 --> 00:37:48,081 And that's the subject of Wednesday, 769 00:37:48,081 --> 00:37:49,682 which is a whole other type of bonding 770 00:37:49,682 --> 00:37:50,950 that we're going to talk about. 771 00:37:53,219 --> 00:37:56,956 OK, so now, the last digit of the element group, OK, good. 772 00:37:56,956 --> 00:37:59,959 So there it predicts number of bonds formed by most elements 773 00:37:59,959 --> 00:38:01,294 in their compounds, good. 774 00:38:01,294 --> 00:38:02,195 And there is the dots. 775 00:38:02,195 --> 00:38:05,732 Look at that example, fluorine, or using 776 00:38:05,732 --> 00:38:09,669 noble gas notation, helium, that really saved us time. 777 00:38:09,669 --> 00:38:11,371 I didn't have to write 1s2. 778 00:38:11,371 --> 00:38:13,873 Actually, this looks like four strokes of the pen. 779 00:38:13,873 --> 00:38:15,475 1s2 would have been three. 780 00:38:15,475 --> 00:38:16,943 I don't know, honestly. 781 00:38:16,943 --> 00:38:20,080 But anyway, OK, there is fluorine. 782 00:38:20,080 --> 00:38:21,181 And look, one dot? 783 00:38:21,181 --> 00:38:21,681 No. 784 00:38:21,681 --> 00:38:22,182 Two dots? 785 00:38:22,182 --> 00:38:24,651 No, because you add a dot for the valence. 786 00:38:24,651 --> 00:38:28,421 So fluorine has seven dots until you reach the valence, 787 00:38:28,421 --> 00:38:31,057 until you reach the valence. 788 00:38:31,057 --> 00:38:35,161 That is the key of the Lewis picture. 789 00:38:35,161 --> 00:38:37,497 And we talked about this before. 790 00:38:37,497 --> 00:38:38,665 We talked about this before. 791 00:38:38,665 --> 00:38:41,868 Because it showed there were three really important things 792 00:38:41,868 --> 00:38:44,404 that come out of the Lewis picture. 793 00:38:44,404 --> 00:38:48,842 One is it tells us, as I've just told you, 794 00:38:48,842 --> 00:38:52,745 it tells us about bond formation. 795 00:38:59,119 --> 00:39:02,222 It tells us about bond formation. 796 00:39:02,222 --> 00:39:12,899 And it makes the assumption that the valence electrons 797 00:39:12,899 --> 00:39:20,106 are what matter for chemistry. 798 00:39:20,106 --> 00:39:21,374 And this is critical. 799 00:39:21,374 --> 00:39:23,877 And I've alluded to this before. 800 00:39:23,877 --> 00:39:25,945 You now have a real sense of this, though. 801 00:39:25,945 --> 00:39:28,615 From these energy diagrams, you have a sense of this. 802 00:39:28,615 --> 00:39:33,720 Because look, if I want to rip an electron off of lithium, 803 00:39:33,720 --> 00:39:35,855 I got to spend 5.4 electron volts. 804 00:39:35,855 --> 00:39:37,323 If I want to rip the next one off, 805 00:39:37,323 --> 00:39:40,026 I got to spend over 100 electron volts. 806 00:39:40,026 --> 00:39:42,495 And we said, well, we'll do PES with all these energies. 807 00:39:42,495 --> 00:39:43,229 It doesn't matter. 808 00:39:43,229 --> 00:39:43,997 I'll get 'em all. 809 00:39:43,997 --> 00:39:47,066 But what if I just want to say, well, 810 00:39:47,066 --> 00:39:51,905 what electrons are going to be available to participate 811 00:39:51,905 --> 00:39:53,973 in something like a bond? 812 00:39:53,973 --> 00:39:54,807 Which ones? 813 00:39:54,807 --> 00:39:56,376 It's going to be these ones. 814 00:39:56,376 --> 00:39:58,678 It's not going to be the ones all the way in close 815 00:39:58,678 --> 00:40:01,447 to the core that don't want to be bothered 816 00:40:01,447 --> 00:40:04,851 and they've got so much energy. 