1
00:00:00,000 --> 00:00:00,840


2
00:00:00,840 --> 00:00:02,610
So we have two different
molecules here.

3
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This is hydrogen peroxide.

4
00:00:04,010 --> 00:00:08,109
We call it peroxide, because
it has this oxygen-oxygen bond.

5
00:00:08,109 --> 00:00:11,050
And here we have
oxygen difluoride,

6
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where oxygen is bonded to
two different fluorines.

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00:00:14,840 --> 00:00:17,460
And what I want you to do
is pause this video, use

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00:00:17,460 --> 00:00:19,891
this periodic table of
elements I have here,

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00:00:19,891 --> 00:00:21,890
and this is more than
just a typical information

10
00:00:21,890 --> 00:00:23,310
of periodic table of elements.

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It also gives you the
electronegativities

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00:00:26,654 --> 00:00:27,820
of these different elements.

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00:00:27,820 --> 00:00:29,260
And these
electronegativities are

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00:00:29,260 --> 00:00:32,720
based on the Pauling scale
named after famous biologist

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00:00:32,720 --> 00:00:35,480
and chemist Linus Pauling.

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And so using the
information here

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00:00:37,240 --> 00:00:39,660
and what you know already
about oxidation states,

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00:00:39,660 --> 00:00:42,840
think about the oxidation
states or the oxidation numbers

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00:00:42,840 --> 00:00:46,840
for each of the constituent
elements in these molecules.

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So pause the video now.

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00:00:49,330 --> 00:00:51,740
So I'm assuming you
have given a shot at it.

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00:00:51,740 --> 00:00:53,560
And you might have
immediately realized

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that something very
interesting is going on.

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We've said in the
past that because it's

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two valence electrons away
from a full valence shell,

26
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because it is so
electronegative,

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oxygen typically takes electrons
from other things, typically

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two electrons, which
typically gives it

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00:01:14,030 --> 00:01:18,395
an oxidation state of
negative-- an oxidation number

30
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or oxidation state
of negative 2.

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This is so electronegative,
and it so typically oxidizes

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other things that we've
called the whole phenomenon

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"oxidation."

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But what's interesting
here is that oxygen

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isn't purely bonded to
things less electronegative

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00:01:32,950 --> 00:01:33,850
than itself.

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And the hydrogen peroxide, yes,
it is bonded to the hydrogen.

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But it's also bonded
to another oxygen.

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And obviously,
these two are going

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to be equally electronegative.

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So what would be
the oxidation states

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or the oxidation numbers here?

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Well, hydrogen, once again,
we portend-- hydrogen,

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because it's less
electronegative,

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00:01:51,370 --> 00:01:53,115
it would have a partially
positive charge,

46
00:01:53,115 --> 00:01:54,490
because the
electrons would spend

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00:01:54,490 --> 00:01:55,860
more time around this oxygen.

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00:01:55,860 --> 00:01:58,420
But when we're talking
about oxidation states,

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we don't like this
partial charge business.

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We want to pretend like
these covalent bonds

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00:02:02,340 --> 00:02:05,070
are ionic bonds,
hypothetical ionic bonds.

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00:02:05,070 --> 00:02:08,080
And if they were hypothetically
ionic bonds, what would happen?

53
00:02:08,080 --> 00:02:11,020
Well, if you had to give
these electrons to somebody,

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00:02:11,020 --> 00:02:12,770
you would give
them to the oxygen,

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00:02:12,770 --> 00:02:15,860
the electrons in this period,
give them to the oxygen,

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00:02:15,860 --> 00:02:18,810
giving it an oxidation
state of negative 1.

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00:02:18,810 --> 00:02:21,360
With the hydrogen having
these electrons taken away,

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00:02:21,360 --> 00:02:24,050
it's going to have an
oxidation state of positive 1.

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00:02:24,050 --> 00:02:26,260
And the same thing's going
to be true for that oxygen

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and that hydrogen
right over there.

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00:02:28,380 --> 00:02:30,310
So this is fascinating,
because this

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00:02:30,310 --> 00:02:33,260
is an example where oxygen
has an oxidation state not

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00:02:33,260 --> 00:02:39,490
of negative 2, but an
oxidation state of negative 1.

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00:02:39,490 --> 00:02:42,030
So this is already
kind of interesting.

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00:02:42,030 --> 00:02:43,550
Now it gets even
more interesting

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00:02:43,550 --> 00:02:46,550
when we go to oxygen difluoride.

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Why is this more interesting?

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Because fluorine is the one
thing on this entire table

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00:02:51,430 --> 00:02:56,160
that is more
electronegative than oxygen.

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00:02:56,160 --> 00:02:59,330
This is a covalent bond, but
in our hypothetical ionic bond,

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00:02:59,330 --> 00:03:01,590
if we had to give
these electrons to one

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of these atoms, you would
give it to the fluorine.

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00:03:04,590 --> 00:03:06,840
So the fluorine,
each of them would

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00:03:06,840 --> 00:03:10,206
have an oxidation
state of negative 1.

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00:03:10,206 --> 00:03:12,080
And the oxygen here--
now, you could imagine,

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00:03:12,080 --> 00:03:13,880
this is nuts for oxygen.

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00:03:13,880 --> 00:03:17,510
The oxidation state for oxygen,
it's giving up these electrons.

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00:03:17,510 --> 00:03:21,214
It would be a positive 2.

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00:03:21,214 --> 00:03:22,630
And we talk about
oxidation states

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00:03:22,630 --> 00:03:24,421
when we write this
little superscript here.

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00:03:24,421 --> 00:03:26,430
We write the sign
after the number.

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And that's just the convention.

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00:03:27,740 --> 00:03:30,050
But it has an oxidation
state of positive 2.

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00:03:30,050 --> 00:03:33,740
Oxygen, the thing that likes
to oxidize other things,

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00:03:33,740 --> 00:03:37,950
it itself has been
oxidized by fluorine.

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00:03:37,950 --> 00:03:40,880
So this is a pretty
dramatic example

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00:03:40,880 --> 00:03:43,920
of how something might stray
from what's typical oxidation

88
00:03:43,920 --> 00:03:46,640
state or it's typical
oxidation number.

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00:03:46,640 --> 00:03:50,260
And in general, oxygen will have
an oxidation state or oxidation

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00:03:50,260 --> 00:03:54,780
number in most
molecules of negative 2.

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00:03:54,780 --> 00:03:58,340
But unless it's bonded
with another oxygen

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00:03:58,340 --> 00:04:03,260
or it's bonded to fluorine,
which is a much more

93
00:04:03,260 --> 00:04:05,770
electronegative-- or
actually, not much more,

94
00:04:05,770 --> 00:04:10,230
but it's the only atom that
is more electronegative than--

95
00:04:10,230 --> 00:04:14,320
or the only element is more
electronegative than oxygen.