hello everybody my name is iman welcome back to my youtube channel and welcome to general chemistry 2. in this first chapter for this course we're going to cover intermolecular forces now intermolecular forces are the forces holding individual molecules and atoms together in say a liquid or solid state we're going to cover four big topics in this chapter starting off with obviously intermolecular forces we're also going to cover phase changes and phase diagrams and then end it off with a conversation about liquids now it's really important for the start of this chapter to have a dis discussion about how to distinguish a chemical bond from an intermolecular bond being able to understand the difference between these two things is going to allow for us to clear the air of misconception and continue on so we can truly understand intermolecular forces now a chemical bond is a strong force of attraction holding atoms together within a molecule or or crystal so if you have a water model a molecule like you do here all right this is a molecule because you have the oxygen atom bound to these hydrogens through an actual covalent bond all right there's a strong force of attraction that is holding these atoms together this oxygen to the hydrogens and we have a water molecule now an intermolecular force or an intermolecular attraction you might hear those two terms being used interchangeably is a weaker force that can cause individual molecules to aggregate leading to the formation of a solid or liquid so what you're going to have here are weaker attractions between different molecules all right so this water molecule all right might have inter might form intermolecular forces with other water molecules we're going to learn what kind of intermolecular force all right it's a weaker molecule that's going to cause these individual water molecules all right to aggregate to form some type of sort of attraction to one another all right so with that distinction being made let's actually officially begin to discuss intermolecular forces now here on this list what you're going to see is um all your forces all right and the definition of what falls under bonding interactions what falls under intermolecular force interactions all right we have covered in general chemistry ionic covalent and metallic bonds ionic bonds are electrostatic uh attractions between oppositely charged particles sodium chloride being a great example table salt all right covalent bonds are negatively charged electrons are going to be shared between two positive nuclei and we've covered in uh general chemistry one nonpolar covalent bonds and polar covalent bonds if you need a reminder on that just check out those videos in general chemistry one playlist and metallic bonds where metallic cations are in a sea of delocalized electrons all right now what we're going to start covering are some of these intermolecular forces and specifically in this chapter we're going to cover three all right the other three are going to be matters of discussion for the next chapter all right in this chapter we're going to talk about hydrogen bond dipole dipole force and london dispersion force all right we're going to discuss in details what these three are now something to remember is that all intermolecular attractive forces are columbic in nature that means they consist of electrostatic attractions between oppositely charged particles and the three important types of intermolecular forces that are present in pure substances that we're going to cover in this chapter are the dipole-dipole forces hydrogen bond and london dispersion all right so we're going to get into we're going to get into these and we're going to start off by looking closely at this dipole-dipole forces all right we learned that a polar molecule is going to be one with an uh with a unequal distribution of charge all right polar molecule is one with an unequal distribution of charge resulting from its shape and the nature of the bond now when placed in a magnetic field when you take a polar mag molecule and you place it in a magnetic field that polar molecule is going to behave as if it has a center of positive charge and a center of negative charge all right so sort of like this distribution all right becomes centralized positive centralized negative charge all right now in other words it's gonna possess a permanent dipole all right it's going to possess a permanent dipole when the partial positive on on one molecule's dipole interacts with the partial negative on another molecules dipole the result is this dipole dipole force all right awesome so let's let's visualize this so far all right when you have a bond like hydrochloric acid all right one place this is a polar molecule all right it's polar molecule because of the electronegative difference between hydrogen and chlorine is pretty is grand enough for this to be a polar molecule all right remember poly polar molecules have an unequal distribution of charge and when you place a polar molecule in a magnetic field it's going to have a center of positive charge and a center of negative charge what we're talking about here is we learned how to identify polar and non-polar covalent bonds this is a polar covalent bond and that means one atom in this bond is going to pull the electrons a little closer to themselves all right they like the electrons just a little more than the other molecule and this is due to the the difference in these two atoms electronegativities all right chlorine is a little is a little more electronegative than hydrogen therefore in this bond that they share the chlorine is going to pull these electrons a little closer to itself what does that cause all right it causes this distribution of charge all right it's going to behave as it has a center of positive charge and a center of negative charge in other words it's going to possess a permanent dipole all right and what is this permanent