WEBVTT

00:00:03.836 --> 00:00:06.526 A:middle
>> Welcome to Atoms
and Elements, Part 3.

00:00:06.526 --> 00:00:10.786 A:middle
In this video lecture, we are
going to look at ionic compounds

00:00:11.206 --> 00:00:16.036 A:middle
as oxidation and reduction
reactions to form the ions.

00:00:16.036 --> 00:00:18.896 A:middle
And so this will just be a
very preliminary introduction

00:00:19.196 --> 00:00:22.206 A:middle
to oxidation and reduction
that we'll continue to build

00:00:22.206 --> 00:00:23.306 A:middle
on throughout the course.

00:00:24.126 --> 00:00:24.966 A:middle
Let's get started.

00:00:25.936 --> 00:00:26.546 A:middle
All right.

00:00:27.016 --> 00:00:29.196 A:middle
So we, in our last video,

00:00:29.196 --> 00:00:31.676 A:middle
we learned that ionic
compounds form

00:00:31.676 --> 00:00:33.466 A:middle
from the transfer of electrons.

00:00:34.146 --> 00:00:39.166 A:middle
So we learned that the
metals lose electrons, right?

00:00:39.266 --> 00:00:40.596 A:middle
To form the cations.

00:00:41.586 --> 00:00:49.136 A:middle
And the non-metals gain
electrons to form the anions.

00:00:49.836 --> 00:00:50.256 A:middle
All right?

00:00:50.496 --> 00:00:54.036 A:middle
Now, the overall
charge on each side

00:00:54.036 --> 00:00:56.556 A:middle
of the reaction must be equal.

00:00:57.166 --> 00:01:00.686 A:middle
So in chemical reaction, we
have reactants on the left

00:01:01.186 --> 00:01:04.846 A:middle
and products on the right, and
then there's our reaction arrow.

00:01:04.846 --> 00:01:06.626 A:middle
So you can think of
that reaction arrow

00:01:07.176 --> 00:01:08.416 A:middle
like an equal sign.

00:01:08.536 --> 00:01:09.046 A:middle
All right?

00:01:10.566 --> 00:01:14.816 A:middle
And we can think of, chemical
reactions are like a blending

00:01:14.816 --> 00:01:17.366 A:middle
of chemistry, English and math.

00:01:17.366 --> 00:01:21.896 A:middle
So when we look at a chemical
reaction, we can treat it

00:01:22.846 --> 00:01:24.976 A:middle
like an algebraic expression.

00:01:25.516 --> 00:01:32.726 A:middle
[ Pen scratching ]

00:01:33.226 --> 00:01:33.986 A:middle
All righty.

00:01:34.376 --> 00:01:36.426 A:middle
And then there's
a little mnemonic

00:01:36.466 --> 00:01:39.986 A:middle
that can help us understand
oxidation and reduction.

00:01:40.386 --> 00:01:41.416 A:middle
There's two of them.

00:01:41.526 --> 00:01:50.556 A:middle
There's "LEO says GER" or
the other one is "OIL RIG".

00:01:51.366 --> 00:01:53.936 A:middle
So as I explain oxidation
and reduction,

00:01:53.936 --> 00:01:56.026 A:middle
I'll show you how these
sayings can help you.

00:01:56.866 --> 00:01:59.516 A:middle
Right? So first we'll
focus on oxidation, right?

00:01:59.586 --> 00:02:05.836 A:middle
So here it is, LEO, loss
of electrons, whoops.

00:02:06.316 --> 00:02:09.946 A:middle
Loss of electrons is oxidation.

00:02:10.606 --> 00:02:11.426 A:middle
Right? LEO.

00:02:12.296 --> 00:02:13.206 A:middle
All right?

00:02:13.466 --> 00:02:15.516 A:middle
Or the OIL would be
oxidation is loss.

00:02:15.936 --> 00:02:17.206 A:middle
Right? So there's our LEO.

00:02:18.056 --> 00:02:25.336 A:middle
So here we have sodium, as
a pure element and we know

00:02:25.336 --> 00:02:27.886 A:middle
that pure elements
have no charge,

00:02:28.526 --> 00:02:31.716 A:middle
and we know that it likes,
it has one valence electron,

00:02:31.856 --> 00:02:34.706 A:middle
so here is the lost electron.

00:02:35.466 --> 00:02:40.906 A:middle
Alrighty. So, one thing

00:02:41.546 --> 00:02:47.326 A:middle
that sometimes students
think is a little strange is

00:02:47.326 --> 00:02:50.006 A:middle
that we lost the electron,
but we put the plus.

