WEBVTT 00:00:00.000 --> 00:00:07.045 align:middle line:90% [MUSIC PLAYING] 00:00:07.045 --> 00:00:08.920 align:middle line:84% JESSICA HARROP: Hi, I'm Jessica and today I'm 00:00:08.920 --> 00:00:11.560 align:middle line:84% going to be talking about a chemical demonstration I 00:00:11.560 --> 00:00:14.920 align:middle line:90% like to call elements on fire. 00:00:14.920 --> 00:00:17.530 align:middle line:84% Let's watch as MIT's Dr. John Dolhun-- 00:00:17.530 --> 00:00:20.350 align:middle line:84% here he is-- creates a rainbow of colors 00:00:20.350 --> 00:00:22.360 align:middle line:84% at the Cambridge Science Festival. 00:00:22.360 --> 00:00:24.160 align:middle line:84% JOHN DOLHUN: So what I'd like to do 00:00:24.160 --> 00:00:32.400 align:middle line:84% is do a grand finale by actually burning 00:00:32.400 --> 00:00:37.175 align:middle line:84% some elements since we're talking about elements. 00:00:37.175 --> 00:00:46.390 align:middle line:90% 00:00:46.390 --> 00:00:53.800 align:middle line:84% And we're going to have a little rondo music to go with this. 00:00:53.800 --> 00:00:56.140 align:middle line:84% So Clifton can go ahead and do that. 00:00:56.140 --> 00:01:03.540 align:middle line:90% 00:01:03.540 --> 00:01:09.900 align:middle line:84% I've got some lithium, some boron, strontium, sodium, 00:01:09.900 --> 00:01:12.030 align:middle line:90% and potassium. 00:01:12.030 --> 00:01:12.850 align:middle line:90% [MUSIC PLAYING] 00:01:12.850 --> 00:01:16.560 align:middle line:84% So there should be quite a broad spectrum of colors here. 00:01:16.560 --> 00:01:22.657 align:middle line:90% 00:01:22.657 --> 00:01:25.560 align:middle line:84% So the boron is a nice green color. 00:01:25.560 --> 00:01:28.980 align:middle line:90% 00:01:28.980 --> 00:01:31.616 align:middle line:90% The lithium is a beautiful red. 00:01:31.616 --> 00:01:35.790 align:middle line:84% The sodium back here is a yellow. 00:01:35.790 --> 00:01:37.860 align:middle line:84% We've got a little bit of strontium which 00:01:37.860 --> 00:01:40.590 align:middle line:90% is kind of the bluish-red. 00:01:40.590 --> 00:01:43.560 align:middle line:84% I think the blue is probably the methanol. 00:01:43.560 --> 00:01:45.570 align:middle line:84% And the potassium is a little bit 00:01:45.570 --> 00:01:49.410 align:middle line:84% of a violet in with a yellow color. 00:01:49.410 --> 00:01:56.200 align:middle line:90% 00:01:56.200 --> 00:01:57.655 align:middle line:90% Can you see those? 00:01:57.655 --> 00:02:02.774 align:middle line:90% 00:02:02.774 --> 00:02:04.190 align:middle line:84% JESSICA HARROP: So Dr. Dolhun puts 00:02:04.190 --> 00:02:09.199 align:middle line:84% salts of five different elements in watch glasses-- 00:02:09.199 --> 00:02:16.820 align:middle line:84% lithium, boron, strontium, sodium, and potassium. 00:02:16.820 --> 00:02:20.210 align:middle line:84% He also adds a little methanol to each watch glass. 00:02:20.210 --> 00:02:22.640 align:middle line:84% Then he lights them all on fire, and they produce 00:02:22.640 --> 00:02:25.580 align:middle line:90% flames of different colors. 00:02:25.580 --> 00:02:26.940 align:middle line:90% Lithium is red. 00:02:26.940 --> 00:02:28.460 align:middle line:90% Boron is green. 00:02:28.460 --> 00:02:31.010 align:middle line:90% Strontium is a blue-red. 00:02:31.010 --> 00:02:32.890 align:middle line:90% Sodium is yellow. 00:02:32.890 --> 00:02:36.620 align:middle line:84% And potassium is violet with yellow streaks. 