1 00:00:16,483 --> 00:00:17,350 How's everyone doing? 2 00:00:17,350 --> 00:00:18,785 [APPLAUSE] 3 00:00:21,554 --> 00:00:24,224 Parents only, how are you doing? 4 00:00:24,224 --> 00:00:26,026 [APPLAUSE] 5 00:00:26,026 --> 00:00:28,228 How is it that the parents were louder than the kids? 6 00:00:28,228 --> 00:00:30,797 Kids, how are you guys doing? 7 00:00:30,797 --> 00:00:32,499 [APPLAUSE] 8 00:00:32,499 --> 00:00:33,166 All right. 9 00:00:33,166 --> 00:00:34,701 Welcome, parents. 10 00:00:34,701 --> 00:00:35,702 Welcome, parents. 11 00:00:35,702 --> 00:00:39,906 I'm really excited to have you here in class. 12 00:00:39,906 --> 00:00:43,676 This is 3091, Introduction to Solid State Chemistry. 13 00:00:43,676 --> 00:00:46,646 And today we're going to have a little bit of fun. 14 00:00:46,646 --> 00:00:49,349 As you can see, we got some activities. 15 00:00:49,349 --> 00:00:53,319 Now, the way I like to frame this-- 16 00:00:53,319 --> 00:00:54,954 are there any other seats? 17 00:00:54,954 --> 00:00:56,623 No, not so much. 18 00:00:56,623 --> 00:00:58,658 But make yourself comfortable. 19 00:00:58,658 --> 00:01:00,660 The way I like to frame this is you've 20 00:01:00,660 --> 00:01:03,363 got a lot of activities going on already. 21 00:01:03,363 --> 00:01:05,732 This is the parent weekend. 22 00:01:05,732 --> 00:01:07,567 So if we look at-- 23 00:01:07,567 --> 00:01:09,269 why is that happening? 24 00:01:09,269 --> 00:01:12,939 If we look at the-- 25 00:01:12,939 --> 00:01:16,910 oh, that's not good. 26 00:01:16,910 --> 00:01:20,146 OK, there we go. 27 00:01:20,146 --> 00:01:25,385 If we look at the MIT family weekend, there is activities. 28 00:01:25,385 --> 00:01:27,253 And so what I thought is that what 29 00:01:27,253 --> 00:01:28,388 we could do in this class-- 30 00:01:28,388 --> 00:01:29,355 we've got to learn a little bit. 31 00:01:29,355 --> 00:01:31,324 We're going to learn about x-rays today. 32 00:01:31,324 --> 00:01:33,560 But what I thought we could do is also 33 00:01:33,560 --> 00:01:37,764 add some ideas for activities that you all 34 00:01:37,764 --> 00:01:40,033 could do with your kids. 35 00:01:40,033 --> 00:01:41,167 But it doesn't even matter. 36 00:01:41,167 --> 00:01:43,336 It could be with any kids. 37 00:01:43,336 --> 00:01:47,473 But just more activities to do to give you more options. 38 00:01:47,473 --> 00:01:50,043 And so in particular, I've got five suggestions for you 39 00:01:50,043 --> 00:01:51,878 that we'll talk about today. 40 00:01:51,878 --> 00:01:53,813 The first one is staying warm. 41 00:01:53,813 --> 00:01:55,315 It's gotten really cold, so we're 42 00:01:55,315 --> 00:01:57,317 going to talk about staying warm. 43 00:01:57,317 --> 00:01:59,185 And then the next thing we'll do is 44 00:01:59,185 --> 00:02:02,155 we'll appreciate the fall and all the colors. 45 00:02:02,155 --> 00:02:03,323 And we'll cook. 46 00:02:03,323 --> 00:02:05,325 Cooking is such a wonderful thing to do. 47 00:02:05,325 --> 00:02:07,127 I hope you guys can do it together. 48 00:02:07,127 --> 00:02:08,261 We'll talk about that. 49 00:02:08,261 --> 00:02:11,431 And we'll talk about phones and how they crack their screens. 50 00:02:11,431 --> 00:02:13,800 And we have some sort of larger versions 51 00:02:13,800 --> 00:02:16,870 here that we'll talk about. 52 00:02:16,870 --> 00:02:18,538 And of course, it wouldn't be complete 53 00:02:18,538 --> 00:02:20,240 if we didn't blow bubbles, because that's 54 00:02:20,240 --> 00:02:24,644 a really fun activity no matter what age you are. 55 00:02:24,644 --> 00:02:26,079 So that's our plan. 56 00:02:26,079 --> 00:02:28,047 That's our plan today. 57 00:02:28,047 --> 00:02:29,949 Now let's get started. 58 00:02:29,949 --> 00:02:32,185 So let's start with the first activity, 59 00:02:32,185 --> 00:02:33,119 and it's staying warm. 60 00:02:36,555 --> 00:02:42,061 So I love candles, and I think a lot of us have seen candles. 61 00:02:42,061 --> 00:02:47,433 The difference is between everyone else's and your kids 62 00:02:47,433 --> 00:02:49,067 who are in this class who see candles 63 00:02:49,067 --> 00:02:50,136 is they don't see candles. 64 00:02:50,136 --> 00:02:54,274 They see C25 H52 combusting. 65 00:02:54,274 --> 00:02:57,143 And your kids now, when they see a candle-- 66 00:02:57,143 --> 00:02:59,879 if you guys go out to dinner and there's a candle on the table, 67 00:02:59,879 --> 00:03:00,346 the first thing-- 68 00:03:00,346 --> 00:03:01,948 I guarantee you the first thing they're 69 00:03:01,948 --> 00:03:04,651 going to do is assess the volume of the room, 70 00:03:04,651 --> 00:03:08,087 figure out how much oxygen in grams there is in that room, 71 00:03:08,087 --> 00:03:09,489 and they're going to decide which 72 00:03:09,489 --> 00:03:13,293 one is the limiting reagent, the candle or you. 73 00:03:13,293 --> 00:03:14,761 And they'll make a choice. 74 00:03:14,761 --> 00:03:17,897 They may get you out of the room because you don't know. 75 00:03:17,897 --> 00:03:18,898 You've got to know that. 76 00:03:18,898 --> 00:03:21,434 And of course, they'll have their periodic tables with them 77 00:03:21,434 --> 00:03:22,535 at the dinner. 78 00:03:22,535 --> 00:03:25,872 Don't be surprised when they take it out. 79 00:03:25,872 --> 00:03:28,241 Now, your students-- oh, yeah, that's perfect. 80 00:03:28,241 --> 00:03:30,043 Your students also know-- 81 00:03:30,043 --> 00:03:31,811 your kids, my students, your kids-- 82 00:03:31,811 --> 00:03:36,049 also know that a lot of the earliest chemistry, going 83 00:03:36,049 --> 00:03:39,819 all the way back to the times of Democritus thousands of years 84 00:03:39,819 --> 00:03:42,855 ago, the way it started was because people 85 00:03:42,855 --> 00:03:46,926 were breaking things and smashing things and lighting 86 00:03:46,926 --> 00:03:48,127 stuff on fire. 87 00:03:48,127 --> 00:03:50,363 And we've got the whole periodic table in this class, 88 00:03:50,363 --> 00:03:54,934 but we still know that the most fun element of all to light 89 00:03:54,934 --> 00:03:56,603 on fire is the very first. 90 00:03:56,603 --> 00:03:57,670 It's hydrogen. 91 00:03:57,670 --> 00:04:01,040 And so I thought I would show you what that's like. 92 00:04:02,008 --> 00:04:02,609 OK. 93 00:04:02,609 --> 00:04:04,677 So here's hydrogen. 94 00:04:04,677 --> 00:04:09,148 And like I said, this is also-- 95 00:04:09,148 --> 00:04:11,150 it's a way to think about-- 96 00:04:11,150 --> 00:04:12,919 oh, that's a beautiful thing. 97 00:04:12,919 --> 00:04:14,254 Is that a beautiful thing? 98 00:04:14,254 --> 00:04:16,723 I've got to do it again. 99 00:04:16,723 --> 00:04:19,559 And as your kids know, I can do this a lot. 100 00:04:19,559 --> 00:04:22,428 But it's just-- and my hand doesn't-- 101 00:04:22,428 --> 00:04:24,297 I don't feel it because of the heat capacity. 102 00:04:24,297 --> 00:04:25,632 But that's another class. 103 00:04:25,632 --> 00:04:30,270 But what we're interested in is combustion. 104 00:04:30,270 --> 00:04:32,272 So there's that one there, too. 105 00:04:32,272 --> 00:04:37,543 So this is all about the context of staying warm, of course. 106 00:04:37,543 --> 00:04:40,580 You don't need to light hydrogen on fire to stay warm. 107 00:04:40,580 --> 00:04:44,150 But I also have suggested discussion topics. 108 00:04:44,150 --> 00:04:46,486 Because I don't want you just to do these activities. 109 00:04:46,486 --> 00:04:47,553 I want you to be engaged. 110 00:04:47,553 --> 00:04:49,956 It might have been a while since you guys have connected-- 111 00:04:49,956 --> 00:04:52,792 I don't know-- in person. 112 00:04:52,792 --> 00:04:56,229 And so here, maybe you don't know what to say at first. 113 00:04:56,229 --> 00:05:00,500 And so for example, you could talk about balancing chemical 114 00:05:00,500 --> 00:05:01,834 reactions. 115 00:05:01,834 --> 00:05:05,171 You could talk about the concept of a mole. 116 00:05:05,171 --> 00:05:06,873 And you could also talk about limiting 117 00:05:06,873 --> 00:05:10,376 reagents, which are really, really important in life. 118 00:05:10,376 --> 00:05:13,413 So that's my first suggested activity. 119 00:05:13,413 --> 00:05:15,882 Like I said, we'll have five new activities. 120 00:05:15,882 --> 00:05:18,818 That's the first one. 121 00:05:18,818 --> 00:05:21,220 But like I also said, we've got to learn something today. 122 00:05:21,220 --> 00:05:24,557 And students, this is not on the exam, as a reminder. 123 00:05:24,557 --> 00:05:27,060 But we do need to learn what X-rays are. 124 00:05:27,060 --> 00:05:30,029 Because next week, we're going to be shining them on stuff. 125 00:05:30,029 --> 00:05:34,200 So today, we're going to learn about how X-rays are generated. 126 00:05:34,200 --> 00:05:36,536 And it all starts with the very first selfie. 