00:02:50.236 --> 00:02:53.016 A:middle
That's because in
chemical reactions,

00:02:53.016 --> 00:02:56.106 A:middle
we only have addition, we
never have subtraction.

00:02:56.496 --> 00:02:59.396 A:middle
The subtraction would be
in the charge, all right?

00:02:59.766 --> 00:03:02.336 A:middle
So here's our lost
electron, so here's LEO,

00:03:02.676 --> 00:03:06.296 A:middle
the lost electron means this
is an oxidation reaction.

00:03:07.046 --> 00:03:09.886 A:middle
And here we go about
balancing the charge, right?

00:03:09.886 --> 00:03:13.966 A:middle
The sodium was a zero,
was neutral on the left,

00:03:14.116 --> 00:03:17.826 A:middle
treat the reaction
arrow as an equal sign;

00:03:18.526 --> 00:03:21.286 A:middle
there's our sodium
ion, that was plus 1,

00:03:22.236 --> 00:03:24.466 A:middle
and then there's the
plus from our reaction.

00:03:25.056 --> 00:03:27.976 A:middle
And so you can think of
it just as "and", right?

00:03:27.976 --> 00:03:29.646 A:middle
So everything is
like "and, and, and".

00:03:29.736 --> 00:03:33.186 A:middle
And then the electron, of
course, has a minus 1 charge.

00:03:33.516 --> 00:03:36.896 A:middle
So plus 1 and minus
1 equals zero, right?

00:03:37.076 --> 00:03:41.056 A:middle
So the overall charge
on the left is zero,

00:03:41.856 --> 00:03:44.236 A:middle
and the overall charge
on the right is zero.

00:03:45.426 --> 00:03:47.486 A:middle
So there's our oxidation
reaction.

00:03:48.406 --> 00:03:49.296 A:middle
Now we've been working

00:03:49.296 --> 00:03:52.536 A:middle
to memorize the variable
charge metals,

00:03:52.536 --> 00:03:56.736 A:middle
and this will help us
understand why they have more

00:03:56.736 --> 00:03:58.786 A:middle
than one charge, right?

00:03:58.786 --> 00:04:01.246 A:middle
So here we have the
pure element iron,

00:04:01.686 --> 00:04:07.956 A:middle
and pure elements
are always zero.

00:04:08.686 --> 00:04:15.876 A:middle
But then the iron can either
lose 2 electrons or 3 electrons.

00:04:16.786 --> 00:04:20.486 A:middle
Right? So here's those
lost electrons, right?

00:04:21.576 --> 00:04:23.846 A:middle
Right is oxidation.

00:04:23.846 --> 00:04:28.786 A:middle
So there's our LEO, and
then we look, so that's why

00:04:29.176 --> 00:04:31.406 A:middle
like for sodium, we just say

00:04:31.406 --> 00:04:34.126 A:middle
that this is a sodium
ion, and everybody knows.

00:04:34.856 --> 00:04:38.946 A:middle
But if we say iron ions, people
will be like, "Well which one?"

00:04:39.556 --> 00:04:43.116 A:middle
So that's why we have to have
those Roman numerals, right?

00:04:43.116 --> 00:04:46.926 A:middle
This is iron(II), and
then this is iron(III).

00:04:47.436 --> 00:04:50.396 A:middle
And if we were to go deeper into
the chemistry, we would learn

00:04:50.396 --> 00:04:53.196 A:middle
that iron(II) and iron(III)
have very different chemistries.

00:04:54.416 --> 00:04:57.036 A:middle
So it's important to
distinguish between them

00:04:57.066 --> 00:04:59.246 A:middle
with the Roman numerals
when we discuss them.

00:04:59.926 --> 00:05:02.146 A:middle
And then just to
double check, right?

00:05:02.146 --> 00:05:05.336 A:middle
Overall charge, we started with
a zero, with the pure element,

00:05:05.556 --> 00:05:07.486 A:middle
and then either way, right?

00:05:07.486 --> 00:05:09.496 A:middle
So if we, we'll just do
this one here, right?

00:05:09.496 --> 00:05:15.386 A:middle
Iron was plus 3, and then we
had 3 electrons, so once again,

00:05:15.386 --> 00:05:18.596 A:middle
the charge on the left equals
the charge on the right.

00:05:18.656 --> 00:05:19.756 A:middle
All right?

00:05:20.026 --> 00:05:23.546 A:middle
So that's oxidation
at its simplest level,

00:05:23.546 --> 00:05:25.796 A:middle
and that's a great
place to start.

