Intermolecular Forces - Video Tutorials & Practice Problems
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Intramolecular Forces are the bonding forces within a molecule. Intermolecular Forces are the attractive forces between 2 molecules.
Intermolecular Forces
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concept
Intermolecular Forces Concept 1
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1m
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We can talk about the intermolecular forces, realize that it is one of 2 major electrostatic forces, the other one being intramolecular forces. Alright? So we have these 2 major electrostatic forces, I e attractive forces that exist. So intramolecular exists within a molecule, and they bond atoms together and they influence the chemical properties of of those molecules. We're gonna say here this influences chemical bonds, which we break down into ionic and covalent, and realize that when it comes to intramolecular forces, they are stronger than intermolecular forces. Now what exactly are intermolecular 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 intramolecular force versus an intermolecular 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. Intermolecular is always between molecules. So here we're talking about the attractive forces between 2 water molecules. And in this image, why are they attracted to one another? Well, remember electronegativity. Hydrogens are less electronegative, so it's partially positive. Oxygen is more electronegative, 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 intramolecular force is the literal bond between atoms, an intermolecular 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 bond between molecules.
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example
Intermolecular Forces Example 1
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2m
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In this example question it says, identify the type of force involved in the situations below as either intermolecular or intramolecular. Now remember, intermolecular forces are the non bonding forces that exist. They're really just the attractive forces that exist between molecules, not the actual bonds. Intramolecular does deal with the bonding forces. So we're talking about atoms connecting to each other. So for the first one, we have the condensation of water vapor. This just means that water is going from its gaseous phase to its liquid phase. Here we'd have closer, reactions between different water molecules with each other. We'd have closer attractive forces for one another, but we're not really making new bonds here. And so here, this would be an intermolecular force. Next, we have the formation of ammonia through the combination of nitrogen and hydrogen. Combination here, we're combining them, we're forming something new by taking n 2 and h to it to make n h three. So we're making new bonds. So this would be intramolecular. Next, we have sugar dissolves in water. Here sugar is polar, water is polar, but we're not really forming a brand new bond between sugar and water. They are dissolving into each other to make a solution here. So this would be an intermolecular force. And then finally, water flowing up the veins of a plant due to capillary action. Capillary action is actually a property that's the result of an intermolecular force. So this would be intermolecular. The hydrogen bonding that exists in water allows it to do this type of phenomenon where it's actually going to move up the roots of the stems of a plant so it can reach the top part of the plant and feed its leaves and the top portion of it. K. So just remember, capillary action is one of those special properties that's a result of intermolecular forces.
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Problem
Problem
The dominant forces between molecules (intermolecular forces) are ____ in origin.
A
electrostatic
B
electrodynamic
C
electromagnetic
D
gravitational
E
magnetic
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Problem
Problem
Intermolecular forces are:
A
between molecules and weaker than a chemical bond
B
between two atoms within a molecule and weaker than a chemical bond
C
between molecules and stronger than a chemical bond
D
between two atoms within a molecule and stronger than a chemical bond.
