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We left off last Wednesday,
last week Wednesday.

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So it's been awhile.

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So I wanted just to pick
up where we left off.

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And then cover some
new things today.

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But where we left off was
with this diagram, OK?

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And, you know, I kind
of went through it.

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And I went through
it sort of quickly.

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But I want to make sure you
understand it very well.

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Because this is such an
important kind of diagram.

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And we'll see it again.

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And you may see it
again in other classes.

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This is a diagram of
attraction and repulsion

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00:00:52,801 --> 00:00:57,239
coming together in a
balance to form a bond.

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So, you know, last Wednesday,
just to remind you,

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we made our first bond.

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All right, we made
the ionic bond.

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And I showed you
how that worked.

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Because, in this
case, the attraction,

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the force of attraction is
the Coulomb potential, right?

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Remember that goes as
minus a constant times--

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I'll just write it
down because why not.

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You're using it
in your goody bag.

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All right, so the
Coulomb energy here

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goes as minus some constant
times the charges, the two

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charges, divided by the
distance between those charges.

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That's an energy.

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It's an energy of attraction.

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But, you know, so
here's the thing though.

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All right, so if you have
a plus and a minus charge,

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those are each 1, right,
charge of electron.

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And then the distance
between them,

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when it's really far this,
energy is pretty weak.

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So that's this green curve here.

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But as it gets
closer and closer,

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that energy gets
lower and lower.

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And remember, happiness
is lower energy.

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All right, these atoms want
to find their happy place.

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And they see each other
and they're like, well,

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we can be happier
if we're closer,

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until a certain thing happens.

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Which is then, they've
got similar charges

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like the electron
shells, negative charge.

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Negative charge, so kind
of coming too close.

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That's the forces of repulsion.

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And so that nets in a
total energy curve, which

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is this white line here,
the green and the red,

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and then you got the
white line there,

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which is the total energy.

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Because if they came
too close, then you're

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going to be on this thing.

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And you're just
gonna be-- you know,

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all those electrons are going
to be overlapping each other

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and very unhappy.

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So this is what we do.

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And we said, OK,
this is the bond

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of an atom and another atom, an
ion and another ion, a cation

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and an anion.

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We did all this Wednesday.

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I'm just getting us
back in the mood.

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And what I told you
is that that bond

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energy is related to the
lattice energy, all right?

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I mean, now, technically,
the lattice energy is--

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and this is something
you're playing around with--

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the lattice energy
would be the energy

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that it takes to go from those
ions, sodium-plus in the gas

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phase, right?

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We put that little guy there.

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Now, that is something that's
going keep coming, too.

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It's in a notation
I've been sneaking in.

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Gas phase, all right, plus
chlorine ion gas phase,

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and they came together
to make NaCl--

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ran out of room--

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solid.

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But I put it underneath,
solid sodium chloride.

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That's salt. Now,
the lattice energy

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is the energy that it
takes to go from these ions

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to the solid.

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And as you can see, well,
here I just did two ions.

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But the lattice energy
is going to be related

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to that bond energy, all right?

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OK?

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So the lattice energy of
the solid that you make

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is going to be [INAUDIBLE].

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And ionic solids, there's
a whole bunch of materials

85
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that form solids this way.

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They're ionic solids.

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And they have properties
that are general.

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They're not always
these properties.

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But for the most part,
these are the properties

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of our ionic solids, right?

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They tend to be solid
at room temperature.

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They tend to have high
melting and boiling points.

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They're often transparent
in the visible.

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They're mostly
electrical insulators.

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They're hard and brittle,
soluble in water.

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But in your goody bag, you're
seeing that's not always true.

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Because sometimes, well,
most of the time there,

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but if this lattice
energy is too high,

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then it may not even dissolve.

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It may still be an-- it just
may be some really, really

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strong ionic solid.

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But these are the general
properties of ionic solids.

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We'll come back as we
learn about other solids

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Wednesday to the
differences in properties

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between different
types of solids.

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OK, so that's where we ended.

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Now, to do this, to get to
here, we had to make ions.

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And so we've been
talking about ions.

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And we're going to
keep talking about ions

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because that's a very
important part of how atoms

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see each other, all right?

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Am I seeing you as a neutral
atom with all your electrons

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in your shell or am I seeing you
with a charge missing or not?

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That makes a big
difference in how

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they approach each other
and therefore how they bond,

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all right?

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This is a critical part of what
we need to learn this semester.

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And so, you know, we showed
this, which is sometimes

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atoms actually don't mind
losing an electron, don't mind.

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Don't mind is like
happiness level

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which has to do with energy.

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And so if we want to look
at this more formally,

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we would look at, for
example, this chart

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from [? Avril ?] which is
the first ionization energy.

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Now, that's something
that we talked about.

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So the first ionization
energy, which

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is how much energy
it takes to remove

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an electron from the outer
shell, the most outer shell

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electron, the first one
you would take away.

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That's the first
ionization energy.

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All right, and we saw, again,
getting us back in the mood.

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Oh, I've got colors there.

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So if you started, for example,
let's just take a look at this.

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OK, so here we are at lithium.

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I'm going to start here.

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And that's first
ionization energy.

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And this is just
the atomic number.

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So there's lithium.

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And remember, we looked
at this last week, lithium

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and beryllium.

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OK, so if you look at that, we
said so for lithium, you had

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three electrons in the core.

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So there's lithium, right?

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And there's the lithium.

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Oh, this is so fun because now
we know what to call this--

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1s2.

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All right, and then
we have another shell.

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These are just pictorial.

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The electron is not in an
orbit, it's in an orbital.

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It's not moving
around like this.

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That's our classical
minds fighting.

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And it's got one more electron.

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Why did I draw a dash?

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It's got one more electron
there in the 2s shell.

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And that's lithium.

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But now, we're going to go
from lithium to beryllium

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and we talked about this.

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So beryllium now is
going to add, OK, it's

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going to add another proton.

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It's got all of them.

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But I'm showing the
one that was added.

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And it's also going to
add an electron here.

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But see, for beryllium
this electron

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is really not shielded any
more, not shielded more

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for the most part.

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You know, it went into the same
shell, the same N, all right,

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and the same L, same
shape, same quantum number.

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So there's nothing
else shielding it.

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And yet, there is a
whole other proton.

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And that's why
beryllium is smaller.

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This is all stuff we
talked about Wednesday.

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But see, look, that's also why
it's harder to pull the outer

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electron off of
beryllium-- there it is--

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than lithium.

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So those really go together.

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All right, all the
radius stuff we

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talked about holds, you
know, that same kind of logic

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in terms of how
these electrons are

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with respect to their nucleus
holds for ionization energy.

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Now, let's go to boron.

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So if we go to boron,
now, we're going over,

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look at what happened.

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Look at that.

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We went from there to there.

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And the ionization
energy got lower.

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00:08:59,054 --> 00:09:01,122
Well, that's also something
we can understand.

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Because now, we're
putting it into the 2p.

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OK, so if I do
that, it would be,

189
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I'm going to put it
under here, 2s2, right?

190
00:09:14,402 --> 00:09:17,238
And now, if I go
to boron, I'm going

191
00:09:17,238 --> 00:09:19,641
to put it here in a 2p shell.

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00:09:19,641 --> 00:09:23,978
So I'm starting a
new L. Now, remember,

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00:09:23,978 --> 00:09:26,414
that means the quantum
number is still 2,

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00:09:26,414 --> 00:09:28,483
but the shape of the
orbital is different.

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And now, we know
also from something

196
00:09:30,485 --> 00:09:33,388
we learned last week that
because of orbital penetration,

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00:09:33,388 --> 00:09:37,192
the energies of the 2p and
2s orbitals are not the same.

198
00:09:37,192 --> 00:09:40,128
All right, the s-energies
are a little lower.

199
00:09:40,128 --> 00:09:42,797
And it lets those electrons
get a little bit closer

200
00:09:42,797 --> 00:09:46,634
to that positive charge
that they want so badly.

201
00:09:46,634 --> 00:09:49,838
So we know that this is going
to be a little further out.

202
00:09:49,838 --> 00:09:55,009
And so there's a little bit of
shielding, a little shielding

203
00:09:55,009 --> 00:09:59,447
that you get for this,
plus orbital penetration

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00:09:59,447 --> 00:10:00,882
that we talked about.

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00:10:00,882 --> 00:10:05,987
And that puts it
further out, all right?

206
00:10:05,987 --> 00:10:09,190
And therefore, the
attraction is a little less.

207
00:10:09,190 --> 00:10:12,994
And therefore, the
ionization energy went down.

208
00:10:12,994 --> 00:10:14,562
And now, we're going
to fill those up.

209
00:10:14,562 --> 00:10:16,297
But it's the same
thing as before.

210
00:10:16,297 --> 00:10:20,101
Now, you're not going further
out, you're just adding

211
00:10:20,101 --> 00:10:23,271
and you're not really
screening while you add.

212
00:10:23,271 --> 00:10:25,774
And so you're adding electrons
into this 2p orbital.

213
00:10:25,774 --> 00:10:27,742
But you're also adding
all the positive charge.

214
00:10:27,742 --> 00:10:29,544
Salute.

215
00:10:29,544 --> 00:10:31,780
And so, the ionization
energy is going

216
00:10:31,780 --> 00:10:36,117
to go up, except look at that,
half filling, right there,

217
00:10:36,117 --> 00:10:38,253
half filling, a little
extra stability.

218
00:10:38,253 --> 00:10:40,288
Remember, we talked
about exceptions, right?

219
00:10:40,288 --> 00:10:42,557
Half filling.

