0:00:00.610,0:00:01.350 If you're wondering 0:00:01.350,0:00:08.350 this is how the most revolutionary course[br]in biology of all time begins. 0:00:08.380,0:00:12.169 Come today to learn about covalent and ionic[br]and hydrogen bonds 0:00:12.169,0:00:13.579 What about electron orbitals 0:00:13.579,0:00:14.700 and the octet rule 0:00:14.700,0:00:18.070 and what does it all have to do with a mad[br]man named Gilbert Lewis? 0:00:18.070,0:00:23.170 It's all contained within. 0:00:23.170,0:00:30.170 Hello, I’m Hank 0:00:31.789,0:00:33.970 I assume you’re here because you’re interested[br]in biology 0:00:33.970,0:00:37.370 and if you are, that makes sense because 0:00:37.370,0:00:42.599 like any good 50 Cent song, biology is just[br]about sex and not dying. 0:00:42.600,0:00:45.960 Everyone watching this should be interested[br]in sex and not dying 0:00:45.960,0:00:49.149 being that you are, I assume, a human being. 0:00:49.149,0:00:52.800 I'm going to be teaching this biology course[br]differently than most courses you've ever 0:00:52.800,0:00:53.500 taken in your life 0:00:53.500,0:00:57.130 For example, I'm not going to spend the first[br]class 0:00:57.130,0:00:59.739 talking about how I’m going to spend the[br]rest of class. 0:00:59.739,0:01:02.860 I'm just going to start teaching you, like[br]right about now. 0:01:02.860,0:01:04.890 I may say one more thing before I start teaching. 0:01:04.890,0:01:06.690 Yes, I am going to! 0:01:06.690,0:01:10.720 It's that: if I’m going too fast for you,[br]the great thing about YouTube is 0:01:10.720,0:01:12.770 that you can just rewind. 0:01:12.770,0:01:14.530 Watch stuff over and over again if it's confusing. 0:01:14.530,0:01:17.140 Hopefully, it will become less confusing. 0:01:17.140,0:01:20.360 And you're even allowed to fast forward through[br]the bits that you already know. 0:01:20.360,0:01:23.780 Another tip, you can actually even use the[br]number keys on your keyboard to move around 0:01:23.780,0:01:24.650 in the video. 0:01:24.650,0:01:28.869 And I promise, you can do this to me as much[br]as you want and I'm totally not going to mind. 0:01:28.869,0:01:31.840 A great professor of mine once told me that[br]in order to really understand any topic 0:01:31.840,0:01:36.280 you have to understand a little bit of the[br]level of complexity just below that topic. 0:01:36.280,0:01:39.290 The level of complexity just below biology[br]is chemistry 0:01:39.290,0:01:43.640 unless you're a biochemist in which case you[br]would argue that it's biochemistry. 0:01:43.640,0:01:48.990 Either way, we're gonna have to know a little[br]bit of chemistry in order to get through biology. 0:01:48.990,0:01:51.920 And so THAT, my friends, is where we're going[br]to start. 0:01:51.920,0:01:56.040 I am a collection of organic molecules called[br]Hank Green. 0:01:56.040,0:01:59.229 Organic compounds are a class of compounds[br]that contain carbon. 0:01:59.229,0:02:04.150 And carbon is this sexy little minx on the[br]periodic table 0:02:04.150,0:02:06.479 that's, you know... 0:02:06.479,0:02:08.119 disinterested in monogamy. 0:02:08.119,0:02:09.489 A jezebel. Bit of a tramp. Hussy. 0:02:09.489,0:02:11.920 When I say carbon is small I mean that it's[br]actually 0:02:11.920,0:02:14.500 as an atom, it's a relatively small atom. 0:02:14.500,0:02:18.569 It has 6 protons and 6 neutrons for a total[br]atomic weight of 12. 0:02:18.569,0:02:20.250 Because of that, carbon doesn't take up a[br]lot of space. 0:02:20.250,0:02:25.760 And so carbon can form itself into weird rings,[br]and sheets and spirals 0:02:25.760,0:02:27.599 and double and even triple bonds. 0:02:27.599,0:02:32.790 It can do all sorts of things that could never[br]be accomplished by more bulky atoms. 0:02:32.790,0:02:37.730 It's basically, your atomic equivalent of[br]an olympic gymnast. 