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PROFESSOR: OK.
 

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Let's get started.
 

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Can you go ahead and take 10
more seconds on this first

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clicker question here?
 

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OK.
 

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So it looks like most of
you got that the electron

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configuration that we're
writing here is for copper.

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So I'm actually going to give
the benefit of the doubt that

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the people that didn't get it
right were rushing to get out

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their clickers and didn't have
time to think it all

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the way through.
 

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Remember that when we're
talking about 4 s 1, 3 d 10,

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that's one of those exceptions
where a completely filled d

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orbital is more stable
than we would expect.

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So, that's actually the
electron configuration we have

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when we're talking about copper
and some other exceptions in

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the periodic table that you're
going to be looking at.

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So, hopefully, if you were to
go back and look you could see

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that this is, in fact, copper.
 

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We're actually going to do one
more clicker question to get

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started with today, and as we
do, I'll explain something

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we're going to be trying today,
which is a little bit of a

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friendly competition in terms
of answering the clicker

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questions correctly.
 

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So we've tagged each of your
numbers to your actual

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recitation, so we can see today
which recitation actually is

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going to be doing the best in
terms of clicker questions,

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who's going to get the
most correct today.

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So, you may or may not know
this about your TAs, but this

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is a pretty competitive group
of TAs we have this year, and

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they like to brag about how
smart their recitation is, how

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good questions they're getting
in the recitation section.

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So, do your TA proud today and
see if you can be part of the

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recitation that gets the most
correct in terms

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of a percentage.
 

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And at the end of class we'll
announce which recitation that

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is, we'll also make sure to
give you a little bit of a

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prize if you are, in fact,
in that recitation.

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So we have extra incentive
to get these clicker

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questions right.
 

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So, in this one we're selecting
the correct electronic

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configuration for an ion.
 

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So, why don't you go ahead and
take 10 more seconds on this

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second clicker question
for our intro.

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OK.
 

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So, it looks like we
have a little bit of a

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mixed consensus here.
 

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Let's go over this question.
 

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And I know there's a lot
to talk about about this

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competition, but let's just get
into listening mode here and

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talk about how we can figure
out what the correct electron

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configuration is for this ion.
 

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Remember, ions are a
little bit different.

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The first thing we need to
do is write the electron

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configuration for the atom
itself, and then we need

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to take an electron away.
 

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So here we're talking about v
plus 1, so if we were to write

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it just for the neutral
electron itself, we would find

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that the electron configuration
is argon, that's the filled

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shell in front of it.
 

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Then 4 s 2 and 3 d 3.
 

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So this would be for
the actual filled, the

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completely neutral atom.
 

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But remember what we said,
which was when we talked about,

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this is at the end of class on
Friday, we said that it turns

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out that even though 3 d is
higher in energy when it's not

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filled, once we fill it with an
electron, these 2 orbitals

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actually switch place
in terms of energy.

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So if we were to write this in
terms of energy, we would

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actually have to rewrite it
has 3 d 3, and then 4 s 2.

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So, which orbital would we take
an electron out of if we were

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ionizing this atom here?
 

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The s.
 

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So, we would actually take an
electron out of the s, which

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gives us 3 d 3 and then 4 s 1.
 

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So, it's a little bit
of a trick when you're

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dealing with ions.
 

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The best suggestion is just to
write it out completely for the

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neutral atom, and then you want
to take an electron out

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of the highest orbital.
 

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It makes sense that it's going
to come out of the highest

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occupied atomic orbital,
because that's going to be the

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lowest amount of energy that's
required to actually

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eject an electron.
 

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All right.
 

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So let's go to today's notes.
 

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And actually before we start
into today's topics, I want to

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remind everyone and hopefully
you all do remember that our

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first exam is coming up and
it's coming up in exactly a

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week, so it'll be a week
from today, next Wednesday.

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And on Friday in class, at the
beginning of class, I'll go

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over just in all the detail you
could possibly imagine

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everything you need to know
logistically for the exam --

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where it is, what you do, what
kind of calculators you can

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bring, which by the way
are any calculator.

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So you'll get all of that
information on Friday.

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So don't worry if you have
some questions right now.

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I just want to let
you know that.

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The other thing I want to let
you know is that instead of

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having a new problem-set that
you'll be assigned this Friday,

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what we'll do instead is we'll
give you some practice

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problems, and these will be
just more of the same type of

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problems that you saw before
but that's another chance

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to try them out more.
 

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These won't be graded, you
don't have to turn them in,

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it's just to give you some
extra practice if you want

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while you're studying
for the exam.

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We'll also post an exam from
a previous year so you can

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actually see exactly what the
format's going to look like.

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So when you go into the exam a
week from today, it'll all look

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really familiar, you'll be
comfortable with the format and

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you can just dive right in and
start answering the questions.

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So you'll have all that
information and we'll get

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it to you on Friday.
 

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The other quick thing I want to
say is that I do have office

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hours today from 3 to 5, so
feel free to stop by if you

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have questions about
problem-set 3 that

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you're finishing up.
 

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And also, for those of you that
did sign up for the pizza forum

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tonight, that's going to be at
5 o'clock, it's in room 56-502,

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so we'll see some of you
tonight for that as well.

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All right.
 

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So, let's move on to what
we're talking about today.

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What we're going to start with
is discussing photoelectron

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spectroscopy, which is a
spectroscopy technique that

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will give us some information
about energy levels in

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multielectron atoms.
 

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We'll then take a turn to
talking about the periodic

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table, we'll look at a bunch of
periodic trends, including

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ionization energy, electron
affinity, electronegativity

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and atomic radius.
 

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And then, if we have time at
the end, we'll introduce

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one last topic, which is
isoelectronic atoms and ions.

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I also want to note that the
end of the material today, so

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this last topic here, that's
the end of the material that's

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going to be on this first exam.
 

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So whether we finish it today,
or more likely when we finish

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it up on Friday, once we get
passed isoelectronic atoms,

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that's it, that's all you need
to study for this first exam.

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So from that point on it'll be
exam 2 material, so depending

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on how you like to come
compartmentalize your

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information, you can separate
that in your brain in terms of

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what you're trying to learn
right now versus what you

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can put off until a
little bit later.

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So, let's start with talking
about photoelectron

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spectroscopy.
 

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This actually relates very
closely to what we discussed in

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class on Friday before the long
weekend, and what we were

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talking about is the energy
levels of multielectron atoms.

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So what we'll start with today
is talking about the technique

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that's primarily used to
actually experimentally figure

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out what these different
energy levels are.

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And this is called
photoelectron spectroscopy, and

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essentially what it is is very
similar conceptually to what we

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were talking about way back in
the first couple lectures when

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we were talking about the
photoelectric effect.

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Because here what we have is
some atom that we're studying,

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in the case, it's going to be a
gas, and we hit it with a

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photon that has some
incident energy.

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So e sub i, some energy that
the photon comes in with, and

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if it has sufficient energy to
eject an electron, it will do

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that, and our electron will be
ejected with a certain kinetic

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energy, which is going to be
whatever energy is left over

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from the initial energy we put
in minus what was taken up in

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order to actually ionize
or eject the electron.

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So, you can see how this can
directly give us different

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ionization energies for
any atom that we're

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interested in studying.
 

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For example, with neon we
can think about all of the

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different orbital energies
we could be looking at.

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In the first case, so
here is the electron

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configuration of neon.
 

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So we can think about what is
our most loosely-bound

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electron, what's that highest
energy orbital, and it's going

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to be the 2 p orbital, that's
going to be what's

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highest in energy.
 

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So if we're going to eject an
electron using a minimum amount

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of energy, that's where
it's going to come from.

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So, you can imagine, that we'll
actually probably have a lot of

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kinetic energy left over if we
put a lot of energy in

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in the first place.
 

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We're only using up a little
bit to eject the electron, then

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we'll have a lot left over.
 

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So, one difference between
photoelectron spectroscopy and,

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for example, the photoelectric
effect is that in this case,

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we're not just looking at one
energy level, which is what we

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were looking at from the
surface of a metal, now we're

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talking about this
gaseous atom.

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So we can actually pop an
electron or eject an electron

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from any single orbital that
is occupied within the atom.

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So, for example, it's not just
the 2 p that we could actually

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take an electron from, we could
also think about ejecting an

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electron from the 2 s orbital.
 

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Now this, of course, is going
to take more energy because a 2

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s is lower, it has has a more
negative binding energy than

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the 2 p, but that's OK as long
as we put in enough energy, but

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what we're going to find is the
kinetic energy coming out with

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the electron is actually going
to be a little bit less, right,

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because we had to use up more
energy to eject the electron,

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so we don't have as
much left over.

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There's actually one more
orbital that we could talk

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about if we're talking about
this sample case of neon, which

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is a 1 s orbital, and if we're
talking about a 1 s orbital,

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now we're going to be even
lower in energy still, so that

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means the minimum energy
required to eject an electron

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is going to be at its highest,
so that means the energy that

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we have left over that turns
into kinetic energy for the

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electron, is now going to
be really quite small.

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And what happens when you
irradiate one of these atoms

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that you're studying with this
light is in photoelectron

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spectroscopy, you want to make
sure that you put in enough

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energy to actually ionize
any single electron that

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you have in the atom.
 

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So the way that we really
make sure this is done

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is that we use x-rays.
 

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So you know that x-rays are
higher frequency than UV light,

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for example, that means it's
also higher energy than UV

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light, and if you think back to
our photoelectric effect

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experiments, do you remember
what type of light we were

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usually using for those?
 