E
between electrons within an atom and stronger than a chemical bond
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concept
Intermolecular Forces Concept 2
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6m
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When talking about the types of intermolecular forces, realize that there are 4 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 they exist between, we talk about their strengths, and then we give an example. So the first type we have is ion dipole. This is the force that exists between ions, so positive and negative ions, and polar compounds. They are the strongest of the intermolecular forces. So anytime you see an ionic compound, you can assume that water is the salt that it can be dissolved in. K? Usually, you'll see, ionic compound with water, but let's say you see only an ionic compound and they ask what's the intermolecular force, just assume it's dissolved in water. When we dissolve sodium chloride in water, we have ions, n a+aqueous and c l minus aqueous. Remember, aqueous 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. CL- 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 the hydrogen will be symbolized by that dotted line. So this is what we mean when we say an ion is aqueous in solution. It's water molecules surrounding it, basically dissolving it. We're gonna say solvating it. These are terms they usually use. So ion dipole is the strongest force. It's indicative of an ionic compound being dissolved within a polar substance such as water. The next one is hydrogen bonding. This is when we have compounds containing hydrogen directly connected to fun, f o n, fluorine, oxygen, and nitrogen. So here this one is the second strongest after ion dipole. Here, we have water and we have n h 4. N h 4 is a polyatomic ion, it's n h 4 positive. It's the ammonium ion. We could show water molecules being attracted to one another, and the dotted lines show that attraction, or we could show n h 4 positive molecules being attracted to one another. Or actually we could show them being attracted to the water, so hydrogen here is partially positive. Oxygen and its lone pair would be attracted to one of these hydrogens. So it's those dotted lines between these molecules that represents the hydrogen bonding. But hydrogen bonding itself can exist unless a molecule is showing an attractive force between hydrogen, fluorine, oxygen, or nitrogen. The next one is dipole dipole. Now before we talk about dipole dipole, realize 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 2 polar covalent compounds. This one here is the 3rd strongest of all the intermolecular forces. So here we have HCl which is polar and s o 2 which is polar. And here we could show the attraction between them. So remember chlorine has its lone pairs. It's more electronegative than hydrogen so it would be partially negative. Hydrogen will be partially positive. Within s o 2, you could show the sulfur with its lone pairs, oxygen with its lone pairs. Oxygen is more electronegative so it'd be partially negative. It would form an attractive connection to the hydrogen of HCl. That dotted line would be the dipole dipole interaction between these 2 molecules, and it could only happen because both molecules are polar. Finally, we have the last and the weakest intermolecular 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 2 nonpolar covalent compounds. Here we have c h 4, which is a hydrocarbon, and here we have CCL 4 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, we have c h 4 and here we have c c l 4. 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 intermolecular forces and what's important to know 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 intermolecular forces being, hydrogen bonding, actually has some London dispersion forces in it. This ionic compound being dissolved in water, its major force is ion dipole, but it also has a little bit of limiting dispersion forces in it as well. So just realize that although dispersion forces are the weakest, they are present in all compounds. So they serve an important purpose.
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example
Intermolecular Forces Example 2
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1m
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It says we need to identify the major type of intermolecular force between the particles of each of the following. So first, we're gonna start out with n 2. Since it's just nitrogen connected to each other, they have the same electronegativity, and therefore there would be no difference in their electronegativities. So this would represent a non polar covalent compound, and therefore London dispersion or dispersion forces or van der Waals forces would be the answer. For the next one, we have c h three o 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 its major intermolecular force. For the next one we have CH 4 and water. We know that water is a polar solvent, and CH 4 is a hydrocarbon, so it's non polar. When you have a nonpolar and a polar, that means that this is dipole induced dipole. Next, we have CH3CL. So here we have carbon in the center connected to 3 hydrogens and 1 chlorine. Because the central element is connected to different surrounding elements, it's a polar covalent compound and therefore its intermolecular force would be dipole dipole. And then finally here we have potassium chloride and CHPOH, which is methanol. So potassium chloride is an ionic compound since it's connected to a metal and nonmetal. And c 3 o 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 intermolecular force is ion dipole. So that's what we can say in terms of the intermolecular force for each one of these options. So those would be our final answers.
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Problem
Problem
Which of the following intermolecular forces are found in ALL molecules?
A
Ionic forces
B
Ion-dipole forces
C
Hydrogen bond forces
D
Dipole-dipole forces
E
Dipole/Induced-Dipole forces
F
London dispersion forces
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Problem
Problem
Which of these molecules exhibit the highest number of different intermolecular forces?
A
CH3CH2CH3
B
CH3CH2OH
C
CH2O
D
Li2CO3
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Problem
Problem
It is common to add Epson salts to bath water when one has been over exercising and has sore muscles. What is the primary intermolecular force that exists between magnesium sulfate, the primary in Epson salts, and the water in the bathtub?
A
dipole-dipole forces
B
ion-dipole forces
C
London forces
D
Hydrogen bonding
E
ionic forces
F
dipole/induced-dipole
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Problem
Problem
Which species is expected to have the largest dispersion forces?
A
CH4
B
CH3CH3
C
CH3CH2CH3
D
C12H26
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