dipole well the hydrogen all right the chlorine is going to be pushing the electrons a little more towards it all right so we draw our dipole arrow towards the chlorine because that's the electrons are being pushed a little more towards it all right what that means is that the chlorine is going to have a partial negative charge all right not a whole charge because this is not an ionic bond and the hydrogen's going to have a partial positive charge all right therefore it possesses a permanent dipole all right so now we have we understand this this one hydrochloric acid molecule how the charges distribute and are our partial charges on this molecule cool what if there's more than one hydrochloric acid molecule in a solution which is probably right more realistic well when a partial positive when a partial positive on one molecules dipole interacts with another partial negative on another molecule's dipole the result is a dipole-dipole force all right so when you have more than one hcl in a solution the hcl molecules are going to interact with one another how in a way where the partial negative of a chlorine of one molecule might interact with the hydrogen the partial positive charge on a hydrogen in another molecule and therefore they have this intermolecular force between each other that's described as a dipole-dipole force all right in other words the positive end of one polar molecule a trap is attracted to the negative end of another polar molecule dipole-dipole forces exist between polar molecules such as hydrogen chloride all right when comparing molecules of similar size all right the strength of dipole-dipole interactions attractions are going to increase with increasing polarity all right so as their dipole moments increase the dipole dipole forces are gonna also increase all right that's an important thing to keep in mind fantastic all right now what we want to talk about are hydrogen bonds all right a hydrogen bond is an intermolecular attraction that's going to be between a polarized hydrogen on one molecule and a very electronegative atom on another all right so when a molecule contains a hydrogen atom that is covalently attached to a fluorine oxygen or nitrogen all right i like to remember that as fun right close to fun but with the oh right if you have a hydrogen atom covalently attached to a fluorine oxygen or nitrogen there's going to be a large difference in electronegativity all right so if you have a hydrogen attached to a fluoride hydrogen attached to an oxygen hydrogen attached to a nitrogen there's going to be a big electronegativity difference between the hydrogen and one of these atoms and so that's going to result in a covalent bond and specifically a polar covalent bond that means the bond all right is polarized all right now that the term hydrogen bond it can be misleading all right a hydrogen bond in regards to intermolecular forces is not a bond in the sense of a covalent bond okay we're going to repeat that for every time we cover an intermolecular force all right these are not chemical bonds that we're talking about when we talk about hydrogen bond in the under the guise of intermolecular forces all right this is a intermolecular force that's occurring between two separate molecules all right awesome so again hydrogen bond is an intermolecular attraction between a polarized hydrogen on one molecule and a very electronegative atom on another all right hydrogen bonding is an especially strong type of dipole-dipole attraction actually all right it's given its own classification because it's actually much stronger than the dipole-dipole attractions all right molecules that are going to be held together by hydrogen bonds guess what they're going to generally have pretty high boiling points are going to have higher boiling points and melting points than other molecules of comparative size hydrogen bonding is actually going to explain all right can explain many important properties of water okay water has high specific heat capacity water has high violent boiling point water has high heat of fusion and vaporization which we'll cover here shortly all right and what explains these properties is hydrogen bonding all right you're going to have the hydrogen of one molecule of water interact with a very electronegative oxygen atom in another water molecule all right and you're going to have this hydrogen bonding that's occurring between different water molecules all right and this hydrogen bonding explains those properties of waters we just listed right now hydrogen bonding is also responsible for this is really cool important characteristics of dna alright so if you recall from your biology class all right dna is this double helix molecule all right that encodes all your genes all right and in this double helix all right what's happening here in this double helix is you have some base pairing on each strand all right different bases will pair with each other all right we can go over a tcg whatever you're gonna have two molecules you're gonna have two base pairs all right that are gonna interact with each other in this double helix structure and guess what is is occurring in between these two molecules that are interacting with each other all right saya a base pair adenosine and thymine all right these are two separate molecules in our dna they're going to be interacting via hydrogen bonding all right and it is hydrogen bonding that's responsible for some of the important characteristics of dna all right hydrogen hydrogen bonding holds two particular bases together all right so that's hydrogen bonding for us all right a polarized hydrogen on one molecule is attracted to a very electronegative atom on another molecule water being a great example fantastic now the third thing we want to cover in terms of intermolecular forces in this chapter is london dispersion forces what is it that holds nonpolar substance together in a solid or liquid