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Does anyone remember?
 

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Yeah.
 

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It was UV light that we used.
 

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Well, we can't guarantee with
UV light we'll have enough

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energy to eject every single
electron, so that's why when we

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use x-rays, they're higher
energy, you can pretty much be

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guaranteed we're going to eject
all of those electrons there.

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So I said that this technique
was used to experimentally

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determine what the different
binding energies or the

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different ionization energies
are for the different states

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in a multielectron atom.
 

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Another way to say states is to
talk about different orbitals.

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So we can do this directly
as long as we have certain

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types of information.
 

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The first that we need to know
the energy of the photon that's

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incident on our gaseous atom.
 

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The second piece of information
we need to know is what

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actually the kinetic energy is
of the ejected electron, and

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that's something we can just
measure by measuring

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its velocity.
 

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So we can use an equation to
relate the incident energy and

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the kinetic energy to the
ionization energy, or the

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energy that's required
to eject an electron.

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This should all sound
incredibly familiar, like I'm

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just repeating myself in terms
of photoelectric effect,

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because essentially that's what
I'm doing, and that's one

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reason we spent so much time
and did so many problem-set

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problems on the
photoelectric effect.

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So what we're saying here is
the incident energy, so the

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energy coming in, is just equal
to the minimum energy that's

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required to a eject
an electron.

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When we talked about the
photoelectric effect, that was

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called the work function.
 

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In this case, it's called the
ionization energy, plus

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whatever kinetic energy we have
left over in the electron.

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So if we want to solve for
ionization energy, we can just

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rearrange this equation.
 

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Our ionization energy is going
to be equal to the incident

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energy coming in, minus the
kinetic energy of the electron.

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00:12:40 --> 00:12:43
So, let's take a look at the
different kinetic energies that

269
00:12:43 --> 00:12:47
would be observed in a spectrum
for neon where we had this

270
00:12:47 --> 00:12:49
incident energy here.
 

271
00:12:49 --> 00:12:51
And it turns out that the first
kinetic energy that we would

272
00:12:51 --> 00:12:54
see or the highest kinetic
energy, would be 12

273
00:12:54 --> 00:12:56
32 electron volts.
 

274
00:12:56 --> 00:13:00
So if that's the case doing a
quick little calculation, what

275
00:13:00 --> 00:13:03
would the ionization energy be
for a 2 p electron in neon?

276
00:13:03 --> 00:13:07
Yup, 22.
 

277
00:13:07 --> 00:13:12
So, basically all we did was
take 12 54, subtract 12 32,

278
00:13:12 --> 00:13:15
and we got 22 electron volts.
 

279
00:13:15 --> 00:13:17
We can do the same thing
for the other observed

280
00:13:17 --> 00:13:18
kinetic energy.
 

281
00:13:18 --> 00:13:22
So, for example, in the second
case, we say that we see 12 06

282
00:13:22 --> 00:13:24
in terms of the kinetic energy.
 

283
00:13:24 --> 00:13:26
Same sort of subtraction
problem, what do we have

284
00:13:26 --> 00:13:30
for the ionization energy
of the 2 s electron?

285
00:13:30 --> 00:13:30
Good, quick math.
 

286
00:13:30 --> 00:13:32
All right, so 48
electron volts.

287
00:13:32 --> 00:13:35
And let's look at the final
kinetic energy that we'd

288
00:13:35 --> 00:13:39
observe in this spectrum, which
is 384 electron volts, so what

289
00:13:39 --> 00:13:44
is that third corresponding
ionization energy?

290
00:13:44 --> 00:13:46
I couldn't quite hear, but
I have a feeling everyone

291
00:13:46 --> 00:13:50
said 870 electron volts.
 

292
00:13:50 --> 00:13:53
So, we can actually kind of
visualize what we would see

293
00:13:53 --> 00:13:56
if we were looking at a
photoelectron spectrum.

294
00:13:56 --> 00:13:59
And what we would see if we
were graphing, for example,

295
00:13:59 --> 00:14:02
increasing kinetic energy,
is we would see 1 line

296
00:14:02 --> 00:14:06
corresponding to each of
these energies of electrons

297
00:14:06 --> 00:14:07
that we see coming out.
 

298
00:14:07 --> 00:14:10
And, of course, each of those
electrons correspond to an

299
00:14:10 --> 00:14:13
electron coming out of
a particular orbital.

300
00:14:13 --> 00:14:18
So in the case of 12 32, that
is our highest kinetic energy,

301
00:14:18 --> 00:14:21
that means it's our lowest
ionization energy -- it's the

302
00:14:21 --> 00:14:23
smallest amount of energy it
takes to pop an electron

303
00:14:23 --> 00:14:25
out of that orbital.
 

304
00:14:25 --> 00:14:29
So that's why we see the 2 p
here, the 2 s is 12 06, and it

305
00:14:29 --> 00:14:33
makes sense that what we see as
the greatest ionization energy,

306
00:14:33 --> 00:14:36
which is also the smallest
kinetic energy is

307
00:14:36 --> 00:14:37
that 1 s orbital.
 

308
00:14:37 --> 00:14:40
Remember, because that 1 s
orbital is all the way down in

309
00:14:40 --> 00:14:42
terms of if we're thinking
about an energy diagram, we're

310
00:14:42 --> 00:14:45
all the way down here, so we
have a huge amount of energy we

311
00:14:45 --> 00:14:49
have to put into the system in
order to eject an electron.

312
00:14:49 --> 00:14:51
So what I want to point out
when you're kind of looking at

313
00:14:51 --> 00:14:53
these numbers here, what the
significance is, look at that

314
00:14:53 --> 00:14:57
huge difference between what
the ionization energies are for

315
00:14:57 --> 00:15:00
what we call those valence
electrons, those outer shell

316
00:15:00 --> 00:15:03
electrons, versus the
ionization energy for the 1

317
00:15:03 --> 00:15:06
s orbital -- those are
core electrons there.

318
00:15:06 --> 00:15:09
So we can think about something
I mentioned last time, which is

319
00:15:09 --> 00:15:11
when we're thinking about
chemistry and what's really

320
00:15:11 --> 00:15:13
interesting in terms of
chemical reactions, it's mostly

321
00:15:13 --> 00:15:16
valence electrons we're talking
about, those are the ones that

322
00:15:16 --> 00:15:18
tend to be involved in
chemical reactions.

323
00:15:18 --> 00:15:21
It makes a lot of sense when we
look at it energetically,

324
00:15:21 --> 00:15:24
because if we think about a 1 s
core electron, that's going

325
00:15:24 --> 00:15:27
to be held really, really
tightly to the nucleus.

326
00:15:27 --> 00:15:30
We see that we have to put this
huge energy in to actually get

327
00:15:30 --> 00:15:33
a 1 s electron ejected, so it
makes a lot of sense that we

328
00:15:33 --> 00:15:36
wouldn't want to pay that
energy cost in a normal

329
00:15:36 --> 00:15:37
chemical reaction.
 

330
00:15:37 --> 00:15:40
And we don't -- we very rarely
would see these core electrons

331
00:15:40 --> 00:15:44
actually being involved in
any type of a reaction.

332
00:15:44 --> 00:15:47
All right, so one thing that I
want to point out, which I said

333
00:15:47 --> 00:15:50
many, many times on Friday, and
this is perhaps the last time

334
00:15:50 --> 00:15:53
I'll say it, but one last time
is we can think about why we

335
00:15:53 --> 00:15:56
only see a line for the 2 p
orbital, versus we don't see

336
00:15:56 --> 00:16:00
separate lines for a 2 p
x, a 2 p y, and a 2 p z.

337
00:16:00 --> 00:16:03
Remember, we need those three
quantum numbers to completely

338
00:16:03 --> 00:16:04
describe the orbital.
 

339
00:16:04 --> 00:16:06
Why do we just see
one for all the p's?

340
00:16:06 --> 00:16:09
And the reason is that the
energy of the orbitals, depend

341
00:16:09 --> 00:16:12
on two quantum numbers, and
that's quantum number n,

342
00:16:12 --> 00:16:13
and quantum number l.
 

343
00:16:13 --> 00:16:16
M does not actually have an
effect, in this case, on

344
00:16:16 --> 00:16:18
the energy of the orbital.
 

345
00:16:18 --> 00:16:20
So that's why we're not
seeing separate lines

346
00:16:20 --> 00:16:24
in this spectrum.
 

347
00:16:24 --> 00:16:24
All right.
 

348
00:16:24 --> 00:16:28
So let's go ahead and try an
example here in thinking about

349
00:16:28 --> 00:16:29
photoelectron spectroscopy.
 

350
00:16:29 --> 00:16:33
So, let's say we're looking at
an element and we have an

351
00:16:33 --> 00:16:35
emission spectra, and we know
that it has five distinct

352
00:16:35 --> 00:16:38
different kinetic energies
in that spectrum.

353
00:16:38 --> 00:16:42
We might be asked, for example,
to determine what all of the

354
00:16:42 --> 00:16:45
different elements could be
that would produce a spectrum

355
00:16:45 --> 00:16:47
that gave us 5 different lines.
 

356
00:16:47 --> 00:16:49
So the first thing that we want
to do, if we're thinking about

357
00:16:49 --> 00:16:56
something like this, is just to
determine exactly what orbitals

358
00:16:56 --> 00:16:59
are causing the five different
lines that we're seeing

359
00:16:59 --> 00:17:00
in the spectrum.
 