817 00:40:04,851 --> 00:40:08,454 Just to get their attention takes 100 EV. 818 00:40:08,454 --> 00:40:09,722 And even that's not a-- 819 00:40:09,722 --> 00:40:12,592 But here, a little visible light and I 820 00:40:12,592 --> 00:40:15,195 got lithium talking to me. 821 00:40:15,195 --> 00:40:18,865 Well, chemically, it's the same. 822 00:40:18,865 --> 00:40:20,567 That's light, right? 823 00:40:20,567 --> 00:40:23,803 These ones are the ones that want to and can 824 00:40:23,803 --> 00:40:25,672 participate in bonding. 825 00:40:25,672 --> 00:40:29,309 The ones all the way down in energy, way, way, way low, 826 00:40:29,309 --> 00:40:31,244 they're inert. 827 00:40:31,244 --> 00:40:32,645 They're inert, all right? 828 00:40:32,645 --> 00:40:35,081 So most of chemistry happens in the valence. 829 00:40:35,081 --> 00:40:38,952 And Lewis really nailed that. 830 00:40:38,952 --> 00:40:41,888 So these dots are only valence electron dots. 831 00:40:45,091 --> 00:40:46,960 And there's one more rule. 832 00:40:46,960 --> 00:40:50,763 Now, OK, so there is the seven dots for fluorine. 833 00:40:50,763 --> 00:40:55,435 And then, OK, sometimes you'll see this. 834 00:40:55,435 --> 00:40:57,837 Oh, this is just the number of dots. 835 00:40:57,837 --> 00:41:03,610 It's this classification of the columns, all right, 836 00:41:03,610 --> 00:41:04,477 the groups in a pair. 837 00:41:04,477 --> 00:41:08,581 But, no, that is not OK, not standard. 838 00:41:08,581 --> 00:41:11,251 Remember, the IUPAC, which throws 839 00:41:11,251 --> 00:41:15,989 the best, most lively parties and conferences, 840 00:41:15,989 --> 00:41:17,857 they decide on how to name elements. 841 00:41:17,857 --> 00:41:21,394 And many, many other aspects of our lives are decided by them. 842 00:41:21,394 --> 00:41:23,930 And they said, no, that's an old classification. 843 00:41:23,930 --> 00:41:25,398 It's confusing. 844 00:41:25,398 --> 00:41:28,668 So we're going to go with the standard, which is that we 845 00:41:28,668 --> 00:41:32,705 still count 1 to 18, 1 to 18. 846 00:41:32,705 --> 00:41:34,674 1, 2-- s-block. 847 00:41:34,674 --> 00:41:37,644 13 to 18-- p-block. 848 00:41:37,644 --> 00:41:38,177 All right? 849 00:41:38,177 --> 00:41:41,014 OK, that's cool. 850 00:41:41,014 --> 00:41:44,784 3 to 12-- d-block. 851 00:41:44,784 --> 00:41:46,653 We're going back and forth. 852 00:41:46,653 --> 00:41:50,823 But you can just take the last digit there, IUPAC standard. 853 00:41:50,823 --> 00:41:53,359 Even the periodic table talks about it. 854 00:41:53,359 --> 00:41:54,294 It shows it. 855 00:41:54,294 --> 00:41:56,462 It shows the old classification there. 856 00:41:56,462 --> 00:41:59,932 And then it says, no, don't use it, it's confusing. 857 00:41:59,932 --> 00:42:01,701 Well, then why do they show it? 858 00:42:01,701 --> 00:42:03,736 Because some textbooks still show it. 859 00:42:03,736 --> 00:42:07,073 So I want you to be aware of that. 860 00:42:07,073 --> 00:42:13,212 OK, now, you can use Lewis, you can 861 00:42:13,212 --> 00:42:17,550 use this idea of only thinking about the valence 862 00:42:17,550 --> 00:42:22,088 to understand when atoms have similar chemistry, all right? 