127 00:05:36,536 --> 00:05:37,070 This is it. 128 00:05:37,070 --> 00:05:39,639 Does anybody know who that is? 129 00:05:39,639 --> 00:05:45,445 That is Anna Rontgen. That is the wife of Wilhelm Ronten. 130 00:05:45,445 --> 00:05:48,281 That's the very first X-ray ever taken. 131 00:05:48,281 --> 00:05:49,982 That's the very first X-ray ever taken. 132 00:05:49,982 --> 00:05:56,356 And Wilhelm Rontgen was playing around with cathode ray tubes. 133 00:05:56,356 --> 00:05:57,390 And so he-- 134 00:05:57,390 --> 00:05:58,491 I love this quote of him. 135 00:05:58,491 --> 00:06:00,960 He said, I did not think. 136 00:06:00,960 --> 00:06:02,295 I investigated. 137 00:06:02,295 --> 00:06:03,796 And that's-- now, we think. 138 00:06:03,796 --> 00:06:05,365 Of course we think. 139 00:06:05,365 --> 00:06:07,467 But what we do in this class is we investigate. 140 00:06:07,467 --> 00:06:08,901 We're explorers. 141 00:06:08,901 --> 00:06:10,970 Were explorers of chemistry and how chemistry 142 00:06:10,970 --> 00:06:15,742 connects to what we see in life and what we're doing every day. 143 00:06:15,742 --> 00:06:17,910 And so how did Rontgen do this? 144 00:06:17,910 --> 00:06:18,678 OK. 145 00:06:18,678 --> 00:06:27,186 Well, literally, it was a dark and stormy night, literally. 146 00:06:27,186 --> 00:06:29,889 And he was in the basement in his lab. 147 00:06:29,889 --> 00:06:31,157 That's him. 148 00:06:31,157 --> 00:06:33,926 And it's going to be stormy tomorrow, so you guys could 149 00:06:33,926 --> 00:06:38,398 even try to think about how it felt. And so what he did 150 00:06:38,398 --> 00:06:39,165 is he-- 151 00:06:39,165 --> 00:06:42,168 everybody was playing with these cathode ray tubes. 152 00:06:42,168 --> 00:06:45,004 We learned a lot about cathode ray tubes. 153 00:06:45,004 --> 00:06:49,041 So here, you put some kind of cathode here. 154 00:06:49,041 --> 00:06:51,244 And then there is an anode here, and you hook it up 155 00:06:51,244 --> 00:06:53,312 to a voltage. 156 00:06:53,312 --> 00:06:57,183 And what happens is electrons fly. 157 00:06:57,183 --> 00:07:01,087 This is a cathode ray tube, so it's the CRT. 158 00:07:01,087 --> 00:07:04,757 Electrons will fly off of the cathode and go here. 159 00:07:04,757 --> 00:07:07,126 Now, if they go through the anode, 160 00:07:07,126 --> 00:07:09,695 and then you put a screen here, those 161 00:07:09,695 --> 00:07:12,165 are the very first cathode ray tube experiments. 162 00:07:12,165 --> 00:07:14,200 And we talked about how this led to the discovery 163 00:07:14,200 --> 00:07:16,102 of the electron itself. 164 00:07:16,102 --> 00:07:19,172 But what Rontgen did is he said, now, hold on. 165 00:07:19,172 --> 00:07:20,573 What if I changed-- 166 00:07:20,573 --> 00:07:21,474 I put a voltage here. 167 00:07:21,474 --> 00:07:23,075 What if I amp that up? 168 00:07:23,075 --> 00:07:25,711 What if I just keep going? 169 00:07:25,711 --> 00:07:28,915 Oh, by the way, there is a vacuum inside of here. 170 00:07:28,915 --> 00:07:30,049 There has to be a vacuum. 171 00:07:30,049 --> 00:07:31,918 And if I am the voltage up-- you know what? 172 00:07:31,918 --> 00:07:38,491 Actually, I'm going to put a metal here for the anode. 173 00:07:38,491 --> 00:07:40,426 I'm going to make that some kind of metal, 174 00:07:40,426 --> 00:07:43,663 and I'm going to hit the metal with the electrons. 175 00:07:43,663 --> 00:07:45,264 Now, this is exactly what happened. 176 00:07:45,264 --> 00:07:50,570 What happened is the room glowed. 177 00:07:50,570 --> 00:07:51,871 The room glowed. 178 00:07:51,871 --> 00:07:55,808 So Rontgen had-- showing you there, the lights are off. 179 00:07:55,808 --> 00:07:59,111 The lights are off, but the room was lit. 180 00:07:59,111 --> 00:08:00,279 And he said, oh my goodness. 181 00:08:00,279 --> 00:08:02,014 What is going on here? 182 00:08:02,014 --> 00:08:03,649 What is going on? 183 00:08:03,649 --> 00:08:05,485 And what he decided-- 184 00:08:05,485 --> 00:08:08,454 he literally discovered a new type 185 00:08:08,454 --> 00:08:11,190 of ray, a new type of light ray. 186 00:08:11,190 --> 00:08:13,759 And because he didn't know what to call it-- 187 00:08:13,759 --> 00:08:16,929 he didn't have a name on that dark and stormy night-- 188 00:08:16,929 --> 00:08:22,034 he wrote down the letter x, which he regretted later. 189 00:08:22,034 --> 00:08:23,102 He really did. 190 00:08:23,102 --> 00:08:24,704 Because everybody started calling it-- 191 00:08:24,704 --> 00:08:26,672 he didn't know what to call it, so he called it 192 00:08:26,672 --> 00:08:30,843 an X-ray, which is what happens when 193 00:08:30,843 --> 00:08:33,145 you do this experiment with a very high voltage. 194 00:08:33,145 --> 00:08:39,018 You get rays that came off of this and illuminated the room. 195 00:08:39,018 --> 00:08:40,786 And he said, I don't know what to call it. 196 00:08:40,786 --> 00:08:42,855 I'll put the letter x for now. 197 00:08:42,855 --> 00:08:46,092 And that stuck. 198 00:08:46,092 --> 00:08:48,060 Now, these X-rays are unique. 199 00:08:48,060 --> 00:08:51,063 They're unique because they have very high energy. 200 00:08:51,063 --> 00:08:52,198 They have very high energy. 201 00:08:52,198 --> 00:08:54,000 So the X-ray energies-- 202 00:08:54,000 --> 00:09:04,243 the energies are in the range of 100 eV to 100 KeV. 203 00:09:04,243 --> 00:09:06,379 That's a big energy. 204 00:09:06,379 --> 00:09:07,880 But we know how to go back and forth 205 00:09:07,880 --> 00:09:09,181 between energy and wavelengths. 206 00:09:09,181 --> 00:09:13,085 So we know that that means that the wavelength range is 207 00:09:13,085 --> 00:09:16,856 between 0.01 and 10 nanometers. 208 00:09:16,856 --> 00:09:18,624 And that's what's really important. 209 00:09:18,624 --> 00:09:24,230 You came up with a source that has wavelengths in this very, 210 00:09:24,230 --> 00:09:26,532 very special regime. 211 00:09:26,532 --> 00:09:28,334 This is a very special regime because it's 212 00:09:28,334 --> 00:09:32,138 the distance between atoms. 213 00:09:32,138 --> 00:09:34,674 Now, there's two types of x-rays. 214 00:09:34,674 --> 00:09:42,048 But first, let's-- at the time, you might think, people-- 215 00:09:42,048 --> 00:09:46,152 why wasn't he wearing anything, like at the dentist? 216 00:09:46,152 --> 00:09:47,620 Why wasn't he wearing anything? 217 00:09:47,620 --> 00:09:51,724 They didn't know that radiation could be dangerous. 218 00:09:51,724 --> 00:09:54,026 And so if you look at the time, there 219 00:09:54,026 --> 00:09:57,863 were ads like this for a system to remove the hair. 220 00:09:57,863 --> 00:10:01,634 And it was advertised as effective, safe, and painless. 221 00:10:01,634 --> 00:10:06,405 This is-- those are X-rays, one of the first uses of X-rays. 222 00:10:06,405 --> 00:10:10,710 This is a token to get into a bath that's 223 00:10:10,710 --> 00:10:13,546 called a radium bath. 224 00:10:13,546 --> 00:10:17,750 It's a water bath where you have radium that you either drink 225 00:10:17,750 --> 00:10:21,253 or is in the water itself. 226 00:10:21,253 --> 00:10:24,757 And look at what was happening in Paris. 227 00:10:24,757 --> 00:10:27,393 Radium cure, a fad of Paris society. 228 00:10:27,393 --> 00:10:30,763 Patients play bridge and take tea for two hours daily-- 229 00:10:30,763 --> 00:10:32,131 daily-- in a drawing room. 230 00:10:32,131 --> 00:10:33,599 This is what it says. 231 00:10:33,599 --> 00:10:34,333 December 9th. 232 00:10:34,333 --> 00:10:37,203 The afternoon radium cue is the latest craze in Paris society. 233 00:10:37,203 --> 00:10:40,339 The popularity of the treatment, new to Paris, 234 00:10:40,339 --> 00:10:43,509 has devolved quite suddenly and is due, no doubt, to the fact 235 00:10:43,509 --> 00:10:47,046 that it is exceedingly pleasant. 236 00:10:47,046 --> 00:10:48,881 Oh, France. 237 00:10:48,881 --> 00:10:51,517 Right? 238 00:10:51,517 --> 00:10:52,551 They didn't know. 239 00:10:52,551 --> 00:10:53,352 They didn't know. 240 00:10:53,352 --> 00:10:54,920 And it was the same with these X-rays. 241 00:10:54,920 --> 00:10:56,756 What is this thing? 242 00:10:56,756 --> 00:11:00,126 Well, it turned out it was a very, very important type 243 00:11:00,126 --> 00:11:00,893 of light. 244 00:11:00,893 --> 00:11:03,062 And because of its importance, Ronten 245 00:11:03,062 --> 00:11:06,899 won the first ever Nobel Prize given in physics. 246 00:11:06,899 --> 00:11:11,137 There is an element, number 111, named Roentgenium. 247 00:11:11,137 --> 00:11:14,740 And 60 years later, the DNA was discovered-- 248 00:11:14,740 --> 00:11:17,376 the structure of the DNA, the double helix 249 00:11:17,376 --> 00:11:19,812 was discovered because of X-rays. 250 00:11:19,812 --> 00:11:24,083 So the impact of X-rays is tremendous. 