360
00:17:00 --> 00:17:03
So, if we're talking about five
different orbitals and we're

361
00:17:03 --> 00:17:05
talking about a ground state
atom, we know that we just

362
00:17:05 --> 00:17:08
need to start at the bottom
and work our way out up.

363
00:17:08 --> 00:17:10
So, our first orbital
that an electron must be

364
00:17:10 --> 00:17:11
coming from is the 1 s.
 

365
00:17:11 --> 00:17:13
What comes after that?
 

366
00:17:13 --> 00:17:15
2 s.
 

367
00:17:15 --> 00:17:16
All right, then what?
 

368
00:17:16 --> 00:17:20
2 p.
 

369
00:17:20 --> 00:17:22
After that?
 

370
00:17:22 --> 00:17:23
3 s.
 

371
00:17:23 --> 00:17:25
Next?
 

372
00:17:25 --> 00:17:31
3 p, and that's 1, 2, 3, 4 --
that gives us five different

373
00:17:31 --> 00:17:34
options, five different
orbitals, five different

374
00:17:34 --> 00:17:35
energies right there.
 

375
00:17:35 --> 00:17:38
So, then all we need to do to
determine which elements that

376
00:17:38 --> 00:17:41
corresponds to is take a
look at our periodic table.

377
00:17:41 --> 00:17:45
So we want to look at any
element that has a 3 p orbital

378
00:17:45 --> 00:17:49
filled, but that does not then
go on and have a 4 s, because

379
00:17:49 --> 00:17:51
if it had the 4 s filled then
we would actually see six

380
00:17:51 --> 00:17:53
lines in the spectrum.
 

381
00:17:53 --> 00:17:58
So that is relevant for all
of these atoms here, so

382
00:17:58 --> 00:18:00
we actually have several
different possibilities.

383
00:18:00 --> 00:18:06
It could be aluminum, silicone,
phosphorous, sulfur,

384
00:18:06 --> 00:18:09
chlorine or argon.
 

385
00:18:09 --> 00:18:12
Any one of these different
elements could actually produce

386
00:18:12 --> 00:18:16
a photoelectron spectroscopy
spectrum that has

387
00:18:16 --> 00:18:18
five distinct lines.
 

388
00:18:18 --> 00:18:20
If I went on and told you what
the different incident light

389
00:18:20 --> 00:18:24
was, and what the electrons
were ejected with, and then you

390
00:18:24 --> 00:18:28
could look up the ionization
energy for the particular

391
00:18:28 --> 00:18:30
different elements, you should
be able to actually determine

392
00:18:30 --> 00:18:33
exactly which element it is,
but just with the information

393
00:18:33 --> 00:18:36
given, we can only narrow it
down to these choices here.

394
00:18:36 --> 00:18:41
So let's actually let you try
another example of solving a

395
00:18:41 --> 00:18:43
problem that has to do with
one of the spectrums.

396
00:18:43 --> 00:18:46
So, let's turn to another
clicker question here.

397
00:18:46 --> 00:18:49
Remember, your answer holds
great weight in terms

398
00:18:49 --> 00:18:52
of the state of the TA
bragging for next week.

399
00:18:52 --> 00:18:55
So, how many distinct, so
again, we're talking about

400
00:18:55 --> 00:18:58
distinct kinetic energies,
would be displayed if you're

401
00:18:58 --> 00:19:01
talking about a spectrum for
the element hafnium, and I'll

402
00:19:01 --> 00:19:04
tell you here that it has a z
of 72, so you don't have to

403
00:19:04 --> 00:19:07
spend two minutes searching
your periodic table.

404
00:19:07 --> 00:19:10
The period of table's on the
back page of your notes if

405
00:19:10 --> 00:19:46
you don't see that there.
 

406
00:19:46 --> 00:19:46
All right.
 

407
00:19:46 --> 00:19:48
It looks like a lot of you
are done, so let's take

408
00:19:48 --> 00:19:53
10 more seconds here.
 

409
00:19:53 --> 00:19:56
Part of the challenge is speed,
too, how quickly you can get

410
00:19:56 --> 00:19:59
these answers in terms of
getting them in on time.

411
00:19:59 --> 00:20:02
So let's see what we say.
 

412
00:20:02 --> 00:20:02
All right.
 

413
00:20:02 --> 00:20:06
So I think I can safely say
that most people had the right

414
00:20:06 --> 00:20:10
idea and were counting quickly,
though I have a feeling that

415
00:20:10 --> 00:20:13
some people who wrote 13 might
have forgotten about those

416
00:20:13 --> 00:20:16
4 f, the 4 f electrons.
 

417
00:20:16 --> 00:20:19
So, remember when you're
looking at your periodic table,

418
00:20:19 --> 00:20:22
don't forget about the
lanthinides, sometimes

419
00:20:22 --> 00:20:23
they come into play.
 

420
00:20:23 --> 00:20:27
So it's actually 14, and the
way that we got that answer was

421
00:20:27 --> 00:20:29
we just wrote out or just
looked at your period table,

422
00:20:29 --> 00:20:32
figured out all of the
different orbitals that you

423
00:20:32 --> 00:20:36
could have in terms of the
principle quantum number, and

424
00:20:36 --> 00:20:39
then the l quantum number, and
then write them all down -- it

425
00:20:39 --> 00:20:42
turns out to be 14, so
that's what the answer is.

426
00:20:42 --> 00:20:45
So, it looks like this is good,
because we'll have some

427
00:20:45 --> 00:20:48
separation in terms of not
everyone's going to get 100% in

428
00:20:48 --> 00:20:52
terms of recitations here,
which is what we're going for.

429
00:20:52 --> 00:20:52
All right.
 

430
00:20:52 --> 00:20:55
So let's turn our attention to
a new topic, which is thinking

431
00:20:55 --> 00:20:58
a little bit about the periodic
table, and also talking

432
00:20:58 --> 00:21:00
about periodic trends.
 

433
00:21:00 --> 00:21:03
And there's a lot we can
explain by talking about what

434
00:21:03 --> 00:21:06
we see in the periodic table in
terms of what different trends

435
00:21:06 --> 00:21:08
are in grouping different
elements in different spots

436
00:21:08 --> 00:21:10
within the periodic table.
 

437
00:21:10 --> 00:21:13
So, here we have a picture of
Dmitri Mendeleev, who is one of

438
00:21:13 --> 00:21:17
the scientists responsible for
first compiling the

439
00:21:17 --> 00:21:18
periodic table.
 

440
00:21:18 --> 00:21:21
You'll notice I have what's a
very flattering picture of him

441
00:21:21 --> 00:21:24
up here, and if you haven't
done the reading yet you might

442
00:21:24 --> 00:21:27
not think this is particularly
flattering, but if you look at

443
00:21:27 --> 00:21:31
the picture of him in the book,
you'll notice I chose a very

444
00:21:31 --> 00:21:35
flattering picture of Dmitri up
here, and here he's pondering

445
00:21:35 --> 00:21:38
putting these elements
together in a periodic table.

446
00:21:38 --> 00:21:43
And he actually did this in the
late 1800's, back before even

447
00:21:43 --> 00:21:45
all of the elements that we
know today were discovered,

448
00:21:45 --> 00:21:49
really only about 60% or so,
70% were discovered then

449
00:21:49 --> 00:21:51
that we now know today.
 

450
00:21:51 --> 00:21:55
But still, he was able to put
together a periodic table.

451
00:21:55 --> 00:21:57
And what he did what he
actually grouped things

452
00:21:57 --> 00:22:00
in terms of their
chemical properties.

453
00:22:00 --> 00:22:02
So the way that we like to
think of things now is in terms

454
00:22:02 --> 00:22:05
of electron configurations,
right, but at the time that

455
00:22:05 --> 00:22:06
wasn't really understood.
 

456
00:22:06 --> 00:22:09
So, instead, it was amazing he
was able to group things in

457
00:22:09 --> 00:22:11
terms of the properties
that he saw.

458
00:22:11 --> 00:22:15
So, for example, if he was
talking about the group one

459
00:22:15 --> 00:22:18
metals, lithium, sodium,
potassium -- he noticed these

460
00:22:18 --> 00:22:20
were all very soft reactive
metals, those were

461
00:22:20 --> 00:22:21
grouped together.
 

462
00:22:21 --> 00:22:26
Versus looking at, for example,
helium or neon or argon, these

463
00:22:26 --> 00:22:30
are all inert gases, inert
meaning essentially do not

464
00:22:30 --> 00:22:33
react, those were grouped
together in the periodic table.

465
00:22:33 --> 00:22:37
So basically, at the time he
was just going on size and then

466
00:22:37 --> 00:22:42
traits, but what we actually
know today is that we can also

467
00:22:42 --> 00:22:45
order things in the periodic
table by electron

468
00:22:45 --> 00:22:45
configuration.
 

469
00:22:45 --> 00:22:48
In fact, that is the
most logical way for

470
00:22:48 --> 00:22:49
us to look at it now.
 

471
00:22:49 --> 00:22:51
So, for example, if we're
actually thinking about

472
00:22:51 --> 00:22:54
electron configuration and we
look at lithium, sodium and

473
00:22:54 --> 00:22:58
potassium, these all have
one valence electron.

474
00:22:58 --> 00:23:01
So basically, that means one
electron in an s orbital in

475
00:23:01 --> 00:23:03
their outer-most most shell.
 

