0:00:00.000,0:00:00.660


0:00:00.660,0:00:03.420
Throughout our journey through[br]chemistry so far, we've

0:00:03.420,0:00:08.810
touched on the interactions[br]between molecules, metal

0:00:08.810,0:00:11.290
molecules, how they attract each[br]other because of the sea

0:00:11.290,0:00:12.665
of electrons and water[br]molecules.

0:00:12.665,0:00:16.545
But I think it's good to have a[br]general discussion about all

0:00:16.545,0:00:19.100
of the different types of[br]molecular interactions and

0:00:19.100,0:00:21.860
what it means for the boiling[br]points or the melting points

0:00:21.860,0:00:22.890
of a substance.

0:00:22.890,0:00:24.870
So I'll start with the weakest.[br]Let's say I had a

0:00:24.870,0:00:26.120
bunch of helium.

0:00:26.120,0:00:30.100
Helium, you know, I'll just draw[br]it as helium atoms. We'll

0:00:30.100,0:00:33.150
look in the Periodic Table, and[br]what I'm going to do now

0:00:33.150,0:00:35.360
with helium I could do with[br]any of the noble gases.

0:00:35.360,0:00:37.860
Because the point is that[br]noble gases are happy.

0:00:37.860,0:00:39.275
Their outer orbital is filled.

0:00:39.275,0:00:41.590
Let's say, neon or helium--[br]let me do neon, actually,

0:00:41.590,0:00:45.210
because neon has a full eight[br]in its orbital so we could

0:00:45.210,0:00:49.750
write neon like neon and[br]it's completely happy.

0:00:49.750,0:00:53.600
It's completely satisfied[br]with itself.

0:00:53.600,0:00:57.950
And so in a world where it's[br]completely satisfied, there's

0:00:57.950,0:01:00.630
no obvious reason just yet-- I'm[br]going to touch on a reason

0:01:00.630,0:01:02.850
why it should be-- if these[br]electrons are evenly

0:01:02.850,0:01:04.920
distributed around these[br]atoms, then these are

0:01:04.920,0:01:08.040
completely neutral atoms. They[br]don't want to bond with each

0:01:08.040,0:01:11.080
other or do anything else, so[br]they should just float around

0:01:11.080,0:01:13.310
and there's no reason for them[br]to be attracted to each other

0:01:13.310,0:01:15.100
or not attracted[br]to each other.

0:01:15.100,0:01:18.370
But it turns out that neon does[br]have a liquid state, if

0:01:18.370,0:01:21.230
you get cold enough, and so the[br]fact that it has a liquid

0:01:21.230,0:01:26.820
state means that there must be[br]some force that's making the

0:01:26.820,0:01:31.060
neon atoms attracted to each[br]other, some force out there.

0:01:31.060,0:01:33.260
Because it's in a very cold[br]state, because for the most

0:01:33.260,0:01:35.430
part, there is not a lot of[br]force that attracts them so

0:01:35.430,0:01:37.210
it'll be a gas at most[br]temperatures.

0:01:37.210,0:01:40.570
But if you get really cold, you[br]can get a very weak force

0:01:40.570,0:01:44.130
that starts to connect or makes[br]the neon molecules want

0:01:44.130,0:01:46.240
to get towards each other.

0:01:46.240,0:01:49.160
And that force comes out of[br]the reality that we talked

0:01:49.160,0:01:53.950
about early on that electrons[br]are not in a fixed, uniform

0:01:53.950,0:01:54.990
orbit around things.

0:01:54.990,0:01:56.240
They're probablistic.

0:01:56.240,0:02:00.420
And if we imagine, let me say[br]neon now, instead of drawing

0:02:00.420,0:02:04.090
these nice and neat valence[br]dot electrons like that,

0:02:04.090,0:02:07.760
instead, I can kind of draw[br]its electrons as-- it's a

0:02:07.760,0:02:11.060
probability cloud and it's[br]what neon's atomic

0:02:11.060,0:02:12.420
configuration is.

0:02:12.420,0:02:18.630
1s2 and it's outer orbital[br]is 2s2 2p6, right?

0:02:18.630,0:02:20.547
So it's highest energy electron,[br]so, you know, it'll

0:02:20.547,0:02:21.580
look-- I don't know.