251 00:11:24,083 --> 00:11:26,886 Now, the next activity, as I mentioned, 252 00:11:26,886 --> 00:11:30,222 has to do with enjoying the fall. 253 00:11:30,222 --> 00:11:35,027 Now, the thing is that New England has beautiful colors. 254 00:11:35,027 --> 00:11:37,963 And so if you haven't taken a stroll around the parks, 255 00:11:37,963 --> 00:11:41,100 or maybe you go up to a nice hike-- 256 00:11:41,100 --> 00:11:44,303 you'll see these beautiful colors changing in the leaves. 257 00:11:44,303 --> 00:11:47,139 But the thing is that in our class, your kids, 258 00:11:47,139 --> 00:11:50,276 they don't see that anymore. 259 00:11:50,276 --> 00:11:51,277 No. 260 00:11:51,277 --> 00:11:51,777 They don't. 261 00:11:51,777 --> 00:11:53,746 Because when they see colors, they 262 00:11:53,746 --> 00:11:56,248 think about electron levels. 263 00:11:56,248 --> 00:11:57,450 That's what they think about. 264 00:11:57,450 --> 00:11:58,784 They can't help it. 265 00:11:58,784 --> 00:11:59,785 They cannot help it. 266 00:11:59,785 --> 00:12:03,055 So when they see orange or red, all they're thinking about 267 00:12:03,055 --> 00:12:05,458 is, oh, my goodness, there is an electron level here, 268 00:12:05,458 --> 00:12:07,993 and an electron getting excited, and it's coming back down 269 00:12:07,993 --> 00:12:11,964 and emitting a photon, and how those levels are changing 270 00:12:11,964 --> 00:12:14,467 as you go from one leaf to another, 271 00:12:14,467 --> 00:12:18,771 and how chemistry is at the heart of it all. 272 00:12:18,771 --> 00:12:20,873 Chemistry is at the heart of it all. 273 00:12:20,873 --> 00:12:22,508 And so that's what they're thinking of. 274 00:12:22,508 --> 00:12:23,843 And we can use chemistry. 275 00:12:23,843 --> 00:12:27,913 I don't know if we have the next one ready here. 276 00:12:27,913 --> 00:12:34,754 We can use chemistry not only to change the levels of electrons 277 00:12:34,754 --> 00:12:37,790 that are in this material, which then changes the color of light 278 00:12:37,790 --> 00:12:39,225 that comes off of it-- 279 00:12:39,225 --> 00:12:40,993 it's all about the electrons-- 280 00:12:40,993 --> 00:12:43,095 but we can use chemistry to control 281 00:12:43,095 --> 00:12:45,698 how quickly that happens. 282 00:12:45,698 --> 00:12:48,434 Nature does it on this yearly time scale. 283 00:12:48,434 --> 00:12:52,538 We can do it on any time scale because of chemical kinetics. 284 00:12:52,538 --> 00:12:54,673 So we're going to get that experiment out here 285 00:12:54,673 --> 00:12:56,075 in a second. 286 00:12:56,075 --> 00:12:59,278 Meanwhile-- oh, there it is. 287 00:12:59,278 --> 00:13:01,013 Can we give the helpers a huge hand? 288 00:13:01,013 --> 00:13:03,082 Because they are-- thank you, guys. 289 00:13:03,082 --> 00:13:04,984 [APPLAUSE] 290 00:13:08,154 --> 00:13:08,654 All right. 291 00:13:08,654 --> 00:13:12,124 Now what do I do? 292 00:13:12,124 --> 00:13:13,159 And that's it? 293 00:13:13,159 --> 00:13:14,560 This is pre-mixed? 294 00:13:14,560 --> 00:13:15,194 Oh. 295 00:13:15,194 --> 00:13:15,694 OK. 296 00:13:15,694 --> 00:13:19,698 Now, this is an example of how we can change-- 297 00:13:19,698 --> 00:13:25,971 we can control the color of a material using chemistry. 298 00:13:25,971 --> 00:13:27,640 We can control when-- 299 00:13:27,640 --> 00:13:28,340 do I pour it all? 300 00:13:28,340 --> 00:13:29,375 Do I pour it all? 301 00:13:29,375 --> 00:13:29,875 OK. 302 00:13:29,875 --> 00:13:30,376 Why not? 303 00:13:30,376 --> 00:13:32,545 Yeah. 304 00:13:32,545 --> 00:13:33,045 OK. 305 00:13:33,045 --> 00:13:35,881 Now I want you to focus on the larger bottle. 306 00:13:35,881 --> 00:13:38,651 Nothing is happening. 307 00:13:38,651 --> 00:13:39,819 Keep watching it. 308 00:13:39,819 --> 00:13:41,120 You've got to keep watching it. 309 00:13:45,024 --> 00:13:45,825 See? 310 00:13:45,825 --> 00:13:47,226 That's an example. 311 00:13:47,226 --> 00:13:50,729 But your students, your kids are seeing this and they're saying, 312 00:13:50,729 --> 00:13:53,265 no, it's all about electron levels. 313 00:13:53,265 --> 00:13:56,335 I've got to go and write down those electron levels. 314 00:13:56,335 --> 00:13:59,138 I don't care if it's a Bohr model or a semiconductor 315 00:13:59,138 --> 00:13:59,705 bandgap. 316 00:13:59,705 --> 00:14:01,740 I've got to figure out how that happened. 317 00:14:01,740 --> 00:14:03,108 How did the color change? 318 00:14:03,108 --> 00:14:05,644 I changed the electron levels in the liquid. 319 00:14:05,644 --> 00:14:06,378 That's what I did. 320 00:14:06,378 --> 00:14:07,613 And I controlled the kinetics. 321 00:14:07,613 --> 00:14:13,686 So my suggested topics for this one of discussion-- 322 00:14:13,686 --> 00:14:15,187 chemical kinetics. 323 00:14:15,187 --> 00:14:17,189 Now, we're going to talk about chemical kinetics 324 00:14:17,189 --> 00:14:18,657 later in the fall, but you guys can 325 00:14:18,657 --> 00:14:21,026 get a head start this weekend. 326 00:14:21,026 --> 00:14:22,494 Because that's what happened there. 327 00:14:22,494 --> 00:14:25,264 We controlled when it-- it didn't happen right away. 328 00:14:25,264 --> 00:14:26,465 It happened later. 329 00:14:26,465 --> 00:14:28,133 Why? 330 00:14:28,133 --> 00:14:31,003 Acids and bases, also coming later, get a head start. 331 00:14:31,003 --> 00:14:32,538 And then how to paint with electrons, 332 00:14:32,538 --> 00:14:35,574 because that is what we're doing. 333 00:14:35,574 --> 00:14:38,444 We're changing how electrons interact with the material 334 00:14:38,444 --> 00:14:39,545 to change the color. 335 00:14:39,545 --> 00:14:40,746 We are painting. 336 00:14:40,746 --> 00:14:44,183 And that's what nature is doing with its leaves. 337 00:14:44,183 --> 00:14:48,254 Now, you might be on this walk, and you 338 00:14:48,254 --> 00:14:50,289 might be strolling around, and you might not 339 00:14:50,289 --> 00:14:51,790 go into the countryside. 340 00:14:51,790 --> 00:14:54,860 You might just be down Mass Ave. Now, 341 00:14:54,860 --> 00:14:56,729 if you're walking down Mass Ave from here, 342 00:14:56,729 --> 00:14:58,864 and you go not towards Boston but the other way, 343 00:14:58,864 --> 00:15:00,032 you get to another school. 344 00:15:02,635 --> 00:15:03,369 Now, I've got to-- 345 00:15:06,272 --> 00:15:08,607 I have talked to your kids about this already. 346 00:15:08,607 --> 00:15:10,743 What I want to do right now is address the parents. 347 00:15:14,947 --> 00:15:17,917 You have activities you're going to, right? 348 00:15:17,917 --> 00:15:19,685 And some of them may involve-- 349 00:15:19,685 --> 00:15:21,387 I don't know, a dinner or a party, 350 00:15:21,387 --> 00:15:23,789 or a lot of other parents. 351 00:15:23,789 --> 00:15:27,693 Some of those parents may have kids 352 00:15:27,693 --> 00:15:30,596 that go to the other school. 353 00:15:30,596 --> 00:15:34,433 Now, here's what I want to tell you. 354 00:15:34,433 --> 00:15:44,443 It might not be their fault. It might not be their fault. 355 00:15:44,443 --> 00:15:47,046 I'm just saying we do the best we can as parents. 356 00:15:47,046 --> 00:15:49,014 We do. 357 00:15:49,014 --> 00:15:50,449 We do everything we can. 358 00:15:50,449 --> 00:15:52,184 We did everything right. 359 00:15:52,184 --> 00:15:55,354 And then you realize sometimes, kids 360 00:15:55,354 --> 00:15:56,889 have to make their own mistakes. 361 00:15:59,491 --> 00:16:04,863 So I just-- and the last thing I'll say about this-- 362 00:16:04,863 --> 00:16:10,436 look, be nice, because they're probably going 363 00:16:10,436 --> 00:16:12,805 through a really hard time. 364 00:16:12,805 --> 00:16:16,375 So that's what I want to say about the stroll. 365 00:16:16,375 --> 00:16:17,576 You might wind up down there. 366 00:16:17,576 --> 00:16:19,478 I don't know. 367 00:16:19,478 --> 00:16:22,881 OK, back to our X-rays. 368 00:16:22,881 --> 00:16:25,217 Where were we? 369 00:16:25,217 --> 00:16:27,152 So x-rays are coming off of this metal. 370 00:16:27,152 --> 00:16:28,354 It's super high voltage. 371 00:16:28,354 --> 00:16:29,888 It's a a dark and stormy night. 372 00:16:29,888 --> 00:16:34,259 What happened next is that we had 373 00:16:34,259 --> 00:16:39,264 to figure out what were the properties of this light. 374 00:16:39,264 --> 00:16:41,200 And what we really mean are things 375 00:16:41,200 --> 00:16:43,068 like intensity and wavelength. 376 00:16:43,068 --> 00:16:46,805 Now, I wrote down ranges there. 377 00:16:46,805 --> 00:16:51,844 But basically, what you have with X-rays are two types. 378 00:16:51,844 --> 00:17:00,052 You have type 1, which is called continuous. 379 00:17:00,052 --> 00:17:06,558 And it arises continuous-- 380 00:17:06,558 --> 00:17:07,192 continuous. 