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PROFESSOR: OK.

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00:00:22,230 --> 00:00:23,070
Let's get started.

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00:00:23,070 --> 00:00:26,740
Can you go ahead and take 10
more seconds on this first

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00:00:26,740 --> 00:00:46,430
clicker question here?

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00:00:46,430 --> 00:00:46,880
OK.

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00:00:46,880 --> 00:00:51,250
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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00:00:56,450 --> 00:00:58,650
the people that didn't get it
right were rushing to get out

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00:00:58,650 --> 00:01:00,350
their clickers and didn't
have time to think

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00:01:00,350 --> 00:01:02,390
it all the way through.

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00:01:02,390 --> 00:01:06,800
Remember that when we're talking
about 4 s 1, 3 d 10,

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00:01:06,800 --> 00:01:09,480
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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00:01:12,150 --> 00:01:15,190
So, that's actually the electron
configuration we have

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00:01:15,190 --> 00:01:17,180
when we're talking about
copper and some other

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00:01:17,180 --> 00:01:22,250
exceptions in the periodic table
that you're going to be

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looking at.

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00:01:23,040 --> 00:01:25,560
So, hopefully, if you were to go
back and look you could see

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00:01:25,560 --> 00:01:27,960
that this is, in fact, copper.

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00:01:27,960 --> 00:01:30,660
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

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of a friendly competition in
terms of answering the clicker

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00:01:39,020 --> 00:01:40,900
questions correctly.

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00:01:40,900 --> 00:01:44,070
So we've tagged each of your
numbers to your actual

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00:01:44,070 --> 00:01:47,630
recitation, so we can see
today which recitation

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00:01:47,630 --> 00:01:51,000
actually is going to be doing
the best in terms of clicker

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00:01:51,000 --> 00:01:54,870
questions, who's going to get
the most correct today.

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00:01:54,870 --> 00:01:58,670
So, you may or may not know this
about your TAs, but this

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00:01:58,670 --> 00:02:02,260
is a pretty competitive group of
TAs we have this year, and

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00:02:02,260 --> 00:02:05,440
they like to brag about how
smart their recitation is, how

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00:02:05,440 --> 00:02:09,220
good questions they're getting
in the recitation section.

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00:02:09,220 --> 00:02:13,290
So, do your TA proud today and
see if you can be part of the

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00:02:13,290 --> 00:02:16,300
recitation that gets the most
correct in terms of a

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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

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00:02:27,190 --> 00:02:28,260
clicker questions right.

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00:02:28,260 --> 00:02:31,040
So, in this one we're selecting
the correct

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00:02:31,040 --> 00:02:33,470
electronic 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 mixed

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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

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and talk about how we can figure
out what the correct

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electron 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 to

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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

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the filled 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 completely

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00:03:38,980 --> 00:03:40,550
neutral atom.

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00:03:40,550 --> 00:03:43,370
But remember what we said,
which was when we talked

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

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it turns out that even though
3 d is higher in energy when

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it's not filled, once we fill
it with an electron, these 2

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orbitals 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

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were 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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00:04:12,930 --> 00:04:17,650
gives us 3 d 3 and then 4 s 1.

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00:04:17,650 --> 00:04:20,110
So, it's a little bit of
a trick when you're

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00:04:20,110 --> 00:04:20,950
dealing with ions.

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00:04:20,950 --> 00:04:23,820
The best suggestion is just to
write it out completely for

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00:04:23,820 --> 00:04:26,840
the neutral atom, and then you
want to take an electron out

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00:04:26,840 --> 00:04:27,900
of the highest orbital.

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00:04:27,900 --> 00:04:30,380
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

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actually 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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00:04:59,010 --> 00:05:01,670
everything you need to know
logistically for the exam --

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00:05:01,670 --> 00:05:04,240
where it is, what you do, what
kind of calculators you can

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00:05:04,240 --> 00:05:06,400
bring, which by the way
are any calculator.

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00:05:06,400 --> 00:05:09,340
So you'll get all of that
information on Friday.

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00:05:09,340 --> 00:05:12,030
So don't worry if you have
some questions right now.

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00:05:12,030 --> 00:05:13,520
I just want to let
you know that.

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00:05:13,520 --> 00:05:16,120
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

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Friday, what we'll do instead
is we'll give you some

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00:05:22,090 --> 00:05:25,670
practice problems, and these
will be just more of the same

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00:05:25,670 --> 00:05:28,220
type of problems that you saw
before but that's another

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00:05:28,220 --> 00:05:30,020
chance 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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00:05:32,140 --> 00:05:34,050
it's just to give you some extra
practice if you want

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00:05:34,050 --> 00:05:35,910
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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00:05:39,810 --> 00:05:42,610
actually see exactly what the
format's going to look like.

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00:05:42,610 --> 00:05:45,900
So when you go into the exam a
week from today, it'll all

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00:05:45,900 --> 00:05:48,250
look really familiar, you'll be
comfortable with the format

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00:05:48,250 --> 00:05:50,250
and you can just dive
right in and start

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answering the questions.

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00:05:51,320 --> 00:05:53,200
So you'll have all that
information and we'll get it

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00:05:53,200 --> 00:05:54,880
to you on Friday.

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00:05:54,880 --> 00:05:56,510
The other quick thing I want
to say is that I do have

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00:05:56,510 --> 00:06:00,650
office hours today from 3 to 5,
so feel free to stop by if

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00:06:00,650 --> 00:06:03,550
you have questions about
problem-set 3 that you're

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00:06:03,550 --> 00:06:04,750
finishing up.

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00:06:04,750 --> 00:06:07,920
And also, for those of you that
did sign up for the pizza

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00:06:07,920 --> 00:06:10,540
forum tonight, that's going to
be at 5 o'clock, it's in room

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00:06:10,540 --> 00:06:16,380
56-502, so we'll see some of you
tonight for that as well.

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All right.

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00:06:16,690 --> 00:06:18,670
So, let's move on to what we're
talking about today.

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00:06:18,670 --> 00:06:21,560
What we're going to start with
is discussing photoelectron

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00:06:21,560 --> 00:06:24,480
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. We'll then
take a turn to talking

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about the periodic table,
we'll look at a bunch of

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periodic trends, including
ionization energy, electron

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affinity, electronegativity
and atomic radius.

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00:06:40,750 --> 00:06:43,770
And then, if we have time at the
end, we'll introduce one

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00:06:43,770 --> 00:06:47,460
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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00:06:51,370 --> 00:06:54,520
this last topic here, that's the
end of the material that's

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00:06:54,520 --> 00:06:56,470
going to be on this
first exam.

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00:06:56,470 --> 00:06:59,260
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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00:07:04,690 --> 00:07:07,160
that's it, that's all you need
to study for this first exam.

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00:07:07,160 --> 00:07:10,120
So from that point on it'll be
exam 2 material, so depending

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00:07:10,120 --> 00:07:12,170
on how you like to come
compartmentalize your

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00:07:12,170 --> 00:07:15,360
information, you can separate
that in your brain in terms of

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00:07:15,360 --> 00:07:17,590
what you're trying to learn
right now versus what you can

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00:07:17,590 --> 00:07:20,500
put off until a little
bit later.

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00:07:20,500 --> 00:07:23,670
So, let's start with talking
about photoelectron

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00:07:23,670 --> 00:07:27,010
spectroscopy.

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00:07:27,010 --> 00:07:29,820
This actually relates very
closely to what we discussed

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00:07:29,820 --> 00:07:33,510
in class on Friday before the
long weekend, and what we were

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00:07:33,510 --> 00:07:37,710
talking about is the energy
levels of multielectron atoms.

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00:07:37,710 --> 00:07:40,440
So what we'll start with today
is talking about the technique

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00:07:40,440 --> 00:07:43,570
that's primarily used to
actually experimentally figure

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out what these different
energy levels are.

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00:07:45,960 --> 00:07:47,340
And this is called photoelectron
spectroscopy,

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00:07:47,340 --> 00:07:51,960
and essentially what it is is
very similar conceptually to

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00:07:51,960 --> 00:07:54,710
what we were talking about way
back in the first couple

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00:07:54,710 --> 00:07:56,120
lectures when we were
talking about the

165
00:07:56,120 --> 00:07:57,640
photoelectric effect.

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

167
00:08:01,270 --> 00:08:04,900
in the case, it's going to be
a gas, and we hit it with a

168
00:08:04,900 --> 00:08:07,550
photon that has some
incident energy.

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00:08:07,550 --> 00:08:11,590
So e sub i, some energy that the
photon comes in with, and

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00:08:11,590 --> 00:08:14,620
if it has sufficient energy to
eject an electron, it will do

171
00:08:14,620 --> 00:08:18,210
that, and our electron will be
ejected with a certain kinetic

172
00:08:18,210 --> 00:08:21,000
energy, which is going to be
whatever energy is left over

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00:08:21,000 --> 00:08:24,200
from the initial energy we put
in minus what was taken up in

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00:08:24,200 --> 00:08:27,370
order to actually ionize
or eject the electron.

175
00:08:27,370 --> 00:08:29,670
So, you can see how this can
directly give us different

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00:08:29,670 --> 00:08:32,050
ionization energies for
any atom that we're

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00:08:32,050 --> 00:08:33,460
interested in studying.

178
00:08:33,460 --> 00:08:35,880
For example, with neon we can
think about all of the

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00:08:35,880 --> 00:08:38,490
different orbital energies
we could be looking at.

180
00:08:38,490 --> 00:08:40,520
In the first case, so
here is the electron

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00:08:40,520 --> 00:08:42,390
configuration of neon.

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00:08:42,390 --> 00:08:45,880
So we can think about what
is our most loosely-bound

183
00:08:45,880 --> 00:08:49,065
electron, what's that highest
energy orbital, and it's going

184
00:08:49,065 --> 00:08:51,500
to be the 2 p orbital,
that's going to be

185
00:08:51,500 --> 00:08:52,610
what's highest in energy.

186
00:08:52,610 --> 00:08:55,570
So if we're going to eject an
electron using a minimum

187
00:08:55,570 --> 00:08:58,130
amount of energy, that's where
it's going to come from.

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00:08:58,130 --> 00:09:00,470
So, you can imagine, that we'll
actually probably have a

189
00:09:00,470 --> 00:09:03,890
lot of kinetic energy left over
if we put a lot of energy

190
00:09:03,890 --> 00:09:04,790
in in the first place.

191
00:09:04,790 --> 00:09:07,340
We're only using up a little
bit to eject the electron,

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00:09:07,340 --> 00:09:09,480
then we'll have a
lot left over.

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So, one difference between
photoelectron spectroscopy

194
00:09:10,990 --> 00:09:14,760
and, for example, the
photoelectric effect is that

195
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in this case, we're not just
looking at one energy level,

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which is what we were looking
at from the surface of a

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00:09:19,330 --> 00:09:22,530
metal, now we're talking about
this gaseous atom.

198
00:09:22,530 --> 00:09:26,470
So we can actually pop an
electron or eject an electron

199
00:09:26,470 --> 00:09:29,720
from any single orbital that is
occupied within the atom.

200
00:09:29,720 --> 00:09:33,180
So, for example, it's not just
the 2 p that we could actually

201
00:09:33,180 --> 00:09:35,380
take an electron from, we
could also think about

202
00:09:35,380 --> 00:09:38,190
ejecting an electron from
the 2 s orbital.