0:02:21.580,0:02:24.560
It has the 2s shell.

0:02:24.560,0:02:28.110
The 1s shell is inside of that[br]and it has the p-orbitals.

0:02:28.110,0:02:32.160
The p-orbitals look like that[br]in different dimensions.

0:02:32.160,0:02:33.130
That's not the point.

0:02:33.130,0:02:36.680
And then you have another neon[br]atom and these are-- and I'm

0:02:36.680,0:02:38.550
just drawing the probability[br]distribution.

0:02:38.550,0:02:40.350
I'm not trying to[br]draw a rabbit.

0:02:40.350,0:02:42.250
But I think you get the point.

0:02:42.250,0:02:46.620
Watch the electron configuration[br]videos if you

0:02:46.620,0:02:49.440
want more on this, but the idea[br]behind these probability

0:02:49.440,0:02:53.390
distributions is that the[br]electrons could be anywhere.

0:02:53.390,0:02:54.960
There could be a moment in time[br]when all the electrons

0:02:54.960,0:02:55.940
are out over here.

0:02:55.940,0:02:57.330
There could be a moment in time[br]where all the electrons

0:02:57.330,0:02:57.810
are over here.

0:02:57.810,0:02:59.510
Same thing for this neon atom.

0:02:59.510,0:03:01.590
If you think about it, out[br]of all of the possible

0:03:01.590,0:03:04.690
configurations, let's say we[br]have these two neon atoms,

0:03:04.690,0:03:07.290
there's actually a very low[br]likelihood that they're going

0:03:07.290,0:03:09.065
to be completely evenly[br]distributed.

0:03:09.065,0:03:11.760


0:03:11.760,0:03:13.770
There's many more scenarios[br]where the electron

0:03:13.770,0:03:15.560
distribution is a little[br]uneven in one

0:03:15.560,0:03:16.530
neon atom or another.

0:03:16.530,0:03:20.080
So if in this neon atom,[br]temporarily its eight valence

0:03:20.080,0:03:24.230
electrons just happen to be[br]like, you know, one, two,

0:03:24.230,0:03:28.710
three, four, five, six, seven,[br]eight, then what does this

0:03:28.710,0:03:29.540
neon atom look like?

0:03:29.540,0:03:32.240
It temporarily has a[br]slight charge in

0:03:32.240,0:03:33.120
this direction, right?

0:03:33.120,0:03:36.770
It'll feel like this side is[br]more negative than this side

0:03:36.770,0:03:39.170
or this side is more positive[br]than that side.

0:03:39.170,0:03:45.000
Similarly, if at that very same[br]moment I had another neon

0:03:45.000,0:03:49.710
that had one, two, three, four,[br]five, six, seven, eight,

0:03:49.710,0:03:52.940
that had a similar-- actually,[br]let me do that differently.

0:03:52.940,0:03:56.650
Let's say that this neon atom is[br]like this: one, two, three,

0:03:56.650,0:04:00.930
four, five, six, seven, eight.

0:04:00.930,0:04:04.620
So here, and I'll do it in a[br]dark color because it's a very

0:04:04.620,0:04:05.330
faint force.

0:04:05.330,0:04:06.500
So this would be a[br]little negative.

0:04:06.500,0:04:10.055
Temporarly, just for that single[br]moment in time, this

0:04:10.055,0:04:11.130
will be kind of negative.

0:04:11.130,0:04:12.400
That'll be positive.

0:04:12.400,0:04:14.530
This side will be negative.

0:04:14.530,0:04:16.019
This side will be positive.

0:04:16.019,0:04:18.399
So you're going to have a little[br]bit of an attraction

0:04:18.399,0:04:21.910
for that very small moment of[br]time between this neon and

0:04:21.910,0:04:23.340
this neon, and then it'll[br]disappear, because the

0:04:23.340,0:04:25.160
electrons will reconfigure.

0:04:25.160,0:04:29.150
But the important thing to[br]realize is that almost at no

0:04:29.150,0:04:31.580
point is neon's electrons[br]going to be completely

0:04:31.580,0:04:32.140
distributed.

