1 00:00:00,000 --> 00:00:07,045 [MUSIC PLAYING] 2 00:00:07,045 --> 00:00:08,920 JESSICA HARROP: Hi, I'm Jessica and today I'm 3 00:00:08,920 --> 00:00:11,560 going to be talking about a chemical demonstration I 4 00:00:11,560 --> 00:00:14,920 like to call elements on fire. 5 00:00:14,920 --> 00:00:17,530 Let's watch as MIT's Dr. John Dolhun-- 6 00:00:17,530 --> 00:00:20,350 here he is-- creates a rainbow of colors 7 00:00:20,350 --> 00:00:22,360 at the Cambridge Science Festival. 8 00:00:22,360 --> 00:00:24,160 JOHN DOLHUN: So what I'd like to do 9 00:00:24,160 --> 00:00:32,400 is do a grand finale by actually burning 10 00:00:32,400 --> 00:00:37,175 some elements since we're talking about elements. 11 00:00:46,390 --> 00:00:53,800 And we're going to have a little rondo music to go with this. 12 00:00:53,800 --> 00:00:56,140 So Clifton can go ahead and do that. 13 00:01:03,540 --> 00:01:09,900 I've got some lithium, some boron, strontium, sodium, 14 00:01:09,900 --> 00:01:12,030 and potassium. 15 00:01:12,030 --> 00:01:12,850 [MUSIC PLAYING] 16 00:01:12,850 --> 00:01:16,560 So there should be quite a broad spectrum of colors here. 17 00:01:22,657 --> 00:01:25,560 So the boron is a nice green color. 18 00:01:28,980 --> 00:01:31,616 The lithium is a beautiful red. 19 00:01:31,616 --> 00:01:35,790 The sodium back here is a yellow. 20 00:01:35,790 --> 00:01:37,860 We've got a little bit of strontium which 21 00:01:37,860 --> 00:01:40,590 is kind of the bluish-red. 22 00:01:40,590 --> 00:01:43,560 I think the blue is probably the methanol. 23 00:01:43,560 --> 00:01:45,570 And the potassium is a little bit 24 00:01:45,570 --> 00:01:49,410 of a violet in with a yellow color. 25 00:01:56,200 --> 00:01:57,655 Can you see those? 26 00:02:02,774 --> 00:02:04,190 JESSICA HARROP: So Dr. Dolhun puts 27 00:02:04,190 --> 00:02:09,199 salts of five different elements in watch glasses-- 28 00:02:09,199 --> 00:02:16,820 lithium, boron, strontium, sodium, and potassium. 29 00:02:16,820 --> 00:02:20,210 He also adds a little methanol to each watch glass. 30 00:02:20,210 --> 00:02:22,640 Then he lights them all on fire, and they produce 31 00:02:22,640 --> 00:02:25,580 flames of different colors. 32 00:02:25,580 --> 00:02:26,940 Lithium is red. 33 00:02:26,940 --> 00:02:28,460 Boron is green. 34 00:02:28,460 --> 00:02:31,010 Strontium is a blue-red. 35 00:02:31,010 --> 00:02:32,890 Sodium is yellow. 36 00:02:32,890 --> 00:02:36,620 And potassium is violet with yellow streaks. 37 00:02:36,620 --> 00:02:37,930 So what's happening? 38 00:02:37,930 --> 00:02:40,070 Well, the flame heats up the elements giving them 39 00:02:40,070 --> 00:02:42,020 more thermal energy. 40 00:02:42,020 --> 00:02:45,170 This excites the electrons from their ground or lower energy 41 00:02:45,170 --> 00:02:48,552 state to an excited or higher energy state. 42 00:02:48,552 --> 00:02:49,760 This is what that looks like. 43 00:03:02,410 --> 00:03:05,110 Since energy cannot be created or destroyed, 44 00:03:05,110 --> 00:03:10,840 any energy that was absorbed by the atom must be emitted again 45 00:03:10,840 --> 00:03:14,170 as the electron returns to the ground state. 46 00:03:14,170 --> 00:03:17,860 This energy is emitted as light. 47 00:03:17,860 --> 00:03:21,825 So why do different elements have different colored flames? 48 00:03:21,825 --> 00:03:23,950 Because the difference in energy between the ground 49 00:03:23,950 --> 00:03:28,600 state and the excited state is unique for each element. 50 00:03:28,600 --> 00:03:30,830 And what does energy have to do with it? 51 00:03:30,830 --> 00:03:34,210 Well the human eye perceives photons or light particles 52 00:03:34,210 --> 00:03:37,270 of different energies as different colors. 53 00:03:37,270 --> 00:03:39,700 So red light is a lower energy than yellow, which 54 00:03:39,700 --> 00:03:41,350 is a lower energy than blue. 55 00:03:41,350 --> 00:03:43,195 Think about it like a rainbow spectrum. 56 00:03:52,030 --> 00:03:54,330 So energy increases along the spectrum. 57 00:03:54,330 --> 00:03:56,220 Red is low energy light. 58 00:03:56,220 --> 00:03:58,920 And violet is high energy light. 59 00:03:58,920 --> 00:04:02,490 Going back to our atoms' energy levels, 60 00:04:02,490 --> 00:04:05,310 if the difference between the ground state and the excited 61 00:04:05,310 --> 00:04:09,510 state is smaller, the light particle is of lower energy. 62 00:04:09,510 --> 00:04:12,510 And we see that as redder light. 63 00:04:12,510 --> 00:04:15,630 Conversely, if the energy gap is larger, 64 00:04:15,630 --> 00:04:17,820 the light particle is of higher energy. 65 00:04:17,820 --> 00:04:21,000 And we see that as bluer light. 66 00:04:21,000 --> 00:04:23,940 And this is a simplified picture of what's happening. 67 00:04:23,940 --> 00:04:27,390 Each element has a unique set of excited states, which 68 00:04:27,390 --> 00:04:29,890 each leads to a different pattern of light, 69 00:04:29,890 --> 00:04:33,069 which we see as red, green, yellow, et cetera. 70 00:04:33,069 --> 00:04:34,860 [MUSIC PLAYING] Hope you enjoyed the video, 71 00:04:34,860 --> 00:04:37,040 and I'll see you next time.