203
00:09:38,190 --> 00:09:40,460
Now this, of course, is going to
take more energy because a

204
00:09:40,460 --> 00:09:43,610
2 s is lower, it has has a more
negative binding energy

205
00:09:43,610 --> 00:09:46,670
than the 2 p, but that's OK as
long as we put in enough

206
00:09:46,670 --> 00:09:49,470
energy, but what we're going to
find is the kinetic energy

207
00:09:49,470 --> 00:09:52,450
coming out with the electron
is actually going to be a

208
00:09:52,450 --> 00:09:55,090
little bit less, right, because
we had to use up more

209
00:09:55,090 --> 00:09:57,280
energy to eject the electron,
so we don't have

210
00:09:57,280 --> 00:10:00,090
as much left over.

211
00:10:00,090 --> 00:10:02,540
There's actually one more
orbital that we could talk

212
00:10:02,540 --> 00:10:05,430
about if we're talking about
this sample case of neon,

213
00:10:05,430 --> 00:10:09,470
which is a 1 s orbital, and if
we're talking about a 1 s

214
00:10:09,470 --> 00:10:13,030
orbital, now we're going to be
even lower in energy still, so

215
00:10:13,030 --> 00:10:16,440
that means the minimum energy
required to eject an electron

216
00:10:16,440 --> 00:10:19,320
is going to be at its highest,
so that means the energy that

217
00:10:19,320 --> 00:10:22,200
we have left over that turns
into kinetic energy for the

218
00:10:22,200 --> 00:10:26,000
electron, is now going to
be really quite small.

219
00:10:26,000 --> 00:10:30,760
And what happens when you
irradiate one of these atoms

220
00:10:30,760 --> 00:10:34,290
that you're studying with this
light is in photoelectron

221
00:10:34,290 --> 00:10:36,350
spectroscopy, you want to make
sure that you put in enough

222
00:10:36,350 --> 00:10:40,180
energy to actually ionize any
single electron that you have

223
00:10:40,180 --> 00:10:41,000
in the atom.

224
00:10:41,000 --> 00:10:43,270
So the way that we really make
sure this is done is that we

225
00:10:43,270 --> 00:10:44,710
use x-rays.

226
00:10:44,710 --> 00:10:48,200
So you know that x-rays are
higher frequency than UV

227
00:10:48,200 --> 00:10:51,020
light, for example, that means
it's also higher energy than

228
00:10:51,020 --> 00:10:54,880
UV light, and if you think
back to our photoelectric

229
00:10:54,880 --> 00:10:57,465
effect experiments, do you
remember what type of light we

230
00:10:57,465 --> 00:10:58,930
were usually using for those?

231
00:10:58,930 --> 00:11:01,490
Does anyone remember?

232
00:11:01,490 --> 00:11:02,620
Yeah.

233
00:11:02,620 --> 00:11:04,560
It was UV light that we used.

234
00:11:04,560 --> 00:11:06,850
Well, we can't guarantee with
UV light we'll have enough

235
00:11:06,850 --> 00:11:09,450
energy to eject every single
electron, so that's why when

236
00:11:09,450 --> 00:11:12,500
we use x-rays, they're higher
energy, you can pretty much be

237
00:11:12,500 --> 00:11:14,000
guaranteed we're going
to eject all of

238
00:11:14,000 --> 00:11:17,160
those electrons there.

239
00:11:17,160 --> 00:11:19,960
So I said that this technique
was used to experimentally

240
00:11:19,960 --> 00:11:22,580
determine what the different
binding energies or the

241
00:11:22,580 --> 00:11:25,730
different ionization energies
are for the different states

242
00:11:25,730 --> 00:11:27,400
in a multielectron atom.

243
00:11:27,400 --> 00:11:29,140
Another way to say
states is to talk

244
00:11:29,140 --> 00:11:30,650
about different orbitals.

245
00:11:30,650 --> 00:11:33,410
So we can do this directly as
long as we have certain types

246
00:11:33,410 --> 00:11:34,140
of information.

247
00:11:34,140 --> 00:11:37,130
The first that we need to know
the energy of the photon

248
00:11:37,130 --> 00:11:41,030
that's incident on
our gaseous atom.

249
00:11:41,030 --> 00:11:43,590
The second piece of information
we need to know is

250
00:11:43,590 --> 00:11:46,320
what actually the kinetic
energy is of the ejected

251
00:11:46,320 --> 00:11:48,490
electron, and that's something
we can just measure by

252
00:11:48,490 --> 00:11:50,470
measuring its velocity.

253
00:11:50,470 --> 00:11:53,980
So we can use an equation to
relate the incident energy and

254
00:11:53,980 --> 00:11:56,570
the kinetic energy to the
ionization energy, or the

255
00:11:56,570 --> 00:11:58,820
energy that's required
to eject an electron.

256
00:11:58,820 --> 00:12:01,140
This should all sound incredibly
familiar, like I'm

257
00:12:01,140 --> 00:12:03,780
just repeating myself in terms
of photoelectric effect,

258
00:12:03,780 --> 00:12:06,010
because essentially that's what
I'm doing, and that's one

259
00:12:06,010 --> 00:12:08,680
reason we spent so much time
and did so many problem-set

260
00:12:08,680 --> 00:12:10,760
problems on the photoelectric
effect.

261
00:12:10,760 --> 00:12:13,640
So what we're saying here is
the incident energy, so the

262
00:12:13,640 --> 00:12:17,230
energy coming in, is just equal
to the minimum energy

263
00:12:17,230 --> 00:12:19,420
that's required to a
eject an electron.

264
00:12:19,420 --> 00:12:21,580
When we talked about the
photoelectric effect, that was

265
00:12:21,580 --> 00:12:22,660
called the work function.

266
00:12:22,660 --> 00:12:25,970
In this case, it's called the
ionization energy, plus

267
00:12:25,970 --> 00:12:27,860
whatever kinetic energy we have

268
00:12:27,860 --> 00:12:29,810
left over in the electron.

269
00:12:29,810 --> 00:12:32,480
So if we want to solve for
ionization energy, we can just

270
00:12:32,480 --> 00:12:33,980
rearrange this equation.

271
00:12:33,980 --> 00:12:36,700
Our ionization energy is going
to be equal to the incident

272
00:12:36,700 --> 00:12:39,010
energy coming in, minus
the kinetic

273
00:12:39,010 --> 00:12:40,060
energy of the electron.

274
00:12:40,060 --> 00:12:43,810
So, let's take a look at the
different kinetic energies

275
00:12:43,810 --> 00:12:47,500
that would be observed in a
spectrum for neon where we had

276
00:12:47,500 --> 00:12:49,330
this incident energy here.

277
00:12:49,330 --> 00:12:51,560
And it turns out that the first
kinetic energy that we

278
00:12:51,560 --> 00:12:55,030
would see or the highest kinetic
energy, would be 12 32

279
00:12:55,030 --> 00:12:56,800
electron volts.

280
00:12:56,800 --> 00:13:00,080
So if that's the case doing a
quick little calculation, what

281
00:13:00,080 --> 00:13:03,800
would the ionization energy be
for a 2 p electron in neon?

282
00:13:03,800 --> 00:13:07,650
Yup, 22.

283
00:13:07,650 --> 00:13:12,560
So, basically all we did was
take 12 54, subtract 12 32,

284
00:13:12,560 --> 00:13:15,250
and we got 22 electron volts.

285
00:13:15,250 --> 00:13:17,050
We can do the same thing
for the other

286
00:13:17,050 --> 00:13:18,010
observed kinetic energy.

287
00:13:18,010 --> 00:13:22,250
So, for example, in the second
case, we say that we see 12 06

288
00:13:22,250 --> 00:13:24,140
in terms of the kinetic
energy.

289
00:13:24,140 --> 00:13:26,430
Same sort of subtraction
problem, what do we have for

290
00:13:26,430 --> 00:13:30,100
the ionization energy
of the 2 s electron?

291
00:13:30,100 --> 00:13:30,980
Good, quick math.

292
00:13:30,980 --> 00:13:32,230
All right, so 48
electron volts.

293
00:13:32,230 --> 00:13:35,430
And let's look at the final
kinetic energy that we'd

294
00:13:35,430 --> 00:13:38,720
observe in this spectrum, which
is 384 electron volts,

295
00:13:38,720 --> 00:13:40,110
so what is that third

296
00:13:40,110 --> 00:13:44,810
corresponding ionization energy?

297
00:13:44,810 --> 00:13:47,260
I couldn't quite hear, but I
have a feeling everyone said

298
00:13:47,260 --> 00:13:50,460
870 electron volts.

299
00:13:50,460 --> 00:13:54,150
So, we can actually kind of
visualize what we would see if

300
00:13:54,150 --> 00:13:56,640
we were looking at a
photoelectron spectrum.

301
00:13:56,640 --> 00:13:59,220
And what we would see if we were
graphing, for example,

302
00:13:59,220 --> 00:14:02,600
increasing kinetic energy,
is we would see 1 line

303
00:14:02,600 --> 00:14:06,570
corresponding to each of these
energies of electrons that we

304
00:14:06,570 --> 00:14:07,680
see coming out.

305
00:14:07,680 --> 00:14:10,190
And, of course, each of those
electrons correspond to an

306
00:14:10,190 --> 00:14:13,300
electron coming out of
a particular orbital.

307
00:14:13,300 --> 00:14:18,180
So in the case of 12 32, that is
our highest kinetic energy,

308
00:14:18,180 --> 00:14:21,040
that means it's our lowest
ionization energy -- it's the

309
00:14:21,040 --> 00:14:24,140
smallest amount of energy it
takes to pop an electron out

310
00:14:24,140 --> 00:14:25,100
of that orbital.

311
00:14:25,100 --> 00:14:29,770
So that's why we see the 2 p
here, the 2 s is 12 06, and it

312
00:14:29,770 --> 00:14:33,130
makes sense that what we see
as the greatest ionization

313
00:14:33,130 --> 00:14:36,350
energy, which is also the
smallest kinetic energy is

314
00:14:36,350 --> 00:14:37,600
that 1 s orbital.

315
00:14:37,600 --> 00:14:40,130
Remember, because that 1 s
orbital is all the way down in

316
00:14:40,130 --> 00:14:42,310
terms of if we're thinking about
an energy diagram, we're

317
00:14:42,310 --> 00:14:45,210
all the way down here, so we
have a huge amount of energy

318
00:14:45,210 --> 00:14:49,120
we have to put into the system
in order to eject an electron.

319
00:14:49,120 --> 00:14:51,130
So what I want to point out when
you're kind of looking at

320
00:14:51,130 --> 00:14:53,920
these numbers here, what the
significance is, look at that

321
00:14:53,920 --> 00:14:56,850
huge difference between what
the ionization energies are

322
00:14:56,850 --> 00:15:00,160
for what we call those valence
electrons, those outer shell

323
00:15:00,160 --> 00:15:03,460
electrons, versus the ionization
energy for the 1 s

324
00:15:03,460 --> 00:15:06,390
orbital -- those are core
electrons there.