863 00:42:22,088 --> 00:42:27,060 So if the valence of carbon is the same 864 00:42:27,060 --> 00:42:29,729 as the valence of silicon, you've bumped down one quantum 865 00:42:29,729 --> 00:42:33,099 number, but they both have 4 electrons out there 866 00:42:33,099 --> 00:42:34,367 in the valence. 867 00:42:34,367 --> 00:42:36,035 In this case, it's 2. 868 00:42:36,035 --> 00:42:38,271 In this case, it's 3, in terms of the quantum number. 869 00:42:38,271 --> 00:42:39,872 But they both have those same kinds of 870 00:42:39,872 --> 00:42:41,374 and same number of electrons. 871 00:42:41,374 --> 00:42:45,078 So you can maybe expect there to be similar chemistry. 872 00:42:45,078 --> 00:42:46,479 It turns out, in this case, there 873 00:42:46,479 --> 00:42:47,647 is very different chemistry. 874 00:42:47,647 --> 00:42:48,915 But we'll learn about that. 875 00:42:48,915 --> 00:42:50,283 Carbon-- hybridisation. 876 00:42:50,283 --> 00:42:52,852 Silicon-- no. 877 00:42:52,852 --> 00:42:53,853 We'll get to that. 878 00:42:53,853 --> 00:42:56,356 But still, this is how we see silicon now. 879 00:42:56,356 --> 00:42:58,257 We don't see it this way with Lewis. 880 00:42:58,257 --> 00:42:59,425 We see it this way. 881 00:42:59,425 --> 00:43:02,362 This is how we see carbon. 882 00:43:02,362 --> 00:43:05,898 And so I want you to start seeing elements this way. 883 00:43:05,898 --> 00:43:07,967 OK, and so you can look at periodic tables 884 00:43:07,967 --> 00:43:12,205 and take images randomly found online with Lewis dots. 885 00:43:12,205 --> 00:43:15,508 And you can start thinking of atoms 886 00:43:15,508 --> 00:43:18,177 as their Lewis-dot representation. 887 00:43:18,177 --> 00:43:19,645 And like I said, on Wednesday we're 888 00:43:19,645 --> 00:43:23,216 going to make a whole bunch of structures, molecules, 889 00:43:23,216 --> 00:43:26,853 with Lewis dots and show how that teaches us, 890 00:43:26,853 --> 00:43:29,555 not only about how to draw the bonds, 891 00:43:29,555 --> 00:43:32,625 but, literally, about which bonding-- 892 00:43:32,625 --> 00:43:36,596 You know, if I have sodium and chlorine, it's pretty obvious. 893 00:43:36,596 --> 00:43:41,100 If there is a bond, it's between sodium and chlorine, all right? 894 00:43:41,100 --> 00:43:42,769 But as I go to more and more atoms 895 00:43:42,769 --> 00:43:45,171 and I'm trying to form molecules, 896 00:43:45,171 --> 00:43:50,009 it's not so obvious what is bonded to what and how. 897 00:43:50,009 --> 00:43:53,079 All right, and thinking about this 898 00:43:53,079 --> 00:43:56,482 and thinking about the third part of what Lewis 899 00:43:56,482 --> 00:44:00,486 did that was so important is what 900 00:44:00,486 --> 00:44:06,092 allows us to draw a whole bunch of molecules-- 901 00:44:06,092 --> 00:44:11,497 Octet rule, which is that atoms like-- 902 00:44:15,568 --> 00:44:19,806 we now know "like" means lower energy-- 903 00:44:19,806 --> 00:44:28,681 to reach 8 electrons in their valence. 