220
00:10:42,557 --> 00:10:43,191
Half filling.

221
00:10:43,191 --> 00:10:44,926
And so, you see,
now you can see,

222
00:10:44,926 --> 00:10:48,096
we can understand these trends
that were being measured.

223
00:10:48,096 --> 00:10:50,198
All right, and at the
time, these ionization

224
00:10:50,198 --> 00:10:53,668
potentials, but now we
really can understand them.

225
00:10:53,668 --> 00:10:54,702
And you can group them.

226
00:10:54,702 --> 00:10:57,639
And you can see if you group
them, remember, we also grouped

227
00:10:57,639 --> 00:11:00,408
the periodic table a little bit
by electron filling, quantum

228
00:11:00,408 --> 00:11:00,909
numbers.

229
00:11:00,909 --> 00:11:03,511
All right, you had
the s and p blocks.

230
00:11:03,511 --> 00:11:06,648
Those are also often called
the main group elements.

231
00:11:06,648 --> 00:11:08,783
They're in the first
couple of rows of those.

232
00:11:08,783 --> 00:11:10,919
They're the most
abundant elements.

233
00:11:15,690 --> 00:11:17,792
But those trends, now,
you fully understand

234
00:11:17,792 --> 00:11:21,729
from the quantum
mechanical solution

235
00:11:21,729 --> 00:11:23,832
to the atom, all
right, and the electron

236
00:11:23,832 --> 00:11:25,767
filling of those orbitals.

237
00:11:25,767 --> 00:11:27,569
We can actually really
understand it all.

238
00:11:30,305 --> 00:11:32,106
And then the same thing
happens with the d.

239
00:11:32,106 --> 00:11:33,575
But it's a little
more complicated.

240
00:11:33,575 --> 00:11:36,644
By the way, these are often
called transition metals.

241
00:11:36,644 --> 00:11:38,913
The d-block, I told you
about the d-block last week.

242
00:11:38,913 --> 00:11:41,049
They're also called
transition metals.

243
00:11:41,049 --> 00:11:42,584
And the word metal
is something we'll

244
00:11:42,584 --> 00:11:45,887
talk a lot about in a few
weeks when we make metals.

245
00:11:45,887 --> 00:11:49,023
But they're called transitions
because, literally, they

246
00:11:49,023 --> 00:11:51,593
transition in the filling.

247
00:11:51,593 --> 00:11:53,228
They transition.

248
00:11:53,228 --> 00:11:57,599
You're filling d-orbitals,
all right, transitioning.

249
00:11:57,599 --> 00:11:59,367
And that makes it a
little more complex

250
00:11:59,367 --> 00:12:00,869
in terms of what happens.

251
00:12:00,869 --> 00:12:03,037
But the same trends hold.

252
00:12:03,037 --> 00:12:04,806
The same trend holds.

253
00:12:04,806 --> 00:12:07,742
As you add more d-electrons,
the ionization energy

254
00:12:07,742 --> 00:12:08,476
keeps going up.

255
00:12:08,476 --> 00:12:13,481
OK, now, this is extremely
important, this ionization

256
00:12:13,481 --> 00:12:14,115
energy.

257
00:12:14,115 --> 00:12:16,017
The first ionization
energy is very important

258
00:12:16,017 --> 00:12:19,153
because it tells you so much
about the outer electron,

259
00:12:19,153 --> 00:12:23,091
whether an atom is going
to be an anion or a cation.

260
00:12:23,091 --> 00:12:25,393
But all of the
ionization, you could

261
00:12:25,393 --> 00:12:27,629
throw a whole lot of
energy at these atoms

262
00:12:27,629 --> 00:12:30,198
and they'll all
come off, all right.

263
00:12:30,198 --> 00:12:33,268
And, you know, so we played
with this kind of energy.

264
00:12:33,268 --> 00:12:34,235
This is visible light.

265
00:12:34,235 --> 00:12:35,904
You had your goody bag, too.

266
00:12:35,904 --> 00:12:37,171
You got a spectrometer.

267
00:12:37,171 --> 00:12:38,473
You can see lines in here.

268
00:12:38,473 --> 00:12:39,841
This is a continuous spectrum.

269
00:12:39,841 --> 00:12:41,643
But you see, you've
got this whole,

270
00:12:41,643 --> 00:12:44,746
all these different
wavelengths, right?

271
00:12:44,746 --> 00:12:47,849
And now you see this and you
don't just think about colors,

272
00:12:47,849 --> 00:12:51,019
you think about
energies, all right?

273
00:12:51,019 --> 00:12:56,591
And so if you think that
way, because I want to know

274
00:12:56,591 --> 00:12:58,059
how can I measure these things?

275
00:12:58,059 --> 00:13:01,329
Ah, stop, better.

276
00:13:01,329 --> 00:13:09,637
All right, and so, you know, if
I look at energies, energies,

277
00:13:09,637 --> 00:13:14,742
I've got like the visible, which
is around, oh, I don't know,

278
00:13:14,742 --> 00:13:18,279
say 2 to 6 EV.

279
00:13:18,279 --> 00:13:19,714
That's pretty high energy.

280
00:13:19,714 --> 00:13:23,351
And then you've got, well--
now, can I shine visible light

281
00:13:23,351 --> 00:13:27,355
and kick out, you know,
a lithium electron?

282
00:13:27,355 --> 00:13:30,425
Well, the answer is roughly yes.

283
00:13:30,425 --> 00:13:33,661
You know, the lithium energy
ionization, well, let's just

284
00:13:33,661 --> 00:13:34,796
go back and look.

285
00:13:34,796 --> 00:13:38,600
That first ionization energy,
520 kilojoules per mole,

286
00:13:38,600 --> 00:13:41,369
I know that's 5.4 EV-ish.

287
00:13:41,369 --> 00:13:43,605
Because I don't mind going
back and forth, right?

288
00:13:43,605 --> 00:13:46,608
Kilojoules per mole of
electrons, Jules, EV,

289
00:13:46,608 --> 00:13:48,676
moles, you can go
back and forth.

290
00:13:48,676 --> 00:13:51,145
But that's right around here.

291
00:13:51,145 --> 00:13:53,948
So I could shine visible light
and potentially knock that out.

292
00:13:53,948 --> 00:13:59,387
But see if I wanted the
1s electron of lithium,

293
00:13:59,387 --> 00:14:00,955
well, it's much,
much lower in energy.

294
00:14:00,955 --> 00:14:02,624
Because, remember,
we talked about this.

295
00:14:02,624 --> 00:14:04,559
It goes in and in each
time I add charge.

296
00:14:04,559 --> 00:14:07,095
And so it would take
122 electron volts

297
00:14:07,095 --> 00:14:09,097
to knock that out, right?

298
00:14:09,097 --> 00:14:13,568
So but we have that kind
of light, all right.

299
00:14:13,568 --> 00:14:18,806
The UV would be something
like, oh, 10 to 100.

300
00:14:18,806 --> 00:14:20,942
And then, if we really
want to blast these,

301
00:14:20,942 --> 00:14:22,577
we could go x-rays.

302
00:14:22,577 --> 00:14:25,279
Oh, are we going to
have fun with X-rays

303
00:14:25,279 --> 00:14:28,216
later in the semester.

304
00:14:28,216 --> 00:14:30,652
And this would go to
something like 100,000.

305
00:14:30,652 --> 00:14:31,753
And so I got it.

306
00:14:31,753 --> 00:14:35,123
You know, if I wanted to, I
could shine light and ionize

307
00:14:35,123 --> 00:14:36,491
the whole thing.

308
00:14:36,491 --> 00:14:39,827
And that is, in fact, one
of the single most important

309
00:14:39,827 --> 00:14:42,030
experiments we do to
characterize materials.

310
00:14:42,030 --> 00:14:44,532
And so I want you
to know about it.

311
00:14:44,532 --> 00:14:47,301
It's called photoelectron
spectroscopy,

312
00:14:47,301 --> 00:14:54,142
photoelectron spectroscopy.

313
00:14:57,779 --> 00:15:04,686
And, for short, we will not
write that out ever again.

314
00:15:04,686 --> 00:15:07,689
I will write out PES,
photoelectron spectroscopy.

315
00:15:07,689 --> 00:15:11,192
Now, this is a
characterization tool.

316
00:15:11,192 --> 00:15:13,594
I'm basically saying, well,
you know, I need energy.

317
00:15:13,594 --> 00:15:15,430
I'm going to get it
from some photon source.

318
00:15:15,430 --> 00:15:16,998
But I'm going to get
enough to just blast

319
00:15:16,998 --> 00:15:19,333
all the electrons out of this
material, out of this atom.

320
00:15:19,333 --> 00:15:22,170
Because, for now, our
material, they're just atoms.

321
00:15:22,170 --> 00:15:25,139
And I want to know
about these atoms.

322
00:15:25,139 --> 00:15:26,007
So let's take a look.

323
00:15:26,007 --> 00:15:27,942
So what happens when I do this?

324
00:15:27,942 --> 00:15:29,877
Well, let's see,
first of all, I've

325
00:15:29,877 --> 00:15:34,515
got some energy that
we know is h nu.

326
00:15:34,515 --> 00:15:36,551
It's dependent on the frequency.

327
00:15:36,551 --> 00:15:37,852
There are the frequencies.

328
00:15:37,852 --> 00:15:38,486
There they are.

329
00:15:38,486 --> 00:15:39,721
No, there they are.

330
00:15:39,721 --> 00:15:44,926
OK, so now, I've
got some atom here.