476
00:23:03 --> 00:23:05
So that explains why they're so
reactive, they're all very

477
00:23:05 --> 00:23:08
willing to give up that 1 s
orbital and then drop to

478
00:23:08 --> 00:23:10
a lower energy level.
 

479
00:23:10 --> 00:23:14
In contrast, helium, neon, and
argon all have filled shells.

480
00:23:14 --> 00:23:17
That also explains why
they're very stable.

481
00:23:17 --> 00:23:19
They're not going to want to
add on another electron,

482
00:23:19 --> 00:23:22
because then it'll have to jump
a very large energy level and

483
00:23:22 --> 00:23:24
start filling in another shell
-- go from n equals 2,

484
00:23:24 --> 00:23:29
to n equals 3, and n
equals 4, and so on.

485
00:23:29 --> 00:23:31
So it turns out that we can
really know a lot just by

486
00:23:31 --> 00:23:34
looking at the periodic table.
 

487
00:23:34 --> 00:23:37
You will never in this class
have to memorize anything

488
00:23:37 --> 00:23:38
about the periodic table.
 

489
00:23:38 --> 00:23:40
Depending on what kind of
chemistry you go in to, you

490
00:23:40 --> 00:23:43
might accidentally memorize
parts of the table, which is

491
00:23:43 --> 00:23:45
fine, but what you really want
to know how to do is know how

492
00:23:45 --> 00:23:48
to use the periodic table.
 

493
00:23:48 --> 00:23:51
But you actually need to keep a
few caveats in mind as you do

494
00:23:51 --> 00:23:54
this, which is the fact that
trends predict a lot of

495
00:23:54 --> 00:23:57
chemical properties, but they
can't predict everything in

496
00:23:57 --> 00:23:59
terms of biological properties.
 

497
00:23:59 --> 00:24:02
And after the periodic table
was developed in the late

498
00:24:02 --> 00:24:04
1800's, people didn't
understand this quite as

499
00:24:04 --> 00:24:06
well, they took things a
little more literally.

500
00:24:06 --> 00:24:09
They thought, for example, if
you could do something with one

501
00:24:09 --> 00:24:12
element, if you looked at an
element very close to it, it

502
00:24:12 --> 00:24:13
would be similar enough
that you could maybe

503
00:24:13 --> 00:24:15
replace it with that.
 

504
00:24:15 --> 00:24:18
Today we know, for example, if
you can put one certain kind of

505
00:24:18 --> 00:24:21
element in your mouth or eat
that, it doesn't necessarily

506
00:24:21 --> 00:24:23
mean you want to put the
element next to it and your

507
00:24:23 --> 00:24:25
mouth as well, that
might not be safe.

508
00:24:25 --> 00:24:28
But this is things we've
learned as the years

509
00:24:28 --> 00:24:30
have gone past.
 

510
00:24:30 --> 00:24:33
So, let's just take a quick
example to show how not

511
00:24:33 --> 00:24:35
completely you can use these
periodic trends, that

512
00:24:35 --> 00:24:36
there are limits.
 

513
00:24:36 --> 00:24:39
So if we consider lithium,
potassium, and sodium, they're

514
00:24:39 --> 00:24:42
all together in the same group
on the periodic table, knowing

515
00:24:42 --> 00:24:46
what we do about biology we can
immediately think of sodium and

516
00:24:46 --> 00:24:49
potassium, or even just knowing
what you know about table salt,

517
00:24:49 --> 00:24:53
for example, that these are two
elements that we find, and

518
00:24:53 --> 00:24:56
particularly in the ion form in
very high concentrations

519
00:24:56 --> 00:24:57
in our body.
 

520
00:24:57 --> 00:24:59
For example, sodium in our
blood plasma is almost to

521
00:24:59 --> 00:25:02
the point sometimes of 100
millimol or that's very,

522
00:25:02 --> 00:25:04
very concentrated.
 

523
00:25:04 --> 00:25:07
Similarly, we find it in table
salt, we're taking it in all

524
00:25:07 --> 00:25:10
the time, the same with
potassium, think of bananas,

525
00:25:10 --> 00:25:12
were always eating potassium.
 

526
00:25:12 --> 00:25:14
Not so with lithium.
 

527
00:25:14 --> 00:25:16
I don't think too many people
and here are probably

528
00:25:16 --> 00:25:17
taking lithium.
 

529
00:25:17 --> 00:25:21
It turns out there's actually
no natural function known

530
00:25:21 --> 00:25:22
in the body for lithium.
 

531
00:25:22 --> 00:25:25
So there's nothing naturally
going on unless we were to

532
00:25:25 --> 00:25:27
introduce it ourselves in our
body that we know of, at

533
00:25:27 --> 00:25:30
least, that involves lithium.
 

534
00:25:30 --> 00:25:33
But this did not stop people,
for example, in the late

535
00:25:33 --> 00:25:39
1800's, early 1900's, and, in
fact, in 1927 a new soft drink

536
00:25:39 --> 00:25:42
was put on to the market and
they wanted to make a

537
00:25:42 --> 00:25:45
lemon-lime soft drink, these
were very popular in the early

538
00:25:45 --> 00:25:49
1900's, and to get sort of that
lemony flavor, they decided to

539
00:25:49 --> 00:25:51
use citric acid, so that's a
good idea, that gives

540
00:25:51 --> 00:25:53
that soury taste.
 

541
00:25:53 --> 00:25:57
And they wanted to use a
soluble salt of citric acid, so

542
00:25:57 --> 00:25:59
they could have used sodium,
they could have used potassium.

543
00:25:59 --> 00:26:02
But, you know why not do
something a little special,

544
00:26:02 --> 00:26:06
little different, and they
decided instead to use lithium.

545
00:26:06 --> 00:26:09
So, here we have this soda
with lithium citrate, some of

546
00:26:09 --> 00:26:14
you might be familiar with
this, soda is called 7-Up.

547
00:26:14 --> 00:26:20
So, 7-Up no longer has lithium
in it, but from 1927 to 1950 it

548
00:26:20 --> 00:26:24
did, and, in fact, not only did
they not try to hide the fact

549
00:26:24 --> 00:26:26
that there's lithium in the
soda, this they used as a

550
00:26:26 --> 00:26:30
really special marketing
technique, they really pointed

551
00:26:30 --> 00:26:32
out this is something that
stands out about our soda,

552
00:26:32 --> 00:26:34
this is something special.
 

553
00:26:34 --> 00:26:36
There's a lot of good
things about lithium.

554
00:26:36 --> 00:26:38
I don't know if you can see,
probably not, what's written

555
00:26:38 --> 00:26:44
on here, so let me point
out to you a few things.

556
00:26:44 --> 00:26:48
Lithium, slenderizing, that's
great to see in a soda.

557
00:26:48 --> 00:26:50
Other nice things about lithium
in your soda, it dispells

558
00:26:50 --> 00:26:53
hangovers, takes the
ouch out of grouch.

559
00:26:53 --> 00:26:54
That's very nice.
 

560
00:26:54 --> 00:26:58
So basically, you get a lot of
benefit supposedly from this

561
00:26:58 --> 00:27:02
7-Up soda from the
1920's or so.

562
00:27:02 --> 00:27:06
And this went on and was
unregulated for some time, but

563
00:27:06 --> 00:27:10
at some point the Food and Drug
Administration did take a step

564
00:27:10 --> 00:27:13
in, so here's a case where they
did do something important --

565
00:27:13 --> 00:27:20
that's not what I mean at all
-- where they did take the

566
00:27:20 --> 00:27:21
step, they do many things that
are important, often

567
00:27:21 --> 00:27:23
not quickly enough.
 

568
00:27:23 --> 00:27:26
Here's a -- actually here it
did take 25 years, but they

569
00:27:26 --> 00:27:28
did, they did eventually step
on before we started

570
00:27:28 --> 00:27:30
drinking 7-Up.
 

571
00:27:30 --> 00:27:33
And what they said was, look,
you can't put this in, we're

572
00:27:33 --> 00:27:35
starting to notice it does
some strange things.

573
00:27:35 --> 00:27:39
Because it was in the 1950's or
so, maybe the late 1940's, that

574
00:27:39 --> 00:27:41
people started to discover
lithium, even though it had no

575
00:27:41 --> 00:27:45
natural function, it did do
something in our bodies.

576
00:27:45 --> 00:27:49
Does anyone know what
was lithium's used for?

577
00:27:49 --> 00:27:52
Yeah, it's an anti-psychotic
drug, so, for example, some

578
00:27:52 --> 00:27:55
people with bipolar disorder
even today still take it, it

579
00:27:55 --> 00:27:57
works really well for some
people, for other people

580
00:27:57 --> 00:27:58
it doesn't work so well.
 

581
00:27:58 --> 00:28:00
But anyway, this isn't really
something you want to have

582
00:28:00 --> 00:28:04
in your soda, so they did
take it out eventually.

583
00:28:04 --> 00:28:08
Another side effect if you take
too much lithium is death, so

584
00:28:08 --> 00:28:13
that's no good to have in sodas
either, and it might not have

585
00:28:13 --> 00:28:15
been as big a deal back in the
1920's, but you can imagine

586
00:28:15 --> 00:28:19
with supersizing today, this
might be a bigger problem.

587
00:28:19 --> 00:28:23
So anyway, when we talk
about periodic trends, it

588
00:28:23 --> 00:28:24
doesn't always match up.
 