00:05:25.826 --> 00:05:27.846 A:middle
As we can see here
with the iron, right?

00:05:27.846 --> 00:05:31.276 A:middle
This iron plus 2, iron
plus 3 is involved in a lot

00:05:31.276 --> 00:05:33.906 A:middle
of biochemical reactions,
so we'll be coming back

00:05:33.906 --> 00:05:35.366 A:middle
to this, again in the future.

00:05:35.366 --> 00:05:40.976 A:middle
Now let's look a little
more closely at reduction.

00:05:41.996 --> 00:05:46.296 A:middle
So now this is right, gaining,
so this would be our non-metals,

00:05:46.416 --> 00:05:49.056 A:middle
like Sulphur is a
non-metal, right?

00:05:49.056 --> 00:05:53.146 A:middle
Here's our GER, gaining
electrons is reduction.

00:05:53.456 --> 00:05:56.206 A:middle
So there's our GER, right?

00:05:56.206 --> 00:06:07.386 A:middle
Or RIG, for the RIG,
reduction is loss of electrons.

00:06:07.846 --> 00:06:10.446 A:middle
So there's the RIG version.

00:06:10.446 --> 00:06:11.136 A:middle
All right?

00:06:11.136 --> 00:06:14.566 A:middle
So GER, OIL RIG or LEO says GER.

00:06:14.876 --> 00:06:17.306 A:middle
Okay. So now we're
gaining electrons,

00:06:17.556 --> 00:06:18.376 A:middle
so here they are, right?

00:06:18.886 --> 00:06:23.346 A:middle
Gained electrons, right there.

00:06:23.626 --> 00:06:28.506 A:middle
And that's pretty much it.

00:06:28.506 --> 00:06:29.746 A:middle
So let's just double check,

00:06:30.036 --> 00:06:31.856 A:middle
see how we're doing
on our charge, right?

00:06:32.166 --> 00:06:34.966 A:middle
So Sulphur is pure, it's zero,

00:06:35.376 --> 00:06:38.196 A:middle
and now it's gaining
2 electrons,

00:06:38.726 --> 00:06:40.156 A:middle
so that would be minus 2.

00:06:40.796 --> 00:06:44.336 A:middle
Our reaction arrow is our equal,
and then we're forming sulfide,

00:06:44.336 --> 00:06:46.746 A:middle
the anion sulfide,
which has a minus 2,

00:06:47.496 --> 00:06:49.336 A:middle
so I think at this point,
we can just cover this up,

00:06:49.336 --> 00:06:52.116 A:middle
and minus 2 equals
minus 2, right?

00:06:52.426 --> 00:06:55.396 A:middle
So when we have chemical
reactions, the charge,

00:06:55.456 --> 00:06:58.126 A:middle
the overall charge for
each side balances.

00:06:59.286 --> 00:07:02.656 A:middle
Now, you know, this is a
little bit of continuity.

00:07:02.706 --> 00:07:03.916 A:middle
I don't know what
to do about it,

00:07:03.916 --> 00:07:05.246 A:middle
so we're just going
to go for it.

00:07:05.876 --> 00:07:10.516 A:middle
Amongst the non-metals,
we have what are called

00:07:10.546 --> 00:07:11.826 A:middle
diatomic elements.

00:07:12.066 --> 00:07:15.536 A:middle
And you'll learn more about
these in a future video.

00:07:16.006 --> 00:07:20.526 A:middle
But the main thing is that
these elements are all

00:07:20.526 --> 00:07:22.066 A:middle
in their pure form.

00:07:22.646 --> 00:07:26.476 A:middle
In their pure form,
they're like Siamese twins.

00:07:27.496 --> 00:07:30.456 A:middle
They are going to stay together.

00:07:31.316 --> 00:07:33.696 A:middle
So when we look at the-
and they're non-metals,

00:07:33.696 --> 00:07:35.266 A:middle
so they want to gain electrons.

00:07:36.136 --> 00:07:39.196 A:middle
So here we have,
we'll do chlorine.

00:07:39.196 --> 00:07:43.666 A:middle
Here's chlorine in its
pure form, so it's neutral,

00:07:44.366 --> 00:07:47.836 A:middle
and then we've learned,
right, that chlorine

00:07:47.836 --> 00:07:50.566 A:middle
when it reduces,
it forms chloride.

00:07:51.046 --> 00:07:56.606 A:middle
Right? But because of the 2
here, we actually have to allow,

00:07:56.606 --> 00:07:59.966 A:middle
we have to count
the atoms, and so,

00:08:00.166 --> 00:08:01.936 A:middle
to balance the charge, right?