331
00:15:44,926 --> 00:15:47,095
And what do I do?

332
00:15:47,095 --> 00:15:48,763
Well, I look, did
anything happen?

333
00:15:48,763 --> 00:15:49,497
No.

334
00:15:49,497 --> 00:15:50,565
What about now?

335
00:15:50,565 --> 00:15:51,099
I don't know.

336
00:15:51,099 --> 00:15:51,999
OK, what about now?

337
00:15:51,999 --> 00:15:56,504
Oh, all of a sudden, they
come flying out, electrons.

338
00:15:56,504 --> 00:15:58,439
All right?

339
00:15:58,439 --> 00:16:02,610
And I measure their energy.

340
00:16:02,610 --> 00:16:05,379
It goes right back to
the photoelectric effect

341
00:16:05,379 --> 00:16:06,447
that Einstein was doing.

342
00:16:06,447 --> 00:16:11,385
He was shining visible-ish
light onto metals

343
00:16:11,385 --> 00:16:13,121
and seeing what
electron-- but now I'm

344
00:16:13,121 --> 00:16:15,256
shining all sorts of
light onto an atom

345
00:16:15,256 --> 00:16:18,359
and I want them all to come
out, not just the outer one.

346
00:16:18,359 --> 00:16:19,794
And so we will.

347
00:16:19,794 --> 00:16:23,097
You can see if I
measure, so now I'm

348
00:16:23,097 --> 00:16:28,269
going to measure the
kinetic energy of these.

349
00:16:28,269 --> 00:16:33,407
And the ionization
energy of that electron

350
00:16:33,407 --> 00:16:37,278
is going to equal whatever the
energy of the incident photon

351
00:16:37,278 --> 00:16:41,915
was minus the kinetic
energy of the electron.

352
00:16:41,915 --> 00:16:43,618
That's what I want.

353
00:16:43,618 --> 00:16:46,087
I want that ionization energy.

354
00:16:46,087 --> 00:16:52,627
This is, just to be
clear, ionization energy.

355
00:16:52,627 --> 00:16:54,929
And like I said, I want it all.

356
00:16:54,929 --> 00:16:57,765
Not just the first, I want
the second and the third.

357
00:16:57,765 --> 00:16:58,699
So now, you see.

358
00:16:58,699 --> 00:17:01,335
So this is the
experiment that you do.

359
00:17:01,335 --> 00:17:02,203
What are the results?

360
00:17:04,771 --> 00:17:07,541
Well, the results are really
just what we've been doing.

361
00:17:07,541 --> 00:17:09,143
But you turn it over.

362
00:17:09,143 --> 00:17:11,779
So let's look at hydrogen, OK?

363
00:17:11,779 --> 00:17:13,013
Now, what have we been doing?

364
00:17:13,013 --> 00:17:13,948
What do I mean by that?

365
00:17:13,948 --> 00:17:16,349
Well, what we've been doing
is we've been going like this.

366
00:17:16,349 --> 00:17:16,884
What's that?

367
00:17:16,884 --> 00:17:19,686
OK, this is hydrogen 1s1.

368
00:17:19,686 --> 00:17:22,022
I could do that or I could
just label it the 1s and then

369
00:17:22,022 --> 00:17:25,425
you see the one
electron right there.

370
00:17:25,425 --> 00:17:29,564
Now, if I shine light
on this and I measure,

371
00:17:29,564 --> 00:17:34,836
the way that you do a
PES for hydrogen is you

372
00:17:34,836 --> 00:17:39,674
would look at the ionization
energy on the x-axis.

373
00:17:39,674 --> 00:17:45,646
And this would be the relative
electron count on the y-axis.

374
00:17:45,646 --> 00:17:48,983
So you're just
counting, all right?

375
00:17:48,983 --> 00:17:50,518
And what you would
see in hydrogen

376
00:17:50,518 --> 00:17:51,719
is there would be a peak.

377
00:17:51,719 --> 00:17:54,222
It would look like this.

378
00:17:54,222 --> 00:17:54,956
That's it.

379
00:17:54,956 --> 00:17:58,426
If all the electrons
in hydrogen, 1,

380
00:17:58,426 --> 00:18:02,163
are in their ground state,
1s, then you would see a peak

381
00:18:02,163 --> 00:18:05,900
and this would be, you know
that it would be at minus 13.6,

382
00:18:05,900 --> 00:18:06,400
right?

383
00:18:06,400 --> 00:18:08,669
That would be the energy
that it takes to ionize it.

384
00:18:08,669 --> 00:18:12,940
And this would be the 1s peak.

385
00:18:12,940 --> 00:18:14,108
And that's what you measure.

386
00:18:14,108 --> 00:18:17,278
Now, it gets more fun,
because now I can also

387
00:18:17,278 --> 00:18:18,980
look at other elements.

388
00:18:18,980 --> 00:18:21,115
So let's draw helium
underneath it.

389
00:18:21,115 --> 00:18:23,951
I'm gonna try to squeeze it in.

390
00:18:23,951 --> 00:18:30,224
If I look at helium,
well, helium is also 1s.

391
00:18:30,224 --> 00:18:34,161
And its PES would be--

392
00:18:34,161 --> 00:18:36,864
so this is now
ionization energy.

393
00:18:36,864 --> 00:18:39,066
This is the PES plot.

394
00:18:39,066 --> 00:18:43,905
And the PES for helium
would be also the 1s.

395
00:18:43,905 --> 00:18:47,241
But the relative counts
would be twice as high.

396
00:18:47,241 --> 00:18:50,344
So the peak of helium
would be twice as high

397
00:18:50,344 --> 00:18:51,979
as the peak of hydrogen.

398
00:18:51,979 --> 00:18:55,449
Because, you know, for the
same number of photons in,

399
00:18:55,449 --> 00:18:56,817
I'm getting that many more.

400
00:18:56,817 --> 00:19:01,055
I've got both these
electrons coming out.

401
00:19:01,055 --> 00:19:07,495
So the relative peaks, I've
got two more that can come out.

402
00:19:07,495 --> 00:19:09,397
Now, if I go to--

403
00:19:09,397 --> 00:19:11,165
OK, now, it gets
really interesting,

404
00:19:11,165 --> 00:19:16,404
because now, oh,
I even have room,

405
00:19:16,404 --> 00:19:18,506
which is making me very happy.

406
00:19:18,506 --> 00:19:21,776
Because now I can do
lithium right here.

407
00:19:21,776 --> 00:19:27,748
And if you look at
lithium, lithium

408
00:19:27,748 --> 00:19:31,953
goes like this, all right?

409
00:19:31,953 --> 00:19:35,289
And if I look at a PES plot
of lithium, the ionization

410
00:19:35,289 --> 00:19:40,328
energy and the relative
electron count,

411
00:19:40,328 --> 00:19:46,067
OK, I'm going to have
those 1s electrons filled.

412
00:19:46,067 --> 00:19:48,836
And there's going to
be another energy where

413
00:19:48,836 --> 00:19:50,037
the 2s electrons are.

414
00:19:50,037 --> 00:19:51,706
So this is energy here.

415
00:19:51,706 --> 00:19:52,873
These are the orbitals.

416
00:19:52,873 --> 00:19:55,910
And somewhere over here is
going to be a peak that's

417
00:19:55,910 --> 00:19:59,313
exactly half as high, exactly.

418
00:19:59,313 --> 00:20:00,915
I mean, that's
makes a lot of sense

419
00:20:00,915 --> 00:20:04,385
because there's twice
as many electrons.

420
00:20:04,385 --> 00:20:06,520
It's the relative electron
count in the atom.

421
00:20:06,520 --> 00:20:09,323
There's twice as many
electrons coming out

422
00:20:09,323 --> 00:20:10,925
of that 1s orbital and the 2s.

423
00:20:10,925 --> 00:20:13,894
So I'm going to get a half
as high peak here, all right.

424
00:20:13,894 --> 00:20:19,533
And I just told you, the lithium
atom, this electron is 5 point

425
00:20:19,533 --> 00:20:22,570
something, 4-ish
electron volts to remove.

426
00:20:22,570 --> 00:20:24,338
This is 122.

427
00:20:24,338 --> 00:20:27,541
So literally, for lithium,
this would be 122.

428
00:20:27,541 --> 00:20:29,377
This would be 5.4.

429
00:20:29,377 --> 00:20:32,480
And you know, that's the
ionization energy in EV.

430
00:20:32,480 --> 00:20:35,716
And what you would do is you
would draw the axis like that.

431
00:20:35,716 --> 00:20:40,087
So you don't have to put
this all the way over here,

432
00:20:40,087 --> 00:20:41,622
all right?

433
00:20:41,622 --> 00:20:44,925
And all this means is
I've broken up the axis

434
00:20:44,925 --> 00:20:46,627
and it's continuing
to count here

435
00:20:46,627 --> 00:20:49,964
in a different scale, all right?

436
00:20:49,964 --> 00:20:55,870
These PES plots are absolutely
essential in understanding

437
00:20:55,870 --> 00:20:57,605
atoms and materials.

438
00:20:57,605 --> 00:20:58,906
Because look at what you get.

439
00:20:58,906 --> 00:21:04,845
You get, literally, the electron
filling plot turned over.

440
00:21:04,845 --> 00:21:06,414
It's incredible.

441
00:21:06,414 --> 00:21:09,917
You get it turned over.

442
00:21:09,917 --> 00:21:12,486
And you can write this as,
oh, let's just do this.

443
00:21:12,486 --> 00:21:14,588
You know, I could
write this as 1s2.