0:02:37.730,0:02:42.340 It can only do all of those wonderful, beautiful,[br]elegant things because it's kind of tiny. 0:02:42.340,0:02:44.470 It's also said that carbon is kind 0:02:44.470,0:02:48.160 and that's an interesting sort of thing to[br]say about an atom. 0:02:48.160,0:02:49.560 It's not like some other elements that are[br]just 0:02:49.560,0:02:52.020 desperately trying to do anything they can 0:02:52.020,0:02:53.590 to fill up their electron orbitals. 0:02:53.590,0:02:56.620 No, carbon knows what it's like to be alone,[br]and so it's not all 0:02:56.620,0:02:59.300 “Please! I'll do anything for your electrons!” 0:02:59.300,0:03:02.340 needy like fluorine or chlorine or sodium[br]is. 0:03:02.340,0:03:05.050 Elements like chlorine if you breath them[br]in they like literally tear up your insides 0:03:05.050,0:03:10.150 and sodium, sodium is insane if you put it[br]in water it explodes! 0:03:10.150,0:03:10.950 Carbon though... 0:03:10.950,0:03:11.660 Meh. 0:03:11.660,0:03:15.609 It wants more electrons, but it's not gonna[br]kill to get them. 0:03:15.610,0:03:18.569 It makes and breaks bonds like a 13-year old[br]mall rat. 0:03:18.569,0:03:20.220 And it doesn't even hold a grudge. 0:03:20.220,0:03:26.080 Carbon is also, as I mentioned before, a bit[br]of a tramp, because, it needs four extra electrons 0:03:26.080,0:03:28.790 and so it'll bond with pretty much whoever[br]happens to be nearby 0:03:28.790,0:03:32.679 And also because it needs four electrons,[br]it'll bond with two, or three 0:03:32.680,0:03:35.450 or even four of those things at the same time 0:03:35.450,0:03:39.859 And carbon is willing and interested to bond[br]with lots of different molecules 0:03:39.860,0:03:42.060 like hydrogen, oxygen, phosphorous, nitrogen 0:03:42.060,0:03:43.940 or to other molecules of carbon. 0:03:43.940,0:03:46.230 It can do this in infinite configurations 0:03:46.230,0:03:52.179 allowing it to be the core atom of complicated[br]structures that make living things like ourselves 0:03:52.180,0:03:57.900 because carbon is this perfect mix of small,[br]kind, and a little bit trampy 0:03:57.900,0:04:00.390 life is entirely based on this element. 0:04:00.390,0:04:02.929 Carbon is the foundation of biology. 0:04:02.930,0:04:07.349 It's so fundamental that scientists have a[br]pretty difficult time 0:04:07.349,0:04:10.750 even conceiving of life that isn't based on[br]carbon. 0:04:10.750,0:04:15.159 Life is only possible on earth because carbon[br]is always floating around in our atmosphere 0:04:15.159,0:04:16.709 in the form of carbon dioxide. 0:04:16.709,0:04:19.769 So it's important to note, when I talk about[br]carbon bonding with other elements 0:04:19.769,0:04:23.169 I'm not actually talking about sex, it's just[br]a useful analogy. 0:04:23.169,0:04:29.080 Carbon, on it's own, is an atom with 6 protons,[br]6 neutrons, and 6 electrons. 0:04:29.080,0:04:32.849 Atoms, have electron shells, and they need[br]to have these shells filled 0:04:32.849,0:04:35.099 in order to be happy, fulfilled atoms. 0:04:35.099,0:04:37.779 So carbon, has 6 total electrons, 2 for the[br]first shell 0:04:37.779,0:04:38.729 so it's totally happy 0:04:38.729,0:04:41.650 and 4 of the 8 it needs to fill the second[br]shell. 0:04:41.650,0:04:43.419 Carbon forms a type of bond that we call covalent. 0:04:43.419,0:04:46.369 This is when atoms actually are sharing electrons[br]with each other. 0:04:46.369,0:04:51.020 So in the case of methane, which is pretty[br]much the simplest carbon compound ever. 0:04:51.020,0:04:55.080 Carbon is sharing it's 4 electrons, in it's[br]outer electron shell, with 4 atoms of hydrogen. 0:04:55.080,0:04:59.188 Hydrogen atoms only have 1 electron, so they[br]want their first S orbital filled. 0:04:59.189,0:05:01.759 Carbon shares its 4 electrons with those 4[br]hydrogens 0:05:01.759,0:05:04.599 and those 4 hydrogens each share 1 electron[br]with carbon. 