okay keep alluding to this because it's so important this is the driver behind whether um there are intermolecular attractive forces and what they are it's called electronegativity so electronegativity um is different than electron affinity very different just a quick review so e a electron affinity it is actually the energy required or released when an atom gains an electron so e required released when atom gains electrons so i could have fluorine in the gas state remember it's got to be in the gas state that's the definition plus one electron will go um give me the ion fluoride in the gas state and the energy is negative because energy is released okay so fluorine has a high electron affinity now electronegativity is the ability of an atom to attract a bonding electron to itself now we're talking about two atoms that are sharing electrons in a bond in a covalent bond so i could look at carbon and chlorine okay and say well how much electron density or how much electron um if you look at it from lewis's um idea that electrons are particles how much more time is that electron that comes from carbon gonna be spent on fluorine versus carbon where is that electron gonna be is it going to be more towards carbon or it's going to be more towards fluorine um these numbers that you have in your textbook are rounded to the 10th usually and there are numbers that are much better than that we'll just use the ones rounded to the 10 okay so um when i ask to calc you to calculate delta e n um on a quiz you will use the electrons rounded the tent okay so our electronegativity found in the tenth okay so um lewis comes up with this idea of electronegativity and he looks at ionization energy and electron affinity and sizes of atoms he does the calculations and he comes up with this idea and he gives he normalizes it okay um increases from left to right across the periodic table uh no noble gases have numbers okay why is that [Music] well how many times do we find noble gases in molecules i mean uh xenon tetrafluoride didn't exist when lewis was around had to be made synthetically in a lab so noble gases are not assigned electronegativity values so it stops at the halogens so it increases from left to right across the periodic table what else is increasing when you go across the periodic table what are some of the things that increase when you go across the periodic table valence electrons valence electrons what else you can put it in the chat oh i see someone chatting here let's see so valence electrons increase z effective absolutely so these valence electrons are increasing as you go across the periodic table but they are not shielding each other so really what's happening is that it's the protons increasing across the periodic table that are starting to be felt by more of those electrons and things are getting smaller so z effective so what is z effective it is the basically positive charge that valence electrons can feel so if you increase that positive charge the feel or the pull of that positive charge guess what that means electrons in a bond are going to be more attracted to an element on the right hand side of the periodic table and that's exactly what we see so if i look at carbon and fluorine carbon with this four valence electrons and fluorine with its seven okay if i look at that i find that the electron is going to be more located okay if i drew a heat map here where red means electron density is going to be more located on the flooring and it will be less located on the carbon okay so the carbon will be slightly positive and the fluorine will be slightly negative so when i'm looking at the difference in electronegativity now it's also going to decrease as you go down the group again we're talking about how much can the proton in the middle of the atom be felt by something else that comes to bond right so if if there's a big distance between the positive and the middle and the negative that wants to feel it there's a really big distance then you're not going to have as much electronegativity the um the atom that's large isn't going to be pulling things towards itself now the larger the difference in electronegativity the more polar the bond and when i talk about difference in electronegativity okay i am going to use the capital letter d delta in greek and i've done this a lot begin i say what's the difference between volume what's the difference between mass i always use delta so difference right capital d in greek and i'll say e n what is the difference in electronegativity the larger the difference the more polar the bond so what is polar polar is basically charge separation as i drew up here in the cnf that are buried underneath there let me write on my own again okay because fluorine pulls so much electron density towards itself and not as much towards the carbon and you have a large difference in electronegativity you have a large amount of charge separation and notice that i drew that charge separation using lowercase delta so um remember how i said slightly i said slightly slightly i said slightly positive well i say that because that's what i had to use to remember this i go oh look at that little letter it looks like a little s it's not a little s but it looks like it to me because i didn't know greek so i had to learn some greek so when i talk about charge separation um or you'll you'll hear me talk about it in the pre-lab lecture notes um uh partial charges i'll talk about partial charges because it's not it's not carbon is like plus one and fluorine is minus one that's not it's not ionic it's not that extreme but it's a little bit it's like closer to positive and fluorine is closer to negative so i use this little letter this is actually a lowercase delta for difference okay so in greek that's what the lowercase delta looks like and the uppercase delta music uppercase b delta so oh i can't read