444
00:21:14,588 --> 00:21:17,224
We have so many
options now, 2s1.

445
00:21:17,224 --> 00:21:23,397
All right, I could write
this as helium 2s1.

446
00:21:23,397 --> 00:21:25,099
That would be like
using the noble gas.

447
00:21:28,369 --> 00:21:31,005
I could make what people,
you know, there are so many--

448
00:21:31,005 --> 00:21:34,475
I can make box
plots, oh, box plots.

449
00:21:34,475 --> 00:21:35,676
You can do this.

450
00:21:35,676 --> 00:21:37,645
Some people really
like putting things

451
00:21:37,645 --> 00:21:42,616
in boxes, 1s, 2s, box plots.

452
00:21:47,488 --> 00:21:52,560
So these are all meaning,
these all say the same thing--

453
00:21:52,560 --> 00:21:54,028
Lithium.

454
00:21:54,028 --> 00:21:58,632
They all say lithium, all right?

455
00:21:58,632 --> 00:22:00,134
Photoelectron spectra.

456
00:22:00,134 --> 00:22:01,769
So I could ask you
questions like this.

457
00:22:01,769 --> 00:22:03,037
There's one.

458
00:22:03,037 --> 00:22:07,775
Ionization energy, megajoules
per mole, relative number

459
00:22:07,775 --> 00:22:10,978
of electrons, this element
has a charge of 2-plus

460
00:22:10,978 --> 00:22:12,246
and the PES shown below.

461
00:22:12,246 --> 00:22:13,681
What is it?

462
00:22:13,681 --> 00:22:20,121
So, OK, I know, 1s2, 2s2,
and since this is going up

463
00:22:20,121 --> 00:22:24,191
three times as high, that sure
looks like 2p6, doesn't it?

464
00:22:24,191 --> 00:22:25,726
That looks like 2p6.

465
00:22:25,726 --> 00:22:28,329
Remember, it's this
turned over on its side,

466
00:22:28,329 --> 00:22:31,665
all right, where the peak height
corresponds to the filling.

467
00:22:31,665 --> 00:22:34,368
That's what that
experiment gives you, 2p6.

468
00:22:34,368 --> 00:22:35,202
Well, then it must--

469
00:22:35,202 --> 00:22:41,175
But then you have your
periodic table, ah-ha.

470
00:22:41,175 --> 00:22:42,376
Gesundheit.

471
00:22:42,376 --> 00:22:45,646
Neon, it must be neon.

472
00:22:45,646 --> 00:22:47,281
No, who said no?

473
00:22:47,281 --> 00:22:48,382
No.

474
00:22:48,382 --> 00:22:52,786
Don't just-- Yes, it can't be
neon because of the question.

475
00:22:52,786 --> 00:22:56,123
It's got a charge of 2-plus.

476
00:22:56,123 --> 00:23:00,394
Oh, tricky, tricky, tricky.

477
00:23:00,394 --> 00:23:03,564
Magnesium, it must be magnesium.

478
00:23:03,564 --> 00:23:05,633
That is the PES, right?

479
00:23:05,633 --> 00:23:08,068
But it's magnesium 2-plus
because I said it had a charge.

480
00:23:08,068 --> 00:23:11,972
Thank you, shout out,
I appreciate that.

481
00:23:11,972 --> 00:23:16,277
OK, so that's the power of
the photoelectron spectra.

482
00:23:16,277 --> 00:23:18,712
And we'll be using
it in the class.

483
00:23:18,712 --> 00:23:22,683
And this tells us about
how electrons leave atoms.

484
00:23:22,683 --> 00:23:25,419
It tells us about ionization
energies, not just

485
00:23:25,419 --> 00:23:27,388
the first, which is
the one all the way

486
00:23:27,388 --> 00:23:30,391
out here to the right on the
PES plot, but all of them.

487
00:23:30,391 --> 00:23:34,495
Because I shine enough energy
light to get them all out.

488
00:23:34,495 --> 00:23:35,896
Now, you can also--

489
00:23:35,896 --> 00:23:37,765
so that's about
losing electrons--

490
00:23:37,765 --> 00:23:40,067
you can also gain them.

491
00:23:40,067 --> 00:23:44,705
And so I mentioned this a little
bit, but just for completeness,

492
00:23:44,705 --> 00:23:46,707
I want to come back to this.

493
00:23:46,707 --> 00:23:50,044
You have ionization
energy, which

494
00:23:50,044 --> 00:23:52,213
is how much energy it takes
to pull an electron out.

495
00:23:52,213 --> 00:23:55,416
You also have electron affinity.

496
00:23:55,416 --> 00:23:59,820
Because some atoms also
might want electrons.

497
00:23:59,820 --> 00:24:01,322
And so when you
look at those plots,

498
00:24:01,322 --> 00:24:03,290
it actually all
makes sense again.

499
00:24:03,290 --> 00:24:05,659
Look at this, some
atoms like chlorine--

500
00:24:05,659 --> 00:24:07,695
this is electron
affinity by atom number--

501
00:24:07,695 --> 00:24:10,130
some atoms like chlorine
really want another electron.

502
00:24:10,130 --> 00:24:12,032
Why?

503
00:24:12,032 --> 00:24:16,337
Because it's got an
incomplete shell.

504
00:24:16,337 --> 00:24:17,771
It's so close.

505
00:24:17,771 --> 00:24:23,010
It just needs one more electron
to fill that outer shell.

506
00:24:23,010 --> 00:24:24,178
And it wants it.

507
00:24:24,178 --> 00:24:26,880
And that's the electron affinity
is how much does it want it.

508
00:24:26,880 --> 00:24:30,751
Now, want-- happiness,
happiness-- lower energy.

509
00:24:30,751 --> 00:24:31,585
That's what this is.

510
00:24:31,585 --> 00:24:34,255
So if you're not going
to lower your energy

511
00:24:34,255 --> 00:24:36,924
with another electron,
then you're just saying no.

512
00:24:36,924 --> 00:24:38,759
You just say no, 0.

513
00:24:38,759 --> 00:24:41,962
I will not take an electron
because if you give me one,

514
00:24:41,962 --> 00:24:43,130
my energy is going to go up.

515
00:24:43,130 --> 00:24:44,765
And I will be a less happy atom.

516
00:24:44,765 --> 00:24:46,367
Now, that makes
sense, too, right?

517
00:24:46,367 --> 00:24:47,901
Filled shells.

518
00:24:47,901 --> 00:24:52,640
Nitrogen, nitrogen has
got a half-filled shell.

519
00:24:52,640 --> 00:24:55,342
"No" to that electron, I
like my half-filled shell.

520
00:24:55,342 --> 00:24:58,812
It gives me a little added
stability, a little extra kick.

521
00:24:58,812 --> 00:25:01,282
If you give me that
electron, you know,

522
00:25:01,282 --> 00:25:03,651
I'm gonna not have
that added stability.

523
00:25:03,651 --> 00:25:05,319
I don't want it, 0.

524
00:25:05,319 --> 00:25:08,555
All right, 0.

525
00:25:08,555 --> 00:25:12,126
Losing electrons, gaining
electrons, losing electrons,

526
00:25:12,126 --> 00:25:15,996
gaining electrons,
why does it matter?

527
00:25:15,996 --> 00:25:17,798
Why does it matter?

528
00:25:17,798 --> 00:25:19,300
Well, we made a solid last week.

529
00:25:19,300 --> 00:25:21,935
Today, the answer is obvious.

530
00:25:21,935 --> 00:25:27,875
It matters because of
Danish wind, obviously.

531
00:25:27,875 --> 00:25:32,379
43%, in 2014, 43% of all the
electrical energy in Denmark

532
00:25:32,379 --> 00:25:33,347
came from wind.

533
00:25:33,347 --> 00:25:35,015
It's higher now.

534
00:25:35,015 --> 00:25:39,420
But see, now, this is a
quarter of the Danish wind.

535
00:25:39,420 --> 00:25:41,889
I only gave you a two
minute hemodialysis

536
00:25:41,889 --> 00:25:43,357
why this matters on Wednesday.

537
00:25:43,357 --> 00:25:47,261
So I'm going extended
today just a little bit.

538
00:25:47,261 --> 00:25:51,298
Danish wind, people
are very dependable.

539
00:25:51,298 --> 00:25:54,335
So over a three-month period,
this is how much we need,

540
00:25:54,335 --> 00:25:56,670
energy, electricity.

541
00:25:56,670 --> 00:25:59,940
But look at the wind supply.

542
00:25:59,940 --> 00:26:02,242
Sometimes it's
really there for us.

543
00:26:02,242 --> 00:26:03,677
Sometimes it's not at all there.

544
00:26:03,677 --> 00:26:05,079
Sometimes it's predictable.

545
00:26:05,079 --> 00:26:08,982
Sometimes it's not
at all predictable.

546
00:26:08,982 --> 00:26:10,651
With that much of
your electricity

547
00:26:10,651 --> 00:26:14,188
coming from this type
of unreliable resource,

548
00:26:14,188 --> 00:26:16,290
that is a huge challenge.

549
00:26:16,290 --> 00:26:18,125
I mean, even if you
go out to Arizona

550
00:26:18,125 --> 00:26:19,593
and you talk about
solar subsidies,

551
00:26:19,593 --> 00:26:21,061
Arizona is sunny all the time.

552
00:26:21,061 --> 00:26:27,201
No, not sunny all the time, most
of the time, more than Boston.

553
00:26:27,201 --> 00:26:29,470
But this is the sun in Arizona.

554
00:26:29,470 --> 00:26:31,605
That's the power
you're getting from it.