0:04:32.140,0:04:34.460
So as long as there's always[br]going to be this haphazard

0:04:34.460,0:04:37.760
distribution, there's always[br]going to be a little bit of

0:04:37.760,0:04:40.910
a-- I don't want to say polar[br]behavior, because that's

0:04:40.910,0:04:42.285
almost too strong of a word.

0:04:42.285,0:04:45.360
But there will always be a[br]little bit of an extra charge

0:04:45.360,0:04:47.850
on one side or the other side[br]of an atom, which will allow

0:04:47.850,0:04:50.750
it to attract it to the opposite[br]side charges of other

0:04:50.750,0:04:53.040
similarly imbalanced[br]molecules.

0:04:53.040,0:04:55.510
And this is a very, very,[br]very weak force.

0:04:55.510,0:04:59.040
It's called the London[br]dispersion force.

0:04:59.040,0:05:01.500
I think the guy who came up with[br]this, Fritz London, who

0:05:01.500,0:05:05.120
was neither-- well, he[br]was not British.

0:05:05.120,0:05:06.470
I think he was German-American.

0:05:06.470,0:05:12.925
London dispersion force, and[br]it's the weakest of the van

0:05:12.925,0:05:14.175
der Waals forces.

0:05:14.175,0:05:18.980


0:05:18.980,0:05:20.810
I'm sure I'm not pronouncing[br]it correctly.

0:05:20.810,0:05:23.890
And the van der Waals forces[br]are the class of all of the

0:05:23.890,0:05:26.490
intermolecular, and in[br]this case, neon-- the

0:05:26.490,0:05:27.670
molecule, is an atom .

0:05:27.670,0:05:30.040
It's just a one-atom molecule,[br]I guess you could say.

0:05:30.040,0:05:32.760
The van der Waals forces are[br]the class of all of the

0:05:32.760,0:05:36.010
intermolecular forces that are[br]not covalent bonds and that

0:05:36.010,0:05:38.647
aren't ionic bonds like we have[br]in salts, and we'll touch

0:05:38.647,0:05:39.230
on those in a second.

0:05:39.230,0:05:42.260
And the weakest of them are the[br]London dispersion forces.

0:05:42.260,0:05:45.290
So neon, these noble gases,[br]actually, all of these noble

0:05:45.290,0:05:48.800
gases right here, the only thing[br]that they experience are

0:05:48.800,0:05:51.940
London dispersion forces, which[br]are the weakest of all

0:05:51.940,0:05:53.920
of the intermolecular forces.

0:05:53.920,0:05:57.190
And because of that, it takes[br]very little energy to get them

0:05:57.190,0:05:59.460
into a gaseous state.

0:05:59.460,0:06:05.520
So at a very, very low[br]temperature, the noble gases

0:06:05.520,0:06:07.140
will turn into the[br]gaseous state.

0:06:07.140,0:06:09.670
That's why they're called noble[br]gases, first of all.

0:06:09.670,0:06:13.920
And they're the most likely[br]to behave like ideal gases

0:06:13.920,0:06:15.820
because they have[br]very, very small

0:06:15.820,0:06:17.550
attraction to each other.

0:06:17.550,0:06:18.500
Fair enough.

0:06:18.500,0:06:20.880
Now, what happens when we go[br]to situations when we go to

0:06:20.880,0:06:24.230
molecules that have better[br]attractions or that are a

0:06:24.230,0:06:25.290
little bit more polar?

0:06:25.290,0:06:27.670
Let's say I had hydrogen[br]chloride, right?

0:06:27.670,0:06:30.480
Hydrogen, it's a little bit[br]ambivalent about whether or

0:06:30.480,0:06:31.660
not it keeps its electrons.

0:06:31.660,0:06:35.180
Chloride wants to keep[br]the electrons.

0:06:35.180,0:06:37.250
Chloride's quite[br]electronegative.

0:06:37.250,0:06:39.590
It's less electronegative than[br]these guys right here.

0:06:39.590,0:06:42.710
These are kind of the[br]super-duper electron hogs,

0:06:42.710,0:06:46.340
nitrogen, oxygen, and fluorine,[br]but chlorine is

0:06:46.340,0:06:47.650
pretty electronegative.

