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We were talking about the
energies of the various states

00:00:20.000 --> 00:00:25.000
in a multi-electron atom.
And the question is,

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how do we know what these
energies are,

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experimentally?
And the technique that we use

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to know those energies is
something called photoelectron

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spectroscopy.
In principle,

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it is the same kind of
spectroscopy as when we talked

00:00:46.000 --> 00:00:51.000
about photoemission from a
solid, the photoelectron effect

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explained by Einstein.
And, by the way,

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I put on the website an article
that is really very clear about

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what Einstein's contributions
were.

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In particular,
in explaining the photoelectric

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effect.
And it has some sociology in

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it, too.
It is a really easy-to-read

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article.
I encourage you to take a look

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at it as a study break sometime.
Anyway.

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The idea here is the same,
the photoelectron spectroscopy

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off of atoms and molecules.
It is the same thing as the

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photoelectron emission from a
solid, in that you send in a

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photon and that causes an
electron to be ejected.

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But, unlike the solid where we
essentially had just one state

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at a particular energy,
in an atom or a molecule,

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we have many different states
with many different energies.

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And what we typically do,
then, is we send in a photon

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that will be able to ionize all
of those electrons.

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That is, it is a photon with
enough energy to rip off even

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the most strongly bound
electron.

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And so, that photon is
typically an X-ray photon.

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For example,
we take this unsuspecting neon

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atom, and we bring in an X-ray
photon and make neon plus.

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And one of the electrons that

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can come off is,
of course, the 2p electron,

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here, so that the ion
configuration is

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1s 2 2s 2 2p 5.
And then, of course,

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another possible electron to be
pulled off is that 2s electron.

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The electron configuration is
1s 2 2s 1 2p 6.

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And then, finally,

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if the photon has enough
energy, we can pull off the 1s

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electron, to make the 1s 1 2s 2
configuration,

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2s 2p6 configuration.

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And what we then do in this
technique is we measure the

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kinetic energies of all the
electrons that come off.

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We measure the kinetic energies
and disperse them so that we get

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a plot of the number of
electrons with a particular

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kinetic energy.
The plot is what I show you

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here, number of electrons versus
the kinetic energy.

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And what you see is that we
have three kinetic energies that

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show up.
We have electrons with three

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different kinetic energies.
We have three different kinetic

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energies because in neon,
we had three states with

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different energies.
So, for example,

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this energy,
384 eV, that corresponds to the

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electrons that were pulled off,
electrons that were in that 1s

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state.
That is the most strongly bound

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state.
For example,

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if this is the energy of our
incident photon,

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and then this is the ionization
energy, which is going to be

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largest for the 1s electron
because it is most strongly

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bound, well, then,
the energy difference between

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the incident energy and that
ionization energy is the kinetic

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energy of the electron.
That is the leftover energy

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that goes into the kinetic
energy of the electron.

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That is going to be smallest
because that 1s electron is most

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strongly bound.
Then we have this kinetic

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energy here, electrons with that
kinetic energy were electrons

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sitting in the 2s state.
That has higher kinetic energy

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because they are less strongly
bound.

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This is the energy of the
incident photon.

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This is the ionization energy
of that 2s electron.

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That leftover energy,
then, is that kinetic energy.

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And then, finally,
this is the feature that

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represents the electrons in the
2p state.

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They are least strongly bound.
If this is the incident energy,

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this is that ionization energy
for the 2p state.

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All of this energy is leftover
to go into kinetic energy of

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that 2p electron moving away
from the atom.

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And so, in general,
as the kinetic energy goes up,

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the binding energy here is
getting less and less negative.

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It is getting weaker and
weaker.

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Or, in other words,
as the kinetic energy goes up,

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the binding energy is getting
more negative in this direction.

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Very quickly,
if you look at a photoelectron

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spectrum and you see three lines
like this, you know you have

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three states at three different
energies.

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And you always know that the
highest kinetic energy means the

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least strongly bound electron,
the lowest kinetic energy means

00:05:58.000 --> 00:06:02.000
the most strongly bound
electron.

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And then, we can use these
results to actually calculate

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the binding energies of the
electrons by conservation of

00:06:09.000 --> 00:06:12.000
energy.
And this you have to know for

00:06:12.000 --> 00:06:14.000
the exam.
Incident energy is that

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ionization energy or the work
function, in the case of the

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solid, plus the kinetic energy.
Or, I can turn this around.

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I can solve for the ionization
energy.

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That will be the incident
energy, which is right here.