555
00:26:31,605 --> 00:26:34,241
And look at this,
these are just clouds.

556
00:26:34,241 --> 00:26:36,810
Because Arizona
does have clouds.

557
00:26:36,810 --> 00:26:38,779
And they passed by and
they blocked the sun.

558
00:26:38,779 --> 00:26:42,416
Do you know what a nightmare
this is for a grid operator?

559
00:26:42,416 --> 00:26:47,588
If a lot of your customers
get their energy in this way,

560
00:26:47,588 --> 00:26:52,025
you know, and all of a sudden,
half of the your supply

561
00:26:52,025 --> 00:26:56,830
of energy just turns off, I
mean, that's a huge problem.

562
00:26:56,830 --> 00:27:00,501
And this is one of the
most limiting factors

563
00:27:00,501 --> 00:27:02,970
for increasing,
to a large extent,

564
00:27:02,970 --> 00:27:05,939
the amount of renewables
we have on our grid.

565
00:27:05,939 --> 00:27:07,541
And so, of course,
I know a lot of you

566
00:27:07,541 --> 00:27:08,976
are thinking, well,
just store it.

567
00:27:08,976 --> 00:27:11,612
And that's what we need to do.

568
00:27:11,612 --> 00:27:13,647
But it turns out that
really one of the only ways

569
00:27:13,647 --> 00:27:17,518
we have to store energy at this
large scale is pumped hydro.

570
00:27:17,518 --> 00:27:20,220
And you see, we're
pumping water up a hill.

571
00:27:20,220 --> 00:27:23,524
When I have access, I
pump water up a hill.

572
00:27:23,524 --> 00:27:25,559
And then when I need,
I roll it back down

573
00:27:25,559 --> 00:27:27,027
and I turn a turbine with it.

574
00:27:27,027 --> 00:27:31,031
I'm literally just trading
energy, potential energy.

575
00:27:31,031 --> 00:27:32,699
And then I bring it
back, kinetic energy.

576
00:27:32,699 --> 00:27:35,269
And then I make electricity.

577
00:27:35,269 --> 00:27:37,971
The problem is that, you
know, well, as you can see,

578
00:27:37,971 --> 00:27:39,873
pumped hydro is going
to be good where there's

579
00:27:39,873 --> 00:27:41,909
hydro, where there's water.

580
00:27:41,909 --> 00:27:43,811
So that's limiting.

581
00:27:43,811 --> 00:27:48,315
But it also is a very
low areal density.

582
00:27:48,315 --> 00:27:51,251
And there are also a lot
of environmental challenges

583
00:27:51,251 --> 00:27:52,719
with making this
work in a way that

584
00:27:52,719 --> 00:27:54,788
doesn't harm the environment.

585
00:27:54,788 --> 00:27:56,490
So there are a lot of
issues with scaling

586
00:27:56,490 --> 00:27:58,826
up pumped hydro, a lot
of issues as a storage.

587
00:27:58,826 --> 00:28:02,396
And so I ask, well, what
else can we pump up hills?

588
00:28:02,396 --> 00:28:04,298
And we know what the
answer is because it's

589
00:28:04,298 --> 00:28:05,399
what we're talking about--

590
00:28:08,368 --> 00:28:09,036
ions.

591
00:28:09,036 --> 00:28:09,670
Where are they?

592
00:28:09,670 --> 00:28:14,041
Ions, we can pump ions up hills.

593
00:28:14,041 --> 00:28:15,509
There's my picture.

594
00:28:15,509 --> 00:28:17,878
Look at that.

595
00:28:17,878 --> 00:28:21,582
Ions, and you know what
this is, it's a battery.

596
00:28:21,582 --> 00:28:24,184
A battery is two
different materials,

597
00:28:24,184 --> 00:28:28,455
two different metals, a and b,
where one of them has an ion,

598
00:28:28,455 --> 00:28:35,229
I don't know, like
lithium, for example,

599
00:28:35,229 --> 00:28:36,997
that can go back and forth.

600
00:28:36,997 --> 00:28:39,199
And the electrolyte is
this thing in between

601
00:28:39,199 --> 00:28:42,569
that only allows
that ion through, OK?

602
00:28:42,569 --> 00:28:43,570
Now, here's the thing.

603
00:28:43,570 --> 00:28:50,377
So if I'm a metal and I lose
a positively charged atom,

604
00:28:50,377 --> 00:28:53,180
well, then I got
to stay neutral.

605
00:28:53,180 --> 00:28:56,483
And the only way to stay neutral
is to pump an electron out,

606
00:28:56,483 --> 00:28:58,585
all right?

607
00:28:58,585 --> 00:29:01,088
So if I want to draw
electrons out of this,

608
00:29:01,088 --> 00:29:03,924
that's fine as long as
I draw ions out of it.

609
00:29:03,924 --> 00:29:05,692
And then both of
them can do work.

610
00:29:05,692 --> 00:29:09,496
And then they come back and
they roll down an energy hill.

611
00:29:09,496 --> 00:29:11,632
That's what they're doing
and going back and forth,

612
00:29:11,632 --> 00:29:13,800
shuttling back and
forth, back and forth.

613
00:29:13,800 --> 00:29:17,271
They're rolling down a
hill, literally, of energy.

614
00:29:17,271 --> 00:29:21,074
You know, when it's in one
metal, it's higher in energy.

615
00:29:21,074 --> 00:29:24,177
And then, when I, you
know, plug my phone in,

616
00:29:24,177 --> 00:29:28,549
it rolls down that energy hill.

617
00:29:28,549 --> 00:29:31,218
And as it does, it travels
across to the other metal,

618
00:29:31,218 --> 00:29:32,819
gets lower in energy,
and the electron

619
00:29:32,819 --> 00:29:34,621
has got to come around
and do work for me.

620
00:29:34,621 --> 00:29:36,990
Because otherwise, it
wouldn't stay neutral.

621
00:29:36,990 --> 00:29:38,325
That's what a battery is.

622
00:29:38,325 --> 00:29:40,561
It's all about ions, all right?

623
00:29:40,561 --> 00:29:41,395
It's all about ions.

624
00:29:41,395 --> 00:29:42,462
It's like a ski lift.

625
00:29:42,462 --> 00:29:43,764
I like to think of
it, you know, it's

626
00:29:43,764 --> 00:29:45,499
like these ions are
getting into a ski lift

627
00:29:45,499 --> 00:29:47,467
and they're just getting
pumped up the mountain.

628
00:29:47,467 --> 00:29:49,803
And then when you plug it
in, they're ready to ski down

629
00:29:49,803 --> 00:29:50,504
and they go down.

630
00:29:50,504 --> 00:29:53,807
And that's just cruising
across this electrolyte.

631
00:29:53,807 --> 00:29:56,343
And I don't know what the
electron is in this analogy.

632
00:29:56,343 --> 00:29:57,578
But that's all a battery is.

633
00:29:57,578 --> 00:30:01,982
You plug it in and the ski lift
takes it up when you charge it.

634
00:30:01,982 --> 00:30:05,385
And now, you power your phone
on and it rolls back down.

635
00:30:05,385 --> 00:30:08,522
Well, see the thing is
that batteries have seen

636
00:30:08,522 --> 00:30:11,792
a Moore's law of themselves.

637
00:30:11,792 --> 00:30:16,263
If you look at the Moore's
law for batteries, it doubles.

638
00:30:16,263 --> 00:30:18,999
So this is the energy
storage of batteries

639
00:30:18,999 --> 00:30:20,801
over the last 150-ish years.

640
00:30:20,801 --> 00:30:23,370
It doubles every 60 years.

641
00:30:23,370 --> 00:30:25,105
That's not a very
good Moore's law.

642
00:30:25,105 --> 00:30:27,074
But that's completely changed.

643
00:30:27,074 --> 00:30:28,508
That's completely
changed recently.

644
00:30:28,508 --> 00:30:33,780
And the reason is all about
ion shuttling materials and ion

645
00:30:33,780 --> 00:30:35,482
storing materials.

646
00:30:35,482 --> 00:30:37,150
This is why this has happened.

647
00:30:37,150 --> 00:30:39,186
This is why we've
had a revolution

648
00:30:39,186 --> 00:30:41,855
in electrochemical energy
storage, all right.

649
00:30:41,855 --> 00:30:44,691
Because 150 years ago, we
only made batteries out

650
00:30:44,691 --> 00:30:46,193
of about 10 different materials.

651
00:30:46,193 --> 00:30:50,330
And today, there's well over
80 that are commercialized.

652
00:30:50,330 --> 00:30:53,467
There's many hundreds
in research labs.

653
00:30:53,467 --> 00:30:57,104
What is making the difference
is that those materials now

654
00:30:57,104 --> 00:30:59,940
allow the shuttling to happen.

655
00:30:59,940 --> 00:31:02,676
It allows the shuttling to
happen more easily, maybe

656
00:31:02,676 --> 00:31:04,011
faster.

657
00:31:04,011 --> 00:31:06,947
And it allows more of them
to be stored per volume.

658
00:31:06,947 --> 00:31:09,983
It's all about the chemistry
that houses those ions.

659
00:31:09,983 --> 00:31:12,252
It's all about the
chemistry of the ions.

660
00:31:12,252 --> 00:31:13,387
So that's why this matters.

661
00:31:13,387 --> 00:31:19,960
Now, we roll things down
hills to power our world.

662
00:31:19,960 --> 00:31:22,362
I told you this already in
the first or second lecture.

663
00:31:22,362 --> 00:31:26,199
We roll things down hills
all the time, all right?