00:02:36.620 --> 00:02:37.930 align:middle line:90% So what's happening? 00:02:37.930 --> 00:02:40.070 align:middle line:84% Well, the flame heats up the elements giving them 00:02:40.070 --> 00:02:42.020 align:middle line:90% more thermal energy. 00:02:42.020 --> 00:02:45.170 align:middle line:84% This excites the electrons from their ground or lower energy 00:02:45.170 --> 00:02:48.552 align:middle line:84% state to an excited or higher energy state. 00:02:48.552 --> 00:02:49.760 align:middle line:90% This is what that looks like. 00:02:49.760 --> 00:03:02.410 align:middle line:90% 00:03:02.410 --> 00:03:05.110 align:middle line:84% Since energy cannot be created or destroyed, 00:03:05.110 --> 00:03:10.840 align:middle line:84% any energy that was absorbed by the atom must be emitted again 00:03:10.840 --> 00:03:14.170 align:middle line:84% as the electron returns to the ground state. 00:03:14.170 --> 00:03:17.860 align:middle line:90% This energy is emitted as light. 00:03:17.860 --> 00:03:21.825 align:middle line:84% So why do different elements have different colored flames? 00:03:21.825 --> 00:03:23.950 align:middle line:84% Because the difference in energy between the ground 00:03:23.950 --> 00:03:28.600 align:middle line:84% state and the excited state is unique for each element. 00:03:28.600 --> 00:03:30.830 align:middle line:84% And what does energy have to do with it? 00:03:30.830 --> 00:03:34.210 align:middle line:84% Well the human eye perceives photons or light particles 00:03:34.210 --> 00:03:37.270 align:middle line:84% of different energies as different colors. 00:03:37.270 --> 00:03:39.700 align:middle line:84% So red light is a lower energy than yellow, which 00:03:39.700 --> 00:03:41.350 align:middle line:90% is a lower energy than blue. 00:03:41.350 --> 00:03:43.195 align:middle line:84% Think about it like a rainbow spectrum. 00:03:43.195 --> 00:03:52.030 align:middle line:90% 00:03:52.030 --> 00:03:54.330 align:middle line:84% So energy increases along the spectrum. 00:03:54.330 --> 00:03:56.220 align:middle line:90% Red is low energy light. 00:03:56.220 --> 00:03:58.920 align:middle line:90% And violet is high energy light. 00:03:58.920 --> 00:04:02.490 align:middle line:84% Going back to our atoms' energy levels, 00:04:02.490 --> 00:04:05.310 align:middle line:84% if the difference between the ground state and the excited 00:04:05.310 --> 00:04:09.510 align:middle line:84% state is smaller, the light particle is of lower energy. 00:04:09.510 --> 00:04:12.510 align:middle line:90% And we see that as redder light. 00:04:12.510 --> 00:04:15.630 align:middle line:84% Conversely, if the energy gap is larger, 00:04:15.630 --> 00:04:17.820 align:middle line:84% the light particle is of higher energy. 00:04:17.820 --> 00:04:21.000 align:middle line:90% And we see that as bluer light. 00:04:21.000 --> 00:04:23.940 align:middle line:84% And this is a simplified picture of what's happening. 00:04:23.940 --> 00:04:27.390 align:middle line:84% Each element has a unique set of excited states, which 00:04:27.390 --> 00:04:29.890 align:middle line:84% each leads to a different pattern of light, 00:04:29.890 --> 00:04:33.069 align:middle line:84% which we see as red, green, yellow, et cetera. 00:04:33.069 --> 00:04:34.860 align:middle line:84% [MUSIC PLAYING] Hope you enjoyed the video, 00:04:34.860 --> 00:04:37.040 align:middle line:90% and I'll see you next time. 00:04:37.040 --> 00:05:06.038 align:middle line:90%