all right we can't forget our nonpolar substances well after all nonpolar substances they do not possess a permanent dipole with a positive and negative charge if we remember nonpolar covalent bonding happens when two atoms that form a bond are sharing those electrons very equally all right that's what makes them non-polar they also don't possess a permanent dipole where there's a a obvious distribution or obvious centering of positive and negative charges so how do we describe nonpolar substances and their intermolecular attractions or forces that they might participate in well the intermolecular forces that hold nonpolar molecules together are called london dispersion forces london dispersion forces are attractive forces due to temporary induced dipoles all right now take a helium atom a helium atom consists of two electrons symmetrically distributed in a spherical cloud around the nucleus all right here's our helium all right at any given instant the electron cloud of a helium atom can be distorted with more electron density on one side than the other and at that moment that that small moment the helium possesses a temporary dipole all right london dis london dispersion forces describes this temporary induced dipoles that happens in say two helium atoms and their interactions with each other via intermolecular attractions now london dispersion forces increase with increasing polarizability the ease with which the electron cloud of a molecule atom or ion can be distorted the larger the molecule the more polarizable it is and the stronger the stronger its london dispersion forces now all substances both polar and nonpolar are going to experience dispersion forces they are the only intermolecular attractive force that's going to exist between non-polar molecules but they're also present among molecules that experience dipole-dipole forces that experience hydrogen bonding all right now with that we've covered the three intermolecular forces that that span chapter uh this first chapter of general chemistry in the next chapter we're going to cover the other three but now what we want to want to develop is a step-by-step manner in which we can begin to determine which intermolecular forces are present all right and so the step-by-step for identifying intermolecular forces starts with first asking the question well does this molecule does this molecule have any hf ho or hn bonds all right if the answer is yes all right then the intermolecular forces that are present in the molecule are hydrogen bonding and of course london dispersion forces if the answer is no then we move on to our second question is the molecule polar if the answer to this question is yes then you have dipole-dipole forces and of course also london dispersion forces if the answer is no then the only intermolecular forces you have are london dispersion forces only all right at least so far in what we've covered in intermolecular forces cool so let's actually do some practice problems all right let's do this problem it says identify the intermolecular forces present in nitric acid all right and chf3 cool so let's start with this first one hno3 first let's ask the question does this molecule have any hf o or h n bonds all right so let's try to draw this molecule really quickly just so that we can answer this question alright you might know without even drawing but just to verify all right i'm gonna go ahead and draw this molecule for us alrighty there we go all right so we've drawn this molecule fantastic in this molecule all right guess what we see we see that there is a oxygen all right that is bound to a hydrogen so we have a hydrogen to oxygen bond all right the hydrogen is covalently bonded to oxygen so this molecule experiences hydrogen bonding all right remember the hydrogen bond is not the is not the covalent bond between hydrogen and oxygen inside the molecule rather the hydrogen bond is the internal molecular attraction between two different hno3 molecules all right so if we have another if we have another molecule oops all right hydrogen bonding describes the bond that my internal a hydrogen bond is going to explain this intermolecular attraction between this hydrogen of one molecule of hno3 all right to another molecule of hno3 all right fantastic now the second molecule that we're supposed to determine the intermolecular forces is chf3 alright let's draw this molecule really quickly right if you need a reminder how to draw molecules check out my video in general chemistry 1 on how to do lewis structure so that you can refresh if you need to all right so here we have our molecule fantastic all right it has a hydrogen and a fluorine all right and you might you know get excited just looking at this molecule it has a hydrogen fluorine and so when you ask your first question does this molecule have any hf h o or h n bonds you might be a little too excited and just looking at this formula say yes but if you draw it out what you realize is that there is no direct covalent bond between the hydrogen and the fluorine in this molecule yes there is a hydrogen hydrogen yes there are fluorines but they are not bound to each other so you do not have a hydrogen to fluorine bond right so the answer to the first question does the molecule have any of these bonds no it does not all right so this molecule doesn't have hydrogen bonds because in order for it to form hydrogen bonds it needs to possess a polarized hydrogen there is no polarized hydrogen in this molecule carbon and hydrogen are a non-polar bond so we move on to our next question is this molecule polar all right and that's a great question the answer to this question we're going to have to follow a few steps in order to determine whether whether it's polar all right in order to determine whether it's polar truly we're gonna of course draw the lewis structure first and foremost we got that down all right second we need to determine the