664
00:31:26,199 --> 00:31:30,871
So like methane is the core
ingredient in natural gas.

665
00:31:30,871 --> 00:31:33,774
And what we do-- and we talked
about combustion already--

666
00:31:33,774 --> 00:31:35,642
is we light that
methane on fire.

667
00:31:35,642 --> 00:31:39,312
But see, the thing is
that what nature has done

668
00:31:39,312 --> 00:31:44,017
is it has put all this
stuff up the hill for us.

669
00:31:44,017 --> 00:31:46,486
So over tens of
millions of years,

670
00:31:46,486 --> 00:31:50,490
nature has pushed the
chemistry up a hill.

671
00:31:50,490 --> 00:31:53,694
That is literally what
it's done in energy.

672
00:31:53,694 --> 00:31:55,662
Because, you know,
it's made it so

673
00:31:55,662 --> 00:31:59,332
that if I light this on fire,
it will go down the hill.

674
00:31:59,332 --> 00:32:04,805
It will roll down the
hill and give off energy.

675
00:32:04,805 --> 00:32:06,273
Nature has done that for us.

676
00:32:06,273 --> 00:32:10,277
But see, we need to be able
to do this as well as nature.

677
00:32:10,277 --> 00:32:13,647
And so in the last minute
of why this matters,

678
00:32:13,647 --> 00:32:16,783
I want to explain why
this is so challenging.

679
00:32:16,783 --> 00:32:18,118
We need to be able to match.

680
00:32:18,118 --> 00:32:21,888
Because if you look at
the energy per weight

681
00:32:21,888 --> 00:32:25,425
versus the energy per
volume of a material,

682
00:32:25,425 --> 00:32:27,294
that's a very important metric.

683
00:32:27,294 --> 00:32:29,763
We plot this all the time if
you work on energy materials--

684
00:32:29,763 --> 00:32:35,102
the volumetric versus the
gravimetric energy density.

685
00:32:35,102 --> 00:32:37,871
This is good, a lot of
energy per weight and volume.

686
00:32:37,871 --> 00:32:39,906
Well, look at where gasoline is.

687
00:32:39,906 --> 00:32:42,375
I want to do some math here.

688
00:32:42,375 --> 00:32:44,211
Because I think this
is very important.

689
00:32:44,211 --> 00:32:46,046
Because I want you
to see, now, if I

690
00:32:46,046 --> 00:32:48,782
take one liter of
gasoline, so if I

691
00:32:48,782 --> 00:33:03,029
take one liter of gasoline,
now, the cost is around $1.

692
00:33:03,029 --> 00:33:04,998
Well, it fluctuates,
but, you know,

693
00:33:04,998 --> 00:33:07,701
in this country right
around now it's about $1.

694
00:33:07,701 --> 00:33:10,804
OK, now, if I look
at how much energy

695
00:33:10,804 --> 00:33:17,978
is in that gasoline, the
energy stored in those bonds

696
00:33:17,978 --> 00:33:20,981
that nature has pushed up a
hill over millions of years,

697
00:33:20,981 --> 00:33:26,086
the energy stored is
about 33 megajoules.

698
00:33:26,086 --> 00:33:26,987
OK, good.

699
00:33:26,987 --> 00:33:30,323
Now, I'm going to
make a comparison.

700
00:33:30,323 --> 00:33:38,064
One MIT professor,
one MIT professor

701
00:33:38,064 --> 00:33:43,203
operates at around 60 watts.

702
00:33:43,203 --> 00:33:45,739
Now, this is
something like-- well,

703
00:33:45,739 --> 00:33:49,242
this is equal to 60
joules per second.

704
00:33:49,242 --> 00:33:50,710
Now, I know some
professors who can

705
00:33:50,710 --> 00:33:52,813
operate a little higher
than that and maybe some

706
00:33:52,813 --> 00:33:53,446
a little lower.

707
00:33:53,446 --> 00:33:55,749
But that's like the average--

708
00:33:55,749 --> 00:33:56,950
60 joules per second.

709
00:33:56,950 --> 00:34:02,389
Now, the thing is, if I want
to get 33 megajoules out

710
00:34:02,389 --> 00:34:06,893
of this professor, then
I get, at this rate,

711
00:34:06,893 --> 00:34:17,170
33 megajoules takes
the prof 153 hours.

712
00:34:17,170 --> 00:34:18,737
Now, here's why this matters.

713
00:34:18,737 --> 00:34:26,513
Because 153 hours
will cost about $1,530

714
00:34:26,513 --> 00:34:40,393
at the MIT professor salary,
which is around $10 per hour.

715
00:34:40,393 --> 00:34:43,897
And, OK, but look at this.

716
00:34:46,699 --> 00:34:48,068
I dug something
out of the ground

717
00:34:48,068 --> 00:34:51,571
that nature spent 100 million
years making, fine, OK.

718
00:34:51,571 --> 00:34:52,438
And I burned it.

719
00:34:52,438 --> 00:34:53,406
And I got it for a $1.

720
00:34:53,406 --> 00:34:55,041
I got the same amount
of energy that it

721
00:34:55,041 --> 00:34:59,145
would have taken me literally
$1,530 to pay for it.

722
00:34:59,145 --> 00:35:01,581
That's our challenge.

723
00:35:01,581 --> 00:35:03,083
Now, you can plot
other things here.

724
00:35:03,083 --> 00:35:05,619
But look at this. ethanol,
wood, OK, liquid hydrogen,

725
00:35:05,619 --> 00:35:07,053
we're still trying
to compress it.

726
00:35:07,053 --> 00:35:10,257
But look at this, batteries
are way down there.

727
00:35:10,257 --> 00:35:11,324
This is why this matters.

728
00:35:11,324 --> 00:35:13,593
Because we're not even
close to being done.

729
00:35:13,593 --> 00:35:15,262
We're not even close.

730
00:35:15,262 --> 00:35:18,365
See that great uptick in
electrochemical storage.

731
00:35:18,365 --> 00:35:21,101
We need another order
or two of magnitude

732
00:35:21,101 --> 00:35:28,275
still in storing energy,
efficiencies, costs, et cetera.

733
00:35:28,275 --> 00:35:31,811
So that's my "why this
matters" for today.

734
00:35:31,811 --> 00:35:36,449
Now, back to ions and
electrons and atoms.

735
00:35:36,449 --> 00:35:40,487
What I want to take the
last 15 minutes of class

736
00:35:40,487 --> 00:35:43,957
is to introduce a new
way of looking at this.

737
00:35:43,957 --> 00:35:46,660
And some of you may have
seen the Lewis dots, OK?

738
00:35:49,429 --> 00:35:50,864
I'm going to
introduce them today.

739
00:35:50,864 --> 00:35:52,599
And then we're going
to make a whole bunch

740
00:35:52,599 --> 00:35:56,169
of molecular structures
on Wednesday.

741
00:35:56,169 --> 00:35:58,838
And the reason this
is so important

742
00:35:58,838 --> 00:36:03,810
is that it gives us a sense
of these outer electrons.

743
00:36:03,810 --> 00:36:07,280
It gives us a sense of
how those outer electrons

744
00:36:07,280 --> 00:36:11,818
look for the atoms, and
then, very importantly, how

745
00:36:11,818 --> 00:36:13,920
they come together in bonds.

746
00:36:13,920 --> 00:36:17,190
OK, how they come
together in bonds.

747
00:36:17,190 --> 00:36:24,564
So if I just very,
very simply ask,

748
00:36:24,564 --> 00:36:29,569
you know, what does the Lewis
dot structure look like?

749
00:36:29,569 --> 00:36:36,977
Well, first of all,
the number of dots

750
00:36:36,977 --> 00:36:42,983
is equal to the number
of valence electrons.

751
00:36:47,187 --> 00:36:55,061
And this is equal to the
last digit of the group, so

752
00:36:55,061 --> 00:36:57,764
of the element group.

753
00:36:57,764 --> 00:36:59,699
I'll show you that in a second.

754
00:36:59,699 --> 00:37:00,867
OK, so there's Lewis.

755
00:37:00,867 --> 00:37:06,840
Now, Lewis, you know, so there's
one of his drawings in one

756
00:37:06,840 --> 00:37:09,242
of his original papers
in the early 1900s.

757
00:37:09,242 --> 00:37:13,346
He actually was a
professor here, as well.

758
00:37:13,346 --> 00:37:16,383
And then he went and did a lot
of this work out in Berkeley.

759
00:37:16,383 --> 00:37:19,152
And so they named
a hall after him.

760
00:37:19,152 --> 00:37:22,789
And his contribution
was absolutely profound

761
00:37:22,789 --> 00:37:27,827
because in thinking
about atoms with dots

762
00:37:27,827 --> 00:37:31,831
to represent electrons
in the outer valence,

763
00:37:31,831 --> 00:37:37,670
it gave us a way to so
easily think about bonding.

764
00:37:37,670 --> 00:37:40,173
Now, we can think about
ionic bonding for sure,

765
00:37:40,173 --> 00:37:41,207
which is what we've done.

766
00:37:41,207 --> 00:37:43,443
But more importantly,
what Lewis helps

767
00:37:43,443 --> 00:37:45,979
us with is to think
about covalent bonding.

768
00:37:45,979 --> 00:37:48,081
And that's the
subject of Wednesday,

769
00:37:48,081 --> 00:37:49,682
which is a whole
other type of bonding

770
00:37:49,682 --> 00:37:50,950
that we're going to talk about.

771
00:37:53,219 --> 00:37:56,956
OK, so now, the last digit of
the element group, OK, good.