381 00:17:07,192 --> 00:17:09,194 And it actually-- this is a pretty good name, 382 00:17:09,194 --> 00:17:13,932 because it's a continuous energy up to a point. 383 00:17:13,932 --> 00:17:15,501 It's a continuous spectrum. 384 00:17:15,501 --> 00:17:16,568 So what do I mean by that? 385 00:17:16,568 --> 00:17:18,537 Well, what I mean by that-- to understand that, 386 00:17:18,537 --> 00:17:20,873 we have to know how we get it. 387 00:17:20,873 --> 00:17:22,907 There are two types of X-rays. 388 00:17:22,907 --> 00:17:24,810 In this first type, what we have is 389 00:17:24,810 --> 00:17:28,079 we have some atoms with a bunch of protons in there. 390 00:17:28,079 --> 00:17:29,915 This is like that metal atom. 391 00:17:29,915 --> 00:17:33,218 And I've shot really high-energy electrons at it. 392 00:17:33,218 --> 00:17:36,989 But that atom has electrons sitting around it. 393 00:17:36,989 --> 00:17:37,689 We know that. 394 00:17:37,689 --> 00:17:41,326 1, 2, 3, 4, 5, 6, 7, 8. 395 00:17:41,326 --> 00:17:42,661 OK, and then again. 396 00:17:42,661 --> 00:17:44,930 And these are the quantum levels. 397 00:17:44,930 --> 00:17:49,501 This would be n equals 3, n equals 2. 398 00:17:49,501 --> 00:17:52,738 And in here, we've got n equals 1. 399 00:17:52,738 --> 00:17:53,806 But now, here's the thing. 400 00:17:53,806 --> 00:17:57,776 I'm shooting high-energy electrons at this atom. 401 00:17:57,776 --> 00:18:01,580 So one of the first things that can happen is nothing at all. 402 00:18:01,580 --> 00:18:05,317 So if I shoot it, say, up here, way away-- 403 00:18:05,317 --> 00:18:08,320 if it's all the way up here going way away from the atom 404 00:18:08,320 --> 00:18:12,991 and doesn't feel it, then it might just come through. 405 00:18:12,991 --> 00:18:15,794 It might have some energy-- call it e0-- 406 00:18:15,794 --> 00:18:17,329 and it just came all the way through. 407 00:18:17,329 --> 00:18:18,864 It didn't interact. 408 00:18:18,864 --> 00:18:20,232 Well, that's kind of boring. 409 00:18:20,232 --> 00:18:25,104 What if I interacted-- what if I'm out here, and I interact-- 410 00:18:25,104 --> 00:18:28,040 I got through some of those outer electrons. 411 00:18:28,040 --> 00:18:29,475 Immediately, what do I see? 412 00:18:29,475 --> 00:18:33,445 If I'm a negative charge, I see this positive charge, 413 00:18:33,445 --> 00:18:36,181 and I'm like, ah, that looks good. 414 00:18:36,181 --> 00:18:38,016 It's an attraction. 415 00:18:38,016 --> 00:18:43,222 And so the electron curves like that. 416 00:18:43,222 --> 00:18:45,891 Now, that means that it accelerated. 417 00:18:45,891 --> 00:18:48,994 This is not a electron stuck in an orbit. 418 00:18:48,994 --> 00:18:49,628 No. 419 00:18:49,628 --> 00:18:52,664 This one was free, and it remained free. 420 00:18:52,664 --> 00:18:55,834 But because it got inside of the electron cloud of the atom, 421 00:18:55,834 --> 00:18:57,202 it saw a a positive charge. 422 00:18:57,202 --> 00:18:59,138 And that bends it, and that accelerates it. 423 00:18:59,138 --> 00:19:03,475 And when something that's charged accelerates, 424 00:19:03,475 --> 00:19:05,811 it gives off a photon. 425 00:19:05,811 --> 00:19:08,313 It gives off a photon. 426 00:19:08,313 --> 00:19:11,483 So that might be some kind of energy 427 00:19:11,483 --> 00:19:16,722 that it has left over that we call e1. 428 00:19:16,722 --> 00:19:20,025 And this would be like the photon 1. 429 00:19:20,025 --> 00:19:23,495 And we know that it's lost energy to the photon. 430 00:19:23,495 --> 00:19:24,763 It's decelerated. 431 00:19:24,763 --> 00:19:27,499 It's decelerated. 432 00:19:27,499 --> 00:19:31,270 So we know that e0 is greater than e1. 433 00:19:31,270 --> 00:19:35,474 But I could have shot another one through, 434 00:19:35,474 --> 00:19:38,510 and this one got even luckier. 435 00:19:38,510 --> 00:19:41,513 These are my electrons, incoming electrons. 436 00:19:41,513 --> 00:19:44,683 This one got even closer to the positive charge, 437 00:19:44,683 --> 00:19:46,919 felt an even stronger attraction, 438 00:19:46,919 --> 00:19:48,520 and decelerated even more. 439 00:19:52,257 --> 00:19:57,863 And so it also emits a photon. 440 00:19:57,863 --> 00:20:01,433 And so we know that e2 must be smaller than e1. 441 00:20:01,433 --> 00:20:04,469 It's left with less energy. 442 00:20:04,469 --> 00:20:07,739 Now, what you're doing is you're decelerating electrons 443 00:20:07,739 --> 00:20:12,544 by having them pass through the cloud of charge of an atom. 444 00:20:12,544 --> 00:20:14,780 And that deceleration emits photons. 445 00:20:14,780 --> 00:20:16,481 And you can see right away what I'm doing 446 00:20:16,481 --> 00:20:19,351 is I'm breaking the electrons. 447 00:20:19,351 --> 00:20:23,121 Well, that's exactly what this kind of radiation is called. 448 00:20:23,121 --> 00:20:28,994 This radiation is, in fact, called Bremsstrahlung. 449 00:20:37,102 --> 00:20:42,474 And that literally means braking radiation. 450 00:20:42,474 --> 00:20:44,676 Braking radiation. 451 00:20:48,914 --> 00:20:51,550 It means breaking. 452 00:20:51,550 --> 00:20:54,219 Well, if I take this very simple picture, 453 00:20:54,219 --> 00:20:58,423 and I try to make a plot-- like I said, if I want to understand 454 00:20:58,423 --> 00:21:00,492 my light, I've got to know about how 455 00:21:00,492 --> 00:21:04,429 it behaves as a function of, say, wavelength or frequency. 456 00:21:04,429 --> 00:21:11,370 And so if you plotted the wavelength with the intensity, 457 00:21:11,370 --> 00:21:13,639 well, you can see right here I'm going to get-- 458 00:21:13,639 --> 00:21:17,276 OK, so I'm going to get some photon that 459 00:21:17,276 --> 00:21:20,779 comes out that has some lambda, and then 460 00:21:20,779 --> 00:21:23,248 another photon that comes out that has another lambda. 461 00:21:23,248 --> 00:21:27,352 But you can see that that electron could have been 462 00:21:27,352 --> 00:21:31,923 braked at any loss of energy. 463 00:21:31,923 --> 00:21:37,729 And so what you get is something that is very continuous 464 00:21:37,729 --> 00:21:39,331 up to a point. 465 00:21:39,331 --> 00:21:41,133 This is the shape that it looks like. 466 00:21:41,133 --> 00:21:43,602 So I can get-- this is lambda. 467 00:21:43,602 --> 00:21:46,071 So if lambda is out there, this would 468 00:21:46,071 --> 00:21:50,776 be like lower energy photons. 469 00:21:50,776 --> 00:21:55,914 And up here, it's higher, higher-energy photons. 470 00:21:59,985 --> 00:22:01,353 Now, these are all x-rays. 471 00:22:01,353 --> 00:22:05,223 They're in this very high-energy range. 472 00:22:05,223 --> 00:22:07,359 But you've got this continuous spectrum. 473 00:22:07,359 --> 00:22:09,561 Because the electron could have been slowed down 474 00:22:09,561 --> 00:22:14,166 in any way except higher than this point. 475 00:22:14,166 --> 00:22:15,400 Why? 476 00:22:15,400 --> 00:22:18,737 Well, that's just determined by how much energy 477 00:22:18,737 --> 00:22:19,971 that initial electron got. 478 00:22:19,971 --> 00:22:25,177 Because you can imagine this point is a special point. 479 00:22:25,177 --> 00:22:32,584 This represents a fully stopped electron, fully braked, 480 00:22:32,584 --> 00:22:34,419 fully stopped electron. 481 00:22:34,419 --> 00:22:39,224 So that incoming electron has transferred all of its energy 482 00:22:39,224 --> 00:22:40,225 to the photon. 483 00:22:40,225 --> 00:22:42,327 And because this is higher energy, 484 00:22:42,327 --> 00:22:43,795 that's as high as it gets. 485 00:22:43,795 --> 00:22:46,131 That makes sense, right? 486 00:22:46,131 --> 00:22:46,765 OK. 487 00:22:46,765 --> 00:22:48,200 We have a name for that too. 488 00:22:48,200 --> 00:22:49,968 That's the Duane Hunt limit. 489 00:22:55,607 --> 00:22:59,511 And basically, it says that the energy of-- 490 00:22:59,511 --> 00:23:08,153 the maximum energy, e max of the photon that can come out 491 00:23:08,153 --> 00:23:13,024 is equal to the electron times the voltage, the charge 492 00:23:13,024 --> 00:23:15,961 of the electron times the voltage across, ev 493 00:23:15,961 --> 00:23:22,768 across the tube, and that that is equal to hc over lambda min. 494 00:23:22,768 --> 00:23:26,405 This is just saying max energy equals hc over min 495 00:23:26,405 --> 00:23:31,543 wavelength, energy wavelength. 496 00:23:31,543 --> 00:23:32,611 So that's one type. 497 00:23:32,611 --> 00:23:33,378 And if I had-- 498 00:23:33,378 --> 00:23:35,480 but now you can see if I shot it, now I'm 499 00:23:35,480 --> 00:23:37,315 bumping up the voltage even more, 500 00:23:37,315 --> 00:23:40,018 and I'm shooting it with higher-energy electrons. 