589
00:28:24 --> 00:28:28
This was eventually taken out,
and actually just for your

590
00:28:28 --> 00:28:31
interest, there was no overlap
between the time when cocaine

591
00:28:31 --> 00:28:34
was in Coca Cola and lithium
was in 7-Up, so there was a few

592
00:28:34 --> 00:28:36
years difference between those
two times, but it's amazing to

593
00:28:36 --> 00:28:40
think about what does go
into processed foods.

594
00:28:40 --> 00:28:43
And the other thing to point
out, which I don't know if this

595
00:28:43 --> 00:28:46
is true or not, but does anyone
know -- well that's part's

596
00:28:46 --> 00:28:49
true, does anyone know what the
atomic mass of lithium is?

597
00:28:49 --> 00:28:50
Yes, it's 7.
 

598
00:28:50 --> 00:28:53
So, I don't know if this is
true or not, but I wonder if

599
00:28:53 --> 00:28:55
that's where the actual
name 7-Up came from.

600
00:28:55 --> 00:28:57
So, even though we don't have
the lithium anymore, we still

601
00:28:57 --> 00:29:00
keep that atomic
number 7 around.

602
00:29:00 --> 00:29:01
All right.
 

603
00:29:01 --> 00:29:05
So that is an anti-example
of using periodic trends.

604
00:29:05 --> 00:29:09
So let's go to some actual real
examples, which might come

605
00:29:09 --> 00:29:10
more in handy for this class.
 

606
00:29:10 --> 00:29:13
So it's going to keep in mind
the limitations, so let's

607
00:29:13 --> 00:29:17
start off with talking
about ionization energy.

608
00:29:17 --> 00:29:19
Now this is a good place to
start, because we are very

609
00:29:19 --> 00:29:21
familiar with ionization
energy, we've been talking

610
00:29:21 --> 00:29:24
about it in a lot of different
forms for quite a while -- it's

611
00:29:24 --> 00:29:28
that minimum energy required to
remove an electron

612
00:29:28 --> 00:29:29
from an atom.
 

613
00:29:29 --> 00:29:32
And specifically, when we talk
about ionization energy, it's

614
00:29:32 --> 00:29:35
assumed that what we mean is
actually the first

615
00:29:35 --> 00:29:36
ionization energy.
 

616
00:29:36 --> 00:29:39
So, you can imagine, we could
talk about any of the different

617
00:29:39 --> 00:29:41
electrons, or we could talk
about taking out an electron

618
00:29:41 --> 00:29:43
and taking out second electron.
 

619
00:29:43 --> 00:29:47
Whenever you hear the term
ionization energy, make sure

620
00:29:47 --> 00:29:50
you keep in mind that unless
we say otherwise, we're

621
00:29:50 --> 00:29:53
talking about that first
ionization energy.

622
00:29:53 --> 00:29:55
And we know what that's equal
to, this is something we've

623
00:29:55 --> 00:29:58
been over and over, ionization
energy is simply equal to the

624
00:29:58 --> 00:30:00
negative of the binding energy.
 

625
00:30:00 --> 00:30:04
So negative e, which is sub n
l, because it's a function of

626
00:30:04 --> 00:30:08
n and l in terms of
quantum numbers.

627
00:30:08 --> 00:30:12
So, let's think about kind of
differentiating, however,

628
00:30:12 --> 00:30:16
between first ionization energy
or just ionization energy, and

629
00:30:16 --> 00:30:19
other types such as second or
third ionization energy, and

630
00:30:19 --> 00:30:22
let's take boron as
an example here.

631
00:30:22 --> 00:30:24
So, if we want to think about
what the first ionization

632
00:30:24 --> 00:30:27
energy is of boron, what you
want to do is write out the

633
00:30:27 --> 00:30:30
electron configuration, because
then you can think about where

634
00:30:30 --> 00:30:32
it is that the electron's
coming out of.

635
00:30:32 --> 00:30:34
The electron's going to come
out of that highest occupied

636
00:30:34 --> 00:30:37
atomic orbital, that one that's
the highest in energy, because

637
00:30:37 --> 00:30:40
that's going to be the at least
amount of energy it needs

638
00:30:40 --> 00:30:41
to eject something.
 

639
00:30:41 --> 00:30:45
So what we'll end up with is
boron plus, 1 s 2, 2 s 2, and

640
00:30:45 --> 00:30:49
what we say is the delta energy
or the change in energy as the

641
00:30:49 --> 00:30:53
same thing as saying the energy
of the products minus the

642
00:30:53 --> 00:30:55
energy of our reactant here,
and we just call that the

643
00:30:55 --> 00:30:58
ionization energy -- that's how
much energy we have to put into

644
00:30:58 --> 00:31:00
the system to eject
an electron.

645
00:31:00 --> 00:31:03
And again, this is just
the negative, the binding

646
00:31:03 --> 00:31:07
energy, when we're talking
about the 2 p orbital.

647
00:31:07 --> 00:31:11
So, this is first ionization
energy, let's think about

648
00:31:11 --> 00:31:13
second ionization energy.
 

649
00:31:13 --> 00:31:16
So, second ionization energy
simply means you've already

650
00:31:16 --> 00:31:19
taken one electron out, now how
much energy does it take for

651
00:31:19 --> 00:31:21
you to take a second
electron out.

652
00:31:21 --> 00:31:24
So in the case of boron here,
what we're starting with is the

653
00:31:24 --> 00:31:29
ion, boron 1 s 2, 2 s 2, and
now we're going to pull

654
00:31:29 --> 00:31:30
one more electron out.
 

655
00:31:30 --> 00:31:34
The highest occupied orbital is
now the 2 s orbital, so we're

656
00:31:34 --> 00:31:40
going to end up with boron 2
plus 1 s 2, 2 s 1, plus the

657
00:31:40 --> 00:31:42
electron coming out of there.
 

658
00:31:42 --> 00:31:45
And what we say when we talk
about the delta energy is that

659
00:31:45 --> 00:31:49
this is going to be equal to i
e 2, or the second ionization

660
00:31:49 --> 00:31:53
energy, or we could say the
negative of the binding energy

661
00:31:53 --> 00:31:58
of a 2 s electron in b plus. so
it's important to note that

662
00:31:58 --> 00:32:01
it's not in b, now we're
talking about b plus, because

663
00:32:01 --> 00:32:04
we've already taken an
electron out here.

664
00:32:04 --> 00:32:06
So, similarly if we start
talking about our third

665
00:32:06 --> 00:32:09
ionization energy, this is
going to be going from b

666
00:32:09 --> 00:32:12
plus 2, to 1 s 2, 2 s 1.
 

667
00:32:12 --> 00:32:16
Now we're going to pull that
second electron out of the 2 s,

668
00:32:16 --> 00:32:20
so we end up with boron plus 3,
and then the configuration is

669
00:32:20 --> 00:32:24
just 1 s 2, plus our
extra electron here.

670
00:32:24 --> 00:32:28
So, what we call this is the
third ionization energy, or the

671
00:32:28 --> 00:32:31
negative of the binding energy,
again of the 2 s orbital, but

672
00:32:31 --> 00:32:35
now it's in boron plus 2
to we're starting with.

673
00:32:35 --> 00:32:38
So, this raises kind of an
interesting question in terms

674
00:32:38 --> 00:32:41
of what the difference is
between these two cases, and

675
00:32:41 --> 00:32:45
we're talking about
numbers of energy.

676
00:32:45 --> 00:32:48
So let's address this by
considering another example,

677
00:32:48 --> 00:32:51
which should clarify what
the difference is between

678
00:32:51 --> 00:32:52
these ionization energies.
 

679
00:32:52 --> 00:32:56
So let's think about the energy
required now to remove a 2 s

680
00:32:56 --> 00:32:59
electron, let's say we're
removing it from boron plus

681
00:32:59 --> 00:33:01
1 versus neutral boron.
 

682
00:33:01 --> 00:33:06
So, in the case of boron plus
1, what we are starting with

683
00:33:06 --> 00:33:10
is the ion, so we're starting
with a 2 s electron, and then

684
00:33:10 --> 00:33:13
we're going to 2 s 1 here.
 

685
00:33:13 --> 00:33:16
And what we call the binding
energy is negative 2 s in b

686
00:33:16 --> 00:33:19
plus -- this is what we
saw on the last slide.

687
00:33:19 --> 00:33:22
And the second case here looks
a lot more like what we saw

688
00:33:22 --> 00:33:25
when we were talking about
photoelectron spectroscopy,

689
00:33:25 --> 00:33:28
because here we want to remove
a 2 s electron, but it's

690
00:33:28 --> 00:33:32
actually not the highest
occupied orbital, so that's not

691
00:33:32 --> 00:33:34
the one that would naturally
come out first, but let's say

692
00:33:34 --> 00:33:36
we're hitting it with high
energy light sufficient to

693
00:33:36 --> 00:33:39
knock out all the different
electrons, and one that we end

694
00:33:39 --> 00:33:41
up knocking out is
this 2 s here.

695
00:33:41 --> 00:33:45
So if we think about what that
delta energy is, we call that

696
00:33:45 --> 00:33:48
the ionization of the 2 s,
that's different from saying

697
00:33:48 --> 00:33:50
second ionization energy.
 

698
00:33:50 --> 00:33:52
And that's going to be equal to
the negative the binding energy

699
00:33:52 --> 00:33:57
of 2 s in b, in neutral boron.
 

700
00:33:57 --> 00:34:01
So, my question to you is are
these two energies equal?

701
00:34:01 --> 00:34:02
No.
 

702
00:34:02 --> 00:34:03
All right, good answer.
 

