1 00:00:00,000 --> 00:00:07,767 [MUSIC PLAYING] 2 00:00:07,767 --> 00:00:09,100 JESSICA HARROP: Hi, I'm Jessica. 3 00:00:09,100 --> 00:00:11,516 And I'm going to be talking about a chemical demonstration 4 00:00:11,516 --> 00:00:16,090 today that I like to call bringin' home the bacon. 5 00:00:16,090 --> 00:00:18,220 Now, before we get cooking let's take a look 6 00:00:18,220 --> 00:00:20,300 at the chemist's best friend. 7 00:00:20,300 --> 00:00:22,510 This is the periodic table. 8 00:00:22,510 --> 00:00:26,460 It was created in 1869 by the Russian chemist Dmitri 9 00:00:26,460 --> 00:00:31,030 Mendeleev back when only 65 elements were known. 10 00:00:31,030 --> 00:00:32,770 Different elements on the periodic table 11 00:00:32,770 --> 00:00:36,310 require different numbers of electrons to be happy. 12 00:00:36,310 --> 00:00:39,700 Electrons live in the shells surrounding atoms. 13 00:00:39,700 --> 00:00:43,400 And when an atom's outermost shell is filled to capacity, 14 00:00:43,400 --> 00:00:45,100 the atom is happy. 15 00:00:45,100 --> 00:00:50,370 Now hydrogen, over here, has one electron in its outer shell 16 00:00:50,370 --> 00:00:53,110 and needs just one more to fill it. 17 00:00:53,110 --> 00:00:56,650 Carbon has four electrons in its outer shell 18 00:00:56,650 --> 00:01:00,970 and needs four more, a total of eight electrons, to fill it. 19 00:01:00,970 --> 00:01:04,599 Now on the left and middle of the table, we have the metals. 20 00:01:04,599 --> 00:01:07,060 To get to eight electrons in their outer shell, 21 00:01:07,060 --> 00:01:09,440 the metals lose electrons. 22 00:01:09,440 --> 00:01:12,670 And on the right side of the table, we have nonmetals. 23 00:01:12,670 --> 00:01:16,480 To get to eight electrons, these elements gain electrons. 24 00:01:16,480 --> 00:01:18,460 And hydrogen is the only nonmetal 25 00:01:18,460 --> 00:01:21,920 that's on the left hand side of the periodic table. 26 00:01:21,920 --> 00:01:24,940 Now one way atoms get eight electrons in their outer shell 27 00:01:24,940 --> 00:01:26,770 is through chemical bonds. 28 00:01:26,770 --> 00:01:30,800 A bond is the sharing of two electrons between two atoms. 29 00:01:30,800 --> 00:01:32,530 So carbon likes to have four bonds. 30 00:01:32,530 --> 00:01:35,020 And hydrogen likes to have one. 31 00:01:35,020 --> 00:01:37,090 Knowing about where the electrons are 32 00:01:37,090 --> 00:01:39,280 and how they participate in bonding 33 00:01:39,280 --> 00:01:42,770 is central to many important things in the real world. 34 00:01:42,770 --> 00:01:45,850 For example, unsaturated fats have a double bond, 35 00:01:45,850 --> 00:01:47,230 lots of electrons. 36 00:01:47,230 --> 00:01:49,790 And that gives them special reactivity, 37 00:01:49,790 --> 00:01:51,580 which can lead to the spoiling of food 38 00:01:51,580 --> 00:01:53,927 when the bonds react with oxygen. 39 00:01:53,927 --> 00:01:56,260 So we like to know if there are double bonds in our food 40 00:01:56,260 --> 00:01:57,280 molecules. 41 00:01:57,280 --> 00:01:59,770 But how is that determined? 42 00:01:59,770 --> 00:02:04,510 So this is what a happy carbon hydrogen molecule looks like. 43 00:02:04,510 --> 00:02:07,690 But in some cases, there are not enough hydrogen atoms. 44 00:02:07,690 --> 00:02:09,400 And the carbon will have to double bond 45 00:02:09,400 --> 00:02:13,900 with another carbon to share electrons. 46 00:02:13,900 --> 00:02:17,620 This molecule is more reactive than this one 47 00:02:17,620 --> 00:02:19,780 because a carbon-carbon double bond is not 48 00:02:19,780 --> 00:02:23,720 as stable as a carbon-carbon single bond. 49 00:02:23,720 --> 00:02:26,260 Now let's watch as MIT's Dr. John Dolhun 50 00:02:26,260 --> 00:02:29,230 uses bromine to test for the presence of double bonds 51 00:02:29,230 --> 00:02:31,240 in a big ol' slab of bacon. 52 00:02:31,240 --> 00:02:33,520 Here he is at the Cambridge Science Festival. 53 00:02:33,520 --> 00:02:34,230 [WHOOSH] 54 00:02:34,230 --> 00:02:36,271 JOHN DOLHUN: I'm going to trun on my burner here. 55 00:02:42,210 --> 00:02:43,110 OK, there we go. 56 00:02:50,660 --> 00:03:03,704 So I'm going to take my bacon, the fat. 57 00:03:12,180 --> 00:03:14,010 Basically shake it up a bit. 58 00:03:18,730 --> 00:03:21,530 You can see the red color of the bromine is going away. 59 00:03:27,991 --> 00:03:28,990 [WHOOSH] 60 00:03:28,990 --> 00:03:33,730 JESSICA HARROP: So Dr. Dolhun heats up a piece of bacon 61 00:03:33,730 --> 00:03:35,965 and adds it to a flask filled with bromine. 62 00:03:40,300 --> 00:03:42,310 Bromine reacts with anything that has 63 00:03:42,310 --> 00:03:44,260 a carbon-carbon double bond. 64 00:03:44,260 --> 00:03:45,970 This includes the acrolein that's 65 00:03:45,970 --> 00:03:52,120 produced when you cook bacon, which looks like this, 66 00:03:52,120 --> 00:03:54,130 as well as the unsaturated fat that's 67 00:03:54,130 --> 00:03:56,650 already present in the bacon. 68 00:03:56,650 --> 00:03:58,750 Unsaturated fats are fats that have 69 00:03:58,750 --> 00:04:02,570 carbon-carbon double bonds. 70 00:04:02,570 --> 00:04:06,320 Fully saturated fats have no carbon-carbon double bonds. 71 00:04:06,320 --> 00:04:08,690 They're all carbon-carbon single bonds. 72 00:04:08,690 --> 00:04:11,150 And they're the ones that are bad for you. 73 00:04:11,150 --> 00:04:13,490 The breaking of the double bond looks like this. 74 00:04:17,529 --> 00:04:20,220 We can tell that the reaction happens because the red color 75 00:04:20,220 --> 00:04:21,390 disappears. 76 00:04:21,390 --> 00:04:24,480 That's the bromine reacting with those carbon-carbon double 77 00:04:24,480 --> 00:04:26,280 bonds. 78 00:04:26,280 --> 00:04:28,390 In our video recording of the experiment, 79 00:04:28,390 --> 00:04:30,190 it's hard to see the color change. 80 00:04:30,190 --> 00:04:32,130 So watch again very closely. 81 00:04:32,130 --> 00:04:50,346 [WHOOSH] 82 00:04:50,346 --> 00:04:51,470 Hope you enjoyed the video. 83 00:04:51,470 --> 00:04:52,095 [MUSIC PLAYING] 84 00:04:52,095 --> 00:04:53,840 I'll see you next time.