501 00:23:40,018 --> 00:23:43,989 Well, you can imagine that if the electrons I shoot in 502 00:23:43,989 --> 00:23:47,559 have a higher energy, then that point is going 503 00:23:47,559 --> 00:23:52,397 to go in and in like that. 504 00:23:52,397 --> 00:23:56,134 So this would be Bremsstrahlung radiation, 505 00:23:56,134 --> 00:24:02,641 and this would be increasing incident-- inc? 506 00:24:02,641 --> 00:24:03,742 That's not good. 507 00:24:03,742 --> 00:24:08,780 Incident electron energy. 508 00:24:08,780 --> 00:24:15,520 And I will put a box around this so that it's increasing, 509 00:24:15,520 --> 00:24:17,489 that arrow going like that. 510 00:24:17,489 --> 00:24:20,058 So if I shoot it with higher and higher-energy electrons, 511 00:24:20,058 --> 00:24:22,761 I'm still going to have a minimum lambda, 512 00:24:22,761 --> 00:24:24,496 but it's going to get smaller and smaller. 513 00:24:24,496 --> 00:24:27,232 Continuous x-rays. 514 00:24:27,232 --> 00:24:27,833 OK. 515 00:24:27,833 --> 00:24:29,401 That's type 1. 516 00:24:29,401 --> 00:24:32,971 Now, speaking of breaking-- 517 00:24:32,971 --> 00:24:35,707 now, speaking of breaking-- 518 00:24:35,707 --> 00:24:36,208 OK. 519 00:24:36,208 --> 00:24:40,111 Now, here is my third activity, and it's cooking. 520 00:24:40,111 --> 00:24:41,880 And I love cooking, and I hope you do too. 521 00:24:41,880 --> 00:24:43,448 It's a really fun thing to do. 522 00:24:43,448 --> 00:24:46,952 And I think that I love cooking with cast iron. 523 00:24:46,952 --> 00:24:50,689 So maybe you've got a piece of cast iron in your dorm 524 00:24:50,689 --> 00:24:53,959 that you can pull out, and pull out a recipe, 525 00:24:53,959 --> 00:24:55,927 and start making something. 526 00:24:55,927 --> 00:24:57,529 But what I want you to think about-- 527 00:24:57,529 --> 00:24:59,464 and this is the thing-- is your kids, 528 00:24:59,464 --> 00:25:02,167 our students don't see it as cast iron anymore. 529 00:25:02,167 --> 00:25:05,704 They see it as iron with interstitially doped carbon. 530 00:25:05,704 --> 00:25:08,773 That's what they see it as. 531 00:25:08,773 --> 00:25:11,510 And so I want you to see it that way too. 532 00:25:11,510 --> 00:25:13,278 And then that gets you thinking. 533 00:25:13,278 --> 00:25:15,447 How is this cast iron so strong? 534 00:25:15,447 --> 00:25:17,115 And oh, wait, the early chemists-- 535 00:25:17,115 --> 00:25:21,253 I heard they smashed and they lit things on fire. 536 00:25:21,253 --> 00:25:22,821 How could we break this cast iron? 537 00:25:22,821 --> 00:25:24,189 Could it break? 538 00:25:24,189 --> 00:25:25,590 Could it break? 539 00:25:25,590 --> 00:25:27,425 Should we be worried about it? 540 00:25:27,425 --> 00:25:30,295 And so what I think you should do-- oh, yeah, there it is. 541 00:25:30,295 --> 00:25:31,696 Let's take this. 542 00:25:31,696 --> 00:25:32,831 You take the-- 543 00:25:32,831 --> 00:25:34,799 I don't have a pan, but I have this. 544 00:25:34,799 --> 00:25:36,034 Is this filled? 545 00:25:36,034 --> 00:25:37,836 OK. 546 00:25:37,836 --> 00:25:39,371 And you take out a hammer because you 547 00:25:39,371 --> 00:25:42,107 have a hammer in the closet. 548 00:25:42,107 --> 00:25:44,075 And you go like this. 549 00:25:44,075 --> 00:25:46,311 And nothing happens. 550 00:25:46,311 --> 00:25:48,880 And then you do it again. 551 00:25:48,880 --> 00:25:51,182 You say, well, you know what? 552 00:25:51,182 --> 00:25:53,518 Maybe we need to go a little bigger. 553 00:25:53,518 --> 00:25:58,590 And you go into your closet, and you find a sledgehammer. 554 00:25:58,590 --> 00:26:00,292 And you say, you know what? 555 00:26:00,292 --> 00:26:04,529 I think if we just use this handy sledgehammer-- 556 00:26:04,529 --> 00:26:07,299 hopefully not in your dorm-- 557 00:26:07,299 --> 00:26:08,366 then maybe we'll break it. 558 00:26:08,366 --> 00:26:11,436 And so you keep hitting-- 559 00:26:11,436 --> 00:26:13,838 not over the electrical. 560 00:26:13,838 --> 00:26:16,474 And you hit it again. 561 00:26:16,474 --> 00:26:18,577 And I won't use-- 562 00:26:18,577 --> 00:26:21,112 I won't go extreme here, but I will tell you 563 00:26:21,112 --> 00:26:24,082 that I've done it before. 564 00:26:24,082 --> 00:26:25,317 And nothing happens. 565 00:26:25,317 --> 00:26:26,084 Nothing happens. 566 00:26:26,084 --> 00:26:27,452 There's not even a scratch on it. 567 00:26:30,655 --> 00:26:36,161 But these are your kids who go to MIT, not another school. 568 00:26:36,161 --> 00:26:41,366 And they know-- and they know that intermolecular forces 569 00:26:41,366 --> 00:26:42,934 have power. 570 00:26:42,934 --> 00:26:44,202 They've got a lot of power. 571 00:26:44,202 --> 00:26:45,370 And they know about bonding. 572 00:26:45,370 --> 00:26:47,372 And they know about the hydrogen bond, 573 00:26:47,372 --> 00:26:50,475 and the power of the hydrogen bond, and how strong it is, 574 00:26:50,475 --> 00:26:51,543 and why it is. 575 00:26:51,543 --> 00:26:53,812 And then they start thinking about water. 576 00:26:53,812 --> 00:26:57,983 I wonder if we could leverage the power of the hydrogen bond. 577 00:26:57,983 --> 00:27:00,385 Now, do we have liquid nitrogen? 578 00:27:00,385 --> 00:27:01,553 We do. 579 00:27:01,553 --> 00:27:02,053 OK. 580 00:27:04,723 --> 00:27:07,225 So they put it together that we might 581 00:27:07,225 --> 00:27:09,894 be able to leverage that power of the hydrogen. They knew. 582 00:27:09,894 --> 00:27:10,829 They saw the gecko. 583 00:27:10,829 --> 00:27:14,633 They say, the London dispersion lets a gecko climb a wall. 584 00:27:14,633 --> 00:27:16,401 Well, then hydrogen bonds might be what it 585 00:27:16,401 --> 00:27:19,237 takes to break the cast iron. 586 00:27:19,237 --> 00:27:22,374 All that you need is to pull the liquid nitrogen out 587 00:27:22,374 --> 00:27:25,777 of your dorm closet, and-- 588 00:27:25,777 --> 00:27:27,312 yeah, OK. 589 00:27:29,981 --> 00:27:30,915 You want to go ahead? 590 00:27:30,915 --> 00:27:31,416 Yeah. 591 00:27:33,918 --> 00:27:38,089 And fill it with water because you 592 00:27:38,089 --> 00:27:40,625 need to take advantage of the power of the hydrogen bond. 593 00:27:40,625 --> 00:27:44,262 And then let it sit, of course with the blast shield 594 00:27:44,262 --> 00:27:45,897 that you also have handy. 595 00:27:49,868 --> 00:27:50,735 OK. 596 00:27:50,735 --> 00:27:52,504 Well, let's see how this goes. 597 00:27:52,504 --> 00:27:54,105 And we might take a-- 598 00:27:54,105 --> 00:27:56,708 we'll see what happens. 599 00:27:56,708 --> 00:28:02,213 Again, this is a bonding moment. 600 00:28:02,213 --> 00:28:04,983 This is a hydrogen bonding moment. 601 00:28:04,983 --> 00:28:07,118 But this is where the two of you-- 602 00:28:07,118 --> 00:28:09,654 the three of you, the four of you-- it could be a huge group. 603 00:28:09,654 --> 00:28:13,425 This is where you talk about things like the crystal 604 00:28:13,425 --> 00:28:15,627 structure of iron. 605 00:28:15,627 --> 00:28:17,228 This is where you talk about things 606 00:28:17,228 --> 00:28:18,697 like intermolecular forces. 607 00:28:18,697 --> 00:28:20,098 And we've learned them all. 608 00:28:20,098 --> 00:28:22,267 We learned about them all in this class. 609 00:28:22,267 --> 00:28:25,704 Where you talk about the power bonds and the power of the bond 610 00:28:25,704 --> 00:28:29,574 between you as a family. 611 00:28:29,574 --> 00:28:30,308 This is it. 612 00:28:30,308 --> 00:28:35,013 Just do it on this side of the blast shield. 613 00:28:35,013 --> 00:28:35,580 OK. 614 00:28:35,580 --> 00:28:36,581 Now we'll let that sit. 615 00:28:36,581 --> 00:28:39,884 We'll see how that goes. 616 00:28:39,884 --> 00:28:42,487 And OK, yeah. 617 00:28:42,487 --> 00:28:43,221 That's good. 618 00:28:43,221 --> 00:28:45,123 Now, where were we? 619 00:28:45,123 --> 00:28:47,525 Oh, right. 620 00:28:47,525 --> 00:28:49,127 Oh, there's another type of X-ray. 621 00:28:49,127 --> 00:28:51,062 There's another type of X-ray. 622 00:28:51,062 --> 00:28:55,066 And the other type of X-ray-- 623 00:28:55,066 --> 00:28:56,568 that's the only board left. 624 00:29:02,273 --> 00:29:11,449 The other type of X-ray is from a different phenomenon that 625 00:29:11,449 --> 00:29:15,854 also has to do with-- 626 00:29:15,854 --> 00:29:20,592 it also has to do with the atom and the electron. 627 00:29:20,592 --> 00:29:23,394 Because the one type is because the electrons are coming 628 00:29:23,394 --> 00:29:25,130 through this cloud, and they get a little 629 00:29:25,130 --> 00:29:27,398 attracted, and they lose energy, and they give that off 630 00:29:27,398 --> 00:29:28,299 to an X-ray photon. 