325
00:15:06,390 --> 00:15:08,620
So we can think about something
I mentioned last

326
00:15:08,620 --> 00:15:10,560
time, which is when we're
thinking about chemistry and

327
00:15:10,560 --> 00:15:13,560
what's really interesting in
terms of chemical reactions,

328
00:15:13,560 --> 00:15:15,880
it's mostly valence electrons
we're talking about, those are

329
00:15:15,880 --> 00:15:16,750
the ones that tend to be

330
00:15:16,750 --> 00:15:18,660
involved in chemical reactions.

331
00:15:18,660 --> 00:15:21,000
It makes a lot of sense when we
look at it energetically,

332
00:15:21,000 --> 00:15:24,955
because if we think about a 1 s
core electron, that's going

333
00:15:24,955 --> 00:15:27,060
to be held really, really
tightly to the nucleus.

334
00:15:27,060 --> 00:15:29,440
We see that we have to put
this huge energy in to

335
00:15:29,440 --> 00:15:33,410
actually get a 1 s electron
ejected, so it makes a lot of

336
00:15:33,410 --> 00:15:35,640
sense that we wouldn't want to
pay that energy cost in a

337
00:15:35,640 --> 00:15:37,190
normal chemical reaction.

338
00:15:37,190 --> 00:15:40,690
And we don't -- we very rarely
would see these core electrons

339
00:15:40,690 --> 00:15:44,610
actually being involved in
any type of a reaction.

340
00:15:44,610 --> 00:15:47,600
All right, so one thing that I
want to point out, which I

341
00:15:47,600 --> 00:15:49,990
said many, many times on Friday,
and this is perhaps

342
00:15:49,990 --> 00:15:52,990
the last time I'll say it, but
one last time is we can think

343
00:15:52,990 --> 00:15:56,530
about why we only see a line for
the 2 p orbital, versus we

344
00:15:56,530 --> 00:16:00,750
don't see separate lines for a
2 p x, a 2 p y, and a 2 p z.

345
00:16:00,750 --> 00:16:03,450
Remember, we need those three
quantum numbers to completely

346
00:16:03,450 --> 00:16:04,620
describe the orbital.

347
00:16:04,620 --> 00:16:06,870
Why do we just see one
for all the p's?

348
00:16:06,870 --> 00:16:09,650
And the reason is that the
energy of the orbitals, depend

349
00:16:09,650 --> 00:16:12,520
on two quantum numbers, and
that's quantum number n, and

350
00:16:12,520 --> 00:16:13,740
quantum number l.

351
00:16:13,740 --> 00:16:16,620
M does not actually have an
effect, in this case, on the

352
00:16:16,620 --> 00:16:18,350
energy of the orbital.

353
00:16:18,350 --> 00:16:20,100
So that's why we're not
seeing separate

354
00:16:20,100 --> 00:16:24,370
lines in this spectrum.

355
00:16:24,370 --> 00:16:24,600
All right.

356
00:16:24,600 --> 00:16:28,300
So let's go ahead and try an
example here in thinking about

357
00:16:28,300 --> 00:16:29,770
photoelectron spectroscopy.

358
00:16:29,770 --> 00:16:33,120
So, let's say we're looking at
an element and we have an

359
00:16:33,120 --> 00:16:35,950
emission spectra, and we know
that it has five distinct

360
00:16:35,950 --> 00:16:38,860
different kinetic energies
in that spectrum.

361
00:16:38,860 --> 00:16:42,600
We might be asked, for example,
to determine what all

362
00:16:42,600 --> 00:16:44,740
of the different elements could
be that would produce a

363
00:16:44,740 --> 00:16:47,410
spectrum that gave us
5 different lines.

364
00:16:47,410 --> 00:16:49,620
So the first thing that we want
to do, if we're thinking

365
00:16:49,620 --> 00:16:56,210
about something like this, is
just to determine exactly what

366
00:16:56,210 --> 00:16:58,990
orbitals are causing the five
different lines that we're

367
00:16:58,990 --> 00:17:00,690
seeing in the spectrum.

368
00:17:00,690 --> 00:17:03,060
So, if we're talking about five
different orbitals and

369
00:17:03,060 --> 00:17:05,420
we're talking about a ground
state atom, we know that we

370
00:17:05,420 --> 00:17:06,880
just need to start
at the bottom and

371
00:17:06,880 --> 00:17:08,220
work our way out up.

372
00:17:08,220 --> 00:17:10,840
So, our first orbital that an
electron must be coming from

373
00:17:10,840 --> 00:17:11,900
is the 1 s.

374
00:17:11,900 --> 00:17:13,583
What comes after that?

375
00:17:13,583 --> 00:17:15,190
2 s.

376
00:17:15,190 --> 00:17:16,070
All right, then what?

377
00:17:16,070 --> 00:17:20,740
2 p.

378
00:17:20,740 --> 00:17:22,540
After that?

379
00:17:22,540 --> 00:17:23,990
3 s.

380
00:17:23,990 --> 00:17:25,530
Next?

381
00:17:25,530 --> 00:17:31,890
3 p, and that's 1, 2, 3, 4 --
that gives us five different

382
00:17:31,890 --> 00:17:34,200
options, five different
orbitals, five different

383
00:17:34,200 --> 00:17:35,820
energies right there.

384
00:17:35,820 --> 00:17:38,950
So, then all we need to do to
determine which elements that

385
00:17:38,950 --> 00:17:41,960
corresponds to is take a look
at our periodic table.

386
00:17:41,960 --> 00:17:45,490
So we want to look at any
element that has a 3 p orbital

387
00:17:45,490 --> 00:17:49,470
filled, but that does not then
go on and have a 4 s, because

388
00:17:49,470 --> 00:17:51,880
if it had the 4 s filled then
we would actually see six

389
00:17:51,880 --> 00:17:53,360
lines in the spectrum.

390
00:17:53,360 --> 00:17:58,230
So that is relevant for all
of these atoms here, so we

391
00:17:58,230 --> 00:18:00,840
actually have several different
possibilities.

392
00:18:00,840 --> 00:18:06,250
It could be aluminum, silicone,
phosphorous, sulfur,

393
00:18:06,250 --> 00:18:09,530
chlorine or argon.

394
00:18:09,530 --> 00:18:12,000
Any one of these different
elements could actually

395
00:18:12,000 --> 00:18:16,410
produce a photoelectron
spectroscopy spectrum that has

396
00:18:16,410 --> 00:18:18,090
five distinct lines.

397
00:18:18,090 --> 00:18:20,950
If I went on and told you what
the different incident light

398
00:18:20,950 --> 00:18:24,830
was, and what the electrons were
ejected with, and then

399
00:18:24,830 --> 00:18:26,910
you could look up the ionization
energy for the

400
00:18:26,910 --> 00:18:29,780
particular different elements,
you should be able to actually

401
00:18:29,780 --> 00:18:32,450
determine exactly which element
it is, but just with

402
00:18:32,450 --> 00:18:34,830
the information given, we can
only narrow it down to these

403
00:18:34,830 --> 00:18:36,880
choices here.

404
00:18:36,880 --> 00:18:41,350
So let's actually let you try
another example of solving a

405
00:18:41,350 --> 00:18:43,540
problem that has to do with
one of the spectrums. So,

406
00:18:43,540 --> 00:18:46,700
let's turn to another clicker
question here.

407
00:18:46,700 --> 00:18:49,610
Remember, your answer holds
great weight in terms of the

408
00:18:49,610 --> 00:18:52,950
state of the TA bragging
for next week.

409
00:18:52,950 --> 00:18:55,640
So, how many distinct, so again,
we're talking about

410
00:18:55,640 --> 00:18:58,380
distinct kinetic energies, would
be displayed if you're

411
00:18:58,380 --> 00:19:01,990
talking about a spectrum for the
element hafnium, and I'll

412
00:19:01,990 --> 00:19:04,620
tell you here that it has a z
of 72, so you don't have to

413
00:19:04,620 --> 00:19:07,570
spend two minutes searching
your periodic table.

414
00:19:07,570 --> 00:19:10,980
The period of table's on the
back page of your notes if you

415
00:19:10,980 --> 00:19:46,270
don't see that there.

416
00:19:46,270 --> 00:19:46,490
All right.

417
00:19:46,490 --> 00:19:48,640
It looks like a lot of you are
done, so let's take 10 more

418
00:19:48,640 --> 00:19:53,250
seconds here.

419
00:19:53,250 --> 00:19:56,220
Part of the challenge is speed,
too, how quickly you

420
00:19:56,220 --> 00:19:59,680
can get these answers in terms
of getting them in on time.

421
00:19:59,680 --> 00:20:02,120
So let's see what we say.

422
00:20:02,120 --> 00:20:02,730
All right.

423
00:20:02,730 --> 00:20:06,560
So I think I can safely say that
most people had the right

424
00:20:06,560 --> 00:20:10,390
idea and were counting quickly,
though I have a

425
00:20:10,390 --> 00:20:13,330
feeling that some people who
wrote 13 might have forgotten

426
00:20:13,330 --> 00:20:16,960
about those 4 f, the
4 f electrons.

427
00:20:16,960 --> 00:20:19,340
So, remember when you're looking
at your periodic

428
00:20:19,340 --> 00:20:22,180
table, don't forget about the
lanthinides, sometimes they

429
00:20:22,180 --> 00:20:23,840
come into play.

430
00:20:23,840 --> 00:20:27,270
So it's actually 14, and the
way that we got that answer

431
00:20:27,270 --> 00:20:29,990
was we just wrote out or just
looked at your period table,

432
00:20:29,990 --> 00:20:32,590
figured out all of the different
orbitals that you

433
00:20:32,590 --> 00:20:36,720
could have in terms of the
principle quantum number, and

434
00:20:36,720 --> 00:20:39,110
then the l quantum number, and
then write them all down -- it

435
00:20:39,110 --> 00:20:42,970
turns out to be 14, so that's
what the answer is.

436
00:20:42,970 --> 00:20:45,040
So, it looks like this is good,
because we'll have some

437
00:20:45,040 --> 00:20:48,520
separation in terms of not
everyone's going to get 100%

438
00:20:48,520 --> 00:20:52,030
in terms of recitations here,
which is what we're going for.

439
00:20:52,030 --> 00:20:52,870
All right.

440
00:20:52,870 --> 00:20:55,750
So let's turn our attention to a
new topic, which is thinking

441
00:20:55,750 --> 00:20:58,300
a little bit about the periodic
table, and also

442
00:20:58,300 --> 00:21:00,000
talking about periodic trends.

443
00:21:00,000 --> 00:21:03,140
And there's a lot we can explain
by talking about what

444
00:21:03,140 --> 00:21:06,220
we see in the periodic table
in terms of what different

445
00:21:06,220 --> 00:21:08,050
trends are in grouping
different elements in

446
00:21:08,050 --> 00:21:10,860
different spots within
the periodic table.

447
00:21:10,860 --> 00:21:13,840
So, here we have a picture of
Dmitri Mendeleev, who is one

448
00:21:13,840 --> 00:21:17,220
of the scientists responsible
for first compiling the

449
00:21:17,220 --> 00:21:18,560
periodic table.

