0:03 if you're wondering this is how the most
0:06 revolutionary course in biology of all
0:09 time begins come today to learn about
0:12 covalent and ionic and hydrogen bonds
0:13 what about electron orbitals and the
0:15 octet rule and what does it all have to
0:17 do with a madman named gilbert lewis
0:32 hello i'm hank i assume you're here
0:34 because you're interested in biology and
0:37 if you are that makes sense because like
0:40 any good fitty sense song biology is
0:42 just about sex and not dying everyone
0:44 watching this should be interested in
0:47 sex and not dying being that you are i
0:49 assume a human being i'm going to be
0:51 teaching this biology course differently
0:53 than most courses you've ever taken in
0:54 your life for example i'm not going to
0:57 spend the first class talking about how
0:59 i'm going to spend the rest of the class
1:01 i'm just going to start teaching you
1:03 like right about now i might say one
1:05 more thing before i start teaching yes i
1:08 am going to it's that um if i'm going
1:09 too fast for you great thing about
1:12 youtube is that you can just rewind
1:14 watch stuff over and over again if it's
1:15 confusing and hopefully it'll become
1:18 less confusing and you're even allowed
1:19 to fast forward through the bits that
1:20 you already know another tip you can
1:22 actually even use the number keys on
1:23 your keyboard to move around in the
1:26 video and i promise you can do this to
1:28 me as much as you want and i'm totally
1:29 not gonna mind a great professor of mine
1:30 once told me that in order to really
1:32 understand any topic you have to
1:34 understand a little bit of the level of
1:36 complexity just below that topic the
1:38 level of complexity just below biology
1:40 is chemistry and unless you're a
1:42 biochemist in which case you would argue
1:44 that it's biochemistry either way we're
1:46 gonna have to know a little bit of
1:48 chemistry in order to get through
1:51 biology and so that my friends is where
1:52 we're gonna start i am a collection of
1:55 organic molecules called hank green
1:57 organic compounds are class of compounds
1:59 that contain carbon i say carbon is
2:01 small i mean that it's actually you know
2:03 as an atom it's a relatively small atom
2:06 it has six protons and six neutrons for
2:08 a total atomic weight of 12. because of
2:09 that carbon doesn't take up a lot of
2:12 space and so carbon can form itself into
2:15 weird rings and sheets and spirals and
2:17 double and even triple bonds it could do
2:18 all sorts of things that could never be
2:20 accomplished by
2:23 more bulky atoms it's basically uh you
2:26 know you're you're atomic equivalent of
2:28 an olympic gymnast it can only do all of
2:30 those wonderful beautiful elegant things
2:32 because it's kind of tiny also said that
2:34 carbon is kind and that's an interesting
2:37 sort of thing to say about an atom it's
2:38 not like some other elements that are
2:40 just desperately trying to do anything
2:42 they can to fill up their electron
2:44 orbitals no carbon knows what it's like
2:46 to be alone and so it's not all please
2:48 i'll do anything for your electrons
2:50 needy like fluorine or chlorine or
2:52 sodium is elements like chlorine if you
2:53 breathe them in they like literally tear
2:56 up your insides and sodium sodium is
2:57 insane if you if you like put it in
3:00 water it explodes carbon though
3:03 meh it wants more electrons but it's not
3:05 gonna like kill to get them it makes and
3:08 breaks bonds like a 13 year old mall rat
3:09 and it doesn't even hold a grudge carbon
3:12 is also as i mentioned before
3:14 a bit of a because it needs four
3:16 extra electrons and so it'll bond with
3:18 pretty much whoever happens to be nearby
3:20 and also because it needs four electrons
3:22 it'll bond with two or three or even
3:24 four of those things at the same time
3:26 and carbon is you know willing and
3:28 interested to bond with lots of
3:30 different molecules like hydrogen oxygen
3:32 phosphorus nitrogen or to other
3:34 molecules of carbon it can do this in
3:36 infinite configurations allowing it to
3:39 be the core atom of complicated
3:41 structures that make living things like
3:43 ourselves life is entirely based on this
3:45 element carbon is the foundation of
3:47 biology it's so fundamental that
3:50 scientists have a pretty difficult time
3:53 even conceiving of life that isn't based
3:56 on carbon on its own is an atom with six
3:59 protons six neutrons and six electrons
4:01 atoms have electron shells and they need
4:04 to have these shells filled in order to
4:06 be happy fulfilled atoms so carbon has
4:08 six total electrons two for the first
4:10 shell so it's totally happy and four of