772
00:37:56,956 --> 00:37:59,959
So there it predicts number of
bonds formed by most elements

773
00:37:59,959 --> 00:38:01,294
in their compounds, good.

774
00:38:01,294 --> 00:38:02,195
And there is the dots.

775
00:38:02,195 --> 00:38:05,732
Look at that example,
fluorine, or using

776
00:38:05,732 --> 00:38:09,669
noble gas notation, helium,
that really saved us time.

777
00:38:09,669 --> 00:38:11,371
I didn't have to write 1s2.

778
00:38:11,371 --> 00:38:13,873
Actually, this looks like
four strokes of the pen.

779
00:38:13,873 --> 00:38:15,475
1s2 would have been three.

780
00:38:15,475 --> 00:38:16,943
I don't know, honestly.

781
00:38:16,943 --> 00:38:20,080
But anyway, OK,
there is fluorine.

782
00:38:20,080 --> 00:38:21,181
And look, one dot?

783
00:38:21,181 --> 00:38:21,681
No.

784
00:38:21,681 --> 00:38:22,182
Two dots?

785
00:38:22,182 --> 00:38:24,651
No, because you add a
dot for the valence.

786
00:38:24,651 --> 00:38:28,421
So fluorine has seven dots
until you reach the valence,

787
00:38:28,421 --> 00:38:31,057
until you reach the valence.

788
00:38:31,057 --> 00:38:35,161
That is the key of
the Lewis picture.

789
00:38:35,161 --> 00:38:37,497
And we talked about this before.

790
00:38:37,497 --> 00:38:38,665
We talked about this before.

791
00:38:38,665 --> 00:38:41,868
Because it showed there were
three really important things

792
00:38:41,868 --> 00:38:44,404
that come out of
the Lewis picture.

793
00:38:44,404 --> 00:38:48,842
One is it tells us,
as I've just told you,

794
00:38:48,842 --> 00:38:52,745
it tells us about
bond formation.

795
00:38:59,119 --> 00:39:02,222
It tells us about
bond formation.

796
00:39:02,222 --> 00:39:12,899
And it makes the assumption
that the valence electrons

797
00:39:12,899 --> 00:39:20,106
are what matter for chemistry.

798
00:39:20,106 --> 00:39:21,374
And this is critical.

799
00:39:21,374 --> 00:39:23,877
And I've alluded to this before.

800
00:39:23,877 --> 00:39:25,945
You now have a real
sense of this, though.

801
00:39:25,945 --> 00:39:28,615
From these energy diagrams,
you have a sense of this.

802
00:39:28,615 --> 00:39:33,720
Because look, if I want to rip
an electron off of lithium,

803
00:39:33,720 --> 00:39:35,855
I got to spend 5.4
electron volts.

804
00:39:35,855 --> 00:39:37,323
If I want to rip
the next one off,

805
00:39:37,323 --> 00:39:40,026
I got to spend over
100 electron volts.

806
00:39:40,026 --> 00:39:42,495
And we said, well, we'll do
PES with all these energies.

807
00:39:42,495 --> 00:39:43,229
It doesn't matter.

808
00:39:43,229 --> 00:39:43,997
I'll get 'em all.

809
00:39:43,997 --> 00:39:47,066
But what if I just
want to say, well,

810
00:39:47,066 --> 00:39:51,905
what electrons are going to
be available to participate

811
00:39:51,905 --> 00:39:53,973
in something like a bond?

812
00:39:53,973 --> 00:39:54,807
Which ones?

813
00:39:54,807 --> 00:39:56,376
It's going to be these ones.

814
00:39:56,376 --> 00:39:58,678
It's not going to be the
ones all the way in close

815
00:39:58,678 --> 00:40:01,447
to the core that don't
want to be bothered

816
00:40:01,447 --> 00:40:04,851
and they've got so much energy.

817
00:40:04,851 --> 00:40:08,454
Just to get their
attention takes 100 EV.

818
00:40:08,454 --> 00:40:09,722
And even that's not a--

819
00:40:09,722 --> 00:40:12,592
But here, a little
visible light and I

820
00:40:12,592 --> 00:40:15,195
got lithium talking to me.

821
00:40:15,195 --> 00:40:18,865
Well, chemically, it's the same.

822
00:40:18,865 --> 00:40:20,567
That's light, right?

823
00:40:20,567 --> 00:40:23,803
These ones are the ones
that want to and can

824
00:40:23,803 --> 00:40:25,672
participate in bonding.

825
00:40:25,672 --> 00:40:29,309
The ones all the way down in
energy, way, way, way low,

826
00:40:29,309 --> 00:40:31,244
they're inert.

827
00:40:31,244 --> 00:40:32,645
They're inert, all right?

828
00:40:32,645 --> 00:40:35,081
So most of chemistry
happens in the valence.

829
00:40:35,081 --> 00:40:38,952
And Lewis really nailed that.

830
00:40:38,952 --> 00:40:41,888
So these dots are only
valence electron dots.

831
00:40:45,091 --> 00:40:46,960
And there's one more rule.

832
00:40:46,960 --> 00:40:50,763
Now, OK, so there is the
seven dots for fluorine.

833
00:40:50,763 --> 00:40:55,435
And then, OK, sometimes
you'll see this.

834
00:40:55,435 --> 00:40:57,837
Oh, this is just
the number of dots.

835
00:40:57,837 --> 00:41:03,610
It's this classification
of the columns, all right,

836
00:41:03,610 --> 00:41:04,477
the groups in a pair.

837
00:41:04,477 --> 00:41:08,581
But, no, that is not
OK, not standard.

838
00:41:08,581 --> 00:41:11,251
Remember, the
IUPAC, which throws

839
00:41:11,251 --> 00:41:15,989
the best, most lively
parties and conferences,

840
00:41:15,989 --> 00:41:17,857
they decide on how
to name elements.

841
00:41:17,857 --> 00:41:21,394
And many, many other aspects of
our lives are decided by them.

842
00:41:21,394 --> 00:41:23,930
And they said, no, that's
an old classification.

843
00:41:23,930 --> 00:41:25,398
It's confusing.

844
00:41:25,398 --> 00:41:28,668
So we're going to go with the
standard, which is that we

845
00:41:28,668 --> 00:41:32,705
still count 1 to 18, 1 to 18.

846
00:41:32,705 --> 00:41:34,674
1, 2-- s-block.

847
00:41:34,674 --> 00:41:37,644
13 to 18-- p-block.

848
00:41:37,644 --> 00:41:38,177
All right?

849
00:41:38,177 --> 00:41:41,014
OK, that's cool.

850
00:41:41,014 --> 00:41:44,784
3 to 12-- d-block.

851
00:41:44,784 --> 00:41:46,653
We're going back and forth.

852
00:41:46,653 --> 00:41:50,823
But you can just take the last
digit there, IUPAC standard.

853
00:41:50,823 --> 00:41:53,359
Even the periodic
table talks about it.

854
00:41:53,359 --> 00:41:54,294
It shows it.

855
00:41:54,294 --> 00:41:56,462
It shows the old
classification there.

856
00:41:56,462 --> 00:41:59,932
And then it says, no, don't
use it, it's confusing.

857
00:41:59,932 --> 00:42:01,701
Well, then why do they show it?

858
00:42:01,701 --> 00:42:03,736
Because some textbooks
still show it.

859
00:42:03,736 --> 00:42:07,073
So I want you to
be aware of that.

860
00:42:07,073 --> 00:42:13,212
OK, now, you can
use Lewis, you can

861
00:42:13,212 --> 00:42:17,550
use this idea of only
thinking about the valence

862
00:42:17,550 --> 00:42:22,088
to understand when atoms have
similar chemistry, all right?

863
00:42:22,088 --> 00:42:27,060
So if the valence of
carbon is the same

864
00:42:27,060 --> 00:42:29,729
as the valence of silicon,
you've bumped down one quantum

865
00:42:29,729 --> 00:42:33,099
number, but they both
have 4 electrons out there

866
00:42:33,099 --> 00:42:34,367
in the valence.

867
00:42:34,367 --> 00:42:36,035
In this case, it's 2.

868
00:42:36,035 --> 00:42:38,271
In this case, it's 3, in
terms of the quantum number.

869
00:42:38,271 --> 00:42:39,872
But they both have
those same kinds of

870
00:42:39,872 --> 00:42:41,374
and same number of electrons.

871
00:42:41,374 --> 00:42:45,078
So you can maybe expect there
to be similar chemistry.

872
00:42:45,078 --> 00:42:46,479
It turns out, in
this case, there

873
00:42:46,479 --> 00:42:47,647
is very different chemistry.

874
00:42:47,647 --> 00:42:48,915
But we'll learn about that.

875
00:42:48,915 --> 00:42:50,283
Carbon-- hybridisation.

876
00:42:50,283 --> 00:42:52,852
Silicon-- no.

877
00:42:52,852 --> 00:42:53,853
We'll get to that.

878
00:42:53,853 --> 00:42:56,356
But still, this is how
we see silicon now.

879
00:42:56,356 --> 00:42:58,257
We don't see it
this way with Lewis.

880
00:42:58,257 --> 00:42:59,425
We see it this way.

881
00:42:59,425 --> 00:43:02,362
This is how we see carbon.

882
00:43:02,362 --> 00:43:05,898
And so I want you to start
seeing elements this way.

883
00:43:05,898 --> 00:43:07,967
OK, and so you can
look at periodic tables

884
00:43:07,967 --> 00:43:12,205
and take images randomly
found online with Lewis dots.

