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