703
00:34:03 --> 00:34:06
So, we can think about why is
it that these are not equal.

704
00:34:06 --> 00:34:08
In both cases we're taking
an electron out of

705
00:34:08 --> 00:34:11
the 2 s orbital.
 

706
00:34:11 --> 00:34:14
And it turns out that if we're
talking about a 2 s orbital in

707
00:34:14 --> 00:34:18
an ion, that means it doesn't
have as many electrons in it,

708
00:34:18 --> 00:34:20
so what we're going to
see is less sheilding.

709
00:34:20 --> 00:34:23
There are fewer electrons
around to shield some

710
00:34:23 --> 00:34:24
of that nuclear charge.
 

711
00:34:24 --> 00:34:27
So what we're going to see is
less sheilding, which means

712
00:34:27 --> 00:34:31
that it will actually feel
a higher z effective.

713
00:34:31 --> 00:34:35
So even though they're both 2 s
electrons, in one case it's

714
00:34:35 --> 00:34:38
going to think its feeling more
pull from the nucleus, and it,

715
00:34:38 --> 00:34:41
in fact, will be, than in the
other case, and if its feeling

716
00:34:41 --> 00:34:44
a higher z effective, then it's
actually going to require more

717
00:34:44 --> 00:34:47
energy to remove that electron,
right, it's being pulled in

718
00:34:47 --> 00:34:50
closer and more tightly to the
nucleus, you have to put in

719
00:34:50 --> 00:34:54
more energy to rip it away from
that very close interaction.

720
00:34:54 --> 00:34:57
So, that's the difference in
thinking about different types

721
00:34:57 --> 00:35:00
of ionization energy, so it can
get a little bit confusing with

722
00:35:00 --> 00:35:02
terminology if you're just
looking at something quickly,

723
00:35:02 --> 00:35:04
so make sure you look really
carefully about what

724
00:35:04 --> 00:35:05
we're discussing here.
 

725
00:35:05 --> 00:35:08
If you see a problem that asks
you, for example, the third

726
00:35:08 --> 00:35:12
ionization energy versus taking
a second electron out of

727
00:35:12 --> 00:35:14
the 2 s in a photoelectron
spectroscopy experiment, those

728
00:35:14 --> 00:35:17
are two very different things.
 

729
00:35:17 --> 00:35:20
So, let's make sure everyone
kind of has this down, let's do

730
00:35:20 --> 00:35:25
another clicker question here.
 

731
00:35:25 --> 00:35:28
And in this case we're going to
look at silicone, and we'll say

732
00:35:28 --> 00:35:31
if you can point out to me
which requires the least

733
00:35:31 --> 00:35:32
amount of energy.
 

734
00:35:32 --> 00:35:35
So, which has the smallest
energy that you have to put

735
00:35:35 --> 00:35:37
in in order to eject
this electron?

736
00:35:37 --> 00:35:41
Will it be if you take a 3 s
electron from neutral silicone,

737
00:35:41 --> 00:35:45
if you take a 3 p electron from
the neutral atom, or if you

738
00:35:45 --> 00:35:48
take a 3 p from the ion?
 

739
00:35:48 --> 00:35:51
So this you should be able to
know pretty quickly, so let's

740
00:35:51 --> 00:36:05
just take 10 seconds here.
 

741
00:36:05 --> 00:36:05
All right, great.
 

742
00:36:05 --> 00:36:10
So most of you see that, in
fact, the energy that's going

743
00:36:10 --> 00:36:14
to be the least that we need
to put in is in case 2 here.

744
00:36:14 --> 00:36:16
Let's compare case 2 and 3,
since this where some people

745
00:36:16 --> 00:36:18
seem to have gotten confused.
 

746
00:36:18 --> 00:36:22
In case 2, we're taking it out
of -- oh, it's kind of hard to

747
00:36:22 --> 00:36:26
compare case 2 and 3 when
we can't see it anymore.

748
00:36:26 --> 00:36:32
In case 2, we're taking the 3
p out of the neutral atom,

749
00:36:32 --> 00:36:35
whereas in case 3, we're
taking it out of the ion.

750
00:36:35 --> 00:36:38
Remember in the ion, we're
going to have less electrons

751
00:36:38 --> 00:36:42
around to counteract the
pull from the nucleus.

752
00:36:42 --> 00:36:46
So we're going to feel a higher
z effective in the case of

753
00:36:46 --> 00:36:48
the ion compared to
the neutral atom.

754
00:36:48 --> 00:36:50
If we have a higher z
effective, it's pulled in

755
00:36:50 --> 00:36:53
tighter, we have to put in more
energy in order to eject an

756
00:36:53 --> 00:36:57
electron, so it turns out that
that's why case 2 is actually

757
00:36:57 --> 00:36:59
the lowest energy that
we need to put in.

758
00:36:59 --> 00:37:03
The z effective is lower, so
we have to put less energy

759
00:37:03 --> 00:37:07
in to get an ion out.
 

760
00:37:07 --> 00:37:10
So, let's take a look at this
in terms of periodic trends --

761
00:37:10 --> 00:37:14
that's our topic here, we're
talking about periodic trends.

762
00:37:14 --> 00:37:17
So as we go across the row, and
this is my beautiful picture

763
00:37:17 --> 00:37:19
of a periodic table here.
 

764
00:37:19 --> 00:37:21
As we go across the row what
happens is that the ionization

765
00:37:21 --> 00:37:24
energy actually increases, and
we can think about

766
00:37:24 --> 00:37:27
logically why it is that
that's happening.

767
00:37:27 --> 00:37:31
As we go across the row, what
we have happening is that the z

768
00:37:31 --> 00:37:34
or the atomic charge -- I'm not
talking about z effective here,

769
00:37:34 --> 00:37:37
I'm just talking about z -- the
z is increasing as we go across

770
00:37:37 --> 00:37:39
a row, that's easy to see.
 

771
00:37:39 --> 00:37:42
But we're still in the same
shell, so we still have the

772
00:37:42 --> 00:37:45
same n value as we go all
the way across a row

773
00:37:45 --> 00:37:47
in the periodic table.
 

774
00:37:47 --> 00:37:51
So, in general what we're going
to see is that what happens to

775
00:37:51 --> 00:37:53
z effective if we have z
increasing but we're in

776
00:37:53 --> 00:37:56
the same shell here.
 

777
00:37:56 --> 00:38:01
Would it increase or
decrease z effective?

778
00:38:01 --> 00:38:01
All right.
 

779
00:38:01 --> 00:38:04
Kind of mixed thoughts here.
 

780
00:38:04 --> 00:38:07
So it turns out that it
increases, and the reason is

781
00:38:07 --> 00:38:09
because the predominant thing
that's going on here is

782
00:38:09 --> 00:38:11
that z is increasing.
 

783
00:38:11 --> 00:38:14
So the z is increasing, and
what goes along with it is that

784
00:38:14 --> 00:38:17
the z effective is increasing,
because it turns out that while

785
00:38:17 --> 00:38:19
we're in the same n, even
though we know that energy

786
00:38:19 --> 00:38:23
depends on both the n and the l
in terms of quantum numbers,

787
00:38:23 --> 00:38:26
while we're in the same n, the
distance from the nucleus, it's

788
00:38:26 --> 00:38:28
pretty close, it's not
hugely different.

789
00:38:28 --> 00:38:31
So the factor that predominates
is that we're actually

790
00:38:31 --> 00:38:32
increasing z.
 

791
00:38:32 --> 00:38:34
That's why we see z effective
increase, and that's why we see

792
00:38:34 --> 00:38:37
ionization energy increase.
 

793
00:38:37 --> 00:38:40
As we go down a column,
what happens is that the

794
00:38:40 --> 00:38:42
ionization energy decreases.
 

795
00:38:42 --> 00:38:45
We can also think about this
in terms of z effective.

796
00:38:45 --> 00:38:48
This is because even though z,
the atomic number is still

797
00:38:48 --> 00:38:52
increasing, we are also getting
further away from the nucleus.

798
00:38:52 --> 00:38:55
So, remember when we talk about
Coulomb force, what's holding

799
00:38:55 --> 00:38:58
the nucleus and the electron
together, there's 2 things

800
00:38:58 --> 00:38:58
we need to think about.
 

801
00:38:58 --> 00:39:02
The first is this the z
effective, or how much charge

802
00:39:02 --> 00:39:05
is actually in the nucleus
that's felt, or the I guess we

803
00:39:05 --> 00:39:08
would say the z, how much the
charge is on the nucleus that

804
00:39:08 --> 00:39:09
holds it close together.
 

805
00:39:09 --> 00:39:11
But the second factor
is how far away we

806
00:39:11 --> 00:39:12
are from the nucleus.
 

807
00:39:12 --> 00:39:15
So, if we're really close to
the nucleus, that's when z

808
00:39:15 --> 00:39:18
effective is high, but if we
get really far away, then z

809
00:39:18 --> 00:39:20
effective is going to get low,
because even though we have the

810
00:39:20 --> 00:39:23
same charge in the nucleus,
the z effective gets lower.

811
00:39:23 --> 00:39:26
So this is not even thinking
about the other electron

812
00:39:26 --> 00:39:29
shielding, just if we think of
the fact, all we need to think

813
00:39:29 --> 00:39:33
about is that the effect of
going to a further away n

814
00:39:33 --> 00:39:36
actually dominates as
we go down the table.