904 00:44:28,681 --> 00:44:32,985 OK, well, we can already see this for the ionic bond 905 00:44:32,985 --> 00:44:33,986 that we've talked about. 906 00:44:33,986 --> 00:44:35,822 And you can write this. 907 00:44:35,822 --> 00:44:39,559 And I want you to write ionic bonds using Lewis. 908 00:44:39,559 --> 00:44:43,996 But in this case, it's actually pretty straightforward, right? 909 00:44:43,996 --> 00:44:46,632 If I had, for example-- 910 00:44:46,632 --> 00:44:51,037 let's get some more board space over here. 911 00:44:58,744 --> 00:45:02,648 If I had, for example, an ionic bond 912 00:45:02,648 --> 00:45:12,091 between cesium and fluorine, so if I had cesium and fluorine, 913 00:45:12,091 --> 00:45:15,595 then the way I would think about this in the Lewis world 914 00:45:15,595 --> 00:45:22,468 would be this way and this way. 915 00:45:25,037 --> 00:45:27,940 Because I've got 7 valence electrons in fluorine and 1 916 00:45:27,940 --> 00:45:28,608 in cesium. 917 00:45:28,608 --> 00:45:31,410 And then, if I write this as an ionic bond, 918 00:45:31,410 --> 00:45:37,650 the way I would write it is cesium-plus with fluorine 919 00:45:37,650 --> 00:45:39,986 having taken that electron. 920 00:45:42,989 --> 00:45:45,391 And so you would write this still with the minus sign 921 00:45:45,391 --> 00:45:45,892 there. 922 00:45:45,892 --> 00:45:47,660 That emphasizes. 923 00:45:47,660 --> 00:45:50,129 It emphasizes what happened. 924 00:45:50,129 --> 00:45:52,832 But I see my Lewis here. 925 00:45:52,832 --> 00:45:54,767 You know, I see it there. 926 00:45:54,767 --> 00:45:58,237 But I'm emphasizing that this is an ionic bond that's happened. 927 00:45:58,237 --> 00:46:02,008 Because fluorine wasn't supposed to have 8, but then it did. 928 00:46:02,008 --> 00:46:04,210 It's got a super-high electron affinity. 929 00:46:04,210 --> 00:46:07,480 Cesium has a very low ionization energy of its first electron. 930 00:46:07,480 --> 00:46:09,749 And so fluorine just took it. 931 00:46:09,749 --> 00:46:11,417 It literally just took it. 932 00:46:11,417 --> 00:46:12,184 I'll take that. 933 00:46:12,184 --> 00:46:13,052 Thank you very much. 934 00:46:13,052 --> 00:46:16,389 You know, I'm not being judgmental. 935 00:46:16,389 --> 00:46:19,058 But ionic bonds are kind of, you know, 936 00:46:19,058 --> 00:46:22,295 the relationship in a bond-- and I don't want to judge-- 937 00:46:22,295 --> 00:46:25,765 but the relationship is not even. 938 00:46:25,765 --> 00:46:26,599 It's not even. 939 00:46:26,599 --> 00:46:28,367 And that's OK. 940 00:46:28,367 --> 00:46:31,704 But fluorine said, take, take, give. 941 00:46:31,704 --> 00:46:33,573 And cesium atom, OK, fine. 942 00:46:33,573 --> 00:46:36,409 Now, on Wednesday when we do covalent bonds, it's not so-- 943 00:46:36,409 --> 00:46:40,713 then there's a lot more sharing that happens. 944 00:46:40,713 --> 00:46:43,215 And that's why we can model it the way that I-- 945 00:46:43,215 --> 00:46:44,984 yes, I still left there-- 946 00:46:44,984 --> 00:46:46,619 we can model it that way. 947 00:46:46,619 --> 00:46:51,657 Because it is like a charged atom and another charged atom, 948 00:46:51,657 --> 00:46:52,558 all right? 