Intermolecular Potential Energy Bozeman Science English (auto-generated) English

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[Music] hi it's mr. Andersen and this is

chemistry essentials video 54 which is

Hi. It's Mr. Andersen and this is chemistry essentials video 54 which is on intermolecular

on intermolecular potential energy this is a famous macro molecule right here it's DNA and every bond you see is a

potential energy. This is a famous macromolecule right here. It's DNA. And every bond that

covalent bond where you're sharing electrons between atoms but it's a

you see is a covalent bond where you're sharing electrons between atoms. But it's a double

double helix and what that really means is it's a double molecule there are two

helix. And what that really means is it's a double molecule. There are two molecules.

molecules and in the middle they're held together with intermolecular forces

And in the middle they're held together with intermolecular forces. Those are going to

those are going to be hydrogen bonds or dipole-dipole forces which are going to hold those two chains together and so

be hydrogen bonds or dipole-dipole forces which are going to hold those two chains together.

really it's easy to pull DNA apart and for it to zip right back together again

And so really it's easy to pull DNA apart and for it to zip right back together again.

and so we really want to make sure you understand the difference between an

And so we really want to make sure you understand the difference between an intermolecular and

intermolecular and intramolecular an intermolecular is going to be between adjacent molecules between the yellow

intramolecular. An intermolecular is going to be between adjacent molecules. Between

and the yellow and so that would be for example between water and another water

the yellow and the yellow. And so that would be for example between water and another water

molecule what are the intramolecular those are going to be the bonds those

molecule. What are the intramolecular? Those are going to be the bonds. Those are going

are going to be those covalent or ionic bonds that are actually between the atoms within the molecule itself and so

to be those covalent or ionic bonds that are actually between the atoms within the molecule

we're not dealing with bonds in this video we're dealing with those forces

itself. And so we're not dealing with bonds in this video. We're dealing with those forces

between molecules and those forces are based on what those molecules are we can

between molecules. And those forces are based on what those molecules are. We can have an

have an attraction between a dipole and a dipole we can have an attraction

attraction between a dipole and a dipole. We can have an attraction between a dipole

between a dipole and an induced dipole and then also between induced dipoles

and an induced dipole. And then also between induced dipoles. And between each of these

and between each of these there's going to be potential energy in those intermolecular forces it's going to take

there's going to be potential energy in those intermolecular forces. It's going to take

energy to pull those apart and so an example of a dipole dipole would be a hydrogen bond and so what we're doing

energy to pull those apart. And so an example of a dipole-dipole would be a hydrogen bond.

there is we're taking hydrogen atoms of

And so what we're doing there is we're taking hydrogen atoms of one molecule and they're

one molecule and they're being attracted to oxygen nitrogen and fluorine atoms of another molecule and those are both

being attracted to oxygen, nitrogen and fluorine atoms of another molecule. And those are both

dipoles and so what we're getting is an attraction between those two those

dipoles. And so what we're getting is an attraction between those two. Those aren't of the same

aren't of the same molecule they're just holding those two molecules together if we look at between two induced dipoles

molecule. They're just holding those two molecules together. If we look at between a dipole and

that could be for example between argon

an induced dipole that could be for example between argon which normally doesn't have

which normally doesn't have a charge but can get a charge if we hold something like hydrochloric acid right next to it

a charge but can get a charge if we hold something like hydrochloric acid right next to it. And

and then finally we could have two induced dipoles an example of the forces

then finally we could have two induced dipoles. And an example of the forces between those

between those are going to be dispersion forces what are induced dipoles they're

are going to be dispersion forces. What are induced dipoles? They're everything. So there's

everything so there's a force between every and those are called dispersion forces

a force between everything and those are called dispersion forces. And they're based or the

and they're based or the strength of them is based on the number of electrons that you have the more electrons the

strength of them is based on the number of electrons that you have. The more electrons,