what i just wrote do it again d e l t a there it is so we have the uppercase delta is the big triangle and then the lowercase delta is looks like a little s slightly so let's talk about the values that we'll use um we we're gonna we're gonna be using values that are just kind of standard chem 1a values it's not from your textbook this is actually from tro i really like this textbook which is why i have a lot of images from them um but it costs like 350 or something so we're not using that textbook you have a fine graph in the free one and then you have this image here so one of the things that you can see is that it's not perfectly increasing as you go from right to left across the periodic table some very interesting things happening here in the transition elements right but our focus is here where we're going to be looking at the main group elements mostly and what we'll see is um it's pretty straightforward to calculate the difference in electronegativity and between any element if you're given the value i will always be giving you the values or you will have the chart available so that you can know what those values are um [Music] what else i want to say about this i think that's it because i want to just start doing some actual calculations okay so why don't you guys take a moment here when i do my stickers listen which of these lists uh the following elements in order of decreasing electronegativity so you'll have largest on this side you'll have smallest on this side so take a look at your periodic table or maybe you want to go back to that um periodic table i just showed you guys in the notes and answer this question you can put your answer in the chat awesome so if you're still working on this um and you haven't looked at the chat yet i'm seeing the answer coming in right now but if you haven't looked at the chat one of the things you would want to do strategy wise is to say well which of these is the largest uh electronegativity on the periodic table it's always fluorine is the largest so that rules out b and c so b and c can't be correct so the next thing you're left with is a and d and if you look at the periodic table you recognize that these guys are in the same period and then you look at silicon magnesium and calcium so silicon and then mg and ca so basically silicon and magnesium are in the same period and then you have calcium one down so you're going to first rank these by going right to left across the periodic table and then you're going to compare them well what's up and what's down okay um so great yeah hey is that one good job you guys uh again you will have the values around so i'm not going to quiz you on this exactly but it's really useful if you can just get a visual in your head it's going to help you when you are applying um the ideas that are coming up about intermolecular attractive forces stuff okay okay so qualitatively we know um how to rank them and then let's talk about electronegativity difference okay so delta e n so again electronegativity difference i'm going to use delta e n okay and that's what's on the bottom here now notice there's a range of differences in electronegativity and a classification so bond type we're just focusing on bonds here and we're just looking at two atoms at a time bonding okay and what you'll notice is that um there's this breakdown between what we call nonpolar okay so nonpolar i'll do it in blue maybe stand out a little bit zero to 0.4 roughly 0 to 0.4 okay polar roughly point four to two and then there's this whole range what we would consider ionic but the crazy thing is there's even like a range of how much the electrons are transferred okay these are major classifications and they are classifications that are first based on observations okay so when a bond in a molecule is nonpolar okay if i have a bunch of nonpolar molecules okay so i'm looking at molecules with just two atoms in there a bunch of non-polar molecules what i find is they have very different properties from polar molecules and then of course we know the difference between polar and ionic okay so let me just list a couple of things here for you um and then you can kind of think about um these are just simple nonpolar molecules things like uh hydrogen chlorine um will be another one well methane ch4 is a little more complicated because it has four ch bonds right but methane is one h4 um let's see some simple polar molecules could be something like hf or hcl um another one that would be really simple um with carbon but it's more than two atoms in it would be um ch2o this is formaldehyde okay and then ionic we just talked about it ionic compounds like nacl okay so if you think about these molecules think about hydrogen it's a gas you think about chlorine it's a gas you think about methane is a gas and so is propane and so is butane okay their physical properties their physical states at room temperature that's different than hf hf you can buy as solid it's soluble in water same with hcl okay um and you can dissolve it in water make really high concentrations of hydrofluoric acid and hydrochloric acid and same with formaldehyde now formaldehyde is um a liquid but at pretty low temperatures and if you've ever been in biology and you smelled uh the specimens that are preserved in formaldehyde you know the formaldehyde will also be a gas at room temperature but it's soluble in water and they make formalin solutions right so very different than hydrogen chlorine and methane and then of course very different from sodium chloride so these values here the zero to point four you you want to memorize these okay i'm gonna write these um these values zero to point four are not arbitrary they are actually based on physical properties of molecules that exist and you go huh interesting you see this demarcation point between 0.4 and 0.5 where all of a sudden solubility with water starts