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If you're wondering

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this is how the most revolutionary course
in biology of all time begins.

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Come today to learn about covalent and ionic
and hydrogen bonds

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What about electron orbitals

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and the octet rule

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and what does it all have to do with a mad
man named Gilbert Lewis?

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It's all contained within.

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Hello, I’m Hank

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I assume you’re here because you’re interested
in biology

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and if you are, that makes sense because

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like any good 50 Cent song, biology is just
about sex and not dying.

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Everyone watching this should be interested
in sex and not dying

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being that you are, I assume, a human being.

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I'm going to be teaching this biology course
differently than most courses you've ever

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taken in your life

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For example, I'm not going to spend the first
class

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talking about how I’m going to spend the
rest of class.

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I'm just going to start teaching you, like
right about now.

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I may say one more thing before I start teaching.

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Yes, I am going to!

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It's that: if I’m going too fast for you,
the great thing about YouTube is

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that you can just rewind.

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Watch stuff over and over again if it's confusing.

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Hopefully, it will become less confusing.

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And you're even allowed to fast forward through
the bits that you already know.

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Another tip, you can actually even use the
number keys on your keyboard to move around

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in the video.

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And I promise, you can do this to me as much
as you want and I'm totally not going to mind.

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A great professor of mine once told me that
in order to really understand any topic

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you have to understand a little bit of the
level of complexity just below that topic.

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The level of complexity just below biology
is chemistry

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unless you're a biochemist in which case you
would argue that it's biochemistry.

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Either way, we're gonna have to know a little
bit of chemistry in order to get through biology.

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And so THAT, my friends, is where we're going
to start.

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I am a collection of organic molecules called
Hank Green.

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Organic compounds are a class of compounds
that contain carbon.

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And carbon is this sexy little minx on the
periodic table

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that's, you know...

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disinterested in monogamy.

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A jezebel. Bit of a tramp. Hussy.

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When I say carbon is small I mean that it's
actually

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as an atom, it's a relatively small atom.

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It has 6 protons and 6 neutrons for a total
atomic weight of 12.

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Because of that, carbon doesn't take up a
lot of space.

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And so carbon can form itself into weird rings,
and sheets and spirals

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and double and even triple bonds.

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It can do all sorts of things that could never
be accomplished by more bulky atoms.

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It's basically, your atomic equivalent of
an olympic gymnast.

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It can only do all of those wonderful, beautiful,
elegant things because it's kind of tiny.

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It's also said that carbon is kind

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and that's an interesting sort of thing to
say about an atom.

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It's not like some other elements that are
just

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desperately trying to do anything they can

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to fill up their electron orbitals.

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No, carbon knows what it's like to be alone,
and so it's not all

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“Please! I'll do anything for your electrons!”

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needy like fluorine or chlorine or sodium
is.

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Elements like chlorine if you breath them
in they like literally tear up your insides

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and sodium, sodium is insane if you put it
in water it explodes!

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Carbon though...

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Meh.

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It wants more electrons, but it's not gonna
kill to get them.

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It makes and breaks bonds like a 13-year old
mall rat.

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And it doesn't even hold a grudge.

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Carbon is also, as I mentioned before, a bit
of a tramp, because, it needs four extra electrons

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and so it'll bond with pretty much whoever
happens to be nearby

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And also because it needs four electrons,
it'll bond with two, or three

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or even four of those things at the same time

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And carbon is willing and interested to bond
with lots of different molecules

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like hydrogen, oxygen, phosphorous, nitrogen

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or to other molecules of carbon.

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It can do this in infinite configurations

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allowing it to be the core atom of complicated
structures that make living things like ourselves

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because carbon is this perfect mix of small,
kind, and a little bit trampy

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life is entirely based on this element.

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Carbon is the foundation of biology.

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It's so fundamental that scientists have a
pretty difficult time

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even conceiving of life that isn't based on
carbon.

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Life is only possible on earth because carbon
is always floating around in our atmosphere

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in the form of carbon dioxide.

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So it's important to note, when I talk about
carbon bonding with other elements

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I'm not actually talking about sex, it's just
a useful analogy.