molecular geometry all right the last chapter in general chemistry one went over vesper theory which helps us determine all right which helps us determine the molecular geometry of a molecule all right now what we need in order to answer what the molecular geometry of this molecule is is one we need to say how many lone pairs are around the central atom there are no lone pairs around the central carbon atom and then two how many um like electron dense areas are are there there's one two three four four electron dense areas and so if you look at the diagram that i've provided before about vesper theory all right this is going to be a molecule that is going to possess tetrahedral geometry all right tetrahedral kubins all right now taking into account the geometry and the lewis structure we've drawn all right now we're going to take into account the bond dipoles and determine whether there are centers of positive and negative charge and how they coincide all right so if we look at this molecule if two atoms in a bond have different electronegativities the bond is polar and there is a bond dipole now fluorine is much more electronegative than carbon so the actual carbon to fluorine bonds in this molecule are polar the fluorine is going to have a partial negative charge all right because of that so let's write our partial negative charges on the flooring in the appropriate geometry now all right we're going to draw this molecule with the appropriate geometry because we now know it's tetrahedral right this wedge means the fluorine is coming out of the page this dash means the fluorine is going into the back of the page all right the fluorines get a partial negative charge because they are more electronegative than the carbon all right hydrogen is less electronegative than carbon so in relation to this carbon hydrogen bond the car the hydrogen actually gets a positive part a partial positive charge all right so now viewed in this structure that what you realize is there's a positive charge at the top of this tetrahedral molecule all the negative charges are at the base of the tetrahedral and therefore the center of positive charge actually doesn't coincide with the center of negative charge you have this charge distribution positive on the top negative at the bottom this is then a polar molecule all right and so chf 3 is a polar molecule and that means it's going to possess dipole-dipole forces and of course also london dispersion all right fantastic we answered the question now what we're going to discuss is the next topic which is phase changes all right a change in a physical state of a substance is called a phase change some phase changes are endothermic things like melting vaporization all right and sublimation all right the reverse changes are exothermic things like freezing condensation and deposition now these describe what these terms describe whenever you're changing from one phase into another when you go from solid to liquid or liquid to solid you're either freezing or melting one of these is endothermic melting and one of these processes is exothermic freezing endothermic you take in heat exothermic you release heat all right and then the change between liquid to gas and gas to liquid all right are can be summarized as vaporization and condensation again vaporization is endothermic condensation is exothermic you can also explain the difference the change in phase between gas and solid and solid and gas those being deposition and sublimation deposition being endothermic sublimation being exothermic we don't have to worry about plasma right now now the enthalpy change that occurs when one wall of a pure solid all right is completely completely melted back to a liquid is called the heat of fusion all right the term fusion in chemistry means melting all right so the enthalpy change that occurs when one mole of a pure solid is completely melted is called the heat of fusion now the enthalpy change that occurs when one mole of pure liquid is completely vaporized all right so whenever you have all right one mole of pure liquid vaporized to a gas all right the enthalpy change is called the heat of vaporization so we're going to write delta h of vape for between the liquid and gas and delta h fuse for fusion for the solid to liquid fantastic substances with strong intermolecular attractive forces are going to have higher values of heat effusion and heat of vaporization now the heat of vaporization of a given substance is going to be generally much higher than its heat of fusion all right when a substance is vaporized its intermolecular forces have to be completely overcome so that the molecules can totally separate and go into the gas phase all right in contrast though when a molecule or when a substance melts its individual molecules are just given a greater freedom of motion but they remain very close all right therefore melting only requires sufficient energy to partially overcome intermolecular forces all right now a heating curve a heating curve for a substance is going to be a plot of temperature as a function of the amount of heat absorbed by the substance all right now the melting point of a substance okay which is kind of the same as its freezing point is the temperature at which the solid and liquid states coexist in equilibrium all right so here what we have is a phase change diagram all right a heating curve if you will all right the melting point of a substance is the same as its freezing point this is the point or temperature which is solid and liquid state coexist so this temperature right here or whatever temperature this coincides to all right is the temperature where solid and liquid coexist all right fantastic now when a substance is at its melting point the rate at which the solid melts equals the rate at which the liquid freezes the heating curve remains flat at that melting point because even though heat continues to be added all the