happening okay and you have different types of intermolecular attractive forces showing up that you don't have in nonpolar right so the zero um to 0.4 cut off and then the next one would be uh 0.5 to 1.9 that's considered polar um now zero is pure covalent uh that is going to be what's happening between same atoms so if you have something that's pure covalent the atoms are the same in a bond hydrogen chlorine and that's pure covalent and then 0.1 to 0.4 now there are some interesting [Music] cases where you have the same electronegativity values but the atoms are different and based on this generalization you get a pure covalent bond that's actually not true okay so um i'm not trying to lie here to you but it's like oh yeah zero is pure covalent not not really okay kinda um if the values have the same are the same we can expect very little um difference in partial charges on the atoms right because in general they both want the electron the same okay general but you'll begin to see some nuances that i'm not covering in this class you'll see it in other classes uh the the 0.1 to 0.4.5 to 1.9 you'll definitely see larger than 2.0 or equal to 2.0 on the bond is considered ionic again rough breakdown here so let's do some calculations and look at bonds and bond polarity so this would be um chlorine and chlorine gas cl2 remember it's a diatomic um delta en is calculated down below okay and three minus three is zeros pure covalent um notice what i'm doing here is that i'm representing um [Music] the difference in charges with the delta again right slightly so uh electronegativity of chlorine is 3.0 the electronegativity of hydrogen is 2.1 so just by looking at these numbers 3.0 is bigger 3.0 means that this atom wants more electron density for itself and so if i'm going to write a partial charge on there i will be giving the negative partial charge to chlorine because it has a larger electronegativity value and then hydrogen gets a smaller one so hydrogen chloride as a gas is a molecular acid if i put it in water or as a solid as a molecular acid if i put it in water it will dissolve and make hydrochloric acid the chlorine will actually take the electron off of hydrogen it wants it so much when it's dissolved in water and you will get h plus cl minus when this is aqueous so hydrochloric acid when it is aqueous this is polar covalent how do i know it's polar covalent because delta e n is between 0.5 to 1.9 okay it's classifies polar covalent and then finally sodium chloride so isn't it interesting the sodium chloride i keep talking about oh it's ionic it's ionic yeah barely right because you could have a difference in electronegativity of like three or four right and that doesn't happen here but we know that electrons are transferred enough to give it all the properties of an ionic compound it's hard it's brittle it conducts electricity when it's dissolved in water or when it's in the liquid state so 2.1 delta en is enough to make the physical properties of this um compound act like it's ionic okay so again um i have these delta here this is partial charges so slightly positive slightly negative and then there's one last thing i need to show you and that is also called a bond dipole which i'm going to get to okay so here's an example of hydrogen fluoride if it's a gas hydrofluoric acid if it's dissolved in water and the difference in electronegativity for h and f is quite significant and so much so that you're gonna have much more negative charge so over here uh on the right hand upper right hand corner is a heat map and the larger or the more red something is the more electron density um these atoms have and so this is fluorine here on the right and then on the left you have hydrogen and you have slightly positive so the electron density is pulled towards the fluorine how do i know that by looking at the numbers 4 is greater than 2.1 and then i can draw what we call a bond dipole so a bond dipole is represented by an arrow the plus part of the arrow aligns with the partial positive charge and the arrow points toward negative okay and this is the representation of a bond dipole what is a dipole die means two poles so you have a positive side and a negative side dipole positive negative so the bond dipole is going to be again represented by the arrow so we have is slightly positive slightly negative that is partial charges represented and then the bond dipole and that's the arrow that you see on top of hf and there's the partial positive partial negative now the cool thing is you can actually test to see whether or not this is true right hf like how do you know this is true well if you have hf flying around with no electric fields versus hf lying around with an electric field okay all of the molecules will align themselves so that the pluses and minuses and the plus the negatives and pluses line up and a really simple experiment that you can do that's super fun at home if you have a um uh like a balloon or you have most people don't have like a plastic rod lying around you can do a balloon so you can take a balloon and you can get some charge on that balloon and you can get that by ruining your hair rubbing it against your head it's an easy way to do it and turn the faucet on and put that balloon that has been charged next to the faucet and you will see the stream of water go literally water itself will align to the electric fields that you have generated on that balloon and you will see the whole stream of water attracted to that balloon so you can see this this is not something that's just like made up and you can't see it the the actual physical properties you can observe all right so i have a couple of examples i want to do and i'm choosing these particular examples because you will see them all the time anybody going into biology or pre-med c-o-c-o to be everywhere c's and o's are gonna be found in every