631 00:29:28,299 --> 00:29:31,936 But see, the other kind comes from a direct excitation, 632 00:29:31,936 --> 00:29:35,774 the same kind that we learned about when 633 00:29:35,774 --> 00:29:38,076 we looked at the Bohr atom. 634 00:29:38,076 --> 00:29:39,477 And so this is drawn here. 635 00:29:39,477 --> 00:29:41,513 Now, there's a very important thing that happens. 636 00:29:41,513 --> 00:29:43,014 As we've learned in this class, when 637 00:29:43,014 --> 00:29:45,517 you go from one area of expertise 638 00:29:45,517 --> 00:29:47,385 to another-- like crystallographers 639 00:29:47,385 --> 00:29:48,353 don't like commas. 640 00:29:48,353 --> 00:29:49,721 They don't like commas. 641 00:29:49,721 --> 00:29:51,356 Don't upset a crystallographer. 642 00:29:51,356 --> 00:29:52,223 It makes no sense. 643 00:29:52,223 --> 00:29:54,159 It's not worth it. 644 00:29:54,159 --> 00:29:57,195 This is the same thing with X-ray specialists. 645 00:29:57,195 --> 00:30:01,099 Don't use n equals 1, n equals 2, n equals 3. 646 00:30:01,099 --> 00:30:03,868 Use KLM, because they prefer that. 647 00:30:03,868 --> 00:30:06,838 So the KLMs there are simply the quantum numbers, 648 00:30:06,838 --> 00:30:08,573 the principle quantum numbers. 649 00:30:08,573 --> 00:30:16,014 So 1 is k, 2 is l, and 3 is m. 650 00:30:16,014 --> 00:30:18,283 And all we're doing is the same kind of excitations 651 00:30:18,283 --> 00:30:20,585 as drawn there very well. 652 00:30:20,585 --> 00:30:23,021 So you see the incident electron comes in, 653 00:30:23,021 --> 00:30:25,423 and now it's got enough energy to excite 654 00:30:25,423 --> 00:30:27,826 one of those core electrons. 655 00:30:27,826 --> 00:30:30,628 It's got enough energy to excite it. 656 00:30:30,628 --> 00:30:33,298 And so what it does is it trades energy with that core electron. 657 00:30:33,298 --> 00:30:36,100 The core electron goes up, and then it comes back down. 658 00:30:36,100 --> 00:30:39,170 Now, if we had, say, an m level-- 659 00:30:39,170 --> 00:30:43,842 so this is n equals 1, 2, 3. 660 00:30:43,842 --> 00:30:45,009 So if we had-- 661 00:30:45,009 --> 00:30:46,010 now I can draw it. 662 00:30:46,010 --> 00:30:50,181 If I had some electron in my k shell, my n equals 1 shell, 663 00:30:50,181 --> 00:30:55,086 and that electron got bumped up to an l shell, well, 664 00:30:55,086 --> 00:30:58,890 now you know-- from our work with the Bohr atom, 665 00:30:58,890 --> 00:31:00,525 you know that when this goes back down, 666 00:31:00,525 --> 00:31:04,062 it's going to emit a photon. 667 00:31:04,062 --> 00:31:06,764 But this is very different now. 668 00:31:06,764 --> 00:31:08,199 This is very different. 669 00:31:08,199 --> 00:31:12,036 This photon has only that energy, nothing in between. 670 00:31:12,036 --> 00:31:13,438 It's not continuous. 671 00:31:13,438 --> 00:31:14,806 I'm getting used to wearing this. 672 00:31:14,806 --> 00:31:16,274 It feels good. 673 00:31:16,274 --> 00:31:17,475 It feels pretty good. 674 00:31:20,278 --> 00:31:23,581 So I could have had an electron-- 675 00:31:23,581 --> 00:31:26,384 instead of going to the l level, maybe it went all the way up 676 00:31:26,384 --> 00:31:27,919 to the m level. 677 00:31:27,919 --> 00:31:31,389 And then from there, it cascades back down, 678 00:31:31,389 --> 00:31:34,659 and it emits a photon. 679 00:31:34,659 --> 00:31:36,661 And the way this works in terms of labeling 680 00:31:36,661 --> 00:31:42,700 is because it goes down to the k level, these are k photons. 681 00:31:42,700 --> 00:31:44,302 And we go in order. 682 00:31:44,302 --> 00:31:46,571 So this is the least energy k photon. 683 00:31:46,571 --> 00:31:47,872 It ended in k. 684 00:31:47,872 --> 00:31:57,448 So that's a k alpha or k-- 685 00:31:57,448 --> 00:32:00,785 I'll just write it out to be clear-- k beta. 686 00:32:00,785 --> 00:32:02,687 Oh, I hear sizzling. 687 00:32:02,687 --> 00:32:05,990 Oh, that's because you're pouring. 688 00:32:05,990 --> 00:32:07,926 That's good. 689 00:32:07,926 --> 00:32:10,929 More liquid nitrogen is never a bad thing. 690 00:32:10,929 --> 00:32:12,363 That's great. 691 00:32:12,363 --> 00:32:13,264 No, no, I'm good. 692 00:32:13,264 --> 00:32:14,599 You guys are doing such a good-- 693 00:32:14,599 --> 00:32:16,834 now, OK. 694 00:32:16,834 --> 00:32:20,038 So if it's k beta-- because it went to k, it ended at k. 695 00:32:20,038 --> 00:32:20,972 It gave off a photon. 696 00:32:20,972 --> 00:32:25,576 The photon is either alpha, beta, gamma, 697 00:32:25,576 --> 00:32:26,544 depending on which one. 698 00:32:26,544 --> 00:32:30,615 But now here's the thing. 699 00:32:30,615 --> 00:32:36,321 You know if you go back to that plot of energy-- 700 00:32:36,321 --> 00:32:38,756 of lambda versus intensity, well, you 701 00:32:38,756 --> 00:32:40,825 know that there's nothing in between. 702 00:32:40,825 --> 00:32:43,394 There are no electronic states in here. 703 00:32:43,394 --> 00:32:45,697 So you can't excite in between. 704 00:32:45,697 --> 00:32:47,632 This is forbidden. 705 00:32:47,632 --> 00:32:48,299 It's forbidden. 706 00:32:48,299 --> 00:32:52,070 So unlike the braking kind of radiation, in this case, 707 00:32:52,070 --> 00:32:55,173 it's very, very discrete. 708 00:32:55,173 --> 00:32:57,675 And so now, if we plot what you get from this, 709 00:32:57,675 --> 00:33:01,512 well, you're going to get a k alpha peak that's very, very 710 00:33:01,512 --> 00:33:05,116 discrete, and you're going to get a k beta peak that's only 711 00:33:05,116 --> 00:33:10,855 at the one energy that is the difference 712 00:33:10,855 --> 00:33:14,592 between these levels, k alpha k beta. 713 00:33:14,592 --> 00:33:15,626 So that's another kind. 714 00:33:15,626 --> 00:33:18,563 This is a type 2. 715 00:33:18,563 --> 00:33:23,368 This is second type of X-ray. 716 00:33:27,338 --> 00:33:29,574 OK. 717 00:33:29,574 --> 00:33:33,644 It sounded interesting. 718 00:33:33,644 --> 00:33:35,546 We'll let it keep going. 719 00:33:35,546 --> 00:33:37,115 We'll let it keep going. 720 00:33:37,115 --> 00:33:39,050 It's good because it gives you a time. 721 00:33:39,050 --> 00:33:42,687 And I hope-- you guys can just leave it. 722 00:33:42,687 --> 00:33:46,024 I hope that during this time that you're here 723 00:33:46,024 --> 00:33:49,227 doing these activities, don't have your phones. 724 00:33:49,227 --> 00:33:50,495 Put them down. 725 00:33:50,495 --> 00:33:54,999 Listen to the sounds of cast iron popping. 726 00:33:54,999 --> 00:33:57,568 You can't appreciate it if you're on your phone 727 00:33:57,568 --> 00:34:01,439 tweeting it or DMing it. 728 00:34:01,439 --> 00:34:03,241 You can't do that. 729 00:34:03,241 --> 00:34:04,275 It's not going to happen. 730 00:34:04,275 --> 00:34:07,412 It won't be as much of a bond. 731 00:34:07,412 --> 00:34:08,478 Did I get it right? 732 00:34:08,478 --> 00:34:09,981 No? 733 00:34:09,981 --> 00:34:11,783 OK. 734 00:34:11,783 --> 00:34:14,552 So we got our second type of X-ray, and it's discreet. 735 00:34:14,552 --> 00:34:16,754 And we're going to put them together in a minute. 736 00:34:16,754 --> 00:34:19,056 But first, we've got to talk about glass. 737 00:34:19,056 --> 00:34:22,726 Now-- oh, more. 738 00:34:22,726 --> 00:34:23,928 OK. 739 00:34:23,928 --> 00:34:25,530 Good. 740 00:34:25,530 --> 00:34:26,496 Good. 741 00:34:26,496 --> 00:34:29,467 Keep going. 742 00:34:29,467 --> 00:34:30,501 Oh, glass. 743 00:34:30,501 --> 00:34:33,471 That's perfect. 744 00:34:33,471 --> 00:34:35,505 The thing is that-- 745 00:34:35,505 --> 00:34:38,009 well, a lot of times this happens to your phone. 746 00:34:38,009 --> 00:34:41,379 And we know about crystals in this glass. 747 00:34:41,379 --> 00:34:42,647 And this is the one-- 748 00:34:42,647 --> 00:34:45,550 if you were willing to pay hundreds of dollars more 749 00:34:45,550 --> 00:34:48,953 for your iWatch, you can get a quartz screen. 750 00:34:48,953 --> 00:34:49,587 This is quartz. 751 00:34:49,587 --> 00:34:50,987 This is what we know now. 752 00:34:50,987 --> 00:34:52,456 We don't look at the Apple ad. 753 00:34:52,456 --> 00:34:55,626 We look at this in this class. 754 00:34:55,626 --> 00:34:56,293 I'm good. 755 00:34:56,293 --> 00:34:58,763 We're good. 756 00:34:58,763 --> 00:35:00,331 Yeah, thank you. 757 00:35:00,331 --> 00:35:02,834 And so we can hand this out because we 758 00:35:02,834 --> 00:35:05,470 like to touch and feel the chemistry in this class. 759 00:35:05,470 --> 00:35:07,004 That is quartz. 760 00:35:07,004 --> 00:35:07,772 That is quartz. 761 00:35:07,772 --> 00:35:09,941 That's not glass, by the way. 762 00:35:09,941 --> 00:35:12,210 And that's another thing we're going to learn. 763 00:35:12,210 --> 00:35:15,012 Glass means amorphous. 764 00:35:15,012 --> 00:35:16,848 It means not crystalline. 765 00:35:16,848 --> 00:35:17,915 It means not crystalline. 766 00:35:17,915 --> 00:35:19,517 That's the thing on the right. 