Now why does this matter?
And I'm going to tell you an example of why this matters.
I'm talking about delocalization to stabilize.
And I'm talking about how the actual structure of a molecule
isn't this rigid two bonds here, one bond there,
that's not what that says, but it was in ozone.
But it's this shared equivalent bonds
where the electron is shared and the whole system is lowered.
Now, there is one molecule where this is very much important
and dictates all of its chemical behavior.
And that's benzene.
And back in the day, in the 1930s, oh, by the way,
Pauling, electronegativity scale. we
talked about him on Wednesday.
But back in the day, they didn't know what benzene was.
They could kind of measure some things.
But none of it worked.
And Pauling wrote a number of structural formulae
have been proposed for benzene, but none of them
is free from very serious objections.
The way they wrote stuff.
Look at these shapes for benzene.
If we don't know the right shape and why you have the right
shape for benzene, then we cannot understand all
of the mega amounts of organic chemistry that we do with
benzene.
So this is what's happening with benzene.
You have these two structures that benzene actually averages
over.
These are resonance structures.
Back in the day, they called them Kekulé structures
because Kekulé, as you can see, was kind of close and thought
about this as well.
These are resonance structures.
It totally dictates the chemistry
of benzene, which then leads to massive amounts of things
that we do with benzene.
Because with benzene, and this is just,
we don't need to look at this in detail,
this is an example of a few out of almost unlimited variations
of benzene that we can make.
Because we can take one of those hydrogen atoms
and put something on it, or two places.
And each time we do that, we get a different material,
a different molecule that gives us
different properties and different uses.
But all of this, even though we draw it, still
with those lines, we know that inside, it's delocalized.
It's delocalized.
Well, it might change once you add stuff to it.
But by itself here, by itself here, it's delocalized.
And that sets up the properties of benzene.
Now OK, let's go a little farther.
So I like these last two here.
Naphthalene, now, you can keep on going,
and keep adding benzenes, and we're
going to get somewhere that I really love.
This is getting me excited.
Oh, look I'm going to add one there.
I'm just going to keep adding benzene.
Now I could stay here, oh, don't get benzene wrong.
I can keep going.
And if I kept going, I might get sheets of benzene
that are now called graphene.
And if I stack those up, I've got graphite.
I've got graphite.
That's what graphite is.
It's these very large sheets of benzene.
Now, there are two very well-known phases
of pure carbon.
One is diamond.
And the other is graphite.
Does anybody know which one is more stable?
How many people think graphite?
How many people think diamonds are forever?
I'm giving you guys some advice, especially like, you're out,
and maybe you're out on a date.
And it's the weekend.
And there's a candle.
And you've talked about combustion.
And you've written that down.
And you talked about how long you have in that room,
because you know about oxygen and the limiting reagent
that it's either you or the candle.
We talked about that.
We also talked about how you need your periodic table
on that date.
And how you may need your spectroscope,
because they might give you an LED candle instead.
You need to talk about LEDs.
And I'm not saying that all of these conversations involving
knowledge you gained in this class
will lead to this place of seriousness,
but it could lead to engagement.
It could.
And now, some people when they get engaged,
one person buys the other a ring.
And sometimes that involves this material.
My point to you right now is when you go to the store,
maybe it's Tiffany's, maybe it's somewhere else,
and you buy that ring, ask for a warranty.
And make sure it's about 100,000 years, because after that time,
that ring is going to turn into graphite,
because graphite is the lowest most energetically
stable form of carbon.
So I'm just, again, always trying to help.
But this is the most stable form of carbon.
And it's a bunch of benzene, but repeated.
Not benzene, the hydrogens are gone.
It's just pure graphene, but repeated
in these beautiful rings.
And when we come back to hybridisation
and molecular orbitals, which we'll start after exam one,
you'll see other beautiful properties
of structures like this.
By the way, speaking of seeing, you can see this material.
What are you throwing at this material to see it like that?
Not light, not photons, you're throwing electrons.
I just came across this the other day in Wired,
New microscope shows the quantum world in crazy detail.
They took electrons and they shine it
on these little particles of platinum and iron.
And they're able to literally see every single atom as they
break apart the particle.
By just throwing electrons at it,
they say, the transmission electron microscope
was designed to break records.
Using its beam of electrons, scientists
have glimpsed many types of viruses, et cetera, et cetera.
They got down to 0.4 angstrom resolution in that work.
It's a beautiful thing.
And being able to see these materials
has revolutionized what we can do with them.