00:08:01.936 --> 00:08:04.136 A:middle
Of our neutral chlorine
molecule,

00:08:04.836 --> 00:08:09.096 A:middle
forms 2 chlorine anions.

00:08:09.096 --> 00:08:12.936 A:middle
We are going to have
to gain 2 electrons.

00:08:14.026 --> 00:08:15.976 A:middle
All right?

00:08:16.226 --> 00:08:18.076 A:middle
And once again, right?

00:08:18.076 --> 00:08:21.236 A:middle
The charge is going to
balance, because we have zero

00:08:21.956 --> 00:08:26.576 A:middle
and then we would have minus
2 equals minus 2, right?

00:08:26.826 --> 00:08:28.846 A:middle
Because we have 2
chlorides altogether.

00:08:30.426 --> 00:08:32.486 A:middle
Right? The 2 in front
says we have 2.

00:08:33.356 --> 00:08:35.376 A:middle
Alrighty. Okay.

00:08:35.926 --> 00:08:40.306 A:middle
So there is the basics of
oxidation and reduction.

00:08:40.796 --> 00:08:44.146 A:middle
So now let's put this
altogether and practice it a bit

00:08:44.146 --> 00:08:46.186 A:middle
to make sure we understand
what's going on.

00:08:46.696 --> 00:08:49.576 A:middle
All right.

00:08:49.856 --> 00:08:54.966 A:middle
So, as I mentioned, whether the
electrons are gained or lost,

00:08:55.106 --> 00:08:57.406 A:middle
they are always added
to the reaction.

00:08:58.686 --> 00:09:03.936 A:middle
So, gained electrons, right,
appear on the reactant side.

00:09:04.756 --> 00:09:12.106 A:middle
So if we had copper, 2 plus,
and it gained 1 electron,

00:09:13.096 --> 00:09:16.986 A:middle
it would go to copper
plus, right?

00:09:17.096 --> 00:09:18.656 A:middle
So there's our reduction.

00:09:20.576 --> 00:09:25.126 A:middle
And just making a plug for those
variable charge metals here,

00:09:25.496 --> 00:09:25.976 A:middle
right?

00:09:26.446 --> 00:09:29.286 A:middle
Has to have, copper 2 has
to have the Roman numeral,

00:09:29.826 --> 00:09:34.676 A:middle
because it can exist in more
than one oxidation state.

00:09:34.786 --> 00:09:37.526 A:middle
So even though this is
reduction, oxidation

00:09:37.526 --> 00:09:41.386 A:middle
and reduction go together, so
we call them oxidation states.

00:09:41.786 --> 00:09:45.456 A:middle
And then the loss
of electrons, right?

00:09:45.716 --> 00:09:47.786 A:middle
Appears on the product side.

00:09:47.856 --> 00:09:50.336 A:middle
So let's look at an
oxidation reaction.

00:09:52.036 --> 00:10:00.286 A:middle
So if we had iron 2 plus,
oxidizing to iron 3 plus, right?

00:10:00.416 --> 00:10:02.496 A:middle
There's our lost electron,

00:10:02.766 --> 00:10:08.716 A:middle
and we've already named
those on the previous page.

00:10:08.836 --> 00:10:09.256 A:middle
All right.

00:10:09.676 --> 00:10:12.046 A:middle
So this would be a good
place to pause the video

00:10:12.446 --> 00:10:15.866 A:middle
and answer these next set
of questions, on your own,

00:10:16.196 --> 00:10:20.496 A:middle
and then restart the video
and see how you're doing.

00:10:21.046 --> 00:10:24.106 A:middle
What we want to do is we want
to add the correct number

00:10:24.106 --> 00:10:26.966 A:middle
of electrons to either the
reactant or the product side.

00:10:27.226 --> 00:10:29.676 A:middle
I left a big gap, so
try not to give it away.

00:10:30.806 --> 00:10:33.716 A:middle
Classify the reactions as
oxidation or reduction,

00:10:33.716 --> 00:10:36.696 A:middle
and then for our ions,

00:10:36.696 --> 00:10:38.866 A:middle
let's just practice
our ion nomenclature.

00:10:39.236 --> 00:10:41.496 A:middle
All right, so I'll give
you a minute to pause.

00:10:46.896 --> 00:10:48.366 A:middle
All right, let's
see how you did.

00:10:49.076 --> 00:10:53.966 A:middle
Okay. So step 1, add the correct
number of electrons, right?

00:10:54.056 --> 00:10:55.926 A:middle
So, remembering that
electrons, right?