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This is the energy of that
X-ray photon,

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1,253 eV, minus the kinetic
energies that we actually

00:06:37.000 --> 00:06:42.000
measure, which are going to give
us those ionization energies for

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each one of the electrons in
their corresponding state.

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And then, once we have those
ionization energies,

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it is easy to turn it into a
binding energy because that

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ionization energy is equal to
minus that binding energy.

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For example,
since the ionization energy,

00:07:04.000 --> 00:07:08.000
the 1s electron,
is 870 eV, the binding energy

00:07:08.000 --> 00:07:12.000
of that 1s electron is minus
eV.

00:07:12.000 --> 00:07:17.000
And I also want you to notice
just how much more strongly

00:07:17.000 --> 00:07:23.000
bound that electron in the 1s
state is compared to the

00:07:23.000 --> 00:07:26.000
electrons in the n equals 2
shell.

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That is because that n equals 1
shell is much closer in to the

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nucleus, where that attractive
interaction is much stronger.

00:07:40.000 --> 00:07:42.000
And, therefore,
this electron is much more

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strongly bound than those
electrons in the n equals 2

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state.
Of course, 2s is lower in

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energy than 2p,
and that is important.

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This is because in the 2s
state, you have a finite

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probability of being really
close to the nucleus.

00:07:57.000 --> 00:08:01.000
That is what makes that 2s a
little bit lower in energy than

00:08:01.000 --> 00:08:07.000
the 2p.
Now, what we are going to do is

00:08:07.000 --> 00:08:14.000
I am going to start lecturing
about trends in the Periodic

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Table, and this is where the
questions come for your section.

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Oh, okay.
Do you have any extra paper?

00:08:27.000 --> 00:08:32.000
Not much.
Well, the way you were going to

00:08:32.000 --> 00:08:38.000
be able to answer a question for
your recitation was by making a

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paper airplane and launching it
to the blackboard after I say

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launch.
And the first paper airplane to

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hit the blackboard,
well, you will have the

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opportunity to answer the
question.

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Your recitation will have that
opportunity to answer the

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question.
And we will keep score.

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Now, we are kind of running out
of extra paper.

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You can take the one page that
asks for the seating plan that

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you will not need again,
as a piece of paper to make an

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airplane.
Do you have any other paper?

00:09:25.000 --> 00:09:30.000
Here are a couple of extra
pages.

00:09:30.000 --> 00:09:34.000
Also, if you need some,
there are some paper airplanes

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up here.
You are welcome to take those.

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Okay.
Some of you are more

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strategically placed than
others, and so you may want to

00:09:51.000 --> 00:09:56.000
designate someone in your
recitation section as a launcher

00:09:56.000 --> 00:10:03.000
and send them down here so that
everybody gets an equal chance.

00:10:03.000 --> 00:10:06.000
That is fine with me.
And, as I said,

00:10:06.000 --> 00:10:09.000
if anybody wants a paper
airplane.

00:10:09.000 --> 00:10:13.000
Oh, also the other thing,
write your recitation section

00:10:13.000 --> 00:10:19.000
number on the airplane so that I
can identify which airplane and

00:10:19.000 --> 00:10:24.000
what section it comes from.
And they have to be airplanes.

00:10:24.000 --> 00:10:28.000
They cannot be wads.
And here are some extra

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airplanes if you want.

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You can take some and pass them
back if you want.

00:10:43.000 --> 00:10:48.000
While you are doing that,
I am going to start lecturing

00:10:48.000 --> 00:10:52.000
here about trends in the
Periodic Table.

00:11:03.000 --> 00:11:05.000
And, of course,
it is these electron

00:11:05.000 --> 00:11:09.000
configurations that allow us to
understand the trends in the

00:11:09.000 --> 00:11:13.000
Periodic Table.
But you should realize that the

00:11:13.000 --> 00:11:18.000
Periodic Table was initially put
together by Mendeleev and others

00:11:18.000 --> 00:11:21.000
in 1850-1870.
And it was put together on the

00:11:21.000 --> 00:11:25.000
basis of the similarity of the
chemical and physical properties

00:11:25.000 --> 00:11:28.000
of the elements.
For example,

00:11:28.000 --> 00:11:32.000
lithium, sodium,
potassium, they were put in the

00:11:32.000 --> 00:11:36.000
same column because those
elements are all soft,

00:11:36.000 --> 00:11:39.000
malleable elements that were
very reactive.

00:11:39.000 --> 00:11:43.000
Helium, neon,
argon were put in the same

00:11:43.000 --> 00:11:47.000
column because they are all
atoms that are very unreactive.

