Major Intermolecular Forces
forcesin between molecules in particular we're talking about the attractive
forcesbetween molecules is really what ends up governing all physical properties and when I say physical properties I mean boiling point melting point viscosity surface tension stuff like that our physical properties and it's really governed by how strongly these molecules are stuck together turns out a lot of these
forcesalso affect the way chemicals react because a lot of these same
forcesgovern the way chemicals come together and then if you can get them together you have the possibility of a chemical reaction we generally cover three basic
forcesthat we give three distinct names the differences are really pretty subtle it all comes down to the difference of a positive charge and a negative charge that's really what the attractive force is about so you have positive and you have negative the more positive it is the more negative is the stronger the force this is simply a cool Amba cat rack ssin positive attracts negative and we have all degrees of this it's just a matter of how positive and how negative most molecules being neutral species do not have full positives and full negatives on them that tends to be the world of ionic molecules so we're constantly writing partial positive and partial negative we even have the way we symbolize it on paper what you should be used to as these partial...
positive and partial negative charges matter of fact if you can get enough distribution within your molecule to where you have a lot of positive charge on one side and negative charge on the other you can get what we call a polar molecule a permanent dipole is a polar molecule and if you have a permanent dipole you're going to have a set up within the molecule where you always have partial positive you always have partial negative and those are going to get together that's called dipole dipole winter action and that is the strongest interaction you can have within a molecule to another molecule now we have a subset of that that's actually the strongest version of that there even stronger than a regular dipole-dipole and we call it hydrogen bonding and it's really because it involves hydrogen being the partial positive part of this molecule anytime hydrogen is covalently bound to a very electronegative element and I'll be specific here it has to be bound to fluorine oxygen or nitrogen and when it is it becomes so partial positive and the oxygen or nitrogen or fluorine becomes so partial negative that you get an even higher amount of attraction so we go ahead and classify that in its own class we call it hydrogen bonding but it's really just dipole-dipole interaction just up a notch at the low end of the scale are nonpolar molecules now nonpolar molecules are molecules that have no dipole moment whatsoever there usually are nonpolar due to symmetry...
arguments meaning that whatever you argue pointing one way there's the opposite wave covered somewhere else on the molecule so all the symmetry wipes out the polarity of the molecule good example of this is carbon tetrachloride carbon tetrachloride has four very polar carbon chlorine bonds but they all nullify each other as far as distribution of charge so it's a non-polar molecule however it will attract another carbon tetrachloride molecule they do stick it is a liquid so there's definitely
forcesthere so what are they they're dispersion
forcesand they are based on what we say our temporary dipole moments temporary dipole moments is when the electrons within the whole molecule are in such flux that at any one point in time you're going to catch it with a slight positive end and a slight negative and another model Pikul is going to get caught in that same time and there's going to be an attraction there this will change over time and time again in very fast timeframe yet the attraction is there so it's a very slight attraction it's not nearly as strong as a permanent dipole but that's what we call dispersion
forcesso that's all three
forcestogether there we've got hydrogen bonding up at the top right under dipole-dipole interaction and a little bit below that we've got dispersion
forcesthose are the three
forcesat play with all molecular substances we can go into details on each one that's another...
story so right now just keep straight what the three types are so that when we talk about them you'll at least know what we're talking about