767 00:35:19,517 --> 00:35:22,019 Now, quartz has a lot of really great properties. 768 00:35:22,019 --> 00:35:23,321 It's a very strong material. 769 00:35:23,321 --> 00:35:26,224 But it's a lot more expensive, which is why this happens. 770 00:35:26,224 --> 00:35:32,730 And you've got all this glass, this amorphous SIO2 that is-- 771 00:35:32,730 --> 00:35:33,931 oh, that was a good one. 772 00:35:36,667 --> 00:35:40,671 Yeah, I see water coming out. 773 00:35:40,671 --> 00:35:42,740 But there are ways to try to make 774 00:35:42,740 --> 00:35:47,178 that stronger, to try to make the amorphous SIO2 stronger. 775 00:35:47,178 --> 00:35:49,814 And there's no better way to think about-- 776 00:35:49,814 --> 00:35:52,650 and I don't want you to break your phone. 777 00:35:52,650 --> 00:35:57,255 But if you think-- speaking of phones-- 778 00:35:57,255 --> 00:35:59,223 if you think about glass, you're probably 779 00:35:59,223 --> 00:36:00,791 thinking about baseball. 780 00:36:00,791 --> 00:36:02,393 And if you're thinking about baseball, 781 00:36:02,393 --> 00:36:05,096 you're thinking about the Red Sox, of course. 782 00:36:05,096 --> 00:36:05,863 Right? 783 00:36:05,863 --> 00:36:06,597 Am I right? 784 00:36:09,233 --> 00:36:11,802 And so I brought glass, and I want 785 00:36:11,802 --> 00:36:13,437 to think about how glass breaks. 786 00:36:13,437 --> 00:36:15,673 That's what we're going to study in a couple of weeks 787 00:36:15,673 --> 00:36:16,274 in this class. 788 00:36:16,274 --> 00:36:17,909 But I thought let's bring this to life. 789 00:36:17,909 --> 00:36:19,343 But I need some volunteers, and I'd 790 00:36:19,343 --> 00:36:20,878 like some parents to come down. 791 00:36:20,878 --> 00:36:23,948 I need some baseball arms, some people who 792 00:36:23,948 --> 00:36:26,250 can throw this at the glass. 793 00:36:26,250 --> 00:36:26,918 It's OK. 794 00:36:26,918 --> 00:36:27,218 Come on. 795 00:36:27,218 --> 00:36:28,019 I need some volunteers. 796 00:36:28,019 --> 00:36:28,553 Come on down. 797 00:36:28,553 --> 00:36:30,054 There you go. 798 00:36:30,054 --> 00:36:35,459 You don't look quite like a parent, but it's OK. 799 00:36:35,459 --> 00:36:37,728 All right. 800 00:36:37,728 --> 00:36:38,229 OK. 801 00:36:38,229 --> 00:36:42,200 Now, OK. 802 00:36:42,200 --> 00:36:44,802 We need to get-- let's get you a little further back. 803 00:36:44,802 --> 00:36:49,106 And we're going to have you put this on. 804 00:36:49,106 --> 00:36:50,975 This is for aim. 805 00:36:50,975 --> 00:36:54,111 And what I want you to try to do is 806 00:36:54,111 --> 00:36:56,581 throw this as hard as you can at that piece of glass 807 00:36:56,581 --> 00:36:57,715 on the left. 808 00:36:57,715 --> 00:36:58,616 Can you do that? 809 00:36:58,616 --> 00:36:59,183 All right. 810 00:36:59,183 --> 00:37:00,284 Really let it go. 811 00:37:00,284 --> 00:37:01,052 Now, hold on. 812 00:37:01,052 --> 00:37:02,220 Hold on. 813 00:37:02,220 --> 00:37:03,955 Let's move you right over here. 814 00:37:03,955 --> 00:37:07,792 The one on the left right there as hard as you can. 815 00:37:07,792 --> 00:37:08,659 OK, that's all right. 816 00:37:08,659 --> 00:37:09,594 Try it again. 817 00:37:09,594 --> 00:37:11,495 We get multiple tries here. 818 00:37:11,495 --> 00:37:12,630 We'll take turns. 819 00:37:12,630 --> 00:37:14,065 We'll take turns. 820 00:37:14,065 --> 00:37:15,132 OK. 821 00:37:15,132 --> 00:37:15,666 Try again. 822 00:37:19,904 --> 00:37:20,404 OK. 823 00:37:20,404 --> 00:37:21,372 That was good. 824 00:37:21,372 --> 00:37:23,007 I think we need to try a little harder. 825 00:37:23,007 --> 00:37:24,475 One more time, and then we'll get-- 826 00:37:24,475 --> 00:37:27,311 what parent? 827 00:37:27,311 --> 00:37:30,548 That's the annealed one, isn't it? 828 00:37:30,548 --> 00:37:31,983 Last year it didn't break, either. 829 00:37:31,983 --> 00:37:33,217 Thank you very much. 830 00:37:33,217 --> 00:37:34,685 Who's next? 831 00:37:34,685 --> 00:37:36,687 I need a volunteer. 832 00:37:36,687 --> 00:37:38,556 Come on down. 833 00:37:38,556 --> 00:37:40,958 Oh, you look too happy not to try. 834 00:37:40,958 --> 00:37:42,727 You look too happy not to try. 835 00:37:42,727 --> 00:37:45,229 Can you hand those to this gentleman right here? 836 00:37:45,229 --> 00:37:45,763 All right. 837 00:37:45,763 --> 00:37:46,564 Come on down. 838 00:37:46,564 --> 00:37:50,334 Now, we're going after that piece of glass on the left. 839 00:37:50,334 --> 00:37:53,004 And we're going to see if it's a good piece of glass 840 00:37:53,004 --> 00:37:54,272 for your phone. 841 00:37:54,272 --> 00:37:54,772 OK? 842 00:37:57,441 --> 00:37:58,075 All right. 843 00:37:58,075 --> 00:38:01,012 Let's let it rip. 844 00:38:01,012 --> 00:38:02,480 Oh, yeah. 845 00:38:02,480 --> 00:38:03,614 That's all right. 846 00:38:03,614 --> 00:38:04,448 Try again. 847 00:38:04,448 --> 00:38:05,683 Try again. 848 00:38:05,683 --> 00:38:06,350 Multiple tries. 849 00:38:13,524 --> 00:38:15,626 You've got this. 850 00:38:15,626 --> 00:38:16,861 Oh. 851 00:38:16,861 --> 00:38:19,330 That's very strong glass. 852 00:38:19,330 --> 00:38:20,665 Try one more time. 853 00:38:26,837 --> 00:38:28,072 Really? 854 00:38:28,072 --> 00:38:29,173 OK. 855 00:38:29,173 --> 00:38:30,941 Let's try the one on the right there. 856 00:38:30,941 --> 00:38:32,910 Let's see if that one breaks. 857 00:38:32,910 --> 00:38:35,146 We might have them reversed. 858 00:38:35,146 --> 00:38:36,314 We don't have them reversed? 859 00:38:36,314 --> 00:38:37,048 No? 860 00:38:37,048 --> 00:38:37,214 All right. 861 00:38:37,214 --> 00:38:38,015 Let's try that one. 862 00:38:40,718 --> 00:38:41,852 OK. 863 00:38:41,852 --> 00:38:43,721 All right. 864 00:38:43,721 --> 00:38:45,456 Thank you very much. 865 00:38:45,456 --> 00:38:48,426 [APPLAUSE] 866 00:38:51,395 --> 00:38:56,067 Now, does anyone else want to try? 867 00:38:56,067 --> 00:38:58,836 Apparently we have very unbreakable glass. 868 00:38:58,836 --> 00:39:03,341 Maybe we've invented something new here at MIT. 869 00:39:03,341 --> 00:39:04,141 The sledgehammer? 870 00:39:04,141 --> 00:39:06,577 Oh, that's a great idea. 871 00:39:06,577 --> 00:39:07,578 No. 872 00:39:07,578 --> 00:39:09,313 But there's a reason for it. 873 00:39:09,313 --> 00:39:13,084 Because, see, what we're going to learn is that baseballs 874 00:39:13,084 --> 00:39:15,152 aren't the only way-- even though this is Boston, 875 00:39:15,152 --> 00:39:15,886 the Red Sox-- 876 00:39:15,886 --> 00:39:17,755 it's not the only way to break glass. 877 00:39:17,755 --> 00:39:20,791 Now, I don't know what's going on with this one. 878 00:39:20,791 --> 00:39:21,759 This is tempered. 879 00:39:21,759 --> 00:39:23,861 That means that it's been treated. 880 00:39:23,861 --> 00:39:25,296 It's been treated so that it's got 881 00:39:25,296 --> 00:39:28,599 super strong mechanical strength this way. 882 00:39:28,599 --> 00:39:30,368 You saw that it didn't break. 883 00:39:30,368 --> 00:39:33,771 Of course, neither did that. 884 00:39:33,771 --> 00:39:36,240 But when a glass is tempered, as we'll realize, 885 00:39:36,240 --> 00:39:38,342 it has to do with putting certain chemistry 886 00:39:38,342 --> 00:39:40,978 inside the glass, ions, that are bigger, 887 00:39:40,978 --> 00:39:43,047 that causes a strain in the material, that 888 00:39:43,047 --> 00:39:45,082 tighten the surface. 889 00:39:45,082 --> 00:39:47,451 And so there's all this stress built up, 890 00:39:47,451 --> 00:39:49,820 and it's all at the very edge. 891 00:39:49,820 --> 00:39:52,390 So this part is super, super strong. 892 00:39:52,390 --> 00:39:56,594 But this part, just a simple little tap-- 893 00:39:56,594 --> 00:39:59,530 I didn't even-- I barely even touched it. 894 00:39:59,530 --> 00:40:01,465 And so that is-- 895 00:40:04,301 --> 00:40:09,206 now, so the moral of that story is 896 00:40:09,206 --> 00:40:12,877 glass might be stronger than you think, I guess, in this one. 897 00:40:12,877 --> 00:40:17,348 And also, don't tap the edges of glass, 898 00:40:17,348 --> 00:40:18,983 especially if it's tempered. 899 00:40:18,983 --> 00:40:22,319 Because that's what makes it so tough on this on the surface. 900 00:40:22,319 --> 00:40:23,754 But the strain builds up. 901 00:40:23,754 --> 00:40:28,426 And if you relieve it with just a tiny, little tap, boom. 902 00:40:28,426 --> 00:40:33,197 Now, where were we? 903 00:40:33,197 --> 00:40:36,667 Discussion topics-- crystal versus glass, 904 00:40:36,667 --> 00:40:39,570 ordered versus disordered, substitutional dopants. 905 00:40:39,570 --> 00:40:40,971 That's how to temper glass. 906 00:40:40,971 --> 00:40:42,873 That's what's in your iPhone glass. 907 00:40:42,873 --> 00:40:46,177 And of course, the Red Sox, which are on tonight. 