additional heat goes into giving the solid state molecules sufficient energy to partially overcome the intermolecular forces until it actually goes into the liquid phase and therefore you've been able to transition from solid to liquid now the same can be said going from liquid to gas there is a temperature where this liquid and gas coexist all right and until this temperature threshold is exceeded then you finally can go from liquid to gas all right now what's really interesting about these kinds of curves is um you can calculate with some information um the heat involved in phase changes and it's really important to know what kind of equations to use at whichever points all right and most of the time you're using your m your mcat equation to calculate to calculate um the heat involved in phase changes if you remember we encountered this equation when we were doing chapter i i believe six where we covered thermodynamics all right this equation which we call our mcat equation because it kind of looks like m c like an a t all right it's going to allow us to calculate um heat changes all right and we're actually going to do a practice problem where we put this into action all right so we're going to uh we can use our mcat equations here when things in our solid are our in our liquid phases and our gases all right to get the heat the heat at these locations we can also use sort of similar equations to figure out the heat at these points where um solids and liquids coexist and gas and liquid coexist and for um solid to liquid we're going to use m delta h of fusion all right and for going from liquid to cat gas at this point where gas and liquid coexist we can determine the heat using m delta h vaporization all right let's put this into action by actually just jumping straight into a practice problem all right this problem says what is the total amount of heat required to convert 75 grams of ice at minus 13 degrees celsius to liquid water at 62.5 degrees celsius now this problem also is going to give us information about the specific heat of water as a solid it's 2.09 joules per gram celsius all right and the specific heat of water as a liquid which is 4.18 joules per gram per celsius all right the heat of fusion of water is 6.02 kilojoule per mole and the melting point of water is 0 degrees celsius so this is all the information they've given us all right we're going to highlight everything we have here as a number all right liquid water at 62 we have a specific heat of solid water liquid heat of fusion and melting point all right now whenever you're asked to calculate the amount of heat when a phase changes it involved all right you should go ahead and just sketch a heating or cooling curve all right in this case we're going to start with ice at the temperature below its freezing point because that's what they give us so we're going to start to draw this out temperature versus heat added right and this is temp beautiful all right we're starting off with ice all right then we're going into this stage where obviously solid and liquid coexist and then we go to water liquid all right so we have q1 here all right this is q2 and this is q3 fantastic all right notice there's three sections to this heating curve all right the first step q1 is going to correspond to heating the ice all right q1 is going to relate to us heating the ice all right we start off at negative 13 degrees celsius we're going to heat it up all right we're going to heat it up to its melting point because where solid and liquid coexist all right this is our melting freezing point that's the same point and they tell us what that is it's zero degrees celsius so our first branch we're starting at negative 13 degrees celsius we're ending up at zero degrees celsius all right fantastic so we can calculate this portion using our end cap equation q1 is going to equal m c delta t m is 75 grams all right our um um c all right is actually going to be our specific heat for water as a solid because it's ice right here all right it's only a liquid at q3 at q2 they both coexist all right so for our trying to find the heat all right trying to find the heat for q1 we're going to use our mcat equation where c is going to be the specific heat of of h2o as a solid which is 2.09 joules per gram celsius fantastic and then our delta t is final minus initial all right final minus initial we plug this into a calculator we're going to get for q1 is 2 0 3 8 joules 2038 joules all right fantastic that's our first part we figured out q1 amazing now the second portion of the curve q2 is flat it's going to occur at the melting point and even though heat is being added the temperature doesn't increase until all the ice is completely completely melted all right so the additional thermal energy that's added allows for the solid molecules to begin to partially overcome those intermolecular forces and then go into the liquid phase all right to calculate this portion of the curve all right we have to use the heat of fusion all right right we we said this before in our heat curve when we were talking about it we need delta h heat of fusion all right the equation to solve all right the equation to solve q 2 all right um can be uh what is it m delta h fusion all right in this case we want to uh be able to cancel out units with the heat of fusion they've given us all right they've given us the heat of fusion here at 6.02 kilojoule per mole all right m we usually have we usually put the mass in here but we have the mass so we can convert it to moles so that when we multiply all right when we multiply this by a a or our heat of fusion which is in kilojoules per mole the moles cancel out and we can get our answer in just kilojoules because that's what we want our heat our kilojoules all right so this is what we're going to do all right we know q2 is m delta h fusion all right we would usually put 75 grams but that won't cancel out with