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Now why does this matter?

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And I'm going to tell you an
example of why this matters.

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I'm talking about
delocalization to stabilize.

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And I'm talking about how the
actual structure of a molecule

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isn't this rigid two bonds
here, one bond there,

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that's not what that
says, but it was in ozone.

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But it's this shared
equivalent bonds

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where the electron is shared
and the whole system is lowered.

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Now, there is one molecule where
this is very much important

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and dictates all of
its chemical behavior.

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And that's benzene.

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And back in the day, in
the 1930s, oh, by the way,

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Pauling, electronegativity
scale. we

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talked about him on Wednesday.

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But back in the day, they
didn't know what benzene was.

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They could kind of
measure some things.

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But none of it worked.

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And Pauling wrote a number
of structural formulae

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have been proposed for
benzene, but none of them

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is free from very
serious objections.

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The way they wrote stuff.

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Look at these
shapes for benzene.

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If we don't know the right
shape and why you have the right

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shape for benzene, then
we cannot understand all

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of the mega amounts of organic
chemistry that we do with

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benzene.

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So this is what's
happening with benzene.

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You have these two structures
that benzene actually averages

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over.

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These are resonance structures.

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Back in the day, they called
them Kekulé structures

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because Kekulé, as you can see,
was kind of close and thought

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about this as well.

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These are resonance structures.

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It totally dictates
the chemistry

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of benzene, which then leads
to massive amounts of things

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that we do with benzene.

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Because with benzene,
and this is just,

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we don't need to look
at this in detail,

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this is an example of a few out
of almost unlimited variations

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of benzene that we can make.

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Because we can take one
of those hydrogen atoms

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and put something on
it, or two places.

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And each time we do that,
we get a different material,

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a different molecule
that gives us

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different properties
and different uses.

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But all of this, even
though we draw it, still

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with those lines, we know
that inside, it's delocalized.

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It's delocalized.

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Well, it might change
once you add stuff to it.

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But by itself here, by itself
here, it's delocalized.

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And that sets up the
properties of benzene.

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Now OK, let's go
a little farther.

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So I like these last two here.

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Naphthalene, now, you
can keep on going,

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and keep adding
benzenes, and we're

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going to get somewhere
that I really love.

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This is getting me excited.

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Oh, look I'm going
to add one there.

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I'm just going to
keep adding benzene.

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Now I could stay here, oh,
don't get benzene wrong.

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I can keep going.

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And if I kept going, I
might get sheets of benzene

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that are now called graphene.

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And if I stack those
up, I've got graphite.

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I've got graphite.

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That's what graphite is.

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It's these very large
sheets of benzene.

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Now, there are two
very well-known phases

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of pure carbon.

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One is diamond.

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And the other is graphite.

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Does anybody know which
one is more stable?

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How many people think graphite?

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How many people think
diamonds are forever?

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I'm giving you guys some advice,
especially like, you're out,

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and maybe you're out on a date.

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And it's the weekend.

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And there's a candle.

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And you've talked
about combustion.

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And you've written that down.

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And you talked about how
long you have in that room,

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because you know about oxygen
and the limiting reagent

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that it's either
you or the candle.

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We talked about that.

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We also talked about how
you need your periodic table

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on that date.

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And how you may need
your spectroscope,

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because they might give
you an LED candle instead.

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You need to talk about LEDs.

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And I'm not saying that all of
these conversations involving

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knowledge you
gained in this class

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will lead to this
place of seriousness,

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but it could lead to engagement.

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It could.

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And now, some people
when they get engaged,

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one person buys
the other a ring.

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And sometimes that
involves this material.

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My point to you right now
is when you go to the store,

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maybe it's Tiffany's,
maybe it's somewhere else,

101
00:05:02,785 --> 00:05:06,656
and you buy that ring,
ask for a warranty.

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And make sure it's about 100,000
years, because after that time,

103
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that ring is going to
turn into graphite,

104
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because graphite is the
lowest most energetically

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stable form of carbon.

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So I'm just, again,
always trying to help.

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But this is the most
stable form of carbon.

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And it's a bunch of
benzene, but repeated.

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Not benzene, the
hydrogens are gone.

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It's just pure
graphene, but repeated

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in these beautiful rings.

112
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And when we come
back to hybridisation

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and molecular orbitals, which
we'll start after exam one,

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you'll see other
beautiful properties

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of structures like this.

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By the way, speaking of seeing,
you can see this material.

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What are you throwing at this
material to see it like that?

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Not light, not photons,
you're throwing electrons.

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I just came across this
the other day in Wired,

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New microscope shows the
quantum world in crazy detail.

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They took electrons
and they shine it

122
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on these little particles
of platinum and iron.

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And they're able to literally
see every single atom as they

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break apart the particle.

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By just throwing
electrons at it,

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they say, the transmission
electron microscope

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was designed to break records.

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Using its beam of
electrons, scientists

129
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have glimpsed many types of
viruses, et cetera, et cetera.

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They got down to 0.4 angstrom
resolution in that work.

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It's a beautiful thing.

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And being able to
see these materials

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has revolutionized what
we can do with them.