Polymerization of Alkenes with Acid

Let's say we have some
chloroethene here, and you

wouldn't have to call this
1-chloro-eth-1-ene, because if

you just go with chloroethene,
there's only

one way to draw this.

And the common name for

chloroethene is vinyl chloride.

So let's say we have a bunch
of chloroethene molecules

along with or mixed with
some hydrogen chloride.

And I've drawn all of the
valence electrons for the

chlorine atom and I've drawn a
little magenta electron, the

one that the hydrogen atom
brought to the table.

So we've seen something
like this before.

What is likely to happen?

Well, maybe one of these carbons
is willing to give up

an electron.

That electron goes to the
hydrogen because this electron

is already being hogged by the
chlorine, so this hydrogen has

a partially positive charge.

Chlorine has a partially
negative charge, so that

electron would be attracted
to the hydrogen.

Then this electron
can be completely

hogged by the chlorine.

And if we had to decide which
of these carbons is more

likely to give up the electron,
you just have to say

which one is bonded to things
that it can share electrons a

little bit with.

This carbon is only bonded to
hydrogens, so it's already

hogging their one electron each,
and there are no more

electrons to share with it.

This guy is bonded to a
chlorine, so the chlorine has

a bunch of valence electrons.

It might be able share a little
bit with this carbon if

this guy became a carbocation.

So this guy will lose
an electron.

This carbon will form the
bond with that hydrogen.

So let's draw it out.

So let's say this carbon's
electron is that blue thing

right there.

Well, we could draw
it like this.

It goes to the hydrogen, and
then the hydrogen's magenta

electron goes to the chlorine.

This is just a plausible
mechanism.

Now, once that happens, what
will our setup look like?

What will it look like?

It will have this carbon over
here bonded to two hydrogens.

It has its single bond to that
other carbon that just lost

its electron, which is bonded to
a hydrogen and a chlorine.

And now this carbon on
the left, it is now

bonded to the hydrogen.

That electron went to the
hydrogen and it formed a bond

with it, so then it
forms a bond.

So that little blue electron is
at this end of the-- I want

to make it blue.

That little blue electron is at
this end of the bond, and

it is now the hydrogen's
electron.

And that magenta electron went
to the chlorine, so now it is

a negative ion.

It is a chloride ion.

So we have a chloride ion.

It has its standard seven
valence electrons that it

started off with, but now it
took that magenta electron

from the hydrogen,
and so now it has

eight valence electrons.

It gained an electron.

It now has a negative charge.

This guy over here
lost an electron.

He now has a positive charge.

Now, the next thing that you
might expect to happen, if we

just followed the pattern of
the last several videos, is

you would say, hey, this guy
will now take an electron from

the chlorine, which is-- or the
chloride anion, I should

say, which is completely
plausible, but there's also a

bunch of the chloroethane.

This isn't the only molecule
of chloroethene.

I should say chloroethene,
not chloroethane.

Chloroethene sitting around.

So let's let us throw another
one of those in there.

So we have more molecules
of this.

So he could take an electron
from this chloride ion, or he

could take an electron from
this guy over here.

Remember, this guy, just like
this guy, who was this guy,

this guy is OK.

It doesn't require a super
amount of energy to make this

guy lose his electron.

He's bonded to other things that
are willing to share with

him a little bit.

Maybe he's willing to lose his
electron as opposed to the

chloride ion.

So this guy has-- let me draw
it in-- so this end of this

bond is green.

And then this goes and bonds
with this carbon.

So this will be a long
bond right here.

So this goes and bonds with
that carbon, essentially

giving that electron
to that carbon.

And then what will our
setup look like?

So after that happens,
we'll look like this.

I probably should have copied
and pasted this

from the get go.

Actually, let me do that before
I-- let me copy and

paste this.

So now let me just draw, copy
and paste this whole thing.

Nope, that's not what
I wanted to do.

Let me select it again.

All right.

Copy and then paste.

There you go.

So then we have that thing.

And let me redraw what I
had erased, so that I

could copy and paste.

And then we have this guy went
over to this carbocation, so

he's no longer a carbocation, so
let me erase this, because

now he's gained an electron.

He gained that green electron
right there.

He gained that green electron.

I'll just draw it right there.

And now he's formed a bond
with this carbon.

And I'll make it blue, just so
we know which carbon we're

talking about.

He's formed a bond.

This bond now moved over to
that carbon because the

electron went with it.

So now that bond is to this
carbon right here.