the specific units they've given us for delta h fusion so we need to convert this 75 grams to moles all right this is of water so we know that water is 18.2 grams of water is one mole of water beautiful and now the grams cancel out here and we have moles of water in inside this all right and we're going to multiply by our heat of fusion our heat of fusion is 6.02 kilojoules per mole and this is fantastic because guess what the moles are going to cancel out we're going to get our answer in kilojoules all right if you plug this into a calculator you're going to get 25.1 kilojoules all right fantastic so that's our second part now all we have to figure out is q3 all right this third step is going to involve heating water from its freezing point to its final temperature all right again we're going to use our mcat equation all right and remember we're going to use our specific heat of liquid water at this step so let's write this down let's use a different color now q3 using our mcat equation all right we know it's 75 grams we know the specific heat of water as of h2o as a liquid 4.18 joules per gram per celsius all right and now where what temperature is this this is zero all right and we're heating it up to what does the problem tell us 62.5 degrees celsius all right so we're gonna have to do final minus initial our final temperature minus initial all right plug this into a calculator and what we're going to get is 19 590 joules fantastic now the total enthalpy change of this kind of reaction is going to be the sum of all of these steps so q total is going to be actually q 1 plus q 2 plus q3 all right and if you plug this into the calculator all right you're going to get 46.7 kilojoules make sure all right to change anyone any any unit that's in joules to kilojoules so this is in joules all right 19 590 joules that's okay we can do this in kilojoules it's just going to be 19.590 uh kilojoules all right um q2 is in kilojoules q1 whereas q1 is in joules so you want to convert this to kilojoules 2.038 kilojoules just a unit conversion all right and then add them all up together and what you get for the total enthalpy change of this reaction is 46.7 kilojoules fantastic awesome now another important topic to talk about is vapor pressure and boiling point it's important to understand the difference between the terms vapor and gas all right a vapor is a gas in every sense of the word it expands to fill a container its particles are in constant random motion its pressure is proportional to a temperature at a given volume now if a gas at a given temperature and pressure can be condensed to a liquid state or can undergo deposition to a solid state then it is appropriate to describe it as a vapor all right in other words the term vapor is going to be used to describe the gas space of a substance that normally exists in the solid or liquid phase at that temperature and or pressure all right vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid or solid state it is a dynamic equilibrium meaning the liquid molecules evaporate and gas molecules condense at the same time and since both processes occur at the same rate there's no overall change in the amount of liquid or gas once equilibrium is changed all right so no vapor pressure of a substance is going to depend on temperature as temperature increases so does vapor pressure at higher temperature more liquid molecules can acquire sufficient kinetic energy all right to evaporate all right to escape the surface of a liquid and go into gas phase vapor pressure also does depend on the strength of intermolecular forces and intermolecular attractive force increases more energy is required to vaporize liquid molecules therefore the stronger the intermolecular attractive forces the lower the vapor pressure all right the vapor pressure is going to be directly related to volatility which describes the ease with which substance can be vaporized substances that are easily vaporized or volatile and substances that are not easily vaporized are non-volatile the stronger the intermolecular attractive forces the lower the vapor pressure and the less volatile a substance is now boiling point on the other hand is defined as the temperature at which the vapor pressure of a liquid equals the external pressure the relationship between boiling point and vapor pressure can help us explain the characteristic appearances of boiling liquids when a liquid such as water boils its molecules are gonna possess enough kinetic energy to overcome intermolecular attractions that hold them together they are able to go into the gas phase not just at the surface but also in the interior of the liquid state all right of the liquid okay resulting in the formation of bubbles that rise to the surface all right so something to keep in mind all right vapor pressure directed directly related to volatility describes the ease which with substance can be vaporized the stronger the intermolecular attractive forces the lower the vapor pressure and the less volatile a substance is all right so with that being said let's do some practice problems all right what which of these two molecules is expected to have a higher boiling point magnesium chloride or sulfur chloride all right remember okay these are binary compounds they consist only two elements all right they can be classified as ionic or molecular depending on the kinds of elements they contain magnesium chloride contains a metal and a non-metal all right that means this is ionic this is an ionic bond ionic bond between the molecules all right cool sulfur chloride although on the other hand sulfur chloride contains two non-metals all right so this is a molecular compound all right fantastic they form covalent bonds now in an ionic molecular crystal right oppositely charged ions are held in a rigid lattice by very strong electrostatic attractions these tend to these kind of molecules tend to have very high melting