00:11:47.000 --> 00:11:51.000
And, of course,
today, we understand why their

00:11:51.000 --> 00:11:55.000
properties are what they are.
And we understand it on the

00:11:55.000 --> 00:12:00.000
basis of the electron
configurations.

00:12:00.000 --> 00:12:03.000
Lithium, sodium,
potassium, we have this extra

00:12:03.000 --> 00:12:09.000
valence electron in the s state
that makes it very reactive.

00:12:09.000 --> 00:12:12.000
Helium, neon,
argon are very unreactive

00:12:12.000 --> 00:12:17.000
because they have this closed
shell, this inner gas

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configuration.
But really, by the late 1800s

00:12:20.000 --> 00:12:24.000
and early 1900s,
the similar chemical

00:12:24.000 --> 00:12:29.000
properties, as you go down a
column of the Periodic Table,

00:12:29.000 --> 00:12:35.000
was really very firmly believed
to an extreme extent.

00:12:35.000 --> 00:12:38.000
So strongly,
that it was known that,

00:12:38.000 --> 00:12:43.000
and, of course,
human beings ate salt and that

00:12:43.000 --> 00:12:48.000
the body had sodium ions in it
and potassium ions in it,

00:12:48.000 --> 00:12:53.000
if that is the case,
if you can consume sodium and

00:12:53.000 --> 00:12:58.000
potassium, why not a little
lithium?

00:12:58.000 --> 00:13:01.000
In 1925 or so,
there was marketed a soft

00:13:01.000 --> 00:13:05.000
drink, and this soft drink
wanted a lemon-lime flavor to

00:13:05.000 --> 00:13:08.000
it.
To get that lemon-lime flavor

00:13:08.000 --> 00:13:12.000
they needed a little bit of
citric acid, but that is not

00:13:12.000 --> 00:13:17.000
very soluble in water.
To make it soluble you make it

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a salt.
And, for whatever reason,

00:13:19.000 --> 00:13:22.000
they used lithium citrate.
Why not?

00:13:22.000 --> 00:13:27.000
Let's use some lithium citrate.
And that soft drink was none

00:13:27.000 --> 00:13:31.000
other than 7-Up.
Honestly.

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And, in fact,
the benefits of lithium were

00:13:36.000 --> 00:13:40.000
touted.
Lithium was claimed to give the

00:13:40.000 --> 00:13:46.000
beverage healthful benefits,
an abundance of energy,

00:13:46.000 --> 00:13:51.000
enthusiasm, clear complexion,
lustrous hair,

00:13:51.000 --> 00:13:55.000
lustrous eyes,
shinning eyes,

00:13:55.000 --> 00:14:01.000
and you have got to drink this
stuff.

00:14:01.000 --> 00:14:05.000
It was the market for 25 years
until the early 1950s,

00:14:05.000 --> 00:14:09.000
when the antipsychotic
properties of lithium were

00:14:09.000 --> 00:14:14.000
beginning to be noticed,
along with the severe side

00:14:14.000 --> 00:14:18.000
effects of lithium.
And it was then taken off the

00:14:18.000 --> 00:14:23.000
market, or at least taken off
the market with the citrate as

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the lithium salt in it.
And it was really only another

00:14:28.000 --> 00:14:32.000
20 years, 1970,
before lithium was actually

00:14:32.000 --> 00:14:36.000
approved as a drug for the
treatment of antipsychotic

00:14:36.000 --> 00:14:40.000
behavior.
I don't know how many

00:14:40.000 --> 00:14:44.000
individuals suffered the side
effects of lithium from drinking

00:14:44.000 --> 00:14:47.000
too much 7-Up,
but there is a moral to this

00:14:47.000 --> 00:14:49.000
story.
And the moral,

00:14:49.000 --> 00:14:53.000
of course, is that even though
we are about to talk about the

00:14:53.000 --> 00:14:56.000
general trends along a column of
a Periodic Table,

00:14:56.000 --> 00:15:00.000
don't put any element in your
mouth just because it is in the

00:15:00.000 --> 00:15:06.000
same column of the Period Table
as some element you do eat.

00:15:06.000 --> 00:15:11.000
This is a for real story.
One of the properties we are

00:15:11.000 --> 00:15:15.000
going to talk about is the
ionization energy.

00:15:15.000 --> 00:15:21.000
And we have already used the
word ionization energy quite a

00:15:21.000 --> 00:15:27.000
lot, but let me just formalize
the definitions here.