450
00:21:18,560 --> 00:21:21,830
You'll notice I have what's a
very flattering picture of him

451
00:21:21,830 --> 00:21:24,860
up here, and if you haven't done
the reading yet you might

452
00:21:24,860 --> 00:21:27,130
not think this is particularly
flattering, but if you look at

453
00:21:27,130 --> 00:21:31,130
the picture of him in the book,
you'll notice I chose a

454
00:21:31,130 --> 00:21:34,820
very flattering picture of
Dmitri up here, and here he's

455
00:21:34,820 --> 00:21:37,450
pondering putting these
elements together in a

456
00:21:37,450 --> 00:21:38,690
periodic table.

457
00:21:38,690 --> 00:21:42,790
And he actually did this in the
late 1800's, back before

458
00:21:42,790 --> 00:21:45,690
even all of the elements that we
know today were discovered,

459
00:21:45,690 --> 00:21:49,740
really only about 60% or so, 70%
were discovered then that

460
00:21:49,740 --> 00:21:51,040
we now know today.

461
00:21:51,040 --> 00:21:55,230
But still, he was able to put
together a periodic table.

462
00:21:55,230 --> 00:21:57,870
And what he did what he actually
grouped things in

463
00:21:57,870 --> 00:22:00,080
terms of their chemical
properties.

464
00:22:00,080 --> 00:22:02,550
So the way that we like to
think of things now is in

465
00:22:02,550 --> 00:22:04,660
terms of electron
configurations, right, but at

466
00:22:04,660 --> 00:22:06,760
the time that wasn't
really understood.

467
00:22:06,760 --> 00:22:09,240
So, instead, it was amazing he
was able to group things in

468
00:22:09,240 --> 00:22:11,390
terms of the properties
that he saw.

469
00:22:11,390 --> 00:22:15,050
So, for example, if he was
talking about the group one

470
00:22:15,050 --> 00:22:18,040
metals, lithium, sodium,
potassium -- he noticed these

471
00:22:18,040 --> 00:22:20,140
were all very soft reactive
metals, those

472
00:22:20,140 --> 00:22:21,540
were grouped together.

473
00:22:21,540 --> 00:22:26,000
Versus looking at, for example,
helium or neon or

474
00:22:26,000 --> 00:22:28,910
argon, these are all inert
gases, inert meaning

475
00:22:28,910 --> 00:22:32,280
essentially do not react, those
were grouped together in

476
00:22:32,280 --> 00:22:33,850
the periodic table.

477
00:22:33,850 --> 00:22:37,070
So basically, at the time he
was just going on size and

478
00:22:37,070 --> 00:22:41,050
then traits, but what we
actually know today is that we

479
00:22:41,050 --> 00:22:45,130
can also order things in the
periodic table by electron

480
00:22:45,130 --> 00:22:45,750
configuration.

481
00:22:45,750 --> 00:22:48,130
In fact, that is the most
logical way for us

482
00:22:48,130 --> 00:22:49,300
to look at it now.

483
00:22:49,300 --> 00:22:51,700
So, for example, if we're
actually thinking about

484
00:22:51,700 --> 00:22:54,150
electron configuration and we
look at lithium, sodium and

485
00:22:54,150 --> 00:22:58,060
potassium, these all have
one valence electron.

486
00:22:58,060 --> 00:23:01,420
So basically, that means one
electron in an s orbital in

487
00:23:01,420 --> 00:23:03,060
their outer-most most shell.

488
00:23:03,060 --> 00:23:05,740
So that explains why they're so
reactive, they're all very

489
00:23:05,740 --> 00:23:08,510
willing to give up that 1 s
orbital and then drop to a

490
00:23:08,510 --> 00:23:10,280
lower energy level.

491
00:23:10,280 --> 00:23:14,690
In contrast, helium, neon, and
argon all have filled shells.

492
00:23:14,690 --> 00:23:17,140
That also explains why
they're very stable.

493
00:23:17,140 --> 00:23:19,480
They're not going to want to
add on another electron,

494
00:23:19,480 --> 00:23:21,950
because then it'll have to jump
a very large energy level

495
00:23:21,950 --> 00:23:24,820
and start filling in another
shell -- go from n equals 2,

496
00:23:24,820 --> 00:23:29,370
to n equals 3, and n equals
4, and so on.

497
00:23:29,370 --> 00:23:31,760
So it turns out that we can
really know a lot just by

498
00:23:31,760 --> 00:23:34,430
looking at the periodic table.

499
00:23:34,430 --> 00:23:37,070
You will never in this class
have to memorize anything

500
00:23:37,070 --> 00:23:38,070
about the periodic table.

501
00:23:38,070 --> 00:23:40,150
Depending on what kind of
chemistry you go in to, you

502
00:23:40,150 --> 00:23:43,120
might accidentally memorize
parts of the table, which is

503
00:23:43,120 --> 00:23:45,710
fine, but what you really want
to know how to do is know how

504
00:23:45,710 --> 00:23:48,110
to use the periodic table.

505
00:23:48,110 --> 00:23:51,160
But you actually need to keep
a few caveats in mind as you

506
00:23:51,160 --> 00:23:54,330
do this, which is the fact that
trends predict a lot of

507
00:23:54,330 --> 00:23:57,490
chemical properties, but they
can't predict everything in

508
00:23:57,490 --> 00:23:59,460
terms of biological
properties.

509
00:23:59,460 --> 00:24:02,370
And after the periodic table
was developed in the late

510
00:24:02,370 --> 00:24:04,760
1800's, people didn't understand
this quite as well,

511
00:24:04,760 --> 00:24:06,170
they took things a little
more literally.

512
00:24:06,170 --> 00:24:09,340
They thought, for example, if
you could do something with

513
00:24:09,340 --> 00:24:12,250
one element, if you looked at
an element very close to it,

514
00:24:12,250 --> 00:24:14,400
it would be similar enough that
you could maybe replace

515
00:24:14,400 --> 00:24:15,400
it with that.

516
00:24:15,400 --> 00:24:18,120
Today we know, for example, if
you can put one certain kind

517
00:24:18,120 --> 00:24:21,030
of element in your mouth
or eat that, it doesn't

518
00:24:21,030 --> 00:24:23,160
necessarily mean you want to put
the element next to it and

519
00:24:23,160 --> 00:24:25,740
your mouth as well, that
might not be safe.

520
00:24:25,740 --> 00:24:29,390
But this is things we've learned
as the years have gone

521
00:24:29,390 --> 00:24:30,370
past.

522
00:24:30,370 --> 00:24:33,840
So, let's just take a quick
example to show how not

523
00:24:33,840 --> 00:24:36,050
completely you can use these
periodic trends, that there

524
00:24:36,050 --> 00:24:36,970
are limits.

525
00:24:36,970 --> 00:24:39,540
So if we consider lithium,
potassium, and sodium, they're

526
00:24:39,540 --> 00:24:42,690
all together in the same group
on the periodic table, knowing

527
00:24:42,690 --> 00:24:45,640
what we do about biology we
can immediately think of

528
00:24:45,640 --> 00:24:48,070
sodium and potassium, or even
just knowing what you know

529
00:24:48,070 --> 00:24:52,160
about table salt, for example,
that these are two elements

530
00:24:52,160 --> 00:24:55,250
that we find, and particularly
in the ion form in very high

531
00:24:55,250 --> 00:24:57,030
concentrations in our body.

532
00:24:57,030 --> 00:24:59,910
For example, sodium in our blood
plasma is almost to the

533
00:24:59,910 --> 00:25:03,130
point sometimes of 100 millimol
or that's very, very

534
00:25:03,130 --> 00:25:04,630
concentrated.

535
00:25:04,630 --> 00:25:07,710
Similarly, we find it in table
salt, we're taking it in all

536
00:25:07,710 --> 00:25:10,160
the time, the same with
potassium, think of bananas,

537
00:25:10,160 --> 00:25:12,200
were always eating potassium.

538
00:25:12,200 --> 00:25:14,270
Not so with lithium.

539
00:25:14,270 --> 00:25:16,200
I don't think too many
people and here are

540
00:25:16,200 --> 00:25:17,560
probably taking lithium.

541
00:25:17,560 --> 00:25:21,490
It turns out there's actually
no natural function known in

542
00:25:21,490 --> 00:25:22,500
the body for lithium.

543
00:25:22,500 --> 00:25:25,310
So there's nothing naturally
going on unless we were to

544
00:25:25,310 --> 00:25:27,992
introduce it ourselves in our
body that we know of, at

545
00:25:27,992 --> 00:25:30,630
least, that involves lithium.

546
00:25:30,630 --> 00:25:33,410
But this did not stop people,
for example, in the late

547
00:25:33,410 --> 00:25:39,910
1800's, early 1900's, and, in
fact, in 1927 a new soft drink

548
00:25:39,910 --> 00:25:42,610
was put on to the market and
they wanted to make a

549
00:25:42,610 --> 00:25:45,230
lemon-lime soft drink, these
were very popular in the early

550
00:25:45,230 --> 00:25:48,880
1900's, and to get sort of
that lemony flavor, they

551
00:25:48,880 --> 00:25:51,880
decided to use citric acid, so
that's a good idea, that gives

552
00:25:51,880 --> 00:25:53,620
that soury taste.

553
00:25:53,620 --> 00:25:56,980
And they wanted to use a soluble
salt of citric acid,

554
00:25:56,980 --> 00:25:58,740
so they could have
used sodium, they

555
00:25:58,740 --> 00:25:59,310
could have used potassium.

556
00:25:59,310 --> 00:26:02,760
But, you know why not do
something a little special,

557
00:26:02,760 --> 00:26:04,240
little different,
and they decided

558
00:26:04,240 --> 00:26:06,370
instead to use lithium.

559
00:26:06,370 --> 00:26:09,160
So, here we have this soda with
lithium citrate, some of

560
00:26:09,160 --> 00:26:14,580
you might be familiar with this,
soda is called 7-Up.

561
00:26:14,580 --> 00:26:20,020
So, 7-Up no longer has lithium
in it, but from 1927 to 1950

562
00:26:20,020 --> 00:26:24,220
it did, and, in fact, not only
did they not try to hide the

563
00:26:24,220 --> 00:26:26,970
fact that there's lithium in the
soda, this they used as a

564
00:26:26,970 --> 00:26:30,400
really special marketing
technique, they really pointed

565
00:26:30,400 --> 00:26:32,670
out this is something that
stands out about our soda,

566
00:26:32,670 --> 00:26:34,420
this is something special.

567
00:26:34,420 --> 00:26:36,510
There's a lot of good things
about lithium.

568
00:26:36,510 --> 00:26:38,910
I don't know if you can see,
probably not, what's written

569
00:26:38,910 --> 00:26:44,170
on here, so let me point out
to you a few things.

570
00:26:44,170 --> 00:26:48,000
Lithium, slenderizing, that's
great to see in a soda.

571
00:26:48,000 --> 00:26:50,140
Other nice things about lithium
in your soda, it

572
00:26:50,140 --> 00:26:53,170
dispells hangovers, takes
the ouch out of grouch.

573
00:26:53,170 --> 00:26:54,520
That's very nice.

574
00:26:54,520 --> 00:26:58,540
So basically, you get a lot of
benefit supposedly from this

575
00:26:58,540 --> 00:27:02,960
7-Up soda from the
1920's or so.

