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