00:15:27.000 --> 00:15:30.000
For example,
we have a boron atom being

00:15:30.000 --> 00:15:32.000
ionized.
The energy difference between

00:15:32.000 --> 00:15:37.000
the products and the reactions
here is that ionization energy.

00:15:37.000 --> 00:15:42.000
But this ionization energy is
minus the binding energy of the

00:15:42.000 --> 00:15:46.000
2p electron in boron.
That is what that ionization

00:15:46.000 --> 00:15:49.000
energy is.
We are ripping off the least

00:15:49.000 --> 00:15:53.000
strongly bound electron.
And when we rip off the least

00:15:53.000 --> 00:15:57.000
strongly bound electron,
we call that the first

00:15:57.000 --> 00:16:02.000
ionization energy.
That is the energy to remove

00:16:02.000 --> 00:16:06.000
the electron from the highest
occupied atomic orbital.

00:16:06.000 --> 00:16:10.000
That is the same idea,
the highest occupied atomic

00:16:10.000 --> 00:16:14.000
orbital, that is the same idea
as the least strongly bound

00:16:14.000 --> 00:16:17.000
electron.
However, most of the time,

00:16:17.000 --> 00:16:22.000
when we talk about ionization
energy, we don't use the word

00:16:22.000 --> 00:16:25.000
first.
If you see a list of ionization

00:16:25.000 --> 00:16:29.000
energies, if you see a table of
ionization energies,

00:16:29.000 --> 00:16:33.000
they don't say first.
That first is implied.

00:16:33.000 --> 00:16:36.000
Now, of course,
there are other kinds of

00:16:36.000 --> 00:16:39.000
ionization energies.
For example,

00:16:39.000 --> 00:16:43.000
the second ionization energy.
We can keep going here.

00:16:43.000 --> 00:16:47.000
We can take boron plus,
rip off the next least strongly

00:16:47.000 --> 00:16:51.000
bound electron to make boron
plus 2.

00:16:51.000 --> 00:16:55.000
That energy change is what we
define as a second ionization

00:16:55.000 --> 00:16:58.000
energy.
That second ionization energy

00:16:58.000 --> 00:17:02.000
is minus the binding energy of
the 2s electron in boron plus.

00:17:02.000 --> 00:17:04.000
And we can keep going.

00:17:04.000 --> 00:17:08.000
There is a third ionization
energy, taking another electron

00:17:08.000 --> 00:17:11.000
from boron plus 2 to
boron plus 3.

00:17:11.000 --> 00:17:14.000
And there is a fourth
ionization energy,

00:17:14.000 --> 00:17:17.000
boron plus 3 to boron
plus 4.

00:17:17.000 --> 00:17:20.000
And a fifth ionization energy,
boron plus 4,

00:17:20.000 --> 00:17:23.000
boron plus 5,
all the way down.

00:17:23.000 --> 00:17:25.000
And now we are the bare
nucleus.

00:17:25.000 --> 00:17:28.000
That is our definition of
ionization energy,

00:17:28.000 --> 00:17:32.000
second, third,
fourth, and fifth.

00:17:32.000 --> 00:17:38.000
Now comes the first question,
and the question is going to be

00:17:38.000 --> 00:17:43.000
on the side boards here.
We have this reaction.

00:17:43.000 --> 00:17:50.000
This is boron plus
going to boron plus 2.

00:17:50.000 --> 00:17:55.000
What we are doing here is
removing a 2s electron.

00:17:55.000 --> 00:18:02.000
[LAUGHTER] Remember about the

00:18:02.000 --> 00:18:08.000
fool aiming for their chemistry
professor?

00:18:16.000 --> 00:18:20.000
Look at the second reaction
here, boron to boron plus.

00:18:20.000 --> 00:18:23.000
Again, we are pulling off a 2s

00:18:23.000 --> 00:18:26.000
electron.
And the question is,

00:18:26.000 --> 00:18:30.000
are these two energies equal?
Now, the way we are going to

00:18:30.000 --> 00:18:34.000
answer it is after I get out of
the way, I am going to say

00:18:34.000 --> 00:18:36.000
launch.
You are going to launch.

00:18:36.000 --> 00:18:39.000
And the first paper airplane to
hit the blackboard,

00:18:39.000 --> 00:18:42.000
we are going to look at that
recitation number and you are

00:18:42.000 --> 00:18:44.000
going to have a chance to
answer.

00:18:44.000 --> 00:18:47.000
Are you ready?
Launch.