885
00:43:12,205 --> 00:43:15,508
And you can start
thinking of atoms

886
00:43:15,508 --> 00:43:18,177
as their Lewis-dot
representation.

887
00:43:18,177 --> 00:43:19,645
And like I said,
on Wednesday we're

888
00:43:19,645 --> 00:43:23,216
going to make a whole bunch
of structures, molecules,

889
00:43:23,216 --> 00:43:26,853
with Lewis dots and show
how that teaches us,

890
00:43:26,853 --> 00:43:29,555
not only about how
to draw the bonds,

891
00:43:29,555 --> 00:43:32,625
but, literally,
about which bonding--

892
00:43:32,625 --> 00:43:36,596
You know, if I have sodium and
chlorine, it's pretty obvious.

893
00:43:36,596 --> 00:43:41,100
If there is a bond, it's between
sodium and chlorine, all right?

894
00:43:41,100 --> 00:43:42,769
But as I go to
more and more atoms

895
00:43:42,769 --> 00:43:45,171
and I'm trying to
form molecules,

896
00:43:45,171 --> 00:43:50,009
it's not so obvious what
is bonded to what and how.

897
00:43:50,009 --> 00:43:53,079
All right, and
thinking about this

898
00:43:53,079 --> 00:43:56,482
and thinking about the
third part of what Lewis

899
00:43:56,482 --> 00:44:00,486
did that was so
important is what

900
00:44:00,486 --> 00:44:06,092
allows us to draw a whole
bunch of molecules--

901
00:44:06,092 --> 00:44:11,497
Octet rule, which
is that atoms like--

902
00:44:15,568 --> 00:44:19,806
we now know "like"
means lower energy--

903
00:44:19,806 --> 00:44:28,681
to reach 8 electrons
in their valence.

904
00:44:28,681 --> 00:44:32,985
OK, well, we can already
see this for the ionic bond

905
00:44:32,985 --> 00:44:33,986
that we've talked about.

906
00:44:33,986 --> 00:44:35,822
And you can write this.

907
00:44:35,822 --> 00:44:39,559
And I want you to write
ionic bonds using Lewis.

908
00:44:39,559 --> 00:44:43,996
But in this case, it's actually
pretty straightforward, right?

909
00:44:43,996 --> 00:44:46,632
If I had, for example--

910
00:44:46,632 --> 00:44:51,037
let's get some more
board space over here.

911
00:44:58,744 --> 00:45:02,648
If I had, for
example, an ionic bond

912
00:45:02,648 --> 00:45:12,091
between cesium and fluorine, so
if I had cesium and fluorine,

913
00:45:12,091 --> 00:45:15,595
then the way I would think
about this in the Lewis world

914
00:45:15,595 --> 00:45:22,468
would be this way and this way.

915
00:45:25,037 --> 00:45:27,940
Because I've got 7 valence
electrons in fluorine and 1

916
00:45:27,940 --> 00:45:28,608
in cesium.

917
00:45:28,608 --> 00:45:31,410
And then, if I write
this as an ionic bond,

918
00:45:31,410 --> 00:45:37,650
the way I would write it is
cesium-plus with fluorine

919
00:45:37,650 --> 00:45:39,986
having taken that electron.

920
00:45:42,989 --> 00:45:45,391
And so you would write this
still with the minus sign

921
00:45:45,391 --> 00:45:45,892
there.

922
00:45:45,892 --> 00:45:47,660
That emphasizes.

923
00:45:47,660 --> 00:45:50,129
It emphasizes what happened.

924
00:45:50,129 --> 00:45:52,832
But I see my Lewis here.

925
00:45:52,832 --> 00:45:54,767
You know, I see it there.

926
00:45:54,767 --> 00:45:58,237
But I'm emphasizing that this is
an ionic bond that's happened.

927
00:45:58,237 --> 00:46:02,008
Because fluorine wasn't supposed
to have 8, but then it did.

928
00:46:02,008 --> 00:46:04,210
It's got a super-high
electron affinity.

929
00:46:04,210 --> 00:46:07,480
Cesium has a very low ionization
energy of its first electron.

930
00:46:07,480 --> 00:46:09,749
And so fluorine just took it.

931
00:46:09,749 --> 00:46:11,417
It literally just took it.

932
00:46:11,417 --> 00:46:12,184
I'll take that.

933
00:46:12,184 --> 00:46:13,052
Thank you very much.

934
00:46:13,052 --> 00:46:16,389
You know, I'm not
being judgmental.

935
00:46:16,389 --> 00:46:19,058
But ionic bonds are
kind of, you know,

936
00:46:19,058 --> 00:46:22,295
the relationship in a bond--
and I don't want to judge--

937
00:46:22,295 --> 00:46:25,765
but the relationship
is not even.

938
00:46:25,765 --> 00:46:26,599
It's not even.

939
00:46:26,599 --> 00:46:28,367
And that's OK.

940
00:46:28,367 --> 00:46:31,704
But fluorine said,
take, take, give.

941
00:46:31,704 --> 00:46:33,573
And cesium atom, OK, fine.

942
00:46:33,573 --> 00:46:36,409
Now, on Wednesday when we do
covalent bonds, it's not so--

943
00:46:36,409 --> 00:46:40,713
then there's a lot more
sharing that happens.

944
00:46:40,713 --> 00:46:43,215
And that's why we can
model it the way that I--

945
00:46:43,215 --> 00:46:44,984
yes, I still left there--

946
00:46:44,984 --> 00:46:46,619
we can model it that way.

947
00:46:46,619 --> 00:46:51,657
Because it is like a charged
atom and another charged atom,

948
00:46:51,657 --> 00:46:52,558
all right?

949
00:46:52,558 --> 00:46:55,061
And it's because
fluorine took it.

950
00:46:55,061 --> 00:46:55,995
Fluorine took it.

951
00:46:55,995 --> 00:46:57,396
It's OK.

952
00:46:57,396 --> 00:46:59,665
Any kind of relationship,
you know, they get along.

953
00:46:59,665 --> 00:47:01,067
They make it work.

954
00:47:01,067 --> 00:47:07,039
Now, what we can also do
just in thinking about this,

955
00:47:07,039 --> 00:47:09,275
just in thinking
about this, I can

956
00:47:09,275 --> 00:47:12,945
go to another
example like calcium.

957
00:47:12,945 --> 00:47:17,850
And if I think about
calcium and fluorine,

958
00:47:17,850 --> 00:47:20,853
well, I know again fluorine
likes to be f-minus.

959
00:47:20,853 --> 00:47:24,490
But see, calcium, when I think
about it as a Lewis atom,

960
00:47:24,490 --> 00:47:28,661
you know, calcium likes
to lose both of those.

961
00:47:28,661 --> 00:47:30,730
Calcium, often,
because, remember,

962
00:47:30,730 --> 00:47:34,500
they want to get
to the Octet rule.

963
00:47:34,500 --> 00:47:36,535
They want to reach
their 8 electrons.

964
00:47:36,535 --> 00:47:38,270
But calcium has got
2, what do I do?

965
00:47:38,270 --> 00:47:42,975
Either somebody gives me
6, not going to happen,

966
00:47:42,975 --> 00:47:45,111
or I can lose 2.

967
00:47:45,111 --> 00:47:47,346
And so what you get is
that calcium will go,

968
00:47:47,346 --> 00:47:50,282
you know, to Ca2-plus.

969
00:47:50,282 --> 00:47:52,151
But fluorine is
still just f-minus.

970
00:47:52,151 --> 00:47:56,322
Right from this I know that
the balance stoichiometry, that

971
00:47:56,322 --> 00:47:59,825
is to say how many
calcium atoms I need

972
00:47:59,825 --> 00:48:03,529
to stabilize this whole
ionic bond situation,

973
00:48:03,529 --> 00:48:04,930
is going to be 2, right?

974
00:48:04,930 --> 00:48:09,201
I got to go to calcium F2.

975
00:48:09,201 --> 00:48:11,570
And if I were
going to write this

976
00:48:11,570 --> 00:48:13,973
with emphasizing
the ionic bond, I

977
00:48:13,973 --> 00:48:17,143
might put brackets around just
so it's really easy to see,

978
00:48:17,143 --> 00:48:17,743
2-plus.

979
00:48:17,743 --> 00:48:19,512
There's no dots left.

980
00:48:19,512 --> 00:48:21,213
Because now I'm writing
it in a way where

981
00:48:21,213 --> 00:48:23,949
I've emphasized that--

982
00:48:23,949 --> 00:48:26,552
gesundheit-- that F took it.

983
00:48:26,552 --> 00:48:27,987
It took it.

984
00:48:27,987 --> 00:48:30,690
And it is minus.

985
00:48:30,690 --> 00:48:34,193
And there's two
of them, you see?

986
00:48:34,193 --> 00:48:38,664
So that would be like thinking
about an ionic bond, all right,

987
00:48:38,664 --> 00:48:41,434
but from the Lewis-dot
vantage point where I really

988
00:48:41,434 --> 00:48:47,673
see that fluorine
took the charge, OK?

989
00:48:47,673 --> 00:48:49,308
OK, so I think--

990
00:48:49,308 --> 00:48:53,145
oh, ho, you could go further.

991
00:48:53,145 --> 00:48:54,080
You can go further.

992
00:48:54,080 --> 00:48:55,214
I think we'll stop there.

993
00:48:55,214 --> 00:48:58,384
And on Wednesday, like I said,
we're going Lewis all the way

994
00:48:58,384 --> 00:49:02,488
and we're doing covalent
molecules, covalent bonds.