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Added: 2026-05-12

[00:00:02]all right guys so we are going to start looking a little bit further at matter with the different types of matter and determining whether matter is a solid liquid or gas is going to depend on what forces are within that matter so I want to explore that a little bit more so we do have the kinetic molecular theory of gases we talked about kinetic molecular theory in chem1 that particles in any substance are in constant motion even in solids um but we're going to deal a lot with gases this unit um whenever we get later into gas laws but looking at the molecular theory of gases um so gases are composed of small hard spheres of insignificant volume so these particles are so tiny there's lots of empty space um so they do not have a lot of volume with gases there's going to be no force of attraction or repulsion between particles um so we're going to talk about intermolecular forces in a little bit those do not exist in gases um we're only going to deal with those in solids and liquids and part of it is cuz the particles are moving very quickly and they tend to be so far apart so the particles in a gas are in continuous rapid random straight line motion so this has a little bit of physics worked in where particles will move in a straight line unless acted on by another Force so the particles will move until they hit something and bounce off in another Direction but each particle is moving independently they are not all moving the same direction um so they're not all moving like towards the right or up every particle is going in a different direction until it hits something and goes a different direction um one thing that we'll talk about a little bit more later whenever we start looking at um reactions is we talk about collisions um but collisions between gas particles are what we refer to as elastic um that means that energy can be transferred whenever those particles do collide and the energy can be transferred from one particle to the other and then they go off in another Direction um but energy is not lost overall it just goes from one particle to the next and then all of these theories with gases describe ideal behavior of most gases at high temperatures and low pressures um we're going to talk about later this unit of when things do not behave as expected or they do not behave ideally but that's going to come up later this unit let's look at our states of matter um we have gases we said there's lots of empty space between gases so they do have a very low density because there's not as many particles trapped within that amount of volume the density is going to be effective by temperature so um if you cool it down those particles slow down they tend to get closer together um with gases because there's empty space they also have a very high compressibility we can push down on gas particles and force them to fill that empty space and then with gases the particles spread out to fill the container so if we take 2 L of gas and pump it in a 5 L container the particles will spread out to fill that 5 L container with solids remember those particles are tightly packed together so it has a greater density density is not affected by temperature because that solid cannot expand or contract it can't be compressed at all um so like I said they are incompressible there's not empty space between the particles that you can force those particles into and with solids they're completely rigid so they have a set shape and volume um so the shape and volume of solids do not change liquids are going to be kind an in between for us um they're more dense than gases but less dense than solids typically um they're virtually incompressible so so you cannot take um like a container of water pushed down into it and it not overflow the water will kind of move out of the way and fill in more space so you can't actually make the particles go closer together and with liquids they take the shape of their container um so if it's in a can it will have that cylindrical shape if you spill it in the floor it will have a shape of a puddle um but these do have a definite volume so like if I have a can of soda that is 12 oz if I pour it in a cup it is still 12 oz the shape can change but the volume stays the same looking at these particle wise in solids and liquids those particles are close together and remember solids they're kind of tightly packed together there's a very nice orderly pattern um liquids are a little bit more random but the particles are still touching whereas in gases those particles are going to be very far apart so you have lots of empty space between those individual particles and a lot of times the state of matter is going to depend on what attractions there are between particles so let's start looking at inner particle ractions are intermolecular forces you'll kind of hear both terms used equally um but these are attractions or forces that hold one particle to another in a solid or liquid so this is the attraction between different molecules holding them together um and like we said this is only in a solid or liquid CU gases do not have attractions between particles so here you can see these would be like water molecules being attracted to one another um this is going to be like a protein structure where they're attracted to one another and in a solid remember those particles are locked in place due to strong attraction between particles so there are different attractions that hold one particle to another in a sample um we've already talked about ionic bonding um and coent bonding so remember ionic bonding the ions transfer electrons and they have an attraction to one another calent bonding they're sharing electrons but we're going to look at those intermolecular forces um and the intermolecular forces are only going to show up whenever it's in one of our condensed States so the liquid are solid um ionic bonding we tend to not be able to reach high enough temperatures to have things that are ionic as gases um but calent bonding still exist even as something is a gas um So within the molecule you can have calent bonding but you will not have those inner particle attractions or inner molecular forces between two different particles so with the