4:11 the eight it needs to fill the second
4:12 shell carbon forms the type of bond that
4:15 we call covalent this is when atoms
4:16 actually are sharing electrons with each
4:19 other so in the case of methane which is
4:20 pretty much the simplest carbon compound
4:22 ever carbon is sharing its four
4:24 electrons in its outer electron shell
4:25 with four atoms of hydrogen hydrogen
4:27 atoms only have one electron so they
4:29 want their first s orbital filled carbon
4:31 shares its four electrons with those
4:33 four hydrogens and those four hydrogens
4:35 each share one electron with carbon so
4:36 everybody's happy in chemistry and
4:38 biology this is often represented by
4:41 what we call lewis dot structures [Music]
4:45 [Music]
4:47 good lord i'm in a chair
4:49 i'm in a chair and there's a book
4:50 uh apparently i have something to tell
4:52 you that's in this book
4:54 which is a book called lewis
4:56 asses and bases
4:59 by hank green gilbert lewis the guy who
5:01 thought up lewis dot structures was also
5:04 the guy behind lewis acids and bases and
5:06 he was nominated for the nobel prize
5:09 35 times this is more nominations than
5:11 anyone else ever in history and the
5:13 number of times he won is roughly the
5:15 same number of times that everyone else
5:17 in the world has won which is zero lewis
5:19 disliked this a great deal it's kind of
5:21 like a baseball player having more hits
5:23 than any other player in history and no
5:25 home runs he may have been the most
5:26 influential chemist of all time he
5:28 coined the term photon he revolutionized
5:30 how we think about acids and bases and
5:32 he produced the first molecule of heavy
5:34 water and he was the first person to
5:35 conceptualize the covalent bond that
5:37 we're talking about right now gilbert
5:40 lewis died alone in his laboratory while
5:41 working on cyanide compounds after
5:43 having had lunch with a younger more
5:45 charismatic colleague who had won the
5:46 nobel prize and who had worked on the
5:49 manhattan project many suspect that he
5:50 killed himself with the cyanide
5:52 compounds that he was working on but the
5:54 medical examiner said heart attack
5:56 without really looking into it i told
5:58 you all of that because uh the the
6:00 little lewis dot structure that we use
6:02 to represent
6:06 how uh atoms bond to each other is
6:10 something that was created by a troubled
6:12 mad genius it's not some abstract
6:14 scientific thing that's always existed
6:16 it's a tool that was thought up by a guy
6:18 and it was so useful that we've been
6:20 using it ever since in biology most
6:22 compounds can be displayed in lewis dot
6:23 structure form and here's how that works
6:24 these structures basically show how
6:27 atoms bond together to make up molecules
6:28 and one of the rules of thumb when
6:30 making these diagrams is that the
6:31 elements that we're working with here
6:32 react with one another in such a way
6:34 that each atom ends up with eight
6:36 electrons in its outermost shell that is
6:38 called the octet rule because atoms want
6:40 to complete their octets of electrons to
6:42 be happy and satisfied oxygen has six
6:44 electrons in its octet and needs two
6:46 which is why we get h2o it can also bond
6:48 with carbon which needs four so you get
6:50 two double bonds to two different oxygen
6:52 atoms and you end up with co2 that pesky
6:54 global warming gas and also the stuff
6:56 that makes all life on earth possible
6:58 nitrogen has five electrons in its outer
7:00 shell here's how we count them there are
7:03 four placeholders each of them wants two
7:04 atoms and like people getting on a bus
7:06 they prefer to start out not sitting
7:08 next to each other i'm not kidding about
7:11 this they really don't double up until
7:12 they have so for maximum happiness
7:14 nitrogen bonds with three hydrogens
7:16 forming ammonia or with two hydrogens
7:18 sticking off another group of atoms
7:20 which we call an amino group and if that
7:22 amino group is bonded to a carbon that
7:25 is bonded to a carboxylic acid group
7:28 then you have an amino acid you've heard
7:30 of those right sometimes electrons are
7:32 shared equally within a covalent bond
7:35 like with o2 that's called a nonpolar
7:38 covalent bond but often one of the
7:40 participants is more greedy in water for
7:42 example the oxygen molecule sucks the
7:44 electrons in and they spend more time
7:46 with the oxygen than with the hydrogens
7:47 this creates a slight positive charge
7:49 around the hydrogens and a slight
7:50 negative charge around the oxygen when
7:53 something has a charge we say that it's
7:55 polar it has a positive and negative
7:57 pole and so it's a polar covalent bond
