Why carbon is a tramp발음듣기
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Why carbon is a tramp
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출처 : 칸아카데미
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If you are, that makes sense, because like any good 50 Cent song, Biology is just about sex and not dying, and everyone watching this should be interested in sex and not dying, being that you are, I assume, a human being.발음듣기
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I'm gonna teach this biology course a little differently than most courses you've ever experienced.발음듣기
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For example, I'm not going to spend the first class talking about how I'm going to teach the class.발음듣기
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First, I just wanted to say if I'm going to fast for you, the great thing about me being a video and not a person is that you can always go back and listen to what I've said again.발음듣기
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A great professor of mine once told me that in order to understand any topic, you only really need to understand a bit of the level of complexity just below that topic.발음듣기
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The level of complexity just below biology is chemistry, or if you're a biochemist, you would probably argue that it's biochemistry, so we need to know a little bit more about chemistry, and that is where we're gonna start.발음듣기
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An organic compound is more or less any chemical that contains carbon, and carbon is awesome.발음듣기
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Because of that, carbon does not take up a lot of space and can form itself into elegant shapes. It can form rings.발음듣기
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It can form spirals and sheets and all kinds of really awesome things that bigger molecules would never manage to do.발음듣기
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It can only do the remarkable and beautiful things it can do because it's petite. Second, carbon is kind.발음듣기
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It's not like other elements that desperately want to gain or lose or share electrons to get the exact number they want.발음듣기
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No, carbon knows what it's like to be lonely, so it's not all, "I can't live without your electrons."발음듣기
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This is why chlorine tears apart your insides if you breathe it in gaseous form, and why sodium metal, if ingested, will explode. Carbon, though, eh.발음듣기
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It makes and breaks bonds like a 13-year-old mall rat, but it doesn't ever really hold a grudge.발음듣기
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Third, carbon loves to bond because it needs 4 extra electrons, so it will bond with whoever happens to be nearby.발음듣기
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It can do this in infinite configurations, allowing it to be the core element of the complicated structures that make living things like ourselves.발음듣기
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So fundamental that scientists have a hard time even conceiving of life that is not carbon-based.발음듣기
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Silicon, which is analogous to carbon in many ways, is often cited as a potential element for alien life to be based on, but it's bulkier, so it doesn't form the same elegant shapes as carbon.발음듣기
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It's also not found in any gases, meaning that life would have to be formed by eating solid silicon, whereas life here on earth is only possible because carbon is constantly floating around in the air in the form of carbon dioxide.발음듣기
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Atoms have electron shells, and they need or want to have these shells filled, in order to be happy, fulfilled atoms.발음듣기
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These are bonds where the atoms actually share electrons, so the simplest carbon compound ever, methane, is carbon sharing 4 electrons with 4 hydrogen atoms.발음듣기
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Carbon shares its 4 electrons with those 4 hydrogens, and those 4 hydrogens each share 1 electron with carbon, so everybody's happy.발음듣기
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Gilbert Lewis, also the guy behind Lewis acids and bases, was nominated for the Nobel Prize 35 times and won none.발음듣기
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This is more nominations than anyone else in history, and roughly the same number of wins as everyone else.발음듣기
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He produced the first the first molecule of heavy water, and he was the first person to conceptualize the covalent bond that we're talking about right now.발음듣기
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He was forced to resign from many important posts, and was also passed up for the Manhattan Project, so while all of his colleagues worked to save his country, Lewis wrote a horrible novel.발음듣기
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Lewis died alone in his laboratory while working on cyanide compounds after having had lunch with a younger, more charismatic colleague who had won the Nobel prize and worked on the Manhattan Project.발음듣기
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Many suspect that he killed himself with the cyanide compounds that he was working on, but the medical examiner said heart attack without really looking into it.발음듣기
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I told you all that because, well, the little Lewis structure that I'm about to show you was created by a deeply troubled genius.발음듣기
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Someone, somewhere, thought it up, and it was such a marvelously useful tool, that we've been using it ever since.발음듣기
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One of the rules of thumb when making these diagrams is that some elements tend to react with each other in such a way that each atom ends up with 8 electrons in its outermost shell.발음듣기
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That's called the octet rule, because these atoms want to complete their octets of electrons to be happy and satisfied.발음듣기
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It can also bond with carbon, which needs 4, so 2 double bonds to 2 different oxygen atoms, you end up with CO2, that pesky global warming gas, and also the stuff that plants and, thus, all life are made of.발음듣기
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Nitrogen has 5 electrons in its outer shell. Here's how we count them. There are four placeholders.발음듣기
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Each wants two atoms, and like people getting on a bus, they prefer to start out not sitting next to each other. I'm not kidding about this.발음듣기
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We count it out. 1, 2, 3, 4, 5. So, for maximum happiness, nitrogen bonds with 3 hydrogens, forming ammonia, or with 2 hydrogens, sticking off another group of atoms which we call an amino group.발음듣기
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And if that amino group is bonded to a carbon that is bonded to a carboxylic acid group, you have an amino acid.발음듣기
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In water, for example, the oxygen molecule sucks the electorns in, and they spend more time around the oxygen than around the hydrogens.발음듣기
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This creates a slight positive charge around the hydrogens and a slight negative charge around the oxygen.발음듣기
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Ionic bonds occur when instead of sharing electrons, atoms just donate or accept an electron from another atom completely and then live happily as a charged atom or ion.발음듣기
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Atoms would, in general, prefer to be neutral but compared with having the full electron shells is not that big of a deal.발음듣기
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The most common ionic compound in our daily lives? that would be good old table salt, NaCl, sodium chloride, but don't be fooled by its deliciousness.발음듣기
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Chlorine is a halogen, or an element that only needs one proton to fill its octet, while sodium is an alkali metal, an element that only has one electron in its octet.발음듣기
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They will happily tear apart any chemical compound they come in contact with, searching to satisfy the octet rule.발음듣기
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They immediately transfer electrons so sodium doesn't have its extra and the chlorine fills its octet.발음듣기
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They become Na+ and Cl-, and are so charged that they stick together, and that stickiness is what we call an ionic bond.발음듣기
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Since water is stuck together with a polar covalent bond, the hydrogen bit of it is a little bit positively-charged and the oxygen is a little negatively-charged.발음듣기
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When water molecules move around, they actually stick together a little bit, hydrogen side to oxygen side.발음듣기
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It's important to note here, bonds, even when they're written with dashes or solid lines, or no lines at all, are not the same strength.발음듣기
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Sometimes ionic bonds are stronger than covalent bonds, though that's the exception rather than the rule, and covalent bond strength varies hugely.발음듣기
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The way that those bonds get made and broken is intensely important to how life and our lives operate.발음듣기
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Even the hottest person you have ever met is just a bunch of chemicals rambling around in a bag of water.발음듣기
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