Intermolecular Forces

before we can talk about the inter molecular forces realize that it is one of two major electrostatic forces, the other one being in truck molecular forces. All right, so, we have these two major electrostatic forces i. E. Attractive forces that exist. So in trump molecular exists within a molecule and they bond atoms together and they influence the chemical properties of those molecules. We're gonna say here this influences chemical bonds which we break down into ionic and co valent and realize that when it comes to intra molecular forces, they are stronger than inter molecular forces. Now, what exactly are inter molecular forces then? Well, these are the attractive forces that exist between molecules and they influence the physical properties. Now they hold liquid and solid molecules together so they are important. So if we take here a look at the visual representation of an intra molecular force versus an inter molecular force intra is inside the molecule. So here we're talking about the actual chemical bond between an oxygen atom and a hydrogen atom within water. In term molecular is always between molecules. So here we're talking about the attractive forces between two water molecules and in this image, why they attracted to one another. Well, remember electro negativity, hydrogen are less electro negative. So it's partially positive oxygen is more electro negative, so it's partially negative. Their differences in polarity make them attracted to one another. And this dotted line shows that attractive force. So realize that an intra molecular force is the literal bond between atoms and inter molecular force is not an actual bond. You'll see that it's shown as a dotted line, symbolizing an attraction between molecules, not a literal bonds between molecules.

which forces our intro molecular and which are inter molecular Alright those along silver to tarnish. All right. The reason silver tarnishes and certain metals tarnish become rusty looking is because they're actually reacting with the oxygen in the air. If we're talking about the reaction between elements which changes the appearance of that element, we're talking about a chemical reaction which is connected to chemical properties. So that would mean that we're dealing with an in trump molecular force. Next those preventing butter from melting in a refrigerator melting is a physical change that happened where we're going from a liquid where we're going from a solid to a liquid. Physical changes are connected to physical properties and those are connected to inter molecular forces. Those preventing oil from evaporating at room temperature. Again, evaporation is another example of of physical change where we're going from a liquid to a gas. Physical changes are connected to physical properties and therefore connected to the inter molecular forces. Then finally those preventing oxygen in air from forming oxygen atoms. So we're changing 02 and O. That means we are breaking chemical bonds. Chemical bonds are the bonds within molecules within molecules. Means that we're dealing with in trump molecular forces. So just remember intra molecular are within they affect chemical properties. They influence chemical changes in term molecular forces are the attractive forces between molecules. They affect physical properties and by extension physical changes can result