more dispersion forces we can have and also the surface area in contact between

the more dispersion forces we could have. And also the surface area and contact between

those two molecules so again in review what is a dipole it's simply a molecule

those two molecules. So again, in review, what is a dipole? It's simply a molecule that

that has uneven distribution of electrons and so if we look at water as

has uneven distribution of electrons. And so if we're to look at water as an example,

an example the oxygen loves those electrons it's highly electronegative so

the oxygen loves those electrons. It's highly electronegative so it's pulling it towards

it's pulling it towards it and so there's going to be a slightly negative charge on this side and a positive

it. And so there's going to be a slightly negative charge on this side. And a positive

charge on the other side of the water molecule it's a dipole if you look at

charge on the other side of the water molecule. It's a dipole. If you look at hydrochloric

hydrochloric acid the same thing here the electrons are going to be pulled toward the chlorine atom and so it's

acid, the same thing here. The electrons are going to be pulled toward the chlorine atoms.

going to have a negative charge right here and a positive charge on the other

And so it's going to have a negative charge right here and a positive charge on the other

side now these two negatives are going to push on each other and so what would a dipole dipole bond look like it's

side. Now these two negatives are going to push on each other and so what would a dipole-dipole

going to be looking like this or rather a force is going to look like that and

bond look like? It's going to be looking like this. Or rather a force is going to look like

it's going to hold those two molecules together but again it's not a bond

that. And it's going to hold those two molecules together. But again it's not a bond between

between the two hydrogen bond is a great example of a dipole dipole force if we

the two. Hydrogen bond is a great example of a dipole-dipole force. If we were to take

were to take water molecules like this you can see that all of their oxygens

water molecules like this, you can see that all of their oxygens are going to have negative

are going to have negative charges and so that's not how it's going to line up in a hydrogen bond the way it would line

charges. And so that's not how it's going to line up. In a hydrogen bond the way it

up would be like this and so we now have an attraction between this hydrogen and

would line up would be like this. And so we now have an attraction between this hydrogen

this oxygen this would be a hydrogen bond right here there'd be another

and this oxygen. This would be a hydrogen bond right here. There would be another hydrogen

hydrogen bond right here another hydrogen bond right here another hydrogen bond right here now a point of

bond right here. Another hydrogen bond right here. Another hydrogen bond right here. Now

confusion remember is that it's not in

a point of confusion remember is that it's not in the same molecule. It's going to be

the same molecule it's going to be between a hydrogen of one molecule and then either nitrogen oxygen or fluorine

between a hydrogen of one molecule and then either nitrogen, oxygen or fluorine of another

of another molecule now this is a huge amount of energy that's held in this and

molecule. Now this is a huge amount of energy that's held in this. And let me give you an

let me give you an example of that what we're looking at now is the boiling point of four different molecules and so

example of that. What we're looking at now is the boiling point of four different molecules.

we'll start right here with hydrogen Telluride that's h2 te and if we look at

And so we'll start right here with hydrogen telluride. That's H2Te. And if we look at

its molecular mass it's over here and then its temperature a boiling point is

its molecular mass, it's over here. And then its temperature of boiling point is going

going to be a little less than zero degrees and so if I go to the next one

to be a little less than zero degrees. And so if I go to the next one up in that group,

up in that group we've got hydrogen selenide and so we can see here that we have a decrease in the molecular mass

we've got hydrogen selenide. And so we can see here that we have decrease in the molecular

and we also have a decrease in the boiling point if we go to the next one

mass. And we also have a decrease in the boiling point. If we go to the next one, hydrogen

hydrogen sulfide you can see that there's a really well-established pattern right here as we move to smaller

sulfide, you can see that there's a really well established pattern right here. As we

atoms we're getting less molecular mass and we're also getting a lower boy

move to smaller atoms we're getting less molecular mass. And we're also getting a lower boiling

so what's going to be the next one if we

point. So what's going to be the next one if we go through this pattern? It's going

go through this pattern it's going to be h2o so that's going to be water could you predict where that's going to be

to be H20. So that's going to be water. Could you predict where that's going to be? Well

well you might think it's going to be something like this but it actually is

you might think it's going to be something like this. But it actually is way up here.