00:18:55.000 --> 00:19:00.000
Recitation four.
Are these two energies equal?

00:19:00.000 --> 00:19:02.000
That is you.

00:19:08.000 --> 00:19:10.000
Are these two energies equal?
No.

00:19:10.000 --> 00:19:13.000
Final answer?
Yes, they are right.

00:19:13.000 --> 00:19:19.000
One point for recitation four.
These energies are not equal.

00:19:19.000 --> 00:19:22.000
Why?
Well, because this ionization

00:19:22.000 --> 00:19:25.000
energy is the second ionization
energy. It is

00:19:25.000 --> 00:19:31.000
minus the binding energy of
the 2s electron in boron plus.

00:19:31.000 --> 00:19:36.000
This energy is the ionization

00:19:36.000 --> 00:19:39.000
energy of the 2s electron in
boron.

00:19:39.000 --> 00:19:46.000
It is minus the binding energy
of the 2s electron in boron.

00:19:46.000 --> 00:19:49.000
They are not equal.
Next question.

00:19:49.000 --> 00:19:54.000
Which one of these binding
energies is greater?

00:19:54.000 --> 00:19:58.000
Wait.
I am getting out of the way.

00:19:58.000 --> 00:20:02.000
Are you ready?
In position.

00:20:02.000 --> 00:20:04.000
Launch.

00:20:09.000 --> 00:20:12.000
Recitation eight.
Where are you,

00:20:12.000 --> 00:20:16.000
eight?
You are over here.

00:20:16.000 --> 00:20:20.000
Eight does not want to identify
itself.

00:20:20.000 --> 00:20:24.000
All right.
Which one is greater,

00:20:24.000 --> 00:20:27.000
top or bottom?
Top.

00:20:27.000 --> 00:20:32.000
Final answer?
Boy, you are right.

00:20:32.000 --> 00:20:36.000
Top one is greater.
Recitation eight.

00:20:36.000 --> 00:20:43.000
It is greater because the
effective charge in boron plus

00:20:43.000 --> 00:20:50.000
is larger than it is in boron.
There are fewer electrons for

00:20:50.000 --> 00:20:55.000
shielding.
The effective charge is larger.

00:20:55.000 --> 00:21:02.000
That binding energy is greater.
Or, that ionization energy

00:21:02.000 --> 00:21:06.000
here, the way I write it,
is greater.

00:21:06.000 --> 00:21:10.000
Fantastic.
Now, we are going to look at

00:21:10.000 --> 00:21:17.000
some trends in the ionization
energy along the Periodic Table.

00:21:17.000 --> 00:21:22.000
The first question is,
here is the Periodic Table,

00:21:22.000 --> 00:21:28.000
as we go across it,
what happens to that ionization

00:21:28.000 --> 00:21:31.000
energy?
Wait.

00:21:31.000 --> 00:21:36.000
Are we in position?
Ready?

00:21:36.000 --> 00:21:39.000
Launch.

00:21:45.000 --> 00:21:49.000
Recitation five.
What happens to the ionization

00:21:49.000 --> 00:21:54.000
energy as you go across the
Periodic Table?

00:21:54.000 --> 00:21:57.000
Is that five?
Is that your answer,

00:21:57.000 --> 00:21:59.000
five?

00:22:05.000 --> 00:22:11.000
What happens to the ionization
energy as you go across the

00:22:11.000 --> 00:22:15.000
Periodic Table from here to
here?

00:22:15.000 --> 00:22:18.000
It increases.
You are right,

00:22:18.000 --> 00:22:22.000
recitation five.
Here is the trend.

00:22:22.000 --> 00:22:26.000
Here is row one,
from hydrogen to helium.

00:22:26.000 --> 00:22:32.000
Here is row two,
from lithium to neon.

00:22:32.000 --> 00:22:35.000
It increases.
It increases because,

00:22:35.000 --> 00:22:41.000
as you go across the Periodic
Table here, Z increases.

00:22:41.000 --> 00:22:45.000
The nuclear charge increases.
But, of course,

00:22:45.000 --> 00:22:50.000
there is another parameter
here, and that is r.

00:22:50.000 --> 00:22:55.000
But, as you go across the
Periodic Table right here,

00:22:55.000 --> 00:23:00.000
you are putting electrons into
the same shell,

00:23:00.000 --> 00:23:05.000
essentially.
You are putting those electrons

00:23:05.000 --> 00:23:09.000
into shells that have,
roughly speaking,

00:23:09.000 --> 00:23:12.000
the same distance of r from the
nucleus.