00:10:56.286 --> 00:10:59.796 A:middle
Electrons are negative,
so if we have a zero,

00:10:59.796 --> 00:11:01.336 A:middle
and a positive, right?

00:11:01.336 --> 00:11:05.256 A:middle
We're going to have to add
2 electrons to the right,

00:11:05.256 --> 00:11:08.616 A:middle
so these are the lost electrons.

00:11:09.146 --> 00:11:13.146 A:middle
So since they're lost electrons,
this is an oxidation reaction,

00:11:14.156 --> 00:11:17.716 A:middle
and then this would
be a magnesium ion.

00:11:20.136 --> 00:11:26.606 A:middle
Okay. Now let's look
at the next one.

00:11:27.386 --> 00:11:31.736 A:middle
Here is nitrogen, and
now we have nitride.

00:11:31.736 --> 00:11:36.286 A:middle
So we have zero on the left, and
we have minus 3 on the right,

00:11:36.286 --> 00:11:37.996 A:middle
I have two of them, minus 6.

00:11:38.116 --> 00:11:41.466 A:middle
So overall, there's minus
6 on the right hand side,

00:11:41.466 --> 00:11:44.216 A:middle
and there's zero on
the left hand side.

00:11:44.576 --> 00:11:47.476 A:middle
So we are going to have
to add 6 electrons.

00:11:47.796 --> 00:11:52.816 A:middle
So here they were lost,
and here they're gained.

00:11:53.196 --> 00:11:54.756 A:middle
All right?

00:11:55.216 --> 00:11:58.436 A:middle
So gaining electrons,
GER, right?

00:11:58.436 --> 00:11:59.586 A:middle
That's reduction.

00:12:02.586 --> 00:12:06.476 A:middle
Okay. So the nitrogen
would gain 6 electrons

00:12:06.476 --> 00:12:11.386 A:middle
to make two nitride ions.

00:12:11.506 --> 00:12:15.826 A:middle
And when nitride, as
soon as we see the

00:12:15.946 --> 00:12:17.996 A:middle
"-ide" we know it's an ion.

00:12:23.286 --> 00:12:26.796 A:middle
[pen scratching] Okay, so
it's not so essential, right?

00:12:26.796 --> 00:12:30.806 A:middle
Here we have the magnesium
element and the magnesium ion.

00:12:31.066 --> 00:12:33.076 A:middle
So then it's important
to write "ion".

00:12:33.466 --> 00:12:34.966 A:middle
But as soon as we
have the suffix,

00:12:34.966 --> 00:12:37.126 A:middle
-ide, everyone will know.

00:12:37.566 --> 00:12:39.436 A:middle
Okay, let's look
at the last one.

00:12:40.366 --> 00:12:43.536 A:middle
Here we have chromium
6 and chromium 3.

00:12:43.796 --> 00:12:46.136 A:middle
So to balance the charge, right?

00:12:46.136 --> 00:12:47.986 A:middle
This has more positive,
so we would need

00:12:47.986 --> 00:12:50.126 A:middle
to add 3 electrons here.

00:12:50.886 --> 00:12:53.356 A:middle
So once again, we're
gaining electrons,

00:12:55.666 --> 00:13:02.636 A:middle
so gained electrons
is reduction, and last

00:13:02.826 --> 00:13:04.206 A:middle
but not least, just to kind

00:13:04.206 --> 00:13:07.986 A:middle
of really emphasize why we need
those Roman numerals, right?

00:13:08.056 --> 00:13:14.686 A:middle
So this would be chromium(VI)
and as soon as we write the

00:13:14.786 --> 00:13:16.536 A:middle
"VI", everybody knows
it's an ion,

00:13:16.536 --> 00:13:22.896 A:middle
and then here chromium
1, 2, 3; chromium(III).

00:13:22.896 --> 00:13:23.836 A:middle
All right?

00:13:23.876 --> 00:13:27.046 A:middle
So if there's a Roman numeral,
or a suffix, we don't have

00:13:27.046 --> 00:13:30.616 A:middle
to worry about saying "ion"
but for those fixed charge,

00:13:30.856 --> 00:13:33.436 A:middle
it's good for clarity.

00:13:33.436 --> 00:13:36.446 A:middle
Okay, so that finishes
up our introduction

00:13:36.446 --> 00:13:38.626 A:middle
to oxidation and reduction.

00:13:39.016 --> 00:13:40.396 A:middle
Now would be a great time

00:13:40.396 --> 00:13:42.546 A:middle
to work a couple
post-video practice problems

00:13:42.546 --> 00:13:44.096 A:middle
to reinforce your understanding.