and boiling point all right so keep that in mind individual molecules like sulfur chloride are going to be held together by much weaker intermolecular forces all right they are usually going to have much lower melting points and boiling points than ionic compounds all right so what that means is this magnesium chloride all right is going to be held together by stronger intermolecular forces than sulfur chloride all right what that means all right is that magnesium chloride is expected to have a higher boiling point than sulfur chloride fantastic this problem says which is expected to have a higher vapor pressure notice how this is boiling point all right we compare ionic to molecular we know that things like ionic um bonds or ionic crystals are going to be held in a rigid lattice so they have very strong electrostatic attractions more so than a molecular compound like sulfur chloride therefore they have higher boiling points this one's asking which is expected to have a higher vapor pressure at a given temperature all right ncl3 or pbr3 both of these compounds are molecular compounds they're both two non-metals so now we need to determine the types of intermolecular forces in each all right so let's draw them out all right we have our ncl3 and we have our p br fantastic cool cool cool all right first we want to ask well is hydrogen bonding present well none of these molecules has a hf or a ho or a hn bond so there's no hydrogen bonding second are these molecules polar or nonpolar all right well we've drawn the lewis structure both of these molecules have three bonds and one lone pair all right so the electron geometry for four groups of electrons where three are bonding pairs and one is a lone pair all right we have uh trigonal pyramidal as the molecular geometry for these all right they have one lone pair and four electron dense areas so it's trigonal pyramidal coulbean so we figured that out well now what we can say is well nitrogen and chlorine for this molecule all right they have very similar electronegativities but the presence of the lone pair electrons on the nitrogen atom along with the unsymmetrical shape of ncl3 all right they have a small dipole moment and the same can be said of pbr3 all right these ncl bonds they have very similar electronegativities but that lone pair contributes to a small dipole moment therefore both of these molecules are polar so we can say they have dipole-dipole forces all right one difference between the two though that we can use as a distinction between the two and maybe be able to determine which one has a higher vapor pressure is their size the mass of ncl3 is 120 grams per mole and for pbr3 271 grams per mole all right remember they are they have dipole-dipole interactions they also obviously also have london dispersion forces something we know about london dispersion forces is the higher the molar mass of one molecule the bigger it is the stronger the london dispersion forces this suggests that pbr3 has stronger london dispersion forces than ncl3 and so in order to compare the vapor pressures between the two substance keep in mind the stronger the intermolecular forces the lower the vapor pressure all right so that means ncl3 has a higher vapor pressure than pbr3 and that's because pbr3 is larger and stronger okay which makes it have a lower vapor pressure fantastic now we want to move on to our third topic phase diagrams all right a phase diagram shows the most stable state of a substance at any given temperature and pressure all right now looking at these examples that we have here all right each point on a phase diagram each point on a phase diagram represents different temperature and pressure here we have that our x-axis is temperature our y-axis as pressure the various regions are labeled to show the most stable state of a substance under those conditions so phase diagrams are great all right because they kind of help you visualize the regions of certain temperatures and pressures all right where gases exist for a molecule all right where solids exist for a molecule all right you can find the temperature and pressure point within any at any point in this region and you know it's a solid at any point in this region know that it's a liquid alright so the various regions are labeled to show the most stable state of a substance under those conditions now what about the solid lines and curves on the ver on the phase diagrams those solid lines and curves they show the temperature and pressure where two states can coexist in equilibrium all right so let's erase some of these doodles here all right and let's look at these solid lines and curves all right we have one right here all right this solid curve shows where uh the temperature and pressure where two states can coexist in this in this line right here that hot that's highlighted blue where solid and gas can co-exist all right now the solid and liquid right here solid and liquid um phase this is called the fusion curve all right this is the fusion curve the solid line that shows where solid and liquid can coexist is called the fusion curve let's write that down fusion curve fantastic at each point on the line it corresponds to temperatures and pressures which solid and liquid coexist in a similar way the curve separating solid and cat gas we draw in in blue and blue highlight here this is called um the vaporization not not the vaporization i'm sorry the sublimation curve all right and then the the curve that we're going to highlight in red here all right where liquid and gas can coexist this is called the vaporization curve fantastic notice the vaporization curve all right it describes conditions where liquids and vapors are in equilibrium now something else that's really really cool there's going to be a one point on the phase diagram where all three curves intersect all right that's going to be called oh you guessed it triple point right where three curves