00:23:12.000 --> 00:23:18.000
And so the factor that wins out
is Z, the effective charge here.

00:23:18.000 --> 00:23:23.000
And the ionization energy as
you go across then increases.

00:23:23.000 --> 00:23:27.000
But you also see that there are
some glitches.

00:23:27.000 --> 00:23:33.000
You see that boron is a little
bit lower energy than --

00:23:38.000 --> 00:23:42.000
What did I want to say here?
I'm sorry.

00:23:42.000 --> 00:23:46.000
I am looking at it from the
side.

00:23:46.000 --> 00:23:51.000
Here is the electron
configuration of beryllium.

00:23:51.000 --> 00:23:56.000
Here it is, boron,
Z equals 5.

00:24:02.000 --> 00:24:04.000
What you see,
here, is that in boron,

00:24:04.000 --> 00:24:09.000
you have to put that extra
electron into the 2p state,

00:24:09.000 --> 00:24:11.000
which requires some more
energy.

00:24:11.000 --> 00:24:16.000
The bottom line is that the
nuclear charge does not increase

00:24:16.000 --> 00:24:20.000
fast enough to compensate
completely for the extra energy

00:24:20.000 --> 00:24:24.000
that you need to have to get to
this 2p state.

00:24:24.000 --> 00:24:28.000
Boron has a little bit lower
ionization energy than

00:24:28.000 --> 00:24:32.000
beryllium.
And to see another glitch,

00:24:32.000 --> 00:24:37.000
that other glitch is between
nitrogen and oxygen.

00:24:37.000 --> 00:24:43.000
Again, we can understand that
glitch by the electron

00:24:43.000 --> 00:24:46.000
configuration.
Here is nitrogen,

00:24:46.000 --> 00:24:49.000
Z equals 7.
Here is oxygen,

00:24:49.000 --> 00:24:53.000
Z equals 8.
And the bottom line here is

00:24:53.000 --> 00:24:57.000
that in oxygen,
you have to put an electron in

00:24:57.000 --> 00:25:04.000
a state in which there already
is an electron.

00:25:04.000 --> 00:25:06.000
That is a repulsive
interaction.

00:25:06.000 --> 00:25:11.000
Again, the increase in the
nuclear charge just is not large

00:25:11.000 --> 00:25:16.000
enough to fully compensate for
that repulsive interaction.

00:25:16.000 --> 00:25:21.000
We can understand those little
glitches in terms of these

00:25:21.000 --> 00:25:24.000
electron configurations.
And, in general,

00:25:24.000 --> 00:25:29.000
here, that ionization increases
as we go across the Periodic

00:25:29.000 --> 00:25:32.000
Table.
Here is the third row.

00:25:32.000 --> 00:25:36.000
You also see there are glitches
in the third row.

00:25:36.000 --> 00:25:41.000
You see there is a glitch
between magnesium and aluminum.

00:25:41.000 --> 00:25:45.000
They are right underneath
beryllium and boron.

00:25:45.000 --> 00:25:48.000
A glitch between phosphorous
and sulfur.

00:25:48.000 --> 00:25:51.000
They are right underneath
nitrogen and oxygen.

00:25:51.000 --> 00:25:55.000
For the same reason,
there is a glitch at those

00:25:55.000 --> 00:26:01.000
elements in the second row.
Now, the next question.

00:26:01.000 --> 00:26:09.000
As we go down a column of the
Periodic Table,

00:26:09.000 --> 00:26:16.000
what happens to the ionization
energy?

00:26:16.000 --> 00:26:18.000
Wait.
Ready?

00:26:18.000 --> 00:26:20.000
Set?
Launch.

00:26:20.000 --> 00:26:26.000
Five.
What happens to the ionization

00:26:26.000 --> 00:26:30.000
energy?
What?

00:26:30.000 --> 00:26:33.000
Decreases.
You are right,

00:26:33.000 --> 00:26:37.000
recitation five.
Why does it decrease?

00:26:37.000 --> 00:26:43.000
It decreases because?
Well, it decreases because you

00:26:43.000 --> 00:26:50.000
are putting electrons into
shells that are farther and

00:26:50.000 --> 00:26:57.000
farther away from the nucleus.
Yes, as you go down the column,

00:26:57.000 --> 00:27:02.000
Z increases.
But it does not increase fast

00:27:02.000 --> 00:27:07.000
enough as r increases.
Remember there are the two

00:27:07.000 --> 00:27:11.000
factors, Z and r.
Although Z increases,

00:27:11.000 --> 00:27:17.000
you are putting the electrons
into shells that are farther

00:27:17.000 --> 00:27:21.000
from the nucleus.
Therefore, that attractive

00:27:21.000 --> 00:27:26.000
interaction does go down,
and the ionization energy goes

00:27:26.000 --> 00:27:29.000
down.
Great.