single amino acid that you have that means it's gonna be in every single protein you have c's and o's will also be found in um dna rna season is going to be everywhere okay now it's really nice to have a couple of these memorized so you just don't have to keep going back and doing the calculations you want to be able to get to this place where you look at a molecule and you're like oh there's a cno i know what's going on and i don't have to do the calculation i can just tell you what's going on right now and then i can go from there to imf's and from there to physical properties okay so that's what you want that's what i want for you okay so we're going to determine electronegativities we can use a table or a textbook we're going to subtract the electronegativities large minus small so these are going to be positive values so c 2.5 oh 3.5 um and one of the ways i mean i've remembered this is just um that they they increased by 0.5 but you can also look at the chart that i have in the uh notes or you can look in your textbook but if you look at it c is 2.5 and then nitrogen is 3 and then oxygen is next and that's 3.5 okay so these are in a bond together and we're going to calculate delta e n it's the large number 3.0 minus the small number two point oh sorry 3.5 okay 3.5 minus 2.5 equals 1.0 okay so the range for polar is between 0.5 to 1.9 and looks like the co bonds right in the middle of there so i'm going to classify the co bond as a polar covalent bond then i'm going to look at the electronegativities and i'm going to see that 3.5 is larger than 2.5 so i'm going to say that the come on change color that the oxygen will have the slightly negative partial charge on it moving faster than my ipad wants to go okay slightly negative that means the carbon will have a slightly positive partial charge on it and if i draw a bond dipole it's going to be pointing from the positive end toward the negative end that's my bond dipole we have a polar covalent bond this is one of the very important drivers for the physical properties that we see in things like hair so why is your hair the way it is it's a protein why are your nails the way they are it's also a protein you have keratin okay what about the collagen in your skin it's a structural protein and if you get all these c's and o's lined up next to each other because guess what pluses and minuses are attracted to each other you can get quite a strong structure especially if you layer it so our hair is a triple helix there's a helix of a protein three of them all wound up together which gives you the integrity of your hair okay and then your nails are made up of what's called beta sheets there's sheets basically long flat sheets of protein and between the sheets of protein there's a strong attractive force um because polar is attracted to polar and if you've ever had your nails kind of peel off like i don't know if you've ever experienced that or had nails chipping or peeling basically what's happening is that something is disrupting the beta sheet it could be something you ate eight months ago it's how long it takes for pretty much for nails to grow out so it could be a dietary deficiency it could be a medication that could be damaged to the nail there's a lot of things right so if you disrupt that polar covalent sheet attractive force then the nails will fall apart the hair will fall apart collagen will fall apart so scurvy right if you don't have your vitamin c you get scurvy within about three months vitamin c is critically important for putting on basically oxidizing proteins so that they can be attracted to each other to um form the basically the structure that you need within collagen you don't have vitamin c you don't have the chemical reactions going on the collagen begins to break down and you get like these kind of swords all over the place i that's why you don't want to get scurvy um okay let's do ch so ch is another really common one and this one we're going to end up with um is it ionic covalent or polar covalent and we're going to look at the c again c is 2.5 and then if you're not sure what the h is you could look at the chart in your notes if you look on your textbook and we have h here it's 2.1 so the difference in electronegativity delta e n is 2.5 minus 2.1 is 0.4 so it's right on that edge right so nonpolar is 0 to zero point four it's non-polar sonic oh non-polar i didn't write the word i'm gonna write it right there so um interestingly you might say well there's no bond dipole here there is it's just tiny it's small compared to polar there is a tiny charge separation okay and when you look at the um website that i'm uh telling you to look at ph i think it's the other way it's p-h-e-t fetch i love this website um you will see that there are little bond dipoles but usually they're um they're represented by small arrows okay so where would this where would the charge separation be there is some it's just tiny but it's not enough to make it to oil and water mix if you just have a pure hydrocarbon sadly a bunch of oil was spilled from the last hurricane that just came through where is that oil it is not mixed with the water it is less dense and is floating on top of the water oil and water don't mix why because polar and nonpolar don't mix so you would have a tiny negative charge on the c you'd have a tiny positive charge on the h not enough to be significant and then you'd have something that a little arrow so by the way these dipoles if you've ever had uh vectors in math dipoles uh symbolize the direction and strength right direction and strength the length of the arrow is related to the strength or the amount of charge separation not much charge separation here if this is between a c and an o you'd have a much larger arrow which would overwhelm the system and you would see the molecule or the co is much larger difference all right that's it