576
00:27:02,960 --> 00:27:06,480
And this went on and was
unregulated for some time, but

577
00:27:06,480 --> 00:27:09,910
at some point the Food and Drug
Administration did take a

578
00:27:09,910 --> 00:27:12,930
step in, so here's a case where
they did do something

579
00:27:12,930 --> 00:27:19,240
important -- that's not what I
mean at all -- where they did

580
00:27:19,240 --> 00:27:21,380
take the step, they do many
things that are important,

581
00:27:21,380 --> 00:27:23,400
often not quickly enough.

582
00:27:23,400 --> 00:27:26,810
Here's a -- actually here it
did take 25 years, but they

583
00:27:26,810 --> 00:27:28,260
did, they did eventually
step on before we

584
00:27:28,260 --> 00:27:30,220
started drinking 7-Up.

585
00:27:30,220 --> 00:27:33,060
And what they said was, look,
you can't put this in, we're

586
00:27:33,060 --> 00:27:35,470
starting to notice it does
some strange things.

587
00:27:35,470 --> 00:27:38,920
Because it was in the 1950's or
so, maybe the late 1940's,

588
00:27:38,920 --> 00:27:41,520
that people started to discover
lithium, even though

589
00:27:41,520 --> 00:27:43,250
it had no natural function,
it did do

590
00:27:43,250 --> 00:27:45,080
something in our bodies.

591
00:27:45,080 --> 00:27:49,030
Does anyone know what was
lithium's used for?

592
00:27:49,030 --> 00:27:52,040
Yeah, it's an anti-psychotic
drug, so, for example, some

593
00:27:52,040 --> 00:27:55,180
people with bipolar disorder
even today still take it, it

594
00:27:55,180 --> 00:27:57,260
works really well for some
people, for other people it

595
00:27:57,260 --> 00:27:58,890
doesn't work so well.

596
00:27:58,890 --> 00:28:01,360
But anyway, this isn't really
something you want to have in

597
00:28:01,360 --> 00:28:04,670
your soda, so they did take
it out eventually.

598
00:28:04,670 --> 00:28:07,580
Another side effect if you
take too much lithium is

599
00:28:07,580 --> 00:28:12,510
death, so that's no good to have
in sodas either, and it

600
00:28:12,510 --> 00:28:15,260
might not have been as big a
deal back in the 1920's, but

601
00:28:15,260 --> 00:28:17,930
you can imagine with supersizing
today, this might

602
00:28:17,930 --> 00:28:19,470
be a bigger problem.

603
00:28:19,470 --> 00:28:23,580
So anyway, when we talk about
periodic trends, it doesn't

604
00:28:23,580 --> 00:28:24,630
always match up.

605
00:28:24,630 --> 00:28:28,100
This was eventually taken out,
and actually just for your

606
00:28:28,100 --> 00:28:31,450
interest, there was no overlap
between the time when cocaine

607
00:28:31,450 --> 00:28:33,910
was in Coca Cola and lithium
was in 7-Up, so there was a

608
00:28:33,910 --> 00:28:36,300
few years difference between
those two times, but it's

609
00:28:36,300 --> 00:28:40,590
amazing to think about what does
go into processed foods.

610
00:28:40,590 --> 00:28:43,200
And the other thing to point
out, which I don't know if

611
00:28:43,200 --> 00:28:46,170
this is true or not, but does
anyone know -- well that's

612
00:28:46,170 --> 00:28:48,300
part's true, does anyone know
what the atomic mass of

613
00:28:48,300 --> 00:28:49,780
lithium is?

614
00:28:49,780 --> 00:28:50,790
Yes, it's 7.

615
00:28:50,790 --> 00:28:53,060
So, I don't know if this is true
or not, but I wonder if

616
00:28:53,060 --> 00:28:55,030
that's where the actual
name 7-Up came from.

617
00:28:55,030 --> 00:28:57,400
So, even though we don't have
the lithium anymore, we still

618
00:28:57,400 --> 00:29:00,960
keep that atomic number
7 around.

619
00:29:00,960 --> 00:29:01,190
All right.

620
00:29:01,190 --> 00:29:05,210
So that is an anti-example
of using periodic trends.

621
00:29:05,210 --> 00:29:09,000
So let's go to some actual real
examples, which might

622
00:29:09,000 --> 00:29:10,750
come more in handy
for this class.

623
00:29:10,750 --> 00:29:13,310
So it's going to keep in mind
the limitations, so let's

624
00:29:13,310 --> 00:29:17,190
start off with talking about
ionization energy.

625
00:29:17,190 --> 00:29:19,410
Now this is a good place to
start, because we are very

626
00:29:19,410 --> 00:29:21,560
familiar with ionization energy,
we've been talking

627
00:29:21,560 --> 00:29:24,250
about it in a lot of different
forms for quite a while --

628
00:29:24,250 --> 00:29:28,220
it's that minimum energy
required to remove an electron

629
00:29:28,220 --> 00:29:29,310
from an atom.

630
00:29:29,310 --> 00:29:32,720
And specifically, when we talk
about ionization energy, it's

631
00:29:32,720 --> 00:29:34,810
assumed that what we mean
is actually the

632
00:29:34,810 --> 00:29:36,780
first ionization energy.

633
00:29:36,780 --> 00:29:39,310
So, you can imagine, we could
talk about any of the

634
00:29:39,310 --> 00:29:41,860
different electrons, or we could
talk about taking out an

635
00:29:41,860 --> 00:29:43,400
electron and taking out
second electron.

636
00:29:43,400 --> 00:29:47,690
Whenever you hear the term
ionization energy, make sure

637
00:29:47,690 --> 00:29:50,210
you keep in mind that unless
we say otherwise, we're

638
00:29:50,210 --> 00:29:53,040
talking about that first
ionization energy.

639
00:29:53,040 --> 00:29:55,490
And we know what that's equal
to, this is something we've

640
00:29:55,490 --> 00:29:58,880
been over and over, ionization
energy is simply equal to the

641
00:29:58,880 --> 00:30:00,840
negative of the binding
energy.

642
00:30:00,840 --> 00:30:04,390
So negative e, which is sub n l,
because it's a function of

643
00:30:04,390 --> 00:30:08,950
n and l in terms of
quantum numbers.

644
00:30:08,950 --> 00:30:12,730
So, let's think about kind of
differentiating, however,

645
00:30:12,730 --> 00:30:15,830
between first ionization energy
or just ionization

646
00:30:15,830 --> 00:30:18,960
energy, and other types such as
second or third ionization

647
00:30:18,960 --> 00:30:22,100
energy, and let's take boron
as an example here.

648
00:30:22,100 --> 00:30:24,510
So, if we want to think about
what the first ionization

649
00:30:24,510 --> 00:30:27,360
energy is of boron, what you
want to do is write out the

650
00:30:27,360 --> 00:30:29,490
electron configuration, because
then you can think

651
00:30:29,490 --> 00:30:32,070
about where it is that the
electron's coming out of.

652
00:30:32,070 --> 00:30:34,900
The electron's going to come out
of that highest occupied

653
00:30:34,900 --> 00:30:37,340
atomic orbital, that one that's
the highest in energy,

654
00:30:37,340 --> 00:30:39,730
because that's going to be the
at least amount of energy it

655
00:30:39,730 --> 00:30:41,120
needs to eject something.

656
00:30:41,120 --> 00:30:45,750
So what we'll end up with is
boron plus, 1 s 2, 2 s 2, and

657
00:30:45,750 --> 00:30:49,450
what we say is the delta energy
or the change in energy

658
00:30:49,450 --> 00:30:52,570
as the same thing as saying
the energy of the products

659
00:30:52,570 --> 00:30:55,210
minus the energy of our reactant
here, and we just

660
00:30:55,210 --> 00:30:57,310
call that the ionization energy
-- that's how much

661
00:30:57,310 --> 00:31:00,660
energy we have to put into the
system to eject an electron.

662
00:31:00,660 --> 00:31:03,560
And again, this is just the
negative, the binding energy,

663
00:31:03,560 --> 00:31:07,920
when we're talking about
the 2 p orbital.

664
00:31:07,920 --> 00:31:11,200
So, this is first ionization
energy, let's think about

665
00:31:11,200 --> 00:31:13,310
second ionization energy.

666
00:31:13,310 --> 00:31:16,040
So, second ionization energy
simply means you've already

667
00:31:16,040 --> 00:31:19,110
taken one electron out, now how
much energy does it take

668
00:31:19,110 --> 00:31:21,180
for you to take a second
electron out.

669
00:31:21,180 --> 00:31:24,210
So in the case of boron here,
what we're starting with is

670
00:31:24,210 --> 00:31:29,080
the ion, boron 1 s 2, 2 s 2,
and now we're going to pull

671
00:31:29,080 --> 00:31:30,850
one more electron out.

672
00:31:30,850 --> 00:31:34,570
The highest occupied orbital
is now the 2 s orbital, so

673
00:31:34,570 --> 00:31:39,470
we're going to end up with boron
2 plus 1 s 2, 2 s 1,

674
00:31:39,470 --> 00:31:42,410
plus the electron coming
out of there.

675
00:31:42,410 --> 00:31:45,490
And what we say when we talk
about the delta energy is that

676
00:31:45,490 --> 00:31:49,840
this is going to be equal to i
e 2, or the second ionization

677
00:31:49,840 --> 00:31:53,510
energy, or we could say the
negative of the binding energy

678
00:31:53,510 --> 00:31:58,400
of a 2 s electron in b plus. so
it's important to note that

679
00:31:58,400 --> 00:32:01,190
it's not in b, now we're talking
about b plus, because

680
00:32:01,190 --> 00:32:04,130
we've already taken an
electron out here.

681
00:32:04,130 --> 00:32:06,340
So, similarly if we start
talking about our third

682
00:32:06,340 --> 00:32:09,930
ionization energy, this is going
to be going from b plus

683
00:32:09,930 --> 00:32:12,690
2, to 1 s 2, 2 s 1.

684
00:32:12,690 --> 00:32:15,320
Now we're going to pull that
second electron out of the 2

685
00:32:15,320 --> 00:32:19,160
s, so we end up with boron
plus 3, and then the

686
00:32:19,160 --> 00:32:24,670
configuration is just 1 s 2,
plus our extra electron here.

687
00:32:24,670 --> 00:32:28,040
So, what we call this is the
third ionization energy, or

688
00:32:28,040 --> 00:32:30,770
the negative of the binding
energy, again of the 2 s

689
00:32:30,770 --> 00:32:35,850
orbital, but now it's in boron
plus 2 to we're starting with.

690
00:32:35,850 --> 00:32:38,830
So, this raises kind of an
interesting question in terms

691
00:32:38,830 --> 00:32:41,800
of what the difference is
between these two cases, and

692
00:32:41,800 --> 00:32:45,150
we're talking about
numbers of energy.

693
00:32:45,150 --> 00:32:48,930
So let's address this by
considering another example,

694
00:32:48,930 --> 00:32:51,830
which should clarify what the
difference is between these

695
00:32:51,830 --> 00:32:52,820
ionization energies.

696
00:32:52,820 --> 00:32:55,730
So let's think about the energy
required now to remove

697
00:32:55,730 --> 00:32:58,920
a 2 s electron, let's say we're
removing it from boron

698
00:32:58,920 --> 00:33:01,340
plus 1 versus neutral boron.