That carbon right over there,
which is bonded to two

hydrogens, and now has a single
bond to the electron

that gave up the carbon, has a
single bond to that character

right over here, who is bonded
to a hydrogen and a chlorine.

And since he now lost an
electron, he now has a

positive charge.

So if you look at this setup
right here, it looks very

similar to this setup, although
we've added one more

vinyl chloride to the mix.

And the one that we added lost
its electron, or this carbon

lost it electron, and now
it's a carbocation.

So what could happen next?

Well, we have more of this vinyl
chloride sitting around.

Let me draw another
vinyl chloride.

So I have a carbon, a hydrogen,
a hydrogen, and then

it is double bonded
to a carbon, a

hydrogen, and a chlorine.

And let me copy and
paste this.

I think you see where this might
be going, how this could

keep on going and
going and going.

So copy.

Well, I just copy
that for now.

So what's going to happen now?

This guy could go and give an
electron to this guy and form

a bond, or we could have the
same process happen over and

over and over again.

Let me get my pen tool going.

So this electron could be given
to this carbocation

right there.

And then what happens?

Well, if that happens, then
we're going to get-- I'll move

to the left now.

We have our original molecule.

I'm going to run out
of space soon.

We have this original molecule,
and now this guy has

bonded to that.

So this carbon right here is
going to be this carbon, and

now it is bonded to this guy.

That orange electron
is now given to

this guy who was positive.

So he now has-- let me make
it a little bit neater.

I can do a better
job than that.

So the carbon's here.

The bond goes to this guy.

He now has the orange
electron.

He no longer has a
positive charge.

He's got all of his valence
electrons now.

And now this guy is bonded
to two hydrogens.

That guy is bonded
to two hydrogens.

And he has a single bond, this
single bond right here to the

carbon that just lost his
electron, who's bonded to a

hydrogen and a chlorine.

And because he lost his
electron, he now is the

carbocation.

He is now a carbocation.

So I think you see where
we're going.

We can just keep adding and
adding and adding to this

chain of vinyl chloride.

So if this process just went
on and on and on, we could

make it like this.

It would look something
like this.

Let me see how well
I can draw it.

So it would look like this.

So this is a CH3.

So I'll just draw it as H3C, and
then this is bonded to a

carbon, that is bonded to a--
well, maybe I'll call it a CH,

which is bonded to a chlorine.

So we're that far
in the molecule.

And then we have-- let's see
the part that repeats.

This part right here is going
to keep repeating.

That part right there is going
to keep repeating, and I'm

going to do it like this.

So I'm just going to draw one
of them, so you have a CH2.

That's that right there,
connected to a CH, which is

that right there, which is
connected to a chlorine.

And so that part right there
will keep repeating.

And then maybe the very last
one, so you have this guy

right here, but maybe the very
last one that joins on-- I

mean, this can happen
millions of times.

I just it made it happen
two or three times.

It could happen millions of
times and form a super long

chain or a polymer.

And what we are describing in
this video is actually a

polymer that you have probably
dealt with at some

point in your life.

In fact, I guarantee there's
some of it in

your house right now.

So then we'd have that
part right there.

And we could just make
that as CH2, CH, Cl.

And now, the way we've drawn
it, it's a carbocation, but

maybe we've run out of all of
the vinyl chloride molecules,

or we could also call them
chloroethene molecules.

And now finally, when everything
is said and done,

this last guy, since he's run
out of vinyl chloride

molecules to take their
electrons from, he now finally

takes it from the chlorine.

So you can imagine this happens
many, many times.

So this repeats many times.

After this repeats many times,
then finally, one of these

electrons from the chlorine go
to that final carbocation,

because they've run out of other
vinyl chlorides, and

then he attaches right over
here to the chlorine.

Now, this is called-- so when we
say that this might happen

many times, you might write an
N here, just to show that it

repeats many, many times.

If you know how many times it
repeats, if you know that

there were a thousand molecules
here, you would

write a thousand repetitions,
but this is called a polymer.

And the name for this molecule
right here is-- each of these

units is vinyl chloride,
right?

Vinyl chloride.

I guess the official name is
chloroethene, but the typical

name, the one people actually
to use, is vinyl chloride.

That's for each of
these units.

It's a polymer.

We have many of them, so we'll
put a poly- in front of it.

So this molecule right here is
polyvinyl chloride, or, and

now I think it'll ring a
bell, or PVC for short.

And you've probably heard
of PVC piping.

It's what most people have
for their plumbing.

It's those plastic pipes.

And that's what it is.

It's polyvinyl chloride.