meet triple point this triple point represents the temperature and pressure at which all three phases of a substance solid liquid and gas coexist in equilibrium all right now there's also a point called the critical point all right i am going to circle it in purple here's our critical point right here the temperature and pressure at the critical point are called the critical temperature and pressure all right cool if the temperature is increased enough the kinetic energy of a gas molecules are eventually going to become so high that the gas cannot be condensed in a liquid regardless of how high the pressure is the critical temperature is therefore defined as the temperature above which it is impossible to condense gas into a liquid all right and the critical pressure is the pressure required to condense a gas at a critical temperature all right so when a substance is at a temperature and pressure beyond the critical point it exists as a supercritical fluid a supercritical fluid is neither a liquid nor a gas but it kind of possesses properties somewhere in between the two all right so that's some cool stuff now one more thing that i want to say all right notice how this line this fusion curve alright notice notice the the the shape of this fusion curve all right it's kind of like a positive uh has a positive really steep slope here it can other other other molecules can have like steeper and steeper or or less steep they can have a range of positive lines for the fusion curve water on the other hand all right is more of a negative downward curve all right so that's how you can distinguish the phase diagram of water all right it's line its fusion curve is not going to be a positive slope it's going to have more of a of a negative slope as opposed to a positive slope all right fantastic so we've been able to find and identify all these regions within a phase diagram fantastic now for the last topic of this chapter what we want to end this off in is by discussing the properties of liquid we're going to discuss three properties um of a liquid that are indicative of the intermolecular attractive forces that hold molecules together in liquid phase these three things are surface tension viscosity and capillary action the first property is surface tension all right surface tension is the energy required to increase the surface area of a liquid by a unit amount surface tension arises because molecules at the surface of a liquid experience fewer intermolecular forces than those in the interior all right the key principle is that the more intermolecular forces experienced by a molecule the lower its potential energy all right so molecules in the interior of a liquid all right they're going to have lower potential energy than those on the surface all right because they experience more intermolecular forces molecules at the surface tend to move inward they tend to move to the uh toward the interior in order to increase the number of attractive interactions and lower their potential energy right now the net result is that liquids tend to have the smallest surface area possible with the fewest number of surface molecules right because the surface molecules tend to move more towards the interior or want to move more towards the interior to increase the number of attractive interactions and lower their potential energy all right so that means that means the energy required to increase the surface area is going to correspond to the surface tension of the liquid in order to increase the surface area molecules in the interior are going to have to overcome attractions to other molecules in the interior to go to the surface all right so this this process is this energy required to increase the surface area corresponds to the surface tension of a liquid in general the stronger the intermolecular forces the greater the surface tension fantastic the second thing property is viscosity viscosity is a measure of a liquid's resistance to flow it occurs because of intermolecular attractive forces internal intermolecular attractive forces within a liquid prevent its molecules from moving around too freely as they could in the absence of these forces so substances with stronger intermolecular forces they tend to be more viscous all right viscosity is also affected by the size and shape of the molecules that comprise the liquid molecules that are large and complex tend to be entangled and it makes them more difficult for them to move around and and increase the liquids viscosity and also in addition to all that um a a liquids intermolecular forces and molecular size and shape don't don't uh along with temperature i'm sorry they affect viscosity so what i mean by that is the increased thermal energy at higher temperatures enables molecules to partially overcome intermolecular forces so as a result with increased temperature they can flow around a little more easily which is why viscosity generally decreases all right viscosity generally decreases with increasing temperature all right last but not least capillary action capillary action is the spontaneous rising of liquid against the pull of gravity through a narrow tube capillary action is really the result of an interplay between cohesive forces which is the intermolecular attractions within a liquid and the adhesive forces which is the intermolecular attraction between the liquids and the wall of the tube if adhesive forces overcome or are greater than the cohesive forces then the water moves up the liquid up the tube sorry then the water moves up the tube all right so that is all i have for you for our first chapter in general chemistry 2. i hope it was helpful let me know if you have any questions at all um feel free to reach out to me if you want to discuss you know advice or you have a problem you need help with happy to help in any way other than that that's all i have for you so good luck happy studying and have a beautiful day