699
00:33:01,340 --> 00:33:06,050
So, in the case of boron plus
1, what we are starting with

700
00:33:06,050 --> 00:33:10,700
is the ion, so we're starting
with a 2 s electron, and then

701
00:33:10,700 --> 00:33:13,160
we're going to 2 s 1 here.

702
00:33:13,160 --> 00:33:16,800
And what we call the binding
energy is negative 2 s in b

703
00:33:16,800 --> 00:33:19,670
plus -- this is what we
saw on the last slide.

704
00:33:19,670 --> 00:33:22,695
And the second case here looks
a lot more like what we saw

705
00:33:22,695 --> 00:33:25,780
when we were talking about
photoelectron spectroscopy,

706
00:33:25,780 --> 00:33:28,610
because here we want to remove
a 2 s electron, but it's

707
00:33:28,610 --> 00:33:32,070
actually not the highest
occupied orbital, so that's

708
00:33:32,070 --> 00:33:34,140
not the one that would naturally
come out first, but

709
00:33:34,140 --> 00:33:36,160
let's say we're hitting it
with high energy light

710
00:33:36,160 --> 00:33:38,800
sufficient to knock out all the
different electrons, and

711
00:33:38,800 --> 00:33:41,810
one that we end up knocking
out is this 2 s here.

712
00:33:41,810 --> 00:33:45,160
So if we think about what that
delta energy is, we call that

713
00:33:45,160 --> 00:33:48,490
the ionization of the 2 s,
that's different from saying

714
00:33:48,490 --> 00:33:50,290
second ionization energy.

715
00:33:50,290 --> 00:33:52,580
And that's going to be equal
to the negative the binding

716
00:33:52,580 --> 00:33:57,020
energy of 2 s in b,
in neutral boron.

717
00:33:57,020 --> 00:34:01,100
So, my question to you is are
these two energies equal?

718
00:34:01,100 --> 00:34:02,290
No.

719
00:34:02,290 --> 00:34:03,730
All right, good answer.

720
00:34:03,730 --> 00:34:06,660
So, we can think about why is
it that these are not equal.

721
00:34:06,660 --> 00:34:08,580
In both cases we're
taking an electron

722
00:34:08,580 --> 00:34:11,130
out of the 2 s orbital.

723
00:34:11,130 --> 00:34:14,210
And it turns out that if we're
talking about a 2 s orbital in

724
00:34:14,210 --> 00:34:18,310
an ion, that means it doesn't
have as many electrons in it,

725
00:34:18,310 --> 00:34:20,410
so what we're going to see
is less sheilding.

726
00:34:20,410 --> 00:34:23,550
There are fewer electrons around
to shield some of that

727
00:34:23,550 --> 00:34:24,700
nuclear charge.

728
00:34:24,700 --> 00:34:27,660
So what we're going to see is
less sheilding, which means

729
00:34:27,660 --> 00:34:31,680
that it will actually feel
a higher z effective.

730
00:34:31,680 --> 00:34:35,410
So even though they're both 2 s
electrons, in one case it's

731
00:34:35,410 --> 00:34:38,300
going to think its feeling more
pull from the nucleus,

732
00:34:38,300 --> 00:34:41,430
and it, in fact, will be, than
in the other case, and if its

733
00:34:41,430 --> 00:34:44,090
feeling a higher z effective,
then it's actually going to

734
00:34:44,090 --> 00:34:46,820
require more energy to remove
that electron, right, it's

735
00:34:46,820 --> 00:34:49,480
being pulled in closer and more
tightly to the nucleus,

736
00:34:49,480 --> 00:34:52,310
you have to put in more energy
to rip it away from that very

737
00:34:52,310 --> 00:34:54,730
close interaction.

738
00:34:54,730 --> 00:34:57,380
So, that's the difference in
thinking about different types

739
00:34:57,380 --> 00:35:00,550
of ionization energy, so it can
get a little bit confusing

740
00:35:00,550 --> 00:35:02,620
with terminology if you're
just looking at something

741
00:35:02,620 --> 00:35:04,670
quickly, so make sure you look
really carefully about what

742
00:35:04,670 --> 00:35:05,460
we're discussing here.

743
00:35:05,460 --> 00:35:08,560
If you see a problem that asks
you, for example, the third

744
00:35:08,560 --> 00:35:11,710
ionization energy versus taking
a second electron out

745
00:35:11,710 --> 00:35:14,740
of the 2 s in a photoelectron
spectroscopy experiment, those

746
00:35:14,740 --> 00:35:17,480
are two very different things.

747
00:35:17,480 --> 00:35:20,200
So, let's make sure everyone
kind of has this down, let's

748
00:35:20,200 --> 00:35:25,030
do another clicker
question here.

749
00:35:25,030 --> 00:35:27,540
And in this case we're going to
look at silicone, and we'll

750
00:35:27,540 --> 00:35:31,120
say if you can point out to me
which requires the least

751
00:35:31,120 --> 00:35:32,310
amount of energy.

752
00:35:32,310 --> 00:35:35,380
So, which has the smallest
energy that you have to put in

753
00:35:35,380 --> 00:35:37,290
in order to eject
this electron?

754
00:35:37,290 --> 00:35:40,970
Will it be if you take a 3
s electron from neutral

755
00:35:40,970 --> 00:35:44,390
silicone, if you take a 3 p
electron from the neutral

756
00:35:44,390 --> 00:35:48,590
atom, or if you take
a 3 p from the ion?

757
00:35:48,590 --> 00:35:51,070
So this you should be able to
know pretty quickly, so let's

758
00:35:51,070 --> 00:36:05,280
just take 10 seconds here.

759
00:36:05,280 --> 00:36:05,950
All right, great.

760
00:36:05,950 --> 00:36:10,580
So most of you see that, in
fact, the energy that's going

761
00:36:10,580 --> 00:36:14,080
to be the least that we need to
put in is in case 2 here.

762
00:36:14,080 --> 00:36:16,950
Let's compare case 2 and 3,
since this where some people

763
00:36:16,950 --> 00:36:18,750
seem to have gotten confused.

764
00:36:18,750 --> 00:36:22,390
In case 2, we're taking it out
of -- oh, it's kind of hard to

765
00:36:22,390 --> 00:36:26,010
compare case 2 and 3 when
we can't see it anymore.

766
00:36:26,010 --> 00:36:32,140
In case 2, we're taking the 3
p out of the neutral atom,

767
00:36:32,140 --> 00:36:35,180
whereas in case 3, we're taking
it out of the ion.

768
00:36:35,180 --> 00:36:38,260
Remember in the ion, we're going
to have less electrons

769
00:36:38,260 --> 00:36:42,400
around to counteract the
pull from the nucleus.

770
00:36:42,400 --> 00:36:46,100
So we're going to feel a higher
z effective in the case

771
00:36:46,100 --> 00:36:48,860
of the ion compared to
the neutral atom.

772
00:36:48,860 --> 00:36:50,800
If we have a higher z effective,
it's pulled in

773
00:36:50,800 --> 00:36:53,670
tighter, we have to put in more
energy in order to eject

774
00:36:53,670 --> 00:36:56,220
an electron, so it turns out
that that's why case 2 is

775
00:36:56,220 --> 00:36:59,000
actually the lowest energy
that we need to put in.

776
00:36:59,000 --> 00:37:03,600
The z effective is lower, so we
have to put less energy in

777
00:37:03,600 --> 00:37:07,030
to get an ion out.

778
00:37:07,030 --> 00:37:10,990
So, let's take a look at this in
terms of periodic trends --

779
00:37:10,990 --> 00:37:14,150
that's our topic here, we're
talking about periodic trends.

780
00:37:14,150 --> 00:37:17,100
So as we go across the row,
and this is my beautiful

781
00:37:17,100 --> 00:37:19,050
picture of a periodic
table here.

782
00:37:19,050 --> 00:37:21,850
As we go across the row what
happens is that the ionization

783
00:37:21,850 --> 00:37:25,240
energy actually increases, and
we can think about logically

784
00:37:25,240 --> 00:37:27,540
why it is that that's
happening.

785
00:37:27,540 --> 00:37:31,020
As we go across the row, what we
have happening is that the

786
00:37:31,020 --> 00:37:32,710
z or the atomic charge --

787
00:37:32,710 --> 00:37:34,300
I'm not talking about z
effective here, I'm just

788
00:37:34,300 --> 00:37:37,960
talking about z -- the z is
increasing as we go across a

789
00:37:37,960 --> 00:37:39,800
row, that's easy to see.

790
00:37:39,800 --> 00:37:42,330
But we're still in the same
shell, so we still have the

791
00:37:42,330 --> 00:37:45,920
same n value as we go all the
way across a row in the

792
00:37:45,920 --> 00:37:47,260
periodic table.

793
00:37:47,260 --> 00:37:50,380
So, in general what we're going
to see is that what

794
00:37:50,380 --> 00:37:53,660
happens to z effective if we
have z increasing but we're in

795
00:37:53,660 --> 00:37:56,150
the same shell here.

796
00:37:56,150 --> 00:38:01,220
Would it increase or decrease
z effective?

797
00:38:01,220 --> 00:38:01,570
All right.

798
00:38:01,570 --> 00:38:04,140
Kind of mixed thoughts here.

799
00:38:04,140 --> 00:38:07,020
So it turns out that it
increases, and the reason is

800
00:38:07,020 --> 00:38:10,230
because the predominant thing
that's going on here is that z

801
00:38:10,230 --> 00:38:11,330
is increasing.

802
00:38:11,330 --> 00:38:13,970
So the z is increasing, and
what goes along with it is

803
00:38:13,970 --> 00:38:16,840
that the z effective is
increasing, because it turns

804
00:38:16,840 --> 00:38:19,430
out that while we're in the same
n, even though we know

805
00:38:19,430 --> 00:38:22,420
that energy depends on both the
n and the l in terms of

806
00:38:22,420 --> 00:38:25,390
quantum numbers, while we're
in the same n, the distance

807
00:38:25,390 --> 00:38:27,280
from the nucleus, it's
pretty close,

808
00:38:27,280 --> 00:38:28,850
it's not hugely different.

809
00:38:28,850 --> 00:38:30,850
So the factor that predominates
is that we're

810
00:38:30,850 --> 00:38:32,300
actually increasing z.

811
00:38:32,300 --> 00:38:34,680
That's why we see z effective
increase, and that's why we

812
00:38:34,680 --> 00:38:37,160
see ionization energy
increase.

813
00:38:37,160 --> 00:38:40,770
As we go down a column, what
happens is that the ionization

814
00:38:40,770 --> 00:38:42,040
energy decreases.

815
00:38:42,040 --> 00:38:45,220
We can also think about this
in terms of z effective.

816
00:38:45,220 --> 00:38:48,450
This is because even though z,
the atomic number is still

817
00:38:48,450 --> 00:38:51,300
increasing, we are also
getting further

818
00:38:51,300 --> 00:38:52,160
away from the nucleus.

819
00:38:52,160 --> 00:38:55,030
So, remember when we talk about
Coulomb force, what's

820
00:38:55,030 --> 00:38:57,750
holding the nucleus and the
electron together, there's 2

821
00:38:57,750 --> 00:38:58,890
things we need to think about.