0:06:47.650,0:06:50.940
So if I have hydrogen chloride,[br]so I have the

0:06:50.940,0:06:57.200
chlorine atom right here, it has[br]seven electrons and then

0:06:57.200,0:07:00.210
it shares an electron[br]with the hydrogen.

0:07:00.210,0:07:02.076
It shares an electron with[br]the hydrogen, and I'll

0:07:02.076,0:07:03.410
just do it like that.

0:07:03.410,0:07:05.710
Because this is a good bit[br]more electronegative than

0:07:05.710,0:07:09.320
hydrogen, the electrons spend[br]a lot of time out here.

0:07:09.320,0:07:12.950
So what you end up having is a[br]partial negative charge on the

0:07:12.950,0:07:14.740
side, where the electron[br]hog is, and a

0:07:14.740,0:07:17.270
partial positive side.

0:07:17.270,0:07:18.860
And this is actually[br]very analogous to

0:07:18.860,0:07:19.870
the hydrogen bonds.

0:07:19.870,0:07:22.710
Hydrogen bonds are actually a[br]class of this type of bond,

0:07:22.710,0:07:25.945
which is called a dipole bond,[br]or dipole-dipole interaction.

0:07:25.945,0:07:28.670
So if I have one chlorine atom[br]like that and if I have

0:07:28.670,0:07:31.700
another chlorine atom,[br]the other chlorine

0:07:31.700,0:07:33.732
atoms looks like this.

0:07:33.732,0:07:37.480
If I have the other chlorine[br]atom-- let me copy and paste

0:07:37.480,0:07:41.650
it-- right there, then[br]you'll have this

0:07:41.650,0:07:44.320
attraction between them.

0:07:44.320,0:07:47.440
You'll have this attraction[br]between these two chlorine

0:07:47.440,0:07:49.490
atoms-- oh, sorry,[br]between these two

0:07:49.490,0:07:51.930
hydrogen chloride molecules.

0:07:51.930,0:07:57.120
And the positive side, the[br]positive pole of this dipole

0:07:57.120,0:07:59.410
is the hydrogen side, because[br]the electrons have kind of

0:07:59.410,0:08:02.600
left it, will be attracted[br]to the chlorine side

0:08:02.600,0:08:04.030
of the other molecules.

0:08:04.030,0:08:07.590
And because this van der Waals[br]force, this dipole-dipole

0:08:07.590,0:08:11.790
interaction is stronger than[br]a London dispersion force.

0:08:11.790,0:08:14.540
And just to be clear, London[br]dispersion forces occur in all

0:08:14.540,0:08:15.960
molecular interactions.

0:08:15.960,0:08:18.630
It's just that it's very weak[br]when you compare it to pretty

0:08:18.630,0:08:19.570
much anything else.

0:08:19.570,0:08:22.810
It only becomes relevant when[br]you talk about things with

0:08:22.810,0:08:23.810
noble gases.

0:08:23.810,0:08:26.960
Even here, they're also London[br]dispersion forces when the

0:08:26.960,0:08:29.360
electron distribution just[br]happens to go one way or the

0:08:29.360,0:08:31.390
other for a single[br]instant of time.

0:08:31.390,0:08:34.190
But this dipole-dipole[br]interaction is much stronger.

0:08:34.190,0:08:38.130
And because it's much stronger,[br]hydrogen chloride is

0:08:38.130,0:08:40.700
going to take more energy to,[br]one, get into the liquid

0:08:40.700,0:08:44.450
state, or even more, get into[br]the gaseous state than, say,

0:08:44.450,0:08:47.530
just a sample of helium gas.

0:08:47.530,0:08:49.700
Now, when you get even more[br]electronegative, when this

0:08:49.700,0:08:51.220
guy's even more electronegative[br]when you're

0:08:51.220,0:08:54.920
dealing with nitrogen, oxygen[br]or fluorine, you get into a

0:08:54.920,0:08:58.720
special case of dipole-dipole[br]interactions, and that's the

0:08:58.720,0:09:00.590
hydrogen bond.

0:09:00.590,0:09:06.480
So it's really the same thing if[br]you have hydrogen fluoride,

0:09:06.480,0:09:12.140
a bunch of hydrogen fluorides[br]around the place.