0:05:04.599,0:05:05.490 So everybody's happy. 0:05:05.490,0:05:10.589 In chemistry and biology this is often represented[br]by what we call Lewis dot structures. 0:05:10.589,0:05:16.649 Good lord, I'm in a chair! 0:05:16.649,0:05:19.490 I'm in a chair and there's a book. 0:05:19.490,0:05:21.949 Apparently I have something to tell you that's[br]in this book. 0:05:21.949,0:05:25.869 Which is a book called Lewis: Acids and Bases. 0:05:25.869,0:05:27.180 By Hank Green 0:05:27.180,0:05:30.229 Gilbert Lewis, the guy who thought up Lewis[br]dot structures 0:05:30.229,0:05:33.008 was also the guy behind Lewis Acids and Bases 0:05:33.009,0:05:35.129 and he was nominated for the nobel prize 0:05:35.129,0:05:37.449 35 times. 0:05:37.449,0:05:40.300 This is more nominations than anyone else[br]ever in history. 0:05:40.300,0:05:43.559 And the number of times he won was roughly[br]the same number of times 0:05:43.559,0:05:45.939 that everyone else in the world has won. 0:05:45.939,0:05:46.629 Which is zero. 0:05:46.629,0:05:48.770 Lewis disliked this a great deal. 0:05:48.770,0:05:52.639 It's kind of like a baseball player having[br]more hits than any other player in history 0:05:52.639,0:05:53.460 and no home runs. 0:05:53.460,0:05:56.188 He may have been the most influential chemist[br]of all time. 0:05:56.189,0:06:00.050 He coined the term photon, he revolutionized[br]how we think about acids and bases 0:06:00.050,0:06:02.309 and he produced the first molecule of heavy[br]water. 0:06:02.309,0:06:06.409 He was the first person to conceptualize the[br]covalent bond that we're talking about right 0:06:06.409,0:06:06.659 now. 0:06:06.499,0:06:10.819 Gilbert Lewis died alone in his laboratory[br]while working on cyanide compounds 0:06:10.819,0:06:14.029 after having had lunch with a younger, more[br]charismatic colleague 0:06:14.029,0:06:17.869 who had won the Nobel Prize and who had worked[br]on the Manhattan project. 0:06:17.869,0:06:21.129 Many suspect that he killed himself with the[br]cyanide compounds he was working on 0:06:21.129,0:06:25.029 but the medical examiner said heart attack,[br]without really looking into it. 0:06:25.029,0:06:27.719 I told you all of that because 0:06:27.719,0:06:34.699 the little Lewis dot structure that we use[br]to represent how atoms bond to each other 0:06:34.699,0:06:40.460 is something that was created by a troubled[br]mad genius. 0:06:40.460,0:06:43.989 It's not some abstract scientific thing that's[br]always existed. 0:06:43.990,0:06:45.830 It's a tool that was thought up by a guy 0:06:45.830,0:06:48.568 and it was so useful that we've been using[br]it ever since. 0:06:48.569,0:06:52.179 In biology most compounds can be displayed[br]in Lewis dot structure form 0:06:52.179,0:06:52.998 and here's how that works: 0:06:52.999,0:06:56.869 These structures basically show how atoms[br]bond together to make up molecules. 0:06:56.869,0:06:59.050 And one of the rules of thumb when you're[br]making these diagrams 0:06:59.050,0:07:02.289 is that the elements that we're working with[br]here react with one another in such a way 0:07:02.289,0:07:05.469 that each atom ends up with 8 electrons in[br]it's outermost shell. 0:07:05.469,0:07:07.179 That is called the Octet Rule. 0:07:07.179,0:07:11.628 Because atoms want to complete their octets[br]of electrons to be happy and satisfied. 0:07:11.629,0:07:15.319 Oxygen has 6 electrons in it's octet and needs[br]2 which is why we get H2O 0:07:15.319,0:07:16.809 It can also bond with carbon 0:07:16.809,0:07:17.909 which needs 4. 0:07:17.909,0:07:21.558 So you get 2 double bonds to 2 different oxygen[br]atoms and you end up with CO2. 0:07:21.559,0:07:26.449 That pesky global warming gas and also the[br]stuff that makes all life on Earth possible. 0:07:26.449,0:07:29.809 Nitrogen has 5 electrons in its outer shell.