this video is about molecular polarity molecular polarity determines how molecules interact with each other at the molecular level a really important vocab word here is called electro negativity and this is the ability of an atom to draw electrons towards towards its nucleus the more electr negative an element is the more it wants electrons so we know that every element is different therefore every element has a different electro negativity value associated with it your general trend for electr negativity up and to the right is the most electronegative element So within a group as you go up a group as you go up a group it is more electr negative and then for a period as you go across meaning from left to right it is more electr negative so that is the Trend Florine is the most electronegative element if you notice on this table all the way to the right are the halogens here this is group 7A so what happened to the noble gases recall that the noble gases are inert they do not react with anything they do not want any electrons so their values are just ignored that is your group trend and that is your period Trend so these differences in electro negativity determine if a bond is polar or non-polar so Bond polarity and molecule polarity are different and we will get to both of them if you have two elements with differing greatly widely differing Electro negativities this leads to what's called partial charges so the element that is more electr negative will have a Delta negative symbol with it so out of h and f here again we already said f is the most electronegative element notice F has the Delta negative and then the element that is not as Electro negative would have the positive sign and that is just showing where the electron cloud is going to be distributed towards if you can see here your electron cloud is bigger to the right at the blue here with H2 just picture two h's bonded to each other they're the same electro negativity so that is an even distribution notice how this is evenly spread that is non-polar non-polar is even distribution and then polar is uneven so this separation of partial charges this is called a dipole so a dipole is drawn like this where it's an arrow and a plus sign so the arrow is pointing towards the more electr negative element that's why the arrow here is pointed towards the right because Florine is on the right and then the little plus sign here if you can see the plus that's on the more on the least electronegative element so this right here is a a dipole nonpolar bonds even distribution there's no dipoles no partial charges their electro negativity values are very similar now how do we know how similar they have to be this these numbers change I've read textbooks before where it's .3 to 1.7 this says 0.5 to 2.0 this can differ but it's it's generally speaking that if your difference in electro negativity values is less than 0.5 that is non-polar less than 0.5 is nonpolar again every element it's a textbook value they're given values like florine's 4.0 hydrogen is 2.1 so Florine 4.0 hydrogen 2.1 if we subtract those we get 1.9 that would be polar between 0.5 and 2.0 is polar and then greater than two you would have an ionic bond you can see electron cloud wise what it looks like again this is an equal sharing cloud looks similar left to right you have an unequal sharing with the cloud being bigger at the more electronegative atom and then ionic you have a complete transfer they're not sharing electrons they are taken and given away so it's complete transfer for ionic bonds and of course we have our catons and our anion so using your periodic table find which is more Electro negative remember the trend is up and to the right is more electronegative so if we're looking at carbon and nitrogen nitrogen is to the right of carbon so nitrogen would be more electronegative nitrogen is above phosphorus so nitrogen again would be more electronegative lithium or chlorine lithium is all the way to the right chlorine is all the way to the left so chlorine would be more electronegative and silicon and nitrogen nitrogen is further up and to the right so nitrogen would win that battle as well so pretty easy Trend to identify now we're going to place a partial positive and partial negative charge on the atoms in these polar bonds so remember it's going to look like this or this you can practice draing that so we just need to know which one is more Electro negative CL in this case is more Electro negative so that'll be our negative and H will be our positive out of c and n n is more Electro negative and we know f is the most Electro negative so that will always be the minus if it's there so that is just for Bond polarity now we're looking at molecules so molecules can also be polar or nonpolar a non-polar molecule is either a molecule with all non-polar bonds so if every bond is non-polar it's a non-polar molecule pretty easy the tricky part is if the molecule has polar bonds but they are symmetrical so symmetrical geometry with polar bonds it is a non-polar molecule then so I like to think of this to help myself symmetry equals nonpolar what happens is the polar bonds cancel each other out resulting in a non-polar molecule so think of this here hydrocarbons hydrocarbon is something with c's and H's only so if we look here look at the Symmetry we have an H here and an H down here they're canceling each other H here H here they're all cancel and then this h on the right is canceling that h on the left so all of that symmetry even though each bond is polar the entire molecule is non-polar diatomic elements same idea here hydrogen has a 2.1 electr negativity so they cancel the pool is canceled out symmetry so that's a non-polar molecule and again that's just because of the cancellation Factor the three uh shapes that you learned about that we need to watch for is linear as in carbon dioxide here that's linear right there's your central one two that's linear that would cancel right this o is pulling here think of identical twins and think of it's kind of tug of-war so this twin is pulling with their power here here let's pretend identical twins have identical strength and this twin is pulling here it would nothing would happen right it would cancel trigonal planer you have to watch for so trigonal planer they're spaced out 120° perfectly let's just pretend that's perfect that would cancel each other and then tetrahedral as well would carbon tetrachloride that would cancel each other as well there's a better depiction than what I drew it's key though that these atoms are identical like in this case they're all FS they're all FS or they're both O's because if they are different atoms then they will have different pools so they have to be twins or triplets or quadruplets for this to work here's a nice little recap slide for you so that's for non-polar a polar molecule is a molecule with one polar bond if it has non symmetry with polar bonds or if it does does have symmetry and it has nonidentical polar bonds so if they are not twins if they have different elements on them so here are examples here so notice this guy still trigonal planer but this o here has a different pull than these H's do so so they do not cancel then if this o was another H now that's non-polar but because it's different it's polar it's very important to know the geometry Like Water for example if you ignore geometry completely and you drew water like that linearly on the 2D on a 2d on P paper that looks like it cancels right cuz it looks linear it looks like okay H H but no we know that water is actually bent and we know the pull is going towards the O so that does not cancel there's no pull up here to cancel the pool down here or vice versa and same idea here this guy is the reason that it is not symmetrical if that was an F it would be non-polar there's a nice recap slide so let's look at these molecules and say if they are polar or nonpolar so a is 2 CL atoms they are diatomic they are twins that is non-polar they would cancel B trigonal planer but this guy is throwing it off right these cl's look fine but that o is throwing it off so that would be polar different explanation would be different dipoles explanation for a would just be it's diatomic it's the same same dipoles see all the fs are the same here it's trigonal pyramidal it looks like because it has three bonding SES in one non-bonding site so this would be nonpolar these have same dipoles D so like a it's only two elements however they are different elements so I and F have different electr negativities they are not twins that is polar e they're all the same that is tetrahedral they're pulling that would cancel their symmetry there that is nonpolar they symmetry identical dipoles and F just like e except a different geometry this is linear but you have two twins pulling that would cancel so the explanation would be the same for f