when talking about the types of inter molecular forces, realize that there are four types of them and they are the forces that attract molecules together. Now here we're going to say polarity of compounds plays a big role in the type of force present. So let's go through this. We have our types of forces. Then we have the exist between. We talk about their strengths and then we give an example. So the first time we have is ion dipole. This is the force that exists between ion so positive and negative ions and polar compounds. They are the strongest of the inter molecular forces. So anytime you see an ionic compound, you can assume that water is the solvent that it can be dissolved in. Okay, usually you'll see ionic compound with water but let's say you see only an ionic compound and they ask what's the inter molecular force. Just assume it's dissolved in water. When we dissolve sodium chloride and water, we have ions and a plus Equus and cl minus acquis remember a quiz, just means that ion is submerged in water. And what's actually happening is that we have our sodium ion here, which is positive. The oxygen end of water which is partially negative, would be attracted to it because opposite charges attract the attractive force would be illustrated by this dotted line. See all minus is negative. So it would be the hydrogen end of water that would be attracted to it because water would be partially positive here. And the attractive force between chlorine and hydrogen will be symbolized by that dotted line. So this is what we mean. When we say an ion is a quiz in solution, it's water molecules surrounding it, basically dissolving it. We're gonna say solving it. These are terms that we usually use. So i on diaper is the strongest force. It's indicative of an ionic compound being dissolved within a poor substance, such as water. The next one is hydrogen bonding. This is when we have compounds containing hydrogen directly connected to fund fon flooring, oxygen and nitrogen. So here this one is the second strongest after ion dipole. Here we have water and we have NH four. NH four is a poly atomic ion. It's NH four positive, it's the ammonium ion. We could show water molecules Being attracted to one another. Yeah. And the dotted lines show that attraction. Or we could show NH four positive molecules being attracted to one another. Or actually we can show them being attracted to the water. So hydrogen years partially positive oxygen and its lone pair would be attracted to one of these hydrogen. So it's those dotted lines between these molecules that represents the hydrogen bonding. But hydrogen bonding itself can't exist unless the molecule is showing an attractive force between hydrogen flooring oxygen or nitrogen. The next one is dipole dipole. Now, before we talk about diapering diaper realized that hydrogen bonding is a special type of dipole dipole. It's also dipole dipole itself is just hydrogen bonding type of dipole dipole. This is when you have two polar koval, it compounds? This one here is the third strongest of all the inter molecular forces. So here we have Hcl which is polar and S. O. To which is polar. And here we could show the attraction between them. So remember chlorine has its lone pairs, it's more electro negative than hydrogen. So it'll be partially negative, hydrogen will be partially positive Within S. 02. You could show the sulfur with its lone pairs, oxygen with its lone pairs, oxygen is more electro negative. So it be partially negative. It would form an attractive connection to the hydrogen of the hcl. That dotted line would be the dipole dipole interaction between these two molecules. And it could only happen because both molecules are polar. Finally, we have the last and the weakest inter molecular force which is called London dispersion. And sometimes it's called dispersion forces and sometimes it's called Van der Waals Forces. This is the dominant force between two non polar covalin compounds. Here we have CH four which is a hydrocarbon and here we have CCL four which is non polar as well. Now if you don't know this, make sure you go back and take a look at my videos on molecular polarity where we show how to draw these structures and explain why exactly they're non polar. So here you have CH four And here we have CCL four. Now both of these are non polar. So why exactly would they all of a sudden be attracted to one another? Well that's because when molecules come too close together there is an instance because of their close proximity to one another that they developed a slight polarity. That slight polarity between each other causes them to become attracted to one another. So we'd say that there is some type of attraction between this molecule and this molecule because of that instance that moment where one being too close to another makes them both slightly polar for a moment. Overall they're still non polar though. We're just talking about that split moment. Now these are our rankings of the inter molecular forces. And what's important though here is that the London dispersion forces, although they're the weakest, they are actually present in all types of compounds. So water which has its main inter molecular forces being, hydrogen bonding actually has some London dispersion forces in it. Mhm. This ionic compound being dissolved in water, it's major forces ion dipole, but it also has a little bit of London dispersion forces in it as well. So just realize that although dispersion forces are the weakest, they are president all compounds, so they serve an important purpose

here, it says we need to identify the major type of inter molecular forces between the particles of each of the following. So first, we're gonna start out with N two. Since it's just nitrogen connected to each other, they have the same electro negativity and therefore there'll be no difference in their electro negativity is. So This would represent a non polar Covalin compound and therefore London Dispersion or dispersion forces or Van Der Waals forces would be the answer for the next one. We have ch three Oh h Here we have hydrogen directly connected to oxygen, which means that this molecule can do hydrogen bonding with other molecules. So here would be hydrogen bonding as this major into molecular force for the next one, we have ch four and water. We know that water is a polar solvent and CH four is a hydrocarbon, so it's non polar. When you have a non polar the polar, that means that this is di pole induced dipole. Next we have ch three cl. So here we have carbon in the center, connected to three hydrogen and one chlorine. Because the central element is connected to different surrounding elements, It's a polar Covalin compound and therefore it's Inter Molecular Force would be disciple disciple. And then finally, here we have potassium chloride and CHD, always, which is methanol. So potassium chloride is an ionic compounds, and it's connected to a metal and nonmetal. And C30. H has hydrogen bonding, like we said earlier, which means that it's polar because hydrogen bonding is a polar force. So remember, when you have an ionic compound with a polar substance, then the inter molecular force is ion dipole. So that's what we can say in terms of the inter molecular forces for each one of these options, so those would be our final answers.