inner particle attractions the type and strength of Attraction is going to affect the physical properties of a substance um so for example the stronger the inner particle attractions we're going to have higher melting points higher boiling points and also a higher viscosity it's going to resist flowing and moving typically so the particles will want to stick together more so like I said in particle attractions or inter molecular forces you'll hear a lot more often um inter molecular forces so a molecular refers to the forces between two different molecules so not within one molecule so it would be one water molecule attracted to another water molecule um if it is within one molecule inside a molecule those are referred to as intra molecular forces these are like our coal bonds or our ionic bonds and molecular um means that it's not present in ionic compounds or Metals so that's where we may look at interparticle Forces versus Inter molecular so inter inter moleculars between molecules that are going to be those coal bonded ones so some things to knowe inter molecular forces because they're between two different molecules are weaker than intr molecular forces so these are going to be weaker than ionic bonds weaker than metallic bonds weaker than coent bonds and for example like it's easier to vaporize water than to actually break apart the calent bond to separate into hydrogen and oxygen we can boil water to make Steam but it's going to take electricity and a lot of energy to actually sever that bond to make hydrogens and oxygens versus water vapor so some things to note during phase change like when we are melting freezing boiling the molecules are still intact if you have ice and you melt it it it went from solid water particles to liquid water particles but it's still water particles whenever you boil those they are now gaseous water particles so you didn't actually break the calent bond whenever you're going through a phase change so the energy required to actually change States is used to separate molecules from one another so that means that it has to overcome or weaken those inner particle attractions or inter molecular forces so whenever we are melting from Ice to water we are weakening those intermolecular forces that are holding the water molecules together whenever we are boiling we are actually like breaking apart that attraction between the water molecules so there are three main types of intermolecular forces we come across and these are ones that we looked at in chem 1 but we're going to dive a little bit deeper in these so we have dipole dipole forces um you'll also hear these referred to as dipole interactions um we also have hydrogen bonding this you heard in biology and chem1 and then we have lond dispersion forces um there are also a couple where we are going to mix some of the forces um these are going to be new ones for you that we did not talk about in chem1 So we also have ion dipole forces and dipole induced dipole forces and we're going to talk about each one of these and when you would see these what type of substances would have these so looking at those dipole dipole forces um here remember a dipole is a substance that has two poles so a positive end and a negative end so with dipole forces the positive and negative ends of polar molecules will interact with one another resulting in a net force of attraction so the positive end of one molecule can be attracted to the negative end of another molecule um this is about 1% as strongest calent bonds so it is weaker than calent bonds and this becomes weaker with a greater distance the further apart those particles are the weaker that dipole attraction is going to be so looking at this we have two polar molecules the positive end of one is attracted to the negative end of another um but you can actually have a bunch of molecules that are attracted to one another so here you notice that the negative end of one molecule is attracted to the positive end of all neighboring molecules um so the attractions you can see in red um they can also repel one another so those are the yellow dotted lines or those repulsions um this is where particles are going to be held in a certain alignment overall we also have hydrogen bonding and like I said this you um talked about in biology with like DNA and proteins and then we talked about it in chem 1 um but hydrogen bonding can be thought of as a very very strong dipole Force um and this is only going to occur between molecules that can contain hydrogen attached to a Florine oxygen or nitrogen so you can remember that hydrogen is fun f n that's whenever we tend to have hydrogen bonding um it's only these three elements because they have a very high electro negativity so there tends to be a very large difference in electr negativities between hydrogen and these three um we also tend to have hydrogen bond because these particles are very small so the molecules can be closer together resulting in a larger attraction um these yet again are still weaker than actual bonds these are about 10% as strong as an actual calent Bond um this a lot of times we said that the inter molecular forces can determine those physical properties of substances um if we look at this chart this has different substances and it shows their boiling points um and you'll notice that the red line the very Peak is that water molecule that is very electronegative but then as soon as you get to those larger atoms like sulfur that's going to be a little bit bigger it doesn't have as high of a boiling point because there's less of an attraction between particles um same thing with like the hydrogen fluoride um it's only an acid if it's aquous so if it's a gas it's hydrogen fluoride but the hydrogen chloride that is right below it has a lower boiling point because there's not as strong of an attraction this is kind of the data that we use to determine which ones specifically have that hydrogen bonding her um so this like we said happens whenever hydrogen is paired with Florine oxygen or nitrogen so whenever it's paired with oxygen it does make water um and like we said this can be thought of as a very strong dipole because oxygen is more electronegative so it is attracting those electrons the oxygen ends up being slightly negative and the