815
00:39:36 --> 00:39:38
We're getting further away from
the nucleus because we're

816
00:39:38 --> 00:39:42
jumping, for example, from the
n equals 2 to the n equals 3

817
00:39:42 --> 00:39:45
shell, or from the n equals
3 to the n equals 4 shell.

818
00:39:45 --> 00:39:46
And when you're switching
n's, you're actually getting

819
00:39:46 --> 00:39:48
quite a bit farther away.
 

820
00:39:48 --> 00:39:51
That's why in the earlier
models of the atom, they're not

821
00:39:51 --> 00:39:54
horrible to sometimes think
about just each n value

822
00:39:54 --> 00:39:55
as a little ring around.
 

823
00:39:55 --> 00:39:58
It's not complete and it's not
accurate, but it's OK to kind

824
00:39:58 --> 00:40:00
of think of it in terms of how
far we're getting away

825
00:40:00 --> 00:40:01
from the nucleus.
 

826
00:40:01 --> 00:40:04
So, as we go down a column,
we see ionization energy's

827
00:40:04 --> 00:40:06
going to decrease.
 

828
00:40:06 --> 00:40:09
So, this means we have the
general trends down, so we

829
00:40:09 --> 00:40:12
should be able to look at
actual atoms in our periodic

830
00:40:12 --> 00:40:15
table and graph them and see
that they match up

831
00:40:15 --> 00:40:16
with our trends.
 

832
00:40:16 --> 00:40:19
So here we have that graphed
here, we have atomic number z

833
00:40:19 --> 00:40:23
graphed against ionization
energy, so, let's fill in what

834
00:40:23 --> 00:40:27
the actual atoms are here, and
we can see in general, yes,

835
00:40:27 --> 00:40:28
we're following the trend.
 

836
00:40:28 --> 00:40:32
For row one, we're increasing,
as we should, across the row.

837
00:40:32 --> 00:40:34
Let's look at row two also.
 

838
00:40:34 --> 00:40:36
Well, we're generally
increasing here, we'll talk

839
00:40:36 --> 00:40:38
about that more in a minute.
 

840
00:40:38 --> 00:40:41
And also in a row three, yeah,
we're generally increasing,

841
00:40:41 --> 00:40:45
there's some glitches here, but
the general trend holds true.

842
00:40:45 --> 00:40:48
Similarly we see as we go down
the table, so as we're going

843
00:40:48 --> 00:40:53
from one row to the next row,
so, for example, between helium

844
00:40:53 --> 00:40:56
and lithium, we see a drop; the
same with neon to sodium,

845
00:40:56 --> 00:40:58
we see a drop here.
 

846
00:40:58 --> 00:41:00
So it looks like we're
generally following our

847
00:41:00 --> 00:41:02
trend, that's a good thing.
 

848
00:41:02 --> 00:41:05
But hopefully, you will not
be satisfied to just make a

849
00:41:05 --> 00:41:09
general statement here when
we do have these glitches.

850
00:41:09 --> 00:41:11
So you can see, for example,
we have several places where

851
00:41:11 --> 00:41:15
instead of going up as we go
across the row, we actually

852
00:41:15 --> 00:41:17
go down in ionization
energy a little bit.

853
00:41:17 --> 00:41:22
So between b e, and b, between
n and o, magesium and aluminum,

854
00:41:22 --> 00:41:25
and then phosphorous and
sulfur, what we see here is

855
00:41:25 --> 00:41:27
that we're kind of going down,
or quite specifically,

856
00:41:27 --> 00:41:29
we are going down.
 

857
00:41:29 --> 00:41:31
So, let's take a look at one of
these rows in more detail to

858
00:41:31 --> 00:41:34
think about why this might be
happening, and it turns out the

859
00:41:34 --> 00:41:39
reason that these glitches
occur are because the sub shell

860
00:41:39 --> 00:41:42
structure predominates in
certain instances, and that's

861
00:41:42 --> 00:41:44
where these glitches
take place.

862
00:41:44 --> 00:41:48
So I've sort of just spread out
what we have as the second

863
00:41:48 --> 00:41:52
row here, graphed against
the ionization energy.

864
00:41:52 --> 00:41:54
So, let's consider specifically
where these glitches

865
00:41:54 --> 00:41:55
are taking place.
 

866
00:41:55 --> 00:41:58
So, let's look at the first
one between beryllium

867
00:41:58 --> 00:42:00
and boron here.
 

868
00:42:00 --> 00:42:04
And the glitch that doesn't
make sense just through

869
00:42:04 --> 00:42:07
periodic trends, is that it
turns out that the ionization

870
00:42:07 --> 00:42:11
energy of boron is actually
less than the ionization

871
00:42:11 --> 00:42:12
energy up beryllium.
 

872
00:42:12 --> 00:42:15
So I put the electron
configurations and actually

873
00:42:15 --> 00:42:17
drew it on an energy diagram
here, so we can actually

874
00:42:17 --> 00:42:19
think about why this
might be happening.

875
00:42:19 --> 00:42:23
So what is this, which
element did I chart here?

876
00:42:23 --> 00:42:28
Which one is that, the
boron or the beryllium?

877
00:42:28 --> 00:42:30
I couldn't tell what
you said, sorry.

878
00:42:30 --> 00:42:34
So, I'm going to assume that
was beryllium, and then it

879
00:42:34 --> 00:42:36
turns out that if that's
beryllium, the other

880
00:42:36 --> 00:42:37
one must be boron.
 

881
00:42:37 --> 00:42:41
So, we have beryllium in the
first case here, it has four

882
00:42:41 --> 00:42:43
electrons, that's how we know
it's beryllium, boron

883
00:42:43 --> 00:42:45
has five electrons.
 

884
00:42:45 --> 00:42:49
So, just looking at putting in
the electrons, filling up the

885
00:42:49 --> 00:42:53
energy diagram here, we should
be able to see a little bit

886
00:42:53 --> 00:42:54
why this is happening.
 

887
00:42:54 --> 00:42:58
And the reason is simply
because the energy that we gain

888
00:42:58 --> 00:43:03
in terms of moving up in z, so
from going to z equals 4 to z

889
00:43:03 --> 00:43:06
equals 5, is actually
outweighed by the energy it

890
00:43:06 --> 00:43:09
takes to go into this
new shell, to go into

891
00:43:09 --> 00:43:10
this new sub shell.
 

892
00:43:10 --> 00:43:14
So to jump from the 2 s to the
2 p, takes more energy than we

893
00:43:14 --> 00:43:17
can actually compensate with by
increasing the pull

894
00:43:17 --> 00:43:18
from the nucleus.
 

895
00:43:18 --> 00:43:23
So, it turns out that in this
case, and any time that we see

896
00:43:23 --> 00:43:27
we're going from a 2 s to 2 p,
filling in of electrons, we

897
00:43:27 --> 00:43:31
actually see that little bit of
glitch in ionization energy.

898
00:43:31 --> 00:43:33
So it's shown here for the
second row, but it's actually

899
00:43:33 --> 00:43:35
also going to be true
for the third row.

900
00:43:35 --> 00:43:37
The same thing when you're
going from filling in the 2

901
00:43:37 --> 00:43:40
s to putting that first
electron into the 2 p.

902
00:43:40 --> 00:43:42
So that explains one of our
glitches here, but we have

903
00:43:42 --> 00:43:46
another glitch, and that
second glitch comes between

904
00:43:46 --> 00:43:48
nitrogen and oxygen.
 

905
00:43:48 --> 00:43:49
So, these sound more
different, so I think I'll

906
00:43:49 --> 00:43:51
be able to distinguish.
 

907
00:43:51 --> 00:43:56
Which element is shown here?
 

908
00:43:56 --> 00:43:57
Yeah, nitrogen.
 

909
00:43:57 --> 00:44:00
So, nitrogen is shown here,
we know that because

910
00:44:00 --> 00:44:01
it has 7 electrons.
 

911
00:44:01 --> 00:44:04
In this case, we're talking
about 8 electrons,

912
00:44:04 --> 00:44:06
which is oxygen.
 

913
00:44:06 --> 00:44:09
So if we're comparing the
difference between these 2 now,

914
00:44:09 --> 00:44:11
what you'll notice is that in
nitrogen we have all

915
00:44:11 --> 00:44:16
half-filled 2 p orbitals, and
now, once we move into oxygen,

916
00:44:16 --> 00:44:19
we actually have to add 1 more
electron into 1 of

917
00:44:19 --> 00:44:20
the 2 p orbitals.
 

918
00:44:20 --> 00:44:23
There's no more 2 p orbitals to
put it into, so we're going to

919
00:44:23 --> 00:44:24
actually have to double up.
 

920
00:44:24 --> 00:44:27
So now we're putting 2
electrons into the same p

921
00:44:27 --> 00:44:29
orbital, that's not a problem,
we can do it, it's not a huge

922
00:44:29 --> 00:44:30
energy cost to do that.
 

923
00:44:30 --> 00:44:33
But actually there is a little
bit of an energy cost into

924
00:44:33 --> 00:44:36
doubling up into a single
orbital, because, of course, it

925
00:44:36 --> 00:44:40
takes energy when you create
more electron repulsion, that's

926
00:44:40 --> 00:44:44
not something we want to do,
but we have to do it here, and

927
00:44:44 --> 00:44:47
it turns out that that effect
predominates over, again, the

928
00:44:47 --> 00:44:49
energy that we gain by
increasing the atomic

929
00:44:49 --> 00:44:51
number by one.
 

