hi this is mr. Goma what we're gonna do in this video is go over the worksheet on intermolecular forces in particular what we're gonna focus on is question six on the backside of the worksheet on question six we had to address two molecules water h2o and carbon dioxide co2 and ultimately we had to identify the kinds of intermolecular forces that each of the molecules experience so let's go ahead and do that there first let's remind ourselves about the three kinds of intermolecular forces the three kinds of intramolecular forces or intermolecular or imf's are dipole-dipole forces hydrogen bonding which is really just a subset of dipole-dipole forces and London dispersion forces so if you remember from this diagram here if we only have nonpolar bonds we're gonna end up with a non-polar molecule this can also happen a non-polar molecule if all of our polar bonds cancel out either way if we have nonpolar molecules the only IMF experienced is London dispersion forces LDF if you have a polar molecule then you could have either dipole-dipole forces or hydrogen bonding hydrogen bonding occurs when you have an H a hydrogen bonded to an N o or F if you remember nitrogen oxygen and fluorine are the most electronegative elements so bonds between hydrogen and nitrogen oxygen and fluorine are going to be the most polar bonds so therefore we have more polar bonds we're gonna have more polar molecules all right so let's go back to our worksheet and we can solve problems sips okay so answer the questions for each of the molecules below so what number one let's draw the lewis dot diagram well oxygen has six valence electrons so we'll draw an O with six valence electrons one two three four five six and there's going to be two hydrogen's one two each with one valence electron our bonds are going to be there so water is h o H on the bottom notes water has this bent structure here it does not have a straight line linear structure so if you drew water with an H o and then an H over here you will almost certainly get the wrong answer for the next part now polar bonds let's go back and take a look at our periodic table hydrogen and oxygen there's a big difference in electronegativity oxygen is the more electronegative element so the electrons are going to get pulled towards oxygen so let's go ahead and diagram that on our sheet here and here okay so now what is this line referring to this line refers to the electron tour sorry this arrow this arrow refers to the electrons in this bond here and this arrow refers to this alou's electrons in this bond it shows where the electrons are getting pulled the electrons are still shared between the oxygen and hydrogen but they're shared unequally they're getting pulled towards the oxygen because oxygen is more electronegative if electrons which have a negative charge are getting pulled towards oxygen oxygen will have a partial negative charge and therefore the hydrogen's will have partial positive charges what we've showed here is that yes there are polar bonds okay I so show the work below I've actually showed the work right up here now it's the molecule polar remember we're gonna end up with a polar molecule if the polar bonds don't cancel out and here do they cancel out no canceling out would be going in exact opposite directions so like that those cancelling out that's cancelling out exact opposites so here let me circle with a black marker it's gonna be yes for polar bonds yes for polar molecule because the polar bonds jumps oops can't write don't don't there we go cancel out okay so now last question here asked us to draw the lewis dot diagram of two molecules with the charges labeled use partial negative partial positive charges if any and the ims labeled if any so let's go ahead and draw two water molecules right down here so h Oh H remembering the bent structure on water h o h two lone pairs remembering the bent structure on water so let's go ahead and label our partial charges we'll label the oxygen remember is a partial negative because the electrons are getting pulled towards the oxygen so electron our negative charge so the oxygens gonna have a partial negative and the hydrogen's have partial positive charges so hydrogen partial positive partial positive partial positive and partial positive now let's go back to our definition of an intermolecular force for a second intermolecular force is the force of attraction that pulls separate molecules together now how do we get attraction well you have to have opposite charges and notice we need separate molecules so we need opposite charges on separate molecules so let's take a look here okay so separate molecules opposite charges we'll look here we've got a partial negative on this oxygen partial positive on this hydrogen negative positive opposite charges so this is going to be the intermolecular force I am F what kind of intermolecular force do we have here well we have a polar molecule so it's got to be either dipole-dipole or hydrogen bonding let's double check well hydrogen bonding occurs if we have an H bonded to an end Oh or F well in water its h2o so we have an H bonded to O so yes this is going to be hydrogen bonding all right so hydrogen bonding is going to be our intermolecular force all right great so that's water now let's take a look at carbon dioxide carbon dioxide it's co2 so let's go ahead and draw a co2 here so lewis dot diagram for carbon four valence electrons one two three four oxygens one two three four five six another oxygen one two three four five I'll put this one over here six all right just like what we did over here if we see unpaired electrons we want to pair them up by sharing from one on each atom so great let's go ahead here they can share notice this oxygen still has another unpaired one that can share there let's go ahead and share these guys here and these guys here so notice there are going to be two pairs of electrons between the carbon and the oxygen and two pairs of electrons over here so we're gonna have Oh double bonded to the carbon double bonded to the oxygen lone pairs on the oxygen lone pairs on the oxygen over here okay let's go back and take a look next question are there polar bonds well if we look here we'll notice that carbon and oxygen are separated on the periodic table oxygen is more electronegative so the electrons are gonna get pulled towards oxygen let's label that up so electrons pulled towards oxygen here electrons pull towards the oxygen here okay so yes we have polar bonds and we showed the workup here now is it a polar molecule well look at these two polar bonds they're pulling in exact opposite directions so they're gonna cancel out so the answer is no it's not going to be a pole molecule because the polar bonds do cancel out okay no so if it's a non-polar molecule it's not a polar molecule let's take a look at what kinds of intermolecular forces can be experienced well let's take a look here go back to our example from the other video if we have a non-polar molecule the only intermolecular forces experienced are London dispersion forces we can't get dipole-dipole those only occur polar molecules we can't get hydrogen bonding those those only occur in polar molecules where the H is bonded to n o or F so we go back to our notes here what can we do so first off we're not gonna worry about labeling partial charges because we don't have a polar molecule so I'm just gonna put this like that okay and I'll do another one over here and there'll be some kind of IMF all right but it's gonna be quite weak compared to the IMF in h2o so I'll just go like that and what kind of IMF is it it's going to be London dispersion forces okay hope that helped