949 00:46:52,558 --> 00:46:55,061 And it's because fluorine took it. 950 00:46:55,061 --> 00:46:55,995 Fluorine took it. 951 00:46:55,995 --> 00:46:57,396 It's OK. 952 00:46:57,396 --> 00:46:59,665 Any kind of relationship, you know, they get along. 953 00:46:59,665 --> 00:47:01,067 They make it work. 954 00:47:01,067 --> 00:47:07,039 Now, what we can also do just in thinking about this, 955 00:47:07,039 --> 00:47:09,275 just in thinking about this, I can 956 00:47:09,275 --> 00:47:12,945 go to another example like calcium. 957 00:47:12,945 --> 00:47:17,850 And if I think about calcium and fluorine, 958 00:47:17,850 --> 00:47:20,853 well, I know again fluorine likes to be f-minus. 959 00:47:20,853 --> 00:47:24,490 But see, calcium, when I think about it as a Lewis atom, 960 00:47:24,490 --> 00:47:28,661 you know, calcium likes to lose both of those. 961 00:47:28,661 --> 00:47:30,730 Calcium, often, because, remember, 962 00:47:30,730 --> 00:47:34,500 they want to get to the Octet rule. 963 00:47:34,500 --> 00:47:36,535 They want to reach their 8 electrons. 964 00:47:36,535 --> 00:47:38,270 But calcium has got 2, what do I do? 965 00:47:38,270 --> 00:47:42,975 Either somebody gives me 6, not going to happen, 966 00:47:42,975 --> 00:47:45,111 or I can lose 2. 967 00:47:45,111 --> 00:47:47,346 And so what you get is that calcium will go, 968 00:47:47,346 --> 00:47:50,282 you know, to Ca2-plus. 969 00:47:50,282 --> 00:47:52,151 But fluorine is still just f-minus. 970 00:47:52,151 --> 00:47:56,322 Right from this I know that the balance stoichiometry, that 971 00:47:56,322 --> 00:47:59,825 is to say how many calcium atoms I need 972 00:47:59,825 --> 00:48:03,529 to stabilize this whole ionic bond situation, 973 00:48:03,529 --> 00:48:04,930 is going to be 2, right? 974 00:48:04,930 --> 00:48:09,201 I got to go to calcium F2. 975 00:48:09,201 --> 00:48:11,570 And if I were going to write this 976 00:48:11,570 --> 00:48:13,973 with emphasizing the ionic bond, I 977 00:48:13,973 --> 00:48:17,143 might put brackets around just so it's really easy to see, 978 00:48:17,143 --> 00:48:17,743 2-plus. 979 00:48:17,743 --> 00:48:19,512 There's no dots left. 980 00:48:19,512 --> 00:48:21,213 Because now I'm writing it in a way where 981 00:48:21,213 --> 00:48:23,949 I've emphasized that-- 982 00:48:23,949 --> 00:48:26,552 gesundheit-- that F took it. 983 00:48:26,552 --> 00:48:27,987 It took it. 984 00:48:27,987 --> 00:48:30,690 And it is minus. 985 00:48:30,690 --> 00:48:34,193 And there's two of them, you see? 986 00:48:34,193 --> 00:48:38,664 So that would be like thinking about an ionic bond, all right, 987 00:48:38,664 --> 00:48:41,434 but from the Lewis-dot vantage point where I really 988 00:48:41,434 --> 00:48:47,673 see that fluorine took the charge, OK? 989 00:48:47,673 --> 00:48:49,308 OK, so I think-- 990 00:48:49,308 --> 00:48:53,145 oh, ho, you could go further. 991 00:48:53,145 --> 00:48:54,080 You can go further. 992 00:48:54,080 --> 00:48:55,214 I think we'll stop there. 993 00:48:55,214 --> 00:48:58,384 And on Wednesday, like I said, we're going Lewis all the way 994 00:48:58,384 --> 00:49:02,488 and we're doing covalent molecules, covalent bonds.