hello everybody this is a continuation of our notes learning how to draw lewis structures so we did our intro lesson this is going to be part b where i show you how to draw things that are covalent that only have single bonds later on i'll show you how to do double and triple bonds so first just a reminder that in a covalent bond we're going to share electrons they may not be sharing equally one element may be more electronegative and may tug harder on those electrons but they are still being shared the question is where does each atom and each electron go in the structure we know they're all connected we know things are being shared we're just trying to figure out where they are the structure tells us a lot about how the molecules participate in reactions so that's why we want to know what structure they have so that we can eventually know what type of reaction they undergo so first i'm going to write an abbreviated set of our steps remember your glue in has a more extensive list but we're going to just draw or write out our abbreviated set so step number one count and sum your valence electrons number two place your atoms number three bond all atoms with single bonds remember we want to assume things are simple unless we learn otherwise step four give all atoms a full shell remember that for most things that's eight but sometimes it might be less sometimes it might be more we may not be able to do this in real life but we're just drawing a model right we're just drawing on our paper so we're going to try to give everything what it wants and if it doesn't work we'll fix step five count the number of electrons right those are our dots used and then step six fix if needed that's what we'll work on another day that's when we use our double or triple bonds so remember if it's too few we're going to put them on the central atom typically if we used too many that's when we're going to make double or triple bonds to fix it so let's go back through here and just highlight the keywords count place single bonds full shell maybe we should say recount maybe that would be better recount and then fix okay so that's kind of a brief overview let's off to the side here put some reminders about how we place our atoms so remember hydrogen goes on the outside remember it kind of terminates our molecule it's like a dead end the next one is least electronegative element goes in the center or the inside however you like to think about it remember in order to know which is less electronegative we have to remember our periodic trends remember francium is going to be the least up to fluorine the most remember our noble gases would technically be the least but they don't typically like to make bonds so we usually just think about going from francium to fluorine and then remember the last one is that symmetry is good and remember that's when possible which doesn't always happen okay so those are our rules remember they're more like suggestions next what i'd like to do is kind of start with the simplest thing i can think of and go from there so the simplest molecule i can think of would be hydrogen gas which is h2 we have two different hydrogens and each hydrogen comes with a valence electron and what's going to happen is they're going to each contribute one electron and they're going to share so the way i draw that is i'm going to kind of squish them together i'm color coding some of these just for the purpose of learning how to do it i don't expect you to color code your structures on homeworks or anything we squish them together we keep the electrons lined up remember on the sides of a box sometimes we don't want to have to draw the dots so we can replace them with a line a single line is the same as two electrons okay now each hydrogen thinks it has two valence electrons it only had one to begin with but now this hydrogen feels like it has two and this hydrogen feels like it has two so they both feel more satisfied more stable than they were beforehand next let's do water a structure we all probably know what it looks like but now we're going to know why we set it up that way so we have a hydrogen remember it has to go on the outside our other hydrogen is going to go on the outside and that leaves oxygen in the middle now oxygen comes with six electrons you can see that i'll squish them together the hydrogens each donate one electron to be shared the oxygen donates one electron over here and one over here if i want to redraw this in lines i would put a line for each bond but you're going to notice these electrons are not participating in a bond with anything there's no atom attached here so i do have to leave them alone i can't put a line i have to leave them as dots that's called a lone pair oxygen has two lone pairs sometimes i'll ask you how many lone pairs a molecule has instead of looking at your drawing it's one way we can turn things into like a multiple choice type question so now if i look at this this hydrogen feels like it has two electrons this one feels like it has two electrons and this oxygen feels like it has eight so they all feel satisfied with their full shells hydrogen thinks it has two which is good that's what it wants and oxygen thinks it has eight valence electrons which is good that's what it wants okay next we're going to do a couple and i'm going to walk us through this list of steps as we do it so you can see kind of how i'm getting to the structure i get all right so now let's do cf4 well step one oops sorry about that i'm throwing my markers everywhere okay step one is that we need to count and sum our valence electrons so i have one carbon carbon comes with four valence electrons i have four fluorines and they each come with seven so when i add that all together i find out that i have 32 valence electrons now one thing that i like to do is realize that these typically come in pairs and it's a lot faster to count pairs than it is individual dots so instead of counting 32 dots i'm going to count 16 pairs okay this is covalent right there's no ions present here this is called carbon tetra fluoride so step two is to place my atoms well if i look at this i have carbon and fluorine while carbon is less electronegative so i'm going to put carbon in the center now remember we're trying to put everything going around on the sides of the box and if you notice i have four fluorines and i have four sides to my box so i'm going to put those on the outside one on each side another little tip hint is that halogens typically will only make a single bond they don't have to they can do some other things but usually they like to make single bonds so that's another clue that i'm going to try to put them around on the outside i'm not going to string them together in a big chain the other thing is that if i look at the rule for symmetry this is very symmetrical so this is a really good way to set these up i'm going to redraw this for the purposes of our notes