822
00:38:58,890 --> 00:39:02,110
The first is this the z
effective, or how much charge

823
00:39:02,110 --> 00:39:05,130
is actually in the nucleus
that's felt, or the I guess we

824
00:39:05,130 --> 00:39:08,510
would say the z, how much the
charge is on the nucleus that

825
00:39:08,510 --> 00:39:09,870
holds it close together.

826
00:39:09,870 --> 00:39:11,970
But the second factor
is how far away we

827
00:39:11,970 --> 00:39:12,810
are from the nucleus.

828
00:39:12,810 --> 00:39:15,500
So, if we're really close to
the nucleus, that's when z

829
00:39:15,500 --> 00:39:18,410
effective is high, but if we
get really far away, then z

830
00:39:18,410 --> 00:39:20,590
effective is going to get low,
because even though we have

831
00:39:20,590 --> 00:39:22,640
the same charge in the
nucleus, the z

832
00:39:22,640 --> 00:39:23,670
effective gets lower.

833
00:39:23,670 --> 00:39:26,460
So this is not even thinking
about the other electron

834
00:39:26,460 --> 00:39:29,540
shielding, just if we think of
the fact, all we need to think

835
00:39:29,540 --> 00:39:33,030
about is that the effect of
going to a further away n

836
00:39:33,030 --> 00:39:36,170
actually dominates as we
go down the table.

837
00:39:36,170 --> 00:39:38,980
We're getting further away from
the nucleus because we're

838
00:39:38,980 --> 00:39:42,070
jumping, for example, from the
n equals 2 to the n equals 3

839
00:39:42,070 --> 00:39:45,030
shell, or from the n equals
3 to the n equals 4 shell.

840
00:39:45,030 --> 00:39:47,270
And when you're switching n's,
you're actually getting quite

841
00:39:47,270 --> 00:39:48,520
a bit farther away.

842
00:39:48,520 --> 00:39:50,980
That's why in the earlier models
of the atom, they're

843
00:39:50,980 --> 00:39:54,080
not horrible to sometimes think
about just each n value

844
00:39:54,080 --> 00:39:55,600
as a little ring around.

845
00:39:55,600 --> 00:39:58,530
It's not complete and it's not
accurate, but it's OK to kind

846
00:39:58,530 --> 00:40:00,840
of think of it in terms of how
far we're getting away from

847
00:40:00,840 --> 00:40:01,890
the nucleus.

848
00:40:01,890 --> 00:40:04,600
So, as we go down a column, we
see ionization energy's going

849
00:40:04,600 --> 00:40:06,850
to decrease.

850
00:40:06,850 --> 00:40:09,440
So, this means we have the
general trends down, so we

851
00:40:09,440 --> 00:40:12,950
should be able to look at actual
atoms in our periodic

852
00:40:12,950 --> 00:40:14,580
table and graph them
and see that they

853
00:40:14,580 --> 00:40:16,040
match up with our trends.

854
00:40:16,040 --> 00:40:19,840
So here we have that graphed
here, we have atomic number z

855
00:40:19,840 --> 00:40:23,720
graphed against ionization
energy, so, let's fill in what

856
00:40:23,720 --> 00:40:27,080
the actual atoms are here, and
we can see in general, yes,

857
00:40:27,080 --> 00:40:28,260
we're following the trend.

858
00:40:28,260 --> 00:40:32,350
For row one, we're increasing,
as we should, across the row.

859
00:40:32,350 --> 00:40:34,550
Let's look at row two also.

860
00:40:34,550 --> 00:40:36,800
Well, we're generally increasing
here, we'll talk

861
00:40:36,800 --> 00:40:38,180
about that more in a minute.

862
00:40:38,180 --> 00:40:41,630
And also in a row three, yeah,
we're generally increasing,

863
00:40:41,630 --> 00:40:43,190
there's some glitches
here, but the

864
00:40:43,190 --> 00:40:45,320
general trend holds true.

865
00:40:45,320 --> 00:40:48,710
Similarly we see as we go down
the table, so as we're going

866
00:40:48,710 --> 00:40:52,780
from one row to the next row,
so, for example, between

867
00:40:52,780 --> 00:40:56,300
helium and lithium, we see a
drop; the same with neon to

868
00:40:56,300 --> 00:40:58,270
sodium, we see a drop here.

869
00:40:58,270 --> 00:41:00,660
So it looks like we're generally
following our trend,

870
00:41:00,660 --> 00:41:02,150
that's a good thing.

871
00:41:02,150 --> 00:41:05,720
But hopefully, you will not be
satisfied to just make a

872
00:41:05,720 --> 00:41:09,280
general statement here when
we do have these glitches.

873
00:41:09,280 --> 00:41:11,930
So you can see, for example, we
have several places where

874
00:41:11,930 --> 00:41:15,220
instead of going up as we go
across the row, we actually go

875
00:41:15,220 --> 00:41:17,460
down in ionization energy
a little bit.

876
00:41:17,460 --> 00:41:21,620
So between b e, and b, between
n and o, magesium and

877
00:41:21,620 --> 00:41:25,170
aluminum, and then phosphorous
and sulfur, what we see here

878
00:41:25,170 --> 00:41:27,700
is that we're kind of going
down, or quite specifically,

879
00:41:27,700 --> 00:41:29,250
we are going down.

880
00:41:29,250 --> 00:41:31,780
So, let's take a look at one of
these rows in more detail

881
00:41:31,780 --> 00:41:34,810
to think about why this might be
happening, and it turns out

882
00:41:34,810 --> 00:41:38,680
the reason that these glitches
occur are because the sub

883
00:41:38,680 --> 00:41:42,660
shell structure predominates
in certain instances, and

884
00:41:42,660 --> 00:41:44,930
that's where these glitches
take place.

885
00:41:44,930 --> 00:41:48,600
So I've sort of just spread out
what we have as the second

886
00:41:48,600 --> 00:41:52,800
row here, graphed against
the ionization energy.

887
00:41:52,800 --> 00:41:54,170
So, let's consider specifically
where these

888
00:41:54,170 --> 00:41:55,540
glitches are taking place.

889
00:41:55,540 --> 00:41:58,300
So, let's look at the first
one between beryllium and

890
00:41:58,300 --> 00:42:00,900
boron here.

891
00:42:00,900 --> 00:42:04,600
And the glitch that doesn't
make sense just through

892
00:42:04,600 --> 00:42:07,500
periodic trends, is that it
turns out that the ionization

893
00:42:07,500 --> 00:42:11,100
energy of boron is actually
less than the ionization

894
00:42:11,100 --> 00:42:12,680
energy up beryllium.

895
00:42:12,680 --> 00:42:15,060
So I put the electron
configurations and actually

896
00:42:15,060 --> 00:42:18,080
drew it on an energy diagram
here, so we can actually think

897
00:42:18,080 --> 00:42:19,880
about why this might
be happening.

898
00:42:19,880 --> 00:42:23,910
So what is this, which element
did I chart here?

899
00:42:23,910 --> 00:42:28,930
Which one is that, the boron
or the beryllium?

900
00:42:28,930 --> 00:42:30,730
I couldn't tell what
you said, sorry.

901
00:42:30,730 --> 00:42:34,530
So, I'm going to assume that
was beryllium, and then it

902
00:42:34,530 --> 00:42:36,210
turns out that if that's
beryllium, the

903
00:42:36,210 --> 00:42:37,930
other one must be boron.

904
00:42:37,930 --> 00:42:41,360
So, we have beryllium in the
first case here, it has four

905
00:42:41,360 --> 00:42:43,630
electrons, that's how we
know it's beryllium,

906
00:42:43,630 --> 00:42:45,500
boron has five electrons.

907
00:42:45,500 --> 00:42:49,370
So, just looking at putting in
the electrons, filling up the

908
00:42:49,370 --> 00:42:53,190
energy diagram here, we should
be able to see a little bit

909
00:42:53,190 --> 00:42:54,430
why this is happening.

910
00:42:54,430 --> 00:42:57,780
And the reason is simply because
the energy that we

911
00:42:57,780 --> 00:43:02,510
gain in terms of moving up in z,
so from going to z equals 4

912
00:43:02,510 --> 00:43:06,160
to z equals 5, is actually
outweighed by the energy it

913
00:43:06,160 --> 00:43:09,250
takes to go into this new
shell, to go into

914
00:43:09,250 --> 00:43:10,410
this new sub shell.

915
00:43:10,410 --> 00:43:14,330
So to jump from the 2 s to the 2
p, takes more energy than we

916
00:43:14,330 --> 00:43:17,580
can actually compensate with
by increasing the pull from

917
00:43:17,580 --> 00:43:18,560
the nucleus.

918
00:43:18,560 --> 00:43:23,020
So, it turns out that in this
case, and any time that we see

919
00:43:23,020 --> 00:43:27,960
we're going from a 2 s to 2 p,
filling in of electrons, we

920
00:43:27,960 --> 00:43:29,350
actually see that little
bit of glitch

921
00:43:29,350 --> 00:43:31,030
in ionization energy.

922
00:43:31,030 --> 00:43:33,350
So it's shown here for the
second row, but it's actually

923
00:43:33,350 --> 00:43:35,280
also going to be true
for the third row.

924
00:43:35,280 --> 00:43:38,080
The same thing when you're going
from filling in the 2 s

925
00:43:38,080 --> 00:43:40,380
to putting that first electron
into the 2 p.

926
00:43:40,380 --> 00:43:42,850
So that explains one of our
glitches here, but we have

927
00:43:42,850 --> 00:43:46,120
another glitch, and that second
glitch comes between

928
00:43:46,120 --> 00:43:48,400
nitrogen and oxygen.

929
00:43:48,400 --> 00:43:50,010
So, these sound more different,
so I think I'll be

930
00:43:50,010 --> 00:43:51,000
able to distinguish.

931
00:43:51,000 --> 00:43:56,630
Which element is shown here?

932
00:43:56,630 --> 00:43:57,290
Yeah, nitrogen.

933
00:43:57,290 --> 00:44:00,220
So, nitrogen is shown
here, we know that

934
00:44:00,220 --> 00:44:01,950
because it has 7 electrons.

935
00:44:01,950 --> 00:44:03,460
In this case, we're
talking about 8

936
00:44:03,460 --> 00:44:06,470
electrons, which is oxygen.

937
00:44:06,470 --> 00:44:08,690
So if we're comparing the
difference between these 2

938
00:44:08,690 --> 00:44:11,950
now, what you'll notice is that
in nitrogen we have all

939
00:44:11,950 --> 00:44:16,700
half-filled 2 p orbitals, and
now, once we move into oxygen,

940
00:44:16,700 --> 00:44:19,340
we actually have to add
1 more electron into

941
00:44:19,340 --> 00:44:20,760
1 of the 2 p orbitals.

942
00:44:20,760 --> 00:44:23,050
There's no more 2 p orbitals to
put it into, so we're going

943
00:44:23,050 --> 00:44:24,540
to actually have to double up.

944
00:44:24,540 --> 00:44:27,570
So now we're putting 2 electrons
into the same p

945
00:44:27,570 --> 00:44:29,670
orbital, that's not a problem,
we can do it, it's not a huge

946
00:44:29,670 --> 00:44:30,980
energy cost to do that.