00:27:29.000 --> 00:27:33.000
Now, we are going to talk about
another property.

00:27:33.000 --> 00:27:38.000
That other property is called
the electron affinity.

00:27:38.000 --> 00:27:42.000
For example,
if I take chlorine and add an

00:27:42.000 --> 00:27:46.000
electron to it to make chlorine
minus.

00:27:46.000 --> 00:27:51.000
There is an energy change here.
That energy change,

00:27:51.000 --> 00:27:56.000
delta E, is equal to minus
kilojoules per mole.

00:27:56.000 --> 00:28:02.000
That is, the fact that this

00:28:02.000 --> 00:28:08.000
energy change is negative,
this tells you that the

00:28:08.000 --> 00:28:13.000
chlorine ion is more stable than
the neutral atom.

00:28:13.000 --> 00:28:19.000
Now, in terms of an equation,
what is the definition here of

00:28:19.000 --> 00:28:24.000
the electron affinity?
That is the next question.

00:28:24.000 --> 00:28:29.000
Are you ready to launch?
Launch.

00:28:34.000 --> 00:28:36.000
Recitation eight.
Where are you?

00:28:36.000 --> 00:28:39.000
You are right here.
No, you are right there.

00:28:39.000 --> 00:28:43.000
Recitation eight,
what is the definition of the

00:28:43.000 --> 00:28:45.000
electron affinity?

00:28:50.000 --> 00:28:55.000
TAs cannot help.
Energy required to add an

00:28:55.000 --> 00:28:59.000
electron, that is --

00:29:09.000 --> 00:29:12.000
Recitation eight,
you are right.

00:29:12.000 --> 00:29:16.000
It is minus delta E.
Fantastic.

00:29:16.000 --> 00:29:20.000
This is the delta E for the
reason.

00:29:20.000 --> 00:29:25.000
The electron affinity is minus
that quantity.

00:29:25.000 --> 00:29:30.000
The electron affinity,
then, of chlorine is

00:29:30.000 --> 00:29:36.000
kilojoules per mole.
Now, unlike the ionization

00:29:36.000 --> 00:29:42.000
energy, the electron affinity
can be positive or negative.

00:29:42.000 --> 00:29:47.000
For example,
if you try to stick an electron

00:29:47.000 --> 00:29:52.000
on a nitrogen atom to make N
minus,

00:29:52.000 --> 00:29:56.000
delta E for that reaction is
positive.

00:29:56.000 --> 00:30:02.000
It is 7 kilojoules per mole.
And so that electron is not

00:30:02.000 --> 00:30:06.000
going to stick onto the
nitrogen.

00:30:06.000 --> 00:30:11.000
The electron affinity in that
case is negative.

00:30:11.000 --> 00:30:14.000
It is minus 7 kilojoules per
mole.

00:30:14.000 --> 00:30:20.000
Again, you can understand that
in terms of the electron

00:30:20.000 --> 00:30:25.000
configuration for the nitrogen.
Here is the electron

00:30:25.000 --> 00:30:32.000
configuration for nitrogen.
If you go and you want to add

00:30:32.000 --> 00:30:35.000
in another electron,
like right there,

00:30:35.000 --> 00:30:37.000
there is a repulsive
interaction.

00:30:37.000 --> 00:30:39.000
And Z equals 7.
In this case,

00:30:39.000 --> 00:30:44.000
that nuclear charge is not
large enough to compensate for

00:30:44.000 --> 00:30:48.000
this repulsive interaction,
so the electron affinity,

00:30:48.000 --> 00:30:51.000
here, is negative.
Noble gases have negative

00:30:51.000 --> 00:30:55.000
electron affinities.
You cannot add an electron to

00:30:55.000 --> 00:30:57.000
that.
It is not stable.

00:30:57.000 --> 00:31:02.000
Why?
Because you are destroying,

00:31:02.000 --> 00:31:10.000
in effect, the electronic
configuration of the rare gas.

00:31:10.000 --> 00:31:17.000
With that, now we want to ask
is how does the electron

00:31:17.000 --> 00:31:23.000
affinity change as you go across
the periodic table?

00:31:23.000 --> 00:31:28.000
That is our next question.
Wait.