i wouldn't expect you to redraw it in a homework so the next rule is bond all atoms with single bonds i don't want these floating around so they need to be connected together keep your dots nice and tidy on the sides of that box okay then i'm gonna have step four remember i'm just redrawing this so that your notes make sense when you go back and you look at them you know what we did in which order so next is give all atoms a full shell i'm just going to give them as many electrons as they want and hope that it works so right now the carbon is already full it already feels like it has eight so now i'm going to do the fluorines it already feels like it has two so it just needs six more and i'm going to keep them on the sides of the boxes make sure your dots are large enough that they are visible everybody likes to use these mechanical pencils and the problem with that is your dots sometimes are not big enough to see especially if you're taking photos and submitting it online you need to make sure your dots are legible okay so now all the fluorines feel like they're happy the carbon feels like it's happy so let's recount we used 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 pairs which is the same as 32 electrons which is good right that's what we wanted so we are all done if you wanted to redraw this with lines for your bonds you can okay and that's carbon tetrafluoride all right let's do another one let's do n h step one is count i have one nitrogen it comes with five valence electrons i have three hydrogens that each come with one so all together i have eight valence electrons which is the same as four pairs i'm not going to recopy it over and over we're just going to kind of do it all at once so step 2 is to place well the hydrogens have to go on the outside which means my only other option is for nitrogen to go on the inside i'm going to place things going around the sides of my box spread them out hydrogens have to be on the outside so that's my only option my next step is to give everything a single bond we don't want any atoms floating around by themselves step four is to give everything a full shell well the hydrogens are full because they already have two nitrogen right now feels like it has one two three four five six electrons so it needs a couple more so now step five i used one two three four pairs which is the same as eight valence electrons which is what i was supposed to do so that's good and we are all done one thing to note if you look this nitrogen has a lone pair on it one of the things that we're going to learn is that lone pairs can really change the shape of a molecule so if i replace this with lines there are my bonds my lone pair gets left alone now this lone pair takes up a lot more space than a bond the electrons are trying to repel and so what's going to end up happening is they are going to push [Music] these hydrogens out of the way sometimes you may even see people draw what looks like kind of like a big i don't know like almost like part of a teardrop or something on top of it showing people how much space it takes up and the little arrows push it down so the three structure of nitrogen ends up a little bit different the hydrogens end up pushed down it distorts the shape so that's something we'll see over and over when we start learning the three-dimensional structure of these so instead of being flat like a pancake what ends up happening is this an h3 ends up it's hard to show you on the camera it's easier in person but it ends up looking like a three-legged piano stool where you have the hydrogens kind of poking down spread out equally and then at the top is the nitrogen with its lone pair all right one last structure for this lesson sometimes you're gonna notice that the formula is what we call chunked okay so sometimes you're gonna see something like let's see ch3oh and what you should notice here is that you have hydrogens in multiple places so we have a ch3 chunk followed by an o h chunk whoops should do that in pink that didn't work okay good enough so we end up with a chunked formula that is not an official term that's just something that i say um and a chunked formula is trying to give you a hint to the structure okay a lot of times this has to do with how the molecule will behave that it's very important for us to know that this o h is on the end of the molecule okay so i'm going to kind of start setting up this chunk and then i'm going to attach this piece okay so if i just look at ch3 the hydrogens have to go on the outside and the carbon has to go on the inside so here's my carbon i'm going to put my hydrogens over here so that this side of the box is left for the rest of the formula okay now i'm going to connect those with a single bond so they're not floating around and you'll notice that the carbon has one more spot available for this oxygen to come in we know now that this hydrogen is attached to the oxygen so this piece is one chunk right we have the oh part and we have the ch3 part and now we connect these pieces together okay so kind of going back to our steps step one was to count so i have one carbon it comes with four valence electrons i have three hydrogens that each come with one i have one oxygen that comes with six and then i have one more hydrogen that comes with one when i add that all together i get seven pairs in my picture okay i've placed my atoms by the chunking i've connected everything with a single bond now my next step is to give everything a full shell so hydrogens are already full with two this oxide or sorry this carbon is already full with eight but this poor oxygen only feels like it has four so let's give it all the electrons at once and now let's count and double check i have one two three four five six seven pairs is what i was supposed to have so i'm all done this molecule has two lone pairs on the oxygen you'll notice that lone pairs tend to end up on things that are more electronegative that's not a firm rule but it is typical oxygens and nitrogens tend to like having lone pairs if i want to replace the dots with lines and then i make sure that my lone pairs are left as dots because they are not participating in a bond and the line represents a bond it is important that you are being neat and tidy and professional with your structures i am not going to put any effort into looking at things that are so messy i can't tell what's happening so please take you know some level of pride in your work and be nice and organized don't try to draw teeny tiny structures use tons of binder paper if you need it right make sure that you're using the space you need so that you can learn adequately so that i can grade your work easily and see what you know and don't know so please make sure you're not squishing your work and being messy with this okay this is um the second part the next part will deal with double and triple bonds all right everybody that's it for this part bye