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