00:31:28.000 --> 00:31:31.000
Okay.
Ready?

00:31:31.000 --> 00:31:34.000
Set?
Launch.

00:31:41.000 --> 00:31:47.000
Six, where are you?
What happens to the electron

00:31:47.000 --> 00:31:52.000
affinity as you go across the
Periodic Table,

00:31:52.000 --> 00:31:56.000
from left to right?
Decreases.

00:31:56.000 --> 00:32:01.000
Is that your final answer?
Yes?

00:32:01.000 --> 00:32:05.000
You are wrong.
The electron affinity,

00:32:05.000 --> 00:32:08.000
as you go across,
increases.

00:32:08.000 --> 00:32:12.000
The halogens,
fluorine, chlorine have very

00:32:12.000 --> 00:32:17.000
large electron affinities,
because adding an electron

00:32:17.000 --> 00:32:21.000
gives you that noble gas
configuration.

00:32:21.000 --> 00:32:28.000
The electron affinity increases
as you go across the Periodic

00:32:28.000 --> 00:32:31.000
Table.
Now what happens to the

00:32:31.000 --> 00:32:35.000
electron affinity as we go down
the Periodic Table?

00:32:35.000 --> 00:32:39.000
You guys, do you have any paper
airplanes?

00:32:39.000 --> 00:32:42.000
We have to give you some.
Are you okay?

00:32:42.000 --> 00:32:46.000
That is our next question.
What happens to the electron

00:32:46.000 --> 00:32:49.000
affinity as we go down the
Periodic Table?

00:32:49.000 --> 00:32:50.000
Ready?
Set?

00:32:50.000 --> 00:32:52.000
Launch.

00:33:00.000 --> 00:33:03.000
Recitation four.
What does it do?

00:33:03.000 --> 00:33:06.000
Does it go down?
Decreases.

00:33:06.000 --> 00:33:09.000
It absolutely does.

00:33:14.000 --> 00:33:17.000
The electron affinity,
as you go down,

00:33:17.000 --> 00:33:21.000
decreases.
It decreases because the

00:33:21.000 --> 00:33:25.000
nuclear charge,
here, is increasing,

00:33:25.000 --> 00:33:31.000
but you are putting electrons
in shells that are farther away

00:33:31.000 --> 00:33:37.000
from the nucleus.
The overall effect is that that

00:33:37.000 --> 00:33:42.000
r dependence dictates,
and the electron affinity goes

00:33:42.000 --> 00:33:43.000
down.

00:33:48.000 --> 00:33:54.000
Let me do one more here.
Or, maybe a couple more.

00:33:54.000 --> 00:34:01.000
Now, what I want to ask is
about the atomic radius.

00:34:07.000 --> 00:34:15.000
And what I want to know is what
happens to r as you go across

00:34:15.000 --> 00:34:21.000
the Periodic Table.
I am getting out of the way.

00:34:21.000 --> 00:34:22.000
Wait.
Ready?

00:34:22.000 --> 00:34:26.000
Set?
I haven't said launch yet.

00:34:26.000 --> 00:34:28.000
Ready?
Set?

00:34:28.000 --> 00:34:32.000
Go.
Recitation one.

00:34:32.000 --> 00:34:36.000
What happens to r?
Decreases.

00:34:36.000 --> 00:34:40.000
It decreases.
It goes down.

00:34:40.000 --> 00:34:44.000
This is important.
It goes down,

00:34:44.000 --> 00:34:51.000
here, because Z is increasing.
Z is increasing,

00:34:51.000 --> 00:35:00.000
and you are putting electrons
into the same shell.

00:35:00.000 --> 00:35:07.000
And so the same shell means the
same distance from the nucleus.

00:35:07.000 --> 00:35:13.000
Larger Z, the radius actually
goes down, the size goes down.

00:35:13.000 --> 00:35:20.000
And then, one more question.
What happens as you go down the

00:35:20.000 --> 00:35:25.000
Periodic Table?
I am going to get out of the

00:35:25.000 --> 00:35:26.000
way.
Ready?

00:35:26.000 --> 00:35:29.000
Set?
Go.

00:35:34.000 --> 00:35:45.000
One.
It decreases?

00:35:45.000 --> 00:36:02.000
What did you say?
Increases.

00:36:02.000 --> 00:36:37.000
It does increase because you
are putting electrons into

00:36:37.000 --> 00:37:10.000
shells farther and farther away.
What is the score,

00:37:10.158 --> 00:37:13.000
Christine?
Fantastic.