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Carbon, on it's own, is an atom with 6 protons,
6 neutrons, and 6 electrons.

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Atoms, have electron shells, and they need
to have these shells filled

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in order to be happy, fulfilled atoms.

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So carbon, has 6 total electrons, 2 for the
first shell

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so it's totally happy

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and 4 of the 8 it needs to fill the second
shell.

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Carbon forms a type of bond that we call covalent.

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This is when atoms actually are sharing electrons
with each other.

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So in the case of methane, which is pretty
much the simplest carbon compound ever.

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Carbon is sharing it's 4 electrons, in it's
outer electron shell, with 4 atoms of hydrogen.

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Hydrogen atoms only have 1 electron, so they
want their first S orbital filled.

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Carbon shares its 4 electrons with those 4
hydrogens

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and those 4 hydrogens each share 1 electron
with carbon.

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So everybody's happy.

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In chemistry and biology this is often represented
by what we call Lewis dot structures.

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Good lord, I'm in a chair!

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I'm in a chair and there's a book.

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Apparently I have something to tell you that's
in this book.

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Which is a book called Lewis: Acids and Bases.

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By Hank Green

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Gilbert Lewis, the guy who thought up Lewis
dot structures

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was also the guy behind Lewis Acids and Bases

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and he was nominated for the nobel prize

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35 times.

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This is more nominations than anyone else
ever in history.

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And the number of times he won was roughly
the same number of times

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that everyone else in the world has won.

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Which is zero.

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Lewis disliked this a great deal.

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It's kind of like a baseball player having
more hits than any other player in history

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and no home runs.

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He may have been the most influential chemist
of all time.

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He coined the term photon, he revolutionized
how we think about acids and bases

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and he produced the first molecule of heavy
water.

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He was the first person to conceptualize the
covalent bond that we're talking about right

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now.

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Gilbert Lewis died alone in his laboratory
while working on cyanide compounds

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after having had lunch with a younger, more
charismatic colleague

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who had won the Nobel Prize and who had worked
on the Manhattan project.

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Many suspect that he killed himself with the
cyanide compounds he was working on

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but the medical examiner said heart attack,
without really looking into it.

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I told you all of that because

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the little Lewis dot structure that we use
to represent how atoms bond to each other

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is something that was created by a troubled
mad genius.

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It's not some abstract scientific thing that's
always existed.

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It's a tool that was thought up by a guy

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and it was so useful that we've been using
it ever since.

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In biology most compounds can be displayed
in Lewis dot structure form

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and here's how that works:

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These structures basically show how atoms
bond together to make up molecules.

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And one of the rules of thumb when you're
making these diagrams

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is that the elements that we're working with
here react with one another in such a way

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that each atom ends up with 8 electrons in
it's outermost shell.

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That is called the Octet Rule.

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Because atoms want to complete their octets
of electrons to be happy and satisfied.

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Oxygen has 6 electrons in it's octet and needs
2 which is why we get H2O

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It can also bond with carbon

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which needs 4.

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So you get 2 double bonds to 2 different oxygen
atoms and you end up with CO2.

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That pesky global warming gas and also the
stuff that makes all life on Earth possible.

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Nitrogen has 5 electrons in its outer shell.
Here's how we count them:

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There are 4 placeholders. Each of them wants
2 atoms.

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And like people getting on a bus they prefer
to start out not sitting next to each other.

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I'm not kidding about this, they really don't
double up until they have to.

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So for maximum happiness, nitrogen bonds with
3 hydrogens, forming ammonia.

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Or with 2 hydrogens sticking off another group
of atoms, which we call an amino group.

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And if that amino group is bonded to a carbon
that is bonded to a carboxylic acid group

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then you have

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an amino acid!

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You've heard of those, right?

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Sometimes electrons are shared equally within
a covalent bond like with O2.

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That's called a non-polar covalent bond. But
often one of the participants is more greedy.

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In water for example, the oxygen molecule
sucks the electrons in

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and they spend more time with the oxygen than
with the hydrogens.

