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 mad
man named Gilbert Lewis?

It's all contained within.

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 50 Cent 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 class.

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

I may say one more thing before I start teaching.

Yes, I am going to!

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

that you can just rewind.

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

Hopefully, it will 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 going to 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

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 going
to start.

I am a collection of organic molecules called
Hank Green.

Organic compounds are a class of compounds
that contain carbon.

And carbon is this sexy little minx on the
periodic table

that's, you know...

disinterested in monogamy.

A jezebel. Bit of a tramp. Hussy.

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

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

It has 6 protons and 6 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 can do all sorts of things that could never
be accomplished by more bulky atoms.

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

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

It's 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 breath them
in they like literally tear up your insides

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

Carbon though...

Meh.

It wants more electrons, but it's not gonna
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 tramp, 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 willing and interested to bond
with lots of different molecules

like hydrogen, oxygen, phosphorous, 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

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

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.

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

in the form of carbon dioxide.

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

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

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

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

in order to be happy, fulfilled atoms.

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

so it's totally happy

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

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

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

Carbon shares its 4 electrons with those 4
hydrogens

and those 4 hydrogens each share 1 electron
with carbon.

So everybody's happy.

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

Good lord, I'm in a chair!

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

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

Which is a book called Lewis: Acids 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 was 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.

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 he was working on

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

I told you all of that because

the little Lewis dot structure that we use
to represent how 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 you're
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 8 electrons in
it's outermost shell.

That is called the Octet Rule.

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

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

It can also bond with carbon

which needs 4.

So you get 2 double bonds to 2 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 5 electrons in its outer shell.
Here's how we count them:

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

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.

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 non-polar 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 is actually 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 salt.

Sodium chloride. NaCl.

The stuff, despite it's 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 it's octet.

And sodium is an alkaline metal which means
that it only has one electron in it's 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
lovin' on each other.

They immediately transfer their electrons.

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

They become Na+ and Cl- 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 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 charge 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 too full

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

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

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

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

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

which are the chemicals that pretty much 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 tend to just write them with a little
line

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

and 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 in a sack of water.

Review time!

Now we have the table of contents

Which 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.

Or didn't learn.

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

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

So thank you for joining us.

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