7:58 now let's talk for a moment about a
8:00 completely different type of bond which
8:03 is an ionic bond and that's when instead
8:05 of sharing electrons atoms just
8:08 completely wholeheartedly donate or
8:09 accept an electron from another atom and
8:12 then live happily as a charged atom and
8:13 there actually is no such thing as a
8:15 charged atom if an atom has a charge
8:17 it's an ion atoms in general prefer to
8:19 be neutral but compared with having a
8:20 full octet
8:22 it's not that big of a deal just like we
8:24 often choose between being emotionally
8:27 balanced and sexually satisfied atoms
8:30 will sometimes make sacrifices for that
8:31 octet the most common ionic compound in
8:34 our daily lives is uh salt uh sodium
8:37 chloride nacl this stuff despite its
8:39 deliciousness as i mentioned previously
8:42 is made up of two really nasty chemicals
8:44 sodium and chlorine chlorine is what we
8:46 call a halogen which is an element that
8:47 only needs one electron to fulfill its
8:50 octet and sodium is an alkaline metal
8:52 which means that it only has one
8:54 electron in its octet so chlorine and
8:57 sodium are so close to being satisfied
8:59 that they will happily destroy anything
9:02 in their path in order to fulfill their
9:04 octet and thus there's actually no
9:06 better outcome than just to get chlorine
9:08 and sodium together and have them loving
9:10 on each other they immediately transfer
9:12 their electrons so that sodium doesn't
9:13 have its one extra and chlorine fills
9:16 its octet they become na plus and cl
9:18 minus and are so charged that they stick
9:20 together and we call that stickiness an
9:22 ionic bond and just like if you have two
9:25 really crazy friends it might be good to
9:26 get them together so that they'll stop
9:28 bothering you same thing works with
9:30 sodium and chlorine you get those two
9:32 together and they'll bother no one and
9:34 suddenly they don't want to destroy they
9:35 just want to be delicious chemical
9:36 changes like this are a big freaking
9:39 deal remember chlorine and sodium just a
9:40 second ago were definitely killing you
9:42 and now they're tasty now we're coming
9:44 to the last bond that we're going to
9:47 discuss in our intro to chemistry here
9:49 and that's the hydrogen bond
9:51 imagine that you remember water i hope
9:53 that you didn't forget water since water
9:55 is stuck together in a polar covalent
9:57 bond the hydrogen bit is positively
9:59 charged and the oxygen bit is negatively
10:00 charged so when water molecules are
10:02 moving around we generally think of them
10:03 as a perfect fluid but they actually
10:05 stick together a little bit hydrogen
10:07 side to oxygen side you can actually see
10:09 this with your eyes if you fill up a
10:11 glass of water uh too full it will
10:13 bubble at the top the
10:15 the water will stick together at the top
10:17 these relatively weak hydrogen bonds
10:18 happen in all sorts of chemical
10:20 compounds they don't just happen in
10:21 water and they actually play an
10:23 extremely important role in proteins
10:25 which are the chemicals that pretty much
10:27 make up our entire bodies a final thing
10:30 to note here is that bonds even covalent
10:31 bonds ionic bonds even with their own
10:35 class are often much different strengths
10:37 and we you know tend to just write them
10:39 with a little line but uh that line can
10:41 represent a very very strong covalent
10:43 bond or a relatively weak covalent bond
10:45 sometimes ionic bonds are stronger than
10:47 covalent bonds though that's generally
10:48 not the case and the strength of
10:51 covalent bonds varies wildly how these
10:54 bonds are made and broken is intensely
10:57 important to life and and to our lives
10:59 making and breaking bonds is in fact the
11:03 key to life itself and like also the key
11:05 to death for example if you were to
11:06 ingest some sodium metal keep this in
11:08 mind as we move forward through biology
11:10 even the sexiest person you have ever
11:13 met in your life is just a collection
11:16 of organic compounds rambling around and
11:20 a sack of water review time now we have
11:21 the table of contents what i know is
11:22 supposed to come at the beginning of
11:25 things but we are revolutionary here
11:27 we're doing it different so you can
11:29 click on any of the things here and you
11:32 can go back and review what you learned
11:34 uh or didn't learn and if you have
11:36 questions please please please please
11:38 please please ask them in the comments
11:41 and we'll be down there uh answering
11:43 them for you so uh
11:46 thank you for joining us it was a
11:48 pleasure it was a pleasure working with