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This creates a slight positive charge around
the hydrogens

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and a slight negative charge around the oxygen.

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When something has a charge we say that it's
polar. It has a positive and negative pole.

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And so it's a polar covalent bond.

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Now let's talk for a moment about a completely
different type of bond, which is an ionic

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bond.

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And that's when, instead of sharing electrons

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atoms just completely wholeheartedly donate
or accept an electron from another atom

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and then live happily as a charged atom.

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And there is actually no such thing as a charged
atom.

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If an atom has a charge, it's an ion.

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Atoms in general prefer to be neutral, but
compared with having a full octet, it's not

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that big of a deal.

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Just like we often choose between being emotionally
balanced and sexually satisfied

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atoms will sometimes make sacrifices for that
octet.

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The most common ionic compound in our daily
lives is salt.

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Sodium chloride. NaCl.

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The stuff, despite it's deliciousness, as
I mentioned previously

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is made up of two really nasty chemicals.
Sodium and chlorine.

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Chlorine is what we call a halogen, which
is an element that only needs one electron

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to fulfill it's octet.

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And sodium is an alkaline metal which means
that it only has one electron in it's octet.

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So chlorine and sodium are so close to being
satisfied

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that they will happily destroy anything in
their path in order to fulfill their octet.

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And thus, there's actually no better outcome
than just to get

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chlorine and sodium together and have them
lovin' on each other.

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They immediately transfer their electrons.

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So that sodium doesn't have it's one extra,
and chlorine fills it's octet.

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They become Na+ and Cl- and are so charged
that they stick together

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and we call that stickiness an ionic bond.

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And just like if you have two really crazy
friends

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it might be good to get them together so that
they'll stop bothering you.

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Same thing works with sodium and chlorine.

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You get those two together, and they'll bother
no one.

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And suddenly, they don't want to destroy,
they just want to be delicious.

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Chemical changes like this are a big deal.

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Remember, chlorine and sodium, just a second
ago, were definitely killing you, and now

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they're tasty.

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Now we're coming to the last bond that we're
going to discuss

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in our intro to chemistry here and that's
the hydrogen bond.

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Imagine that you remember water, I hope that
you didn't forget water.

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Since water is stuck together in a polar covalent
bond

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the hydrogen bit is positively charge and
the oxygen bit is negatively charged.

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So when water molecules are moving around

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we generally think of them as a perfect fluid
but they actually stick together a little

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bit.

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Hydrogen side to oxygen side.

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You can actually see this with your eyes if
you fill up a glass of water too full

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it will bubble at the top. The water will
stick together at the top.

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That's the polar covalent bonds sticking the
water molecules to each other

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so that they don't flow right over the top
of the glass.

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These relatively weak hydrogen bonds happen
in all sorts of chemical compounds

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they don't just happen in water. An they actually
play an extremely important role in proteins

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which are the chemicals that pretty much up
our entire bodies.

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A final thing to note here is that bonds,
even covalent bonds, ionic bonds

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even with their own class

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are often much different strengths.

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And we tend to just write them with a little
line

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but that line can represent a very very strong
covalent bond or a relatively weak covalent

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bond.

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Sometimes ionic bonds are stronger than covalent
bonds

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though that's generally not the case and the
strength of covalent bonds varies wildly.

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How these bonds are made and broken is intensely
important to life.

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And to our lives. Making and breaking bonds
is in fact the key to life itself

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and also the key to death. For example, if
you were to ingest some sodium metal.

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Keep this in mind as we move forward through
biology:

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Even the sexiest person you have ever met
in your life

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is just a collection of organic compounds
rambling around in a sack of water.

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Review time!

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Now we have the table of contents

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Which I know is supposed to come at the beginning
of things

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But we are revolutionary here we're doing
it different

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so you can click on any of the things here

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and you can go back and review what you learned.

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Or didn't learn.

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And if you have questions please please please
please please please please

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ask them in the comments and we'll be down
there answering them for you.

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So thank you for joining us.

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It was a pleasure, it was a pleasure working
with you today.