930
00:44:51 --> 00:44:54
So, our two glitches we see
when we go from the 2 p, or

931
00:44:54 --> 00:44:57
from 2 s to start filling the 2
p, and then we also get another

932
00:44:57 --> 00:45:01
glitch when we've half-filled
the 2 p, and now we're adding

933
00:45:01 --> 00:45:03
and having to double up in
one of those p orbitals.

934
00:45:03 --> 00:45:05
Again, we see the same effect
as we go into different

935
00:45:05 --> 00:45:09
rows as well.
 

936
00:45:09 --> 00:45:13
So let's talk about another
periodic trend, this one is

937
00:45:13 --> 00:45:14
called electron affinity.
 

938
00:45:14 --> 00:45:19
Electron affinity is actually
the ability of an atom, or we

939
00:45:19 --> 00:45:21
could also talk about an
ion to gain electrons.

940
00:45:21 --> 00:45:24
So it's the affinity it has for
electrons, it's how much it

941
00:45:24 --> 00:45:26
likes to get an electron.
 

942
00:45:26 --> 00:45:29
We can write out what it is
for any certain atom or ion

943
00:45:29 --> 00:45:33
x, so it's just x plus an
electron gives us x minus.

944
00:45:33 --> 00:45:35
We have the minus because we're
adding a negative charge

945
00:45:35 --> 00:45:37
from the electron.
 

946
00:45:37 --> 00:45:40
So, basically any time we have
a really high positive number

947
00:45:40 --> 00:45:44
of electron affinity, it means
that that atom or ion really

948
00:45:44 --> 00:45:47
wants to gain another electron,
and it will be very stable

949
00:45:47 --> 00:45:48
and happy if it does so.
 

950
00:45:48 --> 00:45:51
So let's look at an
example of chlorine here.

951
00:45:51 --> 00:45:54
So chlorine, if we talk about
it in terms of electron

952
00:45:54 --> 00:45:58
affinity, we would be writing
that we're actually gaining an

953
00:45:58 --> 00:46:01
electron here, and getting
the ion, c l minus.

954
00:46:01 --> 00:46:04
And the change in energy for
this reaction is negative

955
00:46:04 --> 00:46:07
349 kilojoules per mole.
 

956
00:46:07 --> 00:46:10
So if we have a negative change
in energy for any reaction as

957
00:46:10 --> 00:46:12
it's written, what that
actually means is we're

958
00:46:12 --> 00:46:15
giving off energy as
the reaction proceeds.

959
00:46:15 --> 00:46:19
So, in other words, this c l
minus is actually lower in

960
00:46:19 --> 00:46:21
energy than the reactants were.
 

961
00:46:21 --> 00:46:23
So that's why we're
giving off extra energy.

962
00:46:23 --> 00:46:25
We saw a similar thing as
we saw electrons move

963
00:46:25 --> 00:46:26
from different levels.
 

964
00:46:26 --> 00:46:28
We can think of it in the
same type of way when

965
00:46:28 --> 00:46:31
we're talking about actual
reactions happening.

966
00:46:31 --> 00:46:34
So, if we have energy that's
released, would you say that

967
00:46:34 --> 00:46:38
the chlorine ion is more
or less stable than

968
00:46:38 --> 00:46:38
the chlorine atom?
 

969
00:46:38 --> 00:46:42
Who thinks it's more
stable, show of hands?

970
00:46:42 --> 00:46:45
All right, who thinks
it's less stable?

971
00:46:45 --> 00:46:46
Very good.
 

972
00:46:46 --> 00:46:48
So it turns out it is,
in fact, more stable.

973
00:46:48 --> 00:46:51
It's more stable because you
actually -- this happens

974
00:46:51 --> 00:46:53
spontaneously, you actually
get energy out of the

975
00:46:53 --> 00:46:55
reaction as this happens.
 

976
00:46:55 --> 00:46:57
And we haven't talked about
reactions at all yet, so you

977
00:46:57 --> 00:47:01
don't need to worry about the
specifics of that exactly, but

978
00:47:01 --> 00:47:03
just that if you have this
negative change in energy, you

979
00:47:03 --> 00:47:07
have a more stable product
than you do reactant.

980
00:47:07 --> 00:47:11
So, we were talking, however,
about energy in terms of

981
00:47:11 --> 00:47:14
electron affinity, so we can
actually relate electron

982
00:47:14 --> 00:47:17
affinity to any reaction by
saying if we have this reaction

983
00:47:17 --> 00:47:20
written as here where we're
gaining an electron, we say

984
00:47:20 --> 00:47:23
that electron affinity is just
equal to the negative of

985
00:47:23 --> 00:47:24
that change in energy.
 

986
00:47:24 --> 00:47:28
So, for example, for the
chlorine case, we would say

987
00:47:28 --> 00:47:32
that the electron affinity for
chlorine is actually positive

988
00:47:32 --> 00:47:35
349 kilojoules per mole.
 

989
00:47:35 --> 00:47:38
That's a very large number,
it's all relative, so you don't

990
00:47:38 --> 00:47:40
necessarily know it's large
without me telling you or

991
00:47:40 --> 00:47:43
giving you other ions to
compare to, but chlorine does

992
00:47:43 --> 00:47:46
have a very large affinity,
meaning it's really likes

993
00:47:46 --> 00:47:50
getting an electron and
becoming a chlorine ion.

994
00:47:50 --> 00:47:53
One major difference between
electron affinity and

995
00:47:53 --> 00:47:56
ionization energy is that when
we talked about ionization

996
00:47:56 --> 00:47:58
energy, remember ionization
energy always has

997
00:47:58 --> 00:47:59
to be positive.
 

998
00:47:59 --> 00:48:03
We will never have a case where
ionization energy is negative.

999
00:48:03 --> 00:48:05
Electron affinity, however,
can be either negative

1000
00:48:05 --> 00:48:07
or it can be positive.
 

1001
00:48:07 --> 00:48:09
So let's look at a case
where it's actually

1002
00:48:09 --> 00:48:10
going to be negative.
 

1003
00:48:10 --> 00:48:13
So, if we took the case of
nitrogen, if we add an electron

1004
00:48:13 --> 00:48:15
to nitrogen and go to n
minus, we find that the

1005
00:48:15 --> 00:48:18
change in energy is 7
kilojoules per mole.

1006
00:48:18 --> 00:48:22
This means in order to do that
we actually have to put 7

1007
00:48:22 --> 00:48:24
kilojoules per mole of
energy into the reaction

1008
00:48:24 --> 00:48:26
to make it happen.
 

1009
00:48:26 --> 00:48:28
So this is not going to be a
favorable process, we're going

1010
00:48:28 --> 00:48:31
to find that the electron
affinity is actually a

1011
00:48:31 --> 00:48:34
negative 7 kilojoules
per mole for nitrogen.

1012
00:48:34 --> 00:48:37
So this means nitrogen has
low electron affinity, it

1013
00:48:37 --> 00:48:41
doesn't actually want
to gain an electron.

1014
00:48:41 --> 00:48:45
So, that also tells us that the
n minus ion is less stable

1015
00:48:45 --> 00:48:47
than the neutral atom itself.
 

1016
00:48:47 --> 00:48:50
So, we can think about trends
in electron affinity just like

1017
00:48:50 --> 00:48:53
we did for ionization energy,
and what we see is

1018
00:48:53 --> 00:48:54
a similar trend.
 

1019
00:48:54 --> 00:48:57
Electron affinity increases as
we go across a row in the

1020
00:48:57 --> 00:49:00
periodic table, and it
decreases as we go

1021
00:49:00 --> 00:49:02
down a column.
 

1022
00:49:02 --> 00:49:05
I left out the noble gases here
because they do something a

1023
00:49:05 --> 00:49:07
little bit special, and
actually, I'm going to give you

1024
00:49:07 --> 00:49:10
one last clicker question today
to see if you can tell me what

1025
00:49:10 --> 00:49:12
you think noble gases do.
 

1026
00:49:12 --> 00:49:14
To answer this question you
just really want to think

1027
00:49:14 --> 00:49:16
about what does electron
affinity means.

1028
00:49:16 --> 00:49:19
It means how much a certain
atom actually wants

1029
00:49:19 --> 00:49:21
to get an electron.
 

1030
00:49:21 --> 00:49:23
So do you think noble gases
would have a high positive

1031
00:49:23 --> 00:49:26
electron affinity, a low
positive, or negative

1032
00:49:26 --> 00:49:26
electron affinity?
 

1033
00:49:26 --> 00:49:40
So, let's take 10
seconds on that.

1034
00:49:40 --> 00:49:40
All right.
 

1035
00:49:40 --> 00:49:40
Great.
 

1036
00:49:40 --> 00:49:44
So most of you recognize, if we
switch back to the notes, that

1037
00:49:44 --> 00:49:46
they do have a negative
electron affinity.

1038
00:49:46 --> 00:49:48
This should make sense to you,
because they don't, in fact,

1039
00:49:48 --> 00:49:51
want to gain another electron,
because that would mean that

1040
00:49:51 --> 00:49:54
electron would have to go into
a new value of n, a new shell,

1041
00:49:54 --> 00:49:57
and that's really going to
increase the energy

1042
00:49:57 --> 00:49:58
of the system.
 

1043
00:49:58 --> 00:50:01
So they'd much rather just stay
the way they are and not have

1044
00:50:01 --> 00:50:04
another electron come on, and
it turns out that halogens have

1045
00:50:04 --> 00:50:06
the highest electron
affinities.

1046
00:50:06 --> 00:50:06