way up here why is that because there's all these hydrogen bonds between the

Why is that? Because there's all of these hydrogen bonds between the water molecules.

water molecules and so it really takes a lot of energy to break those apart and

And so it really takes a lot of energy to break those apart and to boil that water.

to boil that water thankfully that's why we're filled with water so our temperature doesn't change that much so

Thankfully that's why we're filled with water. So our temperature doesn't change that much.

what's a dipole induced dipole force well if we have hydrochloric acid and

So what's a dipole-induced dipole force? Well if we have hydrochloric acid and argon mixed

argon mixed together what we'll find is that this argon doesn't have a charge but if we pull it close to a dipole what

together what we'll find is that this argon doesn't have a charge. But if we pull it close

it'll do is it'll actually pull those electrons towards it and so what you get

to a dipole what it will do is it will actually pull those electrons towards it. And so what

is an induced dipole and so this is a force that's holding them together since

you get is an induced dipole. And so this is a force that's holding them together. Since

there are more electrons on this side it has a partial negative charge right here

there are more electrons on this side it has a partial negative charge right here. Now

now how are we going to measure the strength of that bond it's based on two

how are we going to measure the strength of that bond? It's based on two things. It's

things it's based on the strength of that dipole and it's also based on the

based on the strength of that dipole and it's also based on the polarizability, in other

polarizability in other words the number of electrons and how those electrons can be pulled of that induced dipole and

words the number of electrons and how those electrons can be pulled of that induced dipole.

sometimes we'll have molecules that can both form induced dipoles so right here

And sometimes we'll have molecules that can both form induced dipoles. So right here we

we have helium gas as it moves close to another helium atom you can see that

have helium gas. As it moves close to another helium atom you can see that there's an attraction

there's an attraction between the electron and the protons of the adjacent

between the electron and the protons of the adjacent atom. And there's also going to be

atom and there's also going to be repulsion between these electrons and so what we're creating is a temporary

repulsion between these electrons. And so what we're creating is a temporary dipole

dipole for just a fraction in time but it's still going to hold those things

for just a fraction in time. But it's still going to hold those things together. And so

together and so all molecules have these induced dipole to induce dipole forces

all molecules have these induced dipole to induced dipole forces. All molecules have

all molecules have this attraction between them what's going to increase

this attraction between them. What's going to increase that attraction? It's simply going

that attraction it's simply going to be the number of electrons that we have and the surface area and so this is a

to be the number of electrons that we have and the surface area. So this is a picture

picture of a gecko that's climbing up glass and if you look at their foot

of a gecko that's climbing up glass. And if you look at their foot we're going to find

we're gonna find that there are folds and then if you zoom in on those folds

that there are folds. And then if you zoom in on those folds there's folds on the folds

there's folds on the folds on the folds and so how are they magically able to walk up a wall like this

on the folds. And so how are they magically able to walk up a wall like this? It's those

it's those attractions as dispersion forces between them and the wall and so

attractions. Those dispersion forces between them and the wall. And so as they increase

they've increased the surface area increasing the number of electrons and so we can have enough of an attraction

the surface area, increase the number electrons, and so we can have enough of an attraction

to actually hold them up and so did you learn to make claims or predictions

to actually hold them up. And so did you learn to make claims or predictions regarding these

regarding these intermolecular forces again it's based on what's holding them together is a dipole dipole dipole

intermolecular forces? Again it's based on what's holding them together. Is it dipole-dipole,

induced dipole or just induced dipoles these are all intermolecular forces and I hope that was [Music]

dipole-induced dipole or just induced dipoles. These are all intermolecular forces. And I

hope that was helpful.