hydrogen end up being slightly positive so what that results in is when we have a bunch of water molecules the hydrogens are going to be attracted to that electron pair that is on oxygen so you tend to see a lot of these aligned together overall we also looked at hydrogen bonding in biology um the base pairs in your DNA are held together by hydrogen bonds so you can see the double helix here um we're looking at this a this Adine thyine um that attraction those dotted lines are the hydrogen bonds that we're looking at so you can kind of see these dashed lines between the two bases representing those hydrogen bonds um and remember hydrogen is coal bonded to one atom so and then it is hydrogen bonded to another so if you're looking at the a base pair you have this hydrogen is attached to a nitrogen Cove valent and then it is attracted to the oxygen on the other base pair and they don't have to have hydrogen bond to nitrogen oxygen or Florine on both molecules it just tends to be attracted to one of those very electronegative elements on another molecule um this was also how like polymers and proteins are put together um so here you can kind of see the structure overall where we have that hydrogen paired to nitrogen and in the larger structure that's where that attraction occurs now we're going to move move on to lung dispersion forces um these tend to be the weaker Force not always but in general this is the weakest force that we tend to come across and non-polar molecules and atoms can still exert forces on one another even though they're not polar and not having that attraction um or if they did not have some attraction between particles they would never be in a liquid or a solid form so we know there is some attraction between molecules it's just a weaker attraction than those dipole or those hydrogen bonding um so if we take carbon dioxide for instance um carbon dioxide in its solid state is dry ice carbon dioxide if we were to sketch it out if you remember it has those two double bonds with oxygen and there's no dots on the center atom I'm not going to draw the extra dots so that is non-polar if lung dispersion forces did not exist this could not exist as dry ice um same thing about like iodine that's I2 it's one of our datomic ones we know it's non-polar because one iodine is not going to be stronger than the other we do have solid iodine that could not exist without these lond dispersion forces with L dispersion forces the reason that they exist what causes that force of attraction is that electrons are not going to be evenly distributed at every instant in time within a molecule so for a split second the electrons moving in their electron cloud are going to be unevenly dist distributed and that creates an instantaneous dipole so for that Split Second we're going to have part of the molecule that's slightly positive and part of the molecule that's slightly negative and this induces a dipole in the atom next to it so the electrons in one atom can influence the movement of electrons in the following atom so to show you what this looks like here we have two hydrogens that are non-polar right now the electrons are equally distributed but if one of the hydrogens the electrons move more towards one side and we end up with a slightly positive end and a slightly negative end that causes the electrons in the neighboring hydrogen to shift as well creating that dipole that instantaneous dipole with the Positive end and negative end with these lend dispersion forces they are weak and they tend to be very short Liv so they said for a split second those electrons are unevenly distributed but then they go back to normal because they're in constant motion um these forces tend to last longer at lower temperatures so at lower temperatures those forces last longer that's why at lower temperatures those substances can exist as solids um eventually these do last long enough to make liquids and whenever they last even longer they can make solids but these tend to be much weaker than the dipole forces and the hydrogen bonding there will of course be some exceptions but these tend to be the weakest of the three so with dispersion forces their strength is based on polarizability of the molecule this is a word that you will want to use if you're ask like why one has more dispersion forces than the other it's going to be based off of polarizability polarizability is the measure of the extent to which the electron cloud of an atom or molecule can be distorted by an external electrical charge so in general the more electrons something has the more polarizable it is therefore it will have stronger dispersion forces so larger molecules that have more electrons are going to be more polarizable compared to others so here we have a sample of pentane and a sample of neopentane it just looks at the overall arrangement of it with these strength is based off of polarizability of the molecule if we look at these they have the same formula So based off of electrons we could not tell which one of these is more polarizable however we can also look at the overall shape of the molecule to help determine which one would have stronger forces so let's look at these a little bit more based off of their Arrangement so here we have that pentane which is spread out it's elongated there are multiple atoms that can interact with one another so there's a large area that they can interact whereas the neopentane that is more compressed there's only a small portion for for those to interact so that would have weaker forces because there's going to be less interaction between the molecules so let's look at an application of this um you could be asked which one has stronger dispersion forces hydrogen or iodide um if we look at them hydrogen H2 is only going to have two total electrons or even two total electrons iodine by itself has I believe 50 55 electrons sorry I don't have peric table right in front of me so iodine has a larger electron cloud there are more electrons there therefore there are going to be more interactions between the electrons meaning iodine has a higher London dispersion force simply because there are more electrons so it is more polarizable so looking at our three primary intermolecular forces we looked at we said the weakest was