[br]Here's how we count them: 0:07:29.809,0:07:32.949 There are 4 placeholders. Each of them wants[br]2 atoms. 0:07:32.949,0:07:37.349 And like people getting on a bus they prefer[br]to start out not sitting next to each other. 0:07:37.349,0:07:41.050 I'm not kidding about this, they really don't[br]double up until they have to. 0:07:41.050,0:07:44.809 So for maximum happiness, nitrogen bonds with[br]3 hydrogens, forming ammonia. 0:07:44.809,0:07:49.379 Or with 2 hydrogens sticking off another group[br]of atoms, which we call an amino group. 0:07:49.379,0:07:54.489 And if that amino group is bonded to a carbon[br]that is bonded to a carboxylic acid group 0:07:54.489,0:07:56.679 then you have 0:07:56.679,0:07:57.568 an amino acid! 0:07:57.569,0:07:59.149 You've heard of those, right? 0:07:59.149,0:08:03.860 Sometimes electrons are shared equally within[br]a covalent bond like with O2. 0:08:03.860,0:08:09.009 That's called a non-polar covalent bond. But[br]often one of the participants is more greedy. 0:08:09.009,0:08:12.449 In water for example, the oxygen molecule[br]sucks the electrons in 0:08:12.449,0:08:15.649 and they spend more time with the oxygen than[br]with the hydrogens. 0:08:15.649,0:08:18.059 This creates a slight positive charge around[br]the hydrogens 0:08:18.059,0:08:20.309 and a slight negative charge around the oxygen. 0:08:20.309,0:08:25.419 When something has a charge we say that it's[br]polar. It has a positive and negative pole. 0:08:25.419,0:08:27.149 And so it's a polar covalent bond. 0:08:27.149,0:08:31.110 Now let's talk for a moment about a completely[br]different type of bond, which is an ionic 0:08:31.110,0:08:31.610 bond. 0:08:31.610,0:08:34.289 And that's when, instead of sharing electrons 0:08:34.289,0:08:39.059 atoms just completely wholeheartedly donate[br]or accept an electron from another atom 0:08:39.059,0:08:41.549 and then live happily as a charged atom. 0:08:41.549,0:08:43.578 And there is actually no such thing as a charged[br]atom. 0:08:43.578,0:08:46.160 If an atom has a charge, it's an ion. 0:08:46.160,0:08:50.610 Atoms in general prefer to be neutral, but[br]compared with having a full octet, it's not 0:08:50.610,0:08:51.319 that big of a deal. 0:08:51.319,0:08:56.290 Just like we often choose between being emotionally[br]balanced and sexually satisfied 0:08:56.290,0:08:59.849 atoms will sometimes make sacrifices for that[br]octet. 0:08:59.850,0:09:04.240 The most common ionic compound in our daily[br]lives is salt. 0:09:04.240,0:09:05.550 Sodium chloride. NaCl. 0:09:05.550,0:09:09.149 The stuff, despite it's deliciousness, as[br]I mentioned previously 0:09:09.149,0:09:13.449 is made up of two really nasty chemicals.[br]Sodium and chlorine. 0:09:13.449,0:09:17.109 Chlorine is what we call a halogen, which[br]is an element that only needs one electron 0:09:17.110,0:09:18.190 to fulfill it's octet. 0:09:18.190,0:09:23.329 And sodium is an alkaline metal which means[br]that it only has one electron in it's octet. 0:09:23.329,0:09:26.459 So chlorine and sodium are so close to being[br]satisfied 0:09:26.459,0:09:32.420 that they will happily destroy anything in[br]their path in order to fulfill their octet. 0:09:32.420,0:09:36.029 And thus, there's actually no better outcome[br]than just to get 0:09:36.029,0:09:38.930 chlorine and sodium together and have them[br]lovin' on each other. 0:09:38.930,0:09:40.649 They immediately transfer their electrons. 0:09:40.649,0:09:44.199 So that sodium doesn't have it's one extra,[br]and chlorine fills it's octet. 0:09:44.199,0:09:48.089 They become Na+ and Cl- and are so charged[br]that they stick together 0:09:48.089,0:09:50.699 and we call that stickiness an ionic bond. 0:09:50.699,0:09:53.529 And just like if you have two really crazy[br]friends 0:09:53.529,0:09:57.709 it might be good to get them together so that[br]they'll stop bothering you. 0:09:57.709,0:09:59.189 Same thing works with sodium and chlorine. 