947
00:44:30,980 --> 00:44:33,900
But actually there is a little
bit of an energy cost into

948
00:44:33,900 --> 00:44:36,670
doubling up into a single
orbital, because, of course,

949
00:44:36,670 --> 00:44:40,380
it takes energy when you
create more electron

950
00:44:40,380 --> 00:44:42,820
repulsion, that's not something
we want to do, but

951
00:44:42,820 --> 00:44:45,810
we have to do it here, and it
turns out that that effect

952
00:44:45,810 --> 00:44:48,640
predominates over, again, the
energy that we gain by

953
00:44:48,640 --> 00:44:51,160
increasing the atomic
number by one.

954
00:44:51,160 --> 00:44:54,480
So, our two glitches we see when
we go from the 2 p, or

955
00:44:54,480 --> 00:44:57,500
from 2 s to start filling the
2 p, and then we also get

956
00:44:57,500 --> 00:45:00,380
another glitch when we've
half-filled the 2 p, and now

957
00:45:00,380 --> 00:45:02,170
we're adding and having
to double up in

958
00:45:02,170 --> 00:45:03,550
one of those p orbitals.

959
00:45:03,550 --> 00:45:05,510
Again, we see the same
effect as we go into

960
00:45:05,510 --> 00:45:09,410
different rows as well.

961
00:45:09,410 --> 00:45:13,440
So let's talk about another
periodic trend, this one is

962
00:45:13,440 --> 00:45:14,660
called electron affinity.

963
00:45:14,660 --> 00:45:19,140
Electron affinity is actually
the ability of an atom, or we

964
00:45:19,140 --> 00:45:21,880
could also talk about an
ion to gain electrons.

965
00:45:21,880 --> 00:45:24,590
So it's the affinity it has for
electrons, it's how much

966
00:45:24,590 --> 00:45:26,370
it likes to get an electron.

967
00:45:26,370 --> 00:45:30,320
We can write out what it is for
any certain atom or ion x,

968
00:45:30,320 --> 00:45:33,550
so it's just x plus an electron
gives us x minus.

969
00:45:33,550 --> 00:45:35,970
We have the minus because we're
adding a negative charge

970
00:45:35,970 --> 00:45:37,550
from the electron.

971
00:45:37,550 --> 00:45:40,780
So, basically any time we have
a really high positive number

972
00:45:40,780 --> 00:45:44,110
of electron affinity, it means
that that atom or ion really

973
00:45:44,110 --> 00:45:46,620
wants to gain another electron,
and it will be very

974
00:45:46,620 --> 00:45:48,690
stable and happy
if it does so.

975
00:45:48,690 --> 00:45:51,800
So let's look at an example
of chlorine here.

976
00:45:51,800 --> 00:45:54,950
So chlorine, if we talk about
it in terms of electron

977
00:45:54,950 --> 00:45:58,010
affinity, we would be writing
that we're actually gaining an

978
00:45:58,010 --> 00:46:01,230
electron here, and getting
the ion, c l minus.

979
00:46:01,230 --> 00:46:04,760
And the change in energy for
this reaction is negative 349

980
00:46:04,760 --> 00:46:07,490
kilojoules per mole.

981
00:46:07,490 --> 00:46:10,110
So if we have a negative change
in energy for any

982
00:46:10,110 --> 00:46:12,960
reaction as it's written, what
that actually means is we're

983
00:46:12,960 --> 00:46:15,990
giving off energy as the
reaction proceeds.

984
00:46:15,990 --> 00:46:19,640
So, in other words, this c l
minus is actually lower in

985
00:46:19,640 --> 00:46:21,500
energy than the reactants
were.

986
00:46:21,500 --> 00:46:23,500
So that's why we're giving
off extra energy.

987
00:46:23,500 --> 00:46:25,940
We saw a similar thing as we
saw electrons move from

988
00:46:25,940 --> 00:46:26,770
different levels.

989
00:46:26,770 --> 00:46:29,350
We can think of it in the same
type of way when we're talking

990
00:46:29,350 --> 00:46:31,720
about actual reactions
happening.

991
00:46:31,720 --> 00:46:34,930
So, if we have energy that's
released, would you say that

992
00:46:34,930 --> 00:46:38,270
the chlorine ion is more
or less stable than

993
00:46:38,270 --> 00:46:38,830
the chlorine atom?

994
00:46:38,830 --> 00:46:42,300
Who thinks it's more stable,
show of hands?

995
00:46:42,300 --> 00:46:45,260
All right, who thinks
it's less stable?

996
00:46:45,260 --> 00:46:46,450
Very good.

997
00:46:46,450 --> 00:46:48,660
So it turns out it is,
in fact, more stable.

998
00:46:48,660 --> 00:46:51,370
It's more stable because you
actually -- this happens

999
00:46:51,370 --> 00:46:54,610
spontaneously, you actually get
energy out of the reaction

1000
00:46:54,610 --> 00:46:55,410
as this happens.

1001
00:46:55,410 --> 00:46:57,510
And we haven't talked about
reactions at all yet, so you

1002
00:46:57,510 --> 00:47:01,400
don't need to worry about the
specifics of that exactly, but

1003
00:47:01,400 --> 00:47:03,830
just that if you have this
negative change in energy, you

1004
00:47:03,830 --> 00:47:07,430
have a more stable product
than you do reactant.

1005
00:47:07,430 --> 00:47:11,150
So, we were talking, however,
about energy in terms of

1006
00:47:11,150 --> 00:47:14,040
electron affinity, so we can
actually relate electron

1007
00:47:14,040 --> 00:47:17,470
affinity to any reaction by
saying if we have this

1008
00:47:17,470 --> 00:47:20,310
reaction written as here where
we're gaining an electron, we

1009
00:47:20,310 --> 00:47:23,110
say that electron affinity is
just equal to the negative of

1010
00:47:23,110 --> 00:47:24,780
that change in energy.

1011
00:47:24,780 --> 00:47:28,240
So, for example, for the
chlorine case, we would say

1012
00:47:28,240 --> 00:47:32,090
that the electron affinity for
chlorine is actually positive

1013
00:47:32,090 --> 00:47:35,120
349 kilojoules per mole.

1014
00:47:35,120 --> 00:47:37,980
That's a very large number,
it's all relative, so you

1015
00:47:37,980 --> 00:47:39,990
don't necessarily know it's
large without me telling you

1016
00:47:39,990 --> 00:47:43,690
or giving you other ions to
compare to, but chlorine does

1017
00:47:43,690 --> 00:47:46,670
have a very large affinity,
meaning it's really likes

1018
00:47:46,670 --> 00:47:50,170
getting an electron and becoming
a chlorine ion.

1019
00:47:50,170 --> 00:47:53,020
One major difference between
electron affinity and

1020
00:47:53,020 --> 00:47:56,010
ionization energy is that when
we talked about ionization

1021
00:47:56,010 --> 00:47:58,230
energy, remember ionization
energy

1022
00:47:58,230 --> 00:47:59,790
always has to be positive.

1023
00:47:59,790 --> 00:48:01,230
We will never have a case where

1024
00:48:01,230 --> 00:48:03,410
ionization energy is negative.

1025
00:48:03,410 --> 00:48:06,200
Electron affinity, however, can
be either negative or it

1026
00:48:06,200 --> 00:48:07,540
can be positive.

1027
00:48:07,540 --> 00:48:09,160
So let's look at a
case where it's

1028
00:48:09,160 --> 00:48:10,350
actually going to be negative.

1029
00:48:10,350 --> 00:48:12,610
So, if we took the case of
nitrogen, if we add an

1030
00:48:12,610 --> 00:48:15,750
electron to nitrogen and go to
n minus, we find that the

1031
00:48:15,750 --> 00:48:18,600
change in energy is 7
kilojoules per mole.

1032
00:48:18,600 --> 00:48:22,310
This means in order to do that
we actually have to put 7

1033
00:48:22,310 --> 00:48:24,320
kilojoules per mole
of energy into the

1034
00:48:24,320 --> 00:48:26,000
reaction to make it happen.

1035
00:48:26,000 --> 00:48:28,450
So this is not going to be a
favorable process, we're going

1036
00:48:28,450 --> 00:48:31,620
to find that the electron
affinity is actually a

1037
00:48:31,620 --> 00:48:34,590
negative 7 kilojoules per
mole for nitrogen.

1038
00:48:34,590 --> 00:48:38,240
So this means nitrogen has low
electron affinity, it doesn't

1039
00:48:38,240 --> 00:48:41,710
actually want to gain
an electron.

1040
00:48:41,710 --> 00:48:45,440
So, that also tells us that the
n minus ion is less stable

1041
00:48:45,440 --> 00:48:47,950
than the neutral atom itself.

1042
00:48:47,950 --> 00:48:50,930
So, we can think about trends in
electron affinity just like

1043
00:48:50,930 --> 00:48:53,180
we did for ionization energy,
and what we see

1044
00:48:53,180 --> 00:48:54,510
is a similar trend.

1045
00:48:54,510 --> 00:48:57,760
Electron affinity increases as
we go across a row in the

1046
00:48:57,760 --> 00:49:00,500
periodic table, and
it decreases as

1047
00:49:00,500 --> 00:49:02,320
we go down a column.

1048
00:49:02,320 --> 00:49:05,090
I left out the noble gases here
because they do something

1049
00:49:05,090 --> 00:49:07,240
a little bit special, and
actually, I'm going to give

1050
00:49:07,240 --> 00:49:10,320
you one last clicker question
today to see if you can tell

1051
00:49:10,320 --> 00:49:12,480
me what you think
noble gases do.

1052
00:49:12,480 --> 00:49:14,300
To answer this question you
just really want to think

1053
00:49:14,300 --> 00:49:16,020
about what does electron
affinity means.

1054
00:49:16,020 --> 00:49:18,600
It means how much a certain
atom actually

1055
00:49:18,600 --> 00:49:21,370
wants to get an electron.

1056
00:49:21,370 --> 00:49:23,880
So do you think noble gases
would have a high positive

1057
00:49:23,880 --> 00:49:25,910
electron affinity, a
low positive, or

1058
00:49:25,910 --> 00:49:26,700
negative electron affinity?

1059
00:49:26,700 --> 00:49:40,160
So, let's take 10
seconds on that.

1060
00:49:40,160 --> 00:49:40,480
All right.

1061
00:49:40,480 --> 00:49:40,850
Great.

1062
00:49:40,850 --> 00:49:43,800
So most of you recognize, if we
switch back to the notes,

1063
00:49:43,800 --> 00:49:46,150
that they do have a negative
electron affinity.

1064
00:49:46,150 --> 00:49:48,430
This should make sense to you,
because they don't, in fact,

1065
00:49:48,430 --> 00:49:51,450
want to gain another electron,
because that would mean that

1066
00:49:51,450 --> 00:49:54,750
electron would have to go into a
new value of n, a new shell,

1067
00:49:54,750 --> 00:49:56,350
and that's really going
to increase the

1068
00:49:56,350 --> 00:49:58,220
energy of the system.

1069
00:49:58,220 --> 00:50:00,910
So they'd much rather just stay
the way they are and not

1070
00:50:00,910 --> 00:50:04,400
have another electron come on,
and it turns out that halogens

1071
00:50:04,400 --> 00:50:06,570
have the highest electron
affinities.