0:09:12.140,0:09:16.180
Maybe I could write fluoride,[br]and I'll write hydrogen

0:09:16.180,0:09:17.100
fluoride here.

0:09:17.100,0:09:19.030
Fluoride its[br]ultra-electronegative.

0:09:19.030,0:09:23.220
It's one of the three most[br]electronegative atoms on the

0:09:23.220,0:09:27.950
Periodic Table, and[br]so it pretty much

0:09:27.950,0:09:30.290
hogs all of the electrons.

0:09:30.290,0:09:35.080
So this is a super-strong case[br]of the dipole-dipole

0:09:35.080,0:09:37.920
interaction, where here, all of[br]the electrons are going to

0:09:37.920,0:09:40.110
be hogged around the[br]fluorine side.

0:09:40.110,0:09:42.180
So you're going to have a[br]partial positive charge,

0:09:42.180,0:09:46.270
partial negative side, partial[br]positive, partial negative,

0:09:46.270,0:09:49.105
partial positive, partial[br]negative and so on.

0:09:49.105,0:09:52.830
So you're going to have this,[br]which is really a dipole

0:09:52.830,0:09:53.430
interaction.

0:09:53.430,0:09:55.990
But it's a very strong dipole[br]interaction, so people call it

0:09:55.990,0:09:59.470
a hydrogen bond because it's[br]dealing with hydrogen and a

0:09:59.470,0:10:02.640
very electronegative atom, where[br]the electronegative atom

0:10:02.640,0:10:05.690
is pretty much hogging all of[br]hydrogen's one electron.

0:10:05.690,0:10:07.720
So hydrogen is sitting out here[br]with just a proton, so

0:10:07.720,0:10:09.560
it's going to be pretty[br]positive, and it's really

0:10:09.560,0:10:12.660
attracted to the negative[br]side of these molecules.

0:10:12.660,0:10:16.530
But hydrogen, all of these[br]are van der Waals.

0:10:16.530,0:10:19.700
So van der Waals, the weakest[br]is London dispersion.

0:10:19.700,0:10:24.610
Then if you have a molecule with[br]a more electronegative

0:10:24.610,0:10:27.900
atom, then you start having a[br]dipole, where you have one

0:10:27.900,0:10:31.330
side where molecule becomes[br]polar and you have the

0:10:31.330,0:10:33.290
interaction between the positive[br]and the negative side

0:10:33.290,0:10:33.670
of the pole.

0:10:33.670,0:10:36.020
It gets a dipole-dipole[br]interaction.

0:10:36.020,0:10:39.390
And then an even stronger type[br]of bond is a hydrogen bond

0:10:39.390,0:10:41.780
because the[br]super-electronegative atom is

0:10:41.780,0:10:44.670
essentially stripping off the[br]electron of the hydrogen, or

0:10:44.670,0:10:46.060
almost stripping it off.

0:10:46.060,0:10:47.250
It's still shared,[br]but it's all on

0:10:47.250,0:10:49.420
that side of the molecule.

0:10:49.420,0:10:51.940
Since this is even a stronger[br]bond between molecules, it

0:10:51.940,0:10:53.660
will have even a higher[br]boiling point.

0:10:53.660,0:11:01.380
So London dispersion, and you[br]have dipole or polar bonds,

0:11:01.380,0:11:06.370
and then you have[br]hydrogen bonds.

0:11:06.370,0:11:09.310
All of these are van der[br]Waals, but because the

0:11:09.310,0:11:13.360
strength of the intermolecular[br]bond gets stronger, boiling

0:11:13.360,0:11:18.300
point goes up because it takes[br]more and more energy to

0:11:18.300,0:11:21.390
separate these from[br]each other.

0:11:21.390,0:11:23.190
In the next video-- I realize[br]I'm out of time.

0:11:23.190,0:11:26.040
So this is a good survey, I[br]think, of just the different

0:11:26.040,0:11:28.370
types of intermolecular[br]interactions that aren't

0:11:28.370,0:11:29.950
necessarily covalent or ionic.

0:11:29.950,0:11:32.360
In the next video, I'll talk[br]about some of the covalent and

0:11:32.360,0:11:35.900
ionic types of structures that[br]can be formed and how that

0:11:35.900,0:11:38.900
might affect the different[br]boiling points.