going to be those London dispersion forces um this occurs we're going to talk about it majority of the time between non-polar sources um but lend does dispersion forces really exist between everything but it is the primary force present in non-polar substances the strongest intermolecular force is that hydrogen bonding and remember hydrogen bonding only occurs whenever it's hydrogen attached to a Florine Ox nitrogen so remember hydrogen is fun that's how you can remember it and then the the one in between was the dispersion force or not dispersion excuse me dipole forces and remember this occurs between polar molecules where you have that positive end of one molecule attracted to the negative end of another looking at all of these forces um there are interactions that occur and there's a couple of these we still have to talk about but if we are dealing with ions if there are only ions it is an ionic compound meaning that it only has ionic bonding that's going to be the primary force there we're also going to talk about if that ionic compound is interacting with water we're going to look at that in a moment if there's molecules though you have to determine if the molecule is polar or nonpolar non-polar molecules tend to have the dispersion forces um if we have polar molecules we can have dipole forces but if it has the hydrogen with Florine Ox nitrogen that also has hydrogen bonding and then we're going to look at what happens if a polar molecule is trying to interact with a non-polar molecule and that will be a dipole IND dipole so we're going to look at a couple of those special forces for a minute so those ion dipole forces we said occur when you have something ionic interacting with something polar typically water um so here it shows aquous sodium chloride so it's ionic but it would state that it is aquous what happens there I apologize I'm trying to write with my mouse what happens there is whenever that ionic compound is in water if you remember from chem one we talked about net ionic equations where that ionic compound will split into ions here's the reason that it splits into ions whenever it's in water the positively charged end of a polar molecule is attracted to the negative ion in the ionic compound and then the positive end or the negative end of the polar molecule is attracted to the positive ion so that attraction causes the ions to separate and the water molecules will surround them with the Positive ends attracted to the negative ion and the negative ends attracted to the positive ion so anytime you have something that is ionic in aquous form it's going to be one of these ion dipole forces and I don't have a drawing of the um dipole dipole or dipole induced dipole but it's where something like iodine that has a lot of electrons those electrons can be attracted to the positive end of water and that's what causes something like iodine to be in liquid form or in aquous form where we can still dissolve it looking at our overall air molecular forces um our strongest that we've talked about so far is ionic bonding um hydrogen bonding is going to be weaker than actual bonds below hydrogen bonding we have those dipole dipole forces and then remember our absolute weakest are those dispersion forces um we last unit mentioned metallic bonding that tends to be weaker than ionic bonding and here's where there's some discrepancy there's a couple of things that occur Cove valent bonding is typically weaker than ionic bonds in but we're going to talk about some substances where there are a multip multitude of coent bonds causing it to be stronger than even an ionic substance um we're going to go a little bit more in depth with that whenever we look at our solids though and you'll kind of see why some coent bonding is stronger than ionic bonding but if it's something just like within water that can be separated a little bit easier we also have those ion dipole forces those tend to be a little bit stronger than hydrogen bonding um and then we have those dipole induced dipole forces which tend to be a little bit stronger than dispersion um those tend to not come up as much whenever we're comparing one substance to another however and we kind of rank these based off of their forces where people did experiments looked at how these how much energy it took to actually separate some of these different substances um depending on what it was and based off of how much energy it took to break it apart that's how they got these rankings and we talked about the intermolecular forces affect the properties of those substances so kind of going back intermolecular forces affect the melting points and boiling points of substances um so generally the stronger the forces there are it's going to take more energy to break them apart so they tend to have higher melting points and higher boiling points if they have higher intermolecular forces um so since it affects the melting point and boiling points therefore it also affects the physical state of the substance at a given temperature so these inter molecular forces or what determine if a substance is a gas liquid or solid at room temperature um these can also affect the conductivity of a substance um so with things that are Co valent a lot of times if it is completely non-polar it is going to not conduct electricity but something like water that's polar can also interact with ions which could mean that it could conduct electricity um these also affect the chemical reactivity um and we'll look at this a little bit later this unit of if particles do not interact with one another they cannot react but if there's similar forces where particles can interact it can cause a chemical reaction overall um based off of the structure it can also affect the hardness or softness of a certain material um so something like a diamond even though it's just calent bonds is going to be much stronger than something like graphite or your lead in your pencil that is also just calent bonds so a lot of times those intermolecular forces and the overall structure are going to affect kind of the strength of that material this is where we're stopping for today and it is going to go on and talk about solids and what type of solids form and what intermolecular forces are associated with those e e e for