908 00:40:46,177 --> 00:40:47,611 And you should watch game three. 909 00:40:47,611 --> 00:40:53,551 Now, the thing about these peaks is that these 910 00:40:53,551 --> 00:40:56,220 are called characteristic. 911 00:40:56,220 --> 00:41:00,257 And what's nice about them is, in fact, that no matter what, 912 00:41:00,257 --> 00:41:01,892 they only depend-- 913 00:41:01,892 --> 00:41:04,695 I don't care how much energy I send in. 914 00:41:04,695 --> 00:41:08,799 These peaks only depend on the metal atom. 915 00:41:08,799 --> 00:41:13,070 So Ronten put in a metal, and he'd always get the same peaks 916 00:41:13,070 --> 00:41:15,573 if I give it enough energy. 917 00:41:15,573 --> 00:41:17,808 Maybe I don't have enough energy to excite anything 918 00:41:17,808 --> 00:41:18,442 from down here. 919 00:41:18,442 --> 00:41:19,810 Then you don't get these peaks. 920 00:41:19,810 --> 00:41:21,579 You still get Bremsstrahlung, but you don't 921 00:41:21,579 --> 00:41:23,547 get the characteristic peaks. 922 00:41:23,547 --> 00:41:25,449 They're called characteristic because they're 923 00:41:25,449 --> 00:41:26,817 characteristic of the metal. 924 00:41:26,817 --> 00:41:28,752 Now they're dependent on the chemistry. 925 00:41:28,752 --> 00:41:30,221 If I put in different metal in, I'm 926 00:41:30,221 --> 00:41:32,490 going to get different Peaks 927 00:41:32,490 --> 00:41:34,992 And so with these two types of X-rays, 928 00:41:34,992 --> 00:41:38,929 I've got a new kind of light that I can shine on materials. 929 00:41:38,929 --> 00:41:41,065 I've got a new kind of light that I can shine. 930 00:41:41,065 --> 00:41:43,501 And the light-- when I plot it all together, 931 00:41:43,501 --> 00:41:53,410 it might look something like this where maybe these are 932 00:41:53,410 --> 00:41:55,012 the peaks-- 933 00:41:55,012 --> 00:41:55,779 uh oh. 934 00:41:55,779 --> 00:41:56,480 OK. 935 00:41:56,480 --> 00:41:59,483 Maybe these are the peaks due to going down to K, 936 00:41:59,483 --> 00:42:02,486 and these are the ones due to going down to L. 937 00:42:02,486 --> 00:42:08,425 So those are K, and these are L. and the rest is continuous, 938 00:42:08,425 --> 00:42:09,793 and they're on top of each other. 939 00:42:09,793 --> 00:42:11,061 And I get it all. 940 00:42:11,061 --> 00:42:13,797 But with that new kind of light, I can do new things. 941 00:42:13,797 --> 00:42:14,865 And that's very important. 942 00:42:14,865 --> 00:42:19,003 And that's what we're going to do after the exam, which 943 00:42:19,003 --> 00:42:20,604 is on Monday. 944 00:42:20,604 --> 00:42:22,439 The exam. 945 00:42:22,439 --> 00:42:25,476 Don't forget about the exam. 946 00:42:25,476 --> 00:42:26,977 You're doing all these activities. 947 00:42:26,977 --> 00:42:30,214 You've got to think about the exam. 948 00:42:30,214 --> 00:42:32,449 Why is this important? 949 00:42:32,449 --> 00:42:34,718 This is important because we will 950 00:42:34,718 --> 00:42:39,256 be shining x-rays as a source of light onto crystals. 951 00:42:39,256 --> 00:42:41,892 And there's a very important thing 952 00:42:41,892 --> 00:42:44,061 that happens when you shine light onto something. 953 00:42:44,061 --> 00:42:45,296 And you can see it here. 954 00:42:45,296 --> 00:42:46,430 Light is a wave. 955 00:42:46,430 --> 00:42:47,798 Light is a particle. 956 00:42:47,798 --> 00:42:48,632 Light is a wave. 957 00:42:48,632 --> 00:42:49,500 Light is a particle. 958 00:42:49,500 --> 00:42:51,669 Have that discussion too. 959 00:42:51,669 --> 00:42:55,072 But here we're looking at it as a wave, and waves diffract. 960 00:42:55,072 --> 00:42:59,243 That means that they can add or cancel each other, right 961 00:42:59,243 --> 00:43:00,344 like water waves. 962 00:43:00,344 --> 00:43:02,046 But it depends on the size of the thing 963 00:43:02,046 --> 00:43:03,113 they're interacting with. 964 00:43:03,113 --> 00:43:05,149 If the size of the thing they're interacting with 965 00:43:05,149 --> 00:43:07,918 is the same as the wavelength of light, 966 00:43:07,918 --> 00:43:10,454 then you can get a diffraction pattern. 967 00:43:10,454 --> 00:43:13,724 And so when we shine X-rays, which 968 00:43:13,724 --> 00:43:15,859 have wavelengths that are the same 969 00:43:15,859 --> 00:43:20,297 as the spacing between planes in a crystal, 970 00:43:20,297 --> 00:43:21,465 well, then it interacts. 971 00:43:21,465 --> 00:43:22,967 And it can diffract. 972 00:43:22,967 --> 00:43:27,037 And that allows us to determine the structure of the crystal. 973 00:43:27,037 --> 00:43:29,139 That's called X-ray diffraction. 974 00:43:29,139 --> 00:43:31,575 And this is how it all started. 975 00:43:31,575 --> 00:43:34,445 It started with the Bragg father and son 976 00:43:34,445 --> 00:43:36,747 pair, who actually said in their paper 977 00:43:36,747 --> 00:43:40,951 the crystal is, in fact, acting as a diffraction grating. 978 00:43:40,951 --> 00:43:44,388 And from that, you can literally tell us which kind of crystal 979 00:43:44,388 --> 00:43:45,656 it is. 980 00:43:45,656 --> 00:43:48,726 I want to point something out here. 981 00:43:48,726 --> 00:43:51,028 That's a father and son. 982 00:43:51,028 --> 00:43:54,732 They both won the Nobel Prize together for this discovery. 983 00:43:54,732 --> 00:43:59,169 Now, I'm not putting pressure on you guys. 984 00:43:59,169 --> 00:44:01,739 I'm just saying it's not all about the kids. 985 00:44:01,739 --> 00:44:03,207 The parents got to step up too. 986 00:44:05,776 --> 00:44:06,944 So that's Bragg defraction. 987 00:44:06,944 --> 00:44:08,612 And that is one of the most-- 988 00:44:08,612 --> 00:44:10,247 X-ray diffraction-- what we're going 989 00:44:10,247 --> 00:44:12,583 to do with these powerful sources of light, 990 00:44:12,583 --> 00:44:14,151 this is one of the most important ways 991 00:44:14,151 --> 00:44:16,920 to characterize crystals that we have. 992 00:44:16,920 --> 00:44:19,990 And just as a reminder, I mentioned the exam. 993 00:44:19,990 --> 00:44:22,226 Don't forget-- this is what we're talking about. 994 00:44:22,226 --> 00:44:24,928 These planes-- notice the negative. 995 00:44:24,928 --> 00:44:27,097 Remember the 1, 1 bar? 996 00:44:27,097 --> 00:44:29,800 Don't forget about negative directions. 997 00:44:29,800 --> 00:44:31,935 These are the things that we're diffracting off of, 998 00:44:31,935 --> 00:44:34,505 literally the crystal planes. 999 00:44:34,505 --> 00:44:36,674 So just a reminder not to forget about that. 1000 00:44:36,674 --> 00:44:40,611 But I can't end by talking about exam one, 1001 00:44:40,611 --> 00:44:43,380 so I have to end with something happy. 1002 00:44:43,380 --> 00:44:46,183 And bubbles always make us happy, always. 1003 00:44:46,183 --> 00:44:47,217 I love blowing bubbles. 1004 00:44:47,217 --> 00:44:47,985 I always will. 1005 00:44:47,985 --> 00:44:49,620 I always have. 1006 00:44:49,620 --> 00:44:51,989 But we don't just blow bubbles in this class. 1007 00:44:51,989 --> 00:44:53,490 We don't just blow bubbles. 1008 00:44:53,490 --> 00:44:57,528 We really blow bubbles. 1009 00:44:57,528 --> 00:45:02,599 And so what we're going to do is we're 1010 00:45:02,599 --> 00:45:04,568 going to show you how we like to blow bubbles. 1011 00:45:04,568 --> 00:45:05,903 You want to do this? 1012 00:45:05,903 --> 00:45:07,871 You go ahead. 1013 00:45:07,871 --> 00:45:10,708 Now, what we like to do is we like to really blow 1014 00:45:10,708 --> 00:45:12,276 bubbles in this class. 1015 00:45:12,276 --> 00:45:15,679 And so we're going to use exothermic reactions 1016 00:45:15,679 --> 00:45:16,714 to blow bubbles. 1017 00:45:16,714 --> 00:45:20,217 And I think that's really a good way-- 1018 00:45:20,217 --> 00:45:21,385 you go ahead. 1019 00:45:21,385 --> 00:45:22,519 You go ahead. 1020 00:45:22,519 --> 00:45:24,855 You're the one. 1021 00:45:24,855 --> 00:45:25,355 All right. 1022 00:45:30,694 --> 00:45:33,097 That's the only way to blow bubbles. 1023 00:45:33,097 --> 00:45:38,001 That's combining an exothermic reaction with bubbles. 1024 00:45:38,001 --> 00:45:40,270 That's happiness right there in a bottle. 1025 00:45:40,270 --> 00:45:42,039 That is happiness. 1026 00:45:42,039 --> 00:45:43,040 That is happiness. 1027 00:45:43,040 --> 00:45:45,909 [APPLAUSE] 1028 00:45:45,909 --> 00:45:48,145 Oh, yes, and look at this-- 1029 00:45:48,145 --> 00:45:49,580 success. 1030 00:45:49,580 --> 00:45:50,714 Success. 1031 00:45:50,714 --> 00:45:54,351 The power of the hydrogen bond. 1032 00:45:54,351 --> 00:45:55,018 OK. 1033 00:45:55,018 --> 00:45:58,222 I hope you guys have a fantastic weekend, 1034 00:45:58,222 --> 00:46:01,325 and I hope you enjoy yourselves and follow 1035 00:46:01,325 --> 00:46:03,260 some of these discussions. 1036 00:46:03,260 --> 00:46:04,194 [APPLAUSE]