0:09:59.190,0:10:01.839 You get those two together, and they'll bother[br]no one. 0:10:01.839,0:10:04.720 And suddenly, they don't want to destroy,[br]they just want to be delicious. 0:10:04.720,0:10:06.990 Chemical changes like this are a big deal. 0:10:06.990,0:10:10.649 Remember, chlorine and sodium, just a second[br]ago, were definitely killing you, and now 0:10:10.649,0:10:11.529 they're tasty. 0:10:11.529,0:10:14.930 Now we're coming to the last bond that we're[br]going to discuss 0:10:14.930,0:10:18.699 in our intro to chemistry here and that's[br]the hydrogen bond. 0:10:18.699,0:10:22.290 Imagine that you remember water, I hope that[br]you didn't forget water. 0:10:22.290,0:10:25.319 Since water is stuck together in a polar covalent[br]bond 0:10:25.319,0:10:29.329 the hydrogen bit is positively charge and[br]the oxygen bit is negatively charged. 0:10:29.329,0:10:30.719 So when water molecules are moving around 0:10:30.720,0:10:34.100 we generally think of them as a perfect fluid[br]but they actually stick together a little 0:10:34.100,0:10:34.879 bit. 0:10:34.879,0:10:36.279 Hydrogen side to oxygen side. 0:10:36.279,0:10:40.889 You can actually see this with your eyes if[br]you fill up a glass of water too full 0:10:40.889,0:10:45.310 it will bubble at the top. The water will[br]stick together at the top. 0:10:45.310,0:10:50.060 That's the polar covalent bonds sticking the[br]water molecules to each other 0:10:50.060,0:10:52.550 so that they don't flow right over the top[br]of the glass. 0:10:52.550,0:10:56.139 These relatively weak hydrogen bonds happen[br]in all sorts of chemical compounds 0:10:56.139,0:11:00.199 they don't just happen in water. An they actually[br]play an extremely important role in proteins 0:11:00.199,0:11:04.050 which are the chemicals that pretty much up[br]our entire bodies. 0:11:04.050,0:11:07.829 A final thing to note here is that bonds,[br]even covalent bonds, ionic bonds 0:11:07.829,0:11:09.229 even with their own class 0:11:09.230,0:11:11.759 are often much different strengths. 0:11:11.759,0:11:15.300 And we tend to just write them with a little[br]line 0:11:15.300,0:11:20.490 but that line can represent a very very strong[br]covalent bond or a relatively weak covalent 0:11:20.490,0:11:20.990 bond. 0:11:20.990,0:11:23.110 Sometimes ionic bonds are stronger than covalent[br]bonds 0:11:23.110,0:11:28.069 though that's generally not the case and the[br]strength of covalent bonds varies wildly. 0:11:28.069,0:11:33.180 How these bonds are made and broken is intensely[br]important to life. 0:11:33.180,0:11:37.719 And to our lives. Making and breaking bonds[br]is in fact the key to life itself 0:11:37.720,0:11:43.300 and also the key to death. For example, if[br]you were to ingest some sodium metal. 0:11:43.300,0:11:45.569 Keep this in mind as we move forward through[br]biology: 0:11:45.569,0:11:48.540 Even the sexiest person you have ever met[br]in your life 0:11:48.540,0:11:55.529 is just a collection of organic compounds[br]rambling around in a sack of water. 0:11:55.529,0:11:56.360 Review time! 0:11:56.360,0:11:58.149 Now we have the table of contents 0:11:58.149,0:12:00.079 Which I know is supposed to come at the beginning[br]of things 0:12:00.079,0:12:03.839 But we are revolutionary here we're doing[br]it different 0:12:03.839,0:12:05.870 so you can click on any of the things here 0:12:05.870,0:12:09.560 and you can go back and review what you learned. 0:12:09.560,0:12:10.839 Or didn't learn. 0:12:10.839,0:12:14.139 And if you have questions please please please[br]please please please please 0:12:14.139,0:12:18.629 ask them in the comments and we'll be down[br]there answering them for you. 0:12:18.629,0:12:22.379 So thank you for joining us. 0:12:22.379,0:12:24.660 It was a pleasure, it was a pleasure working[br]with you today.