I'll be helping another youtuber Melissa Lucy prepared for her next exam and you know I've even created a free study plan that you can download using the link in the description that study plan has several videos or other resources that I personally recommend for you ok let's learn how to draw Lewis structures properly so today we're basically gonna be focusing on how to draw Lewis structures I know that there's like there's like so many questions that you're thrown with like Lewis structures where they expect you to know one how to draw and then you know the geometries resonance all of these other words that we're gonna learn later on but for now let's at least get a good foundation of just understanding how to actually draw the structure because that's like I'd say that's the most important part because if you don't have that right then everything else is wrong so no pressure but let's focus on just understanding this so we've talked about this before looking at valence electrons and I know I went over this a little bit where I was just talking about one what isn't valence electron it's the electron that's on that outermost shell of an atom and really what I want you to memorize is everything that is highlighted here so just knowing that this this group only has one valence electron the next one has two we're not going to look at anything to do with you know transition metals for lewis structures and then the next one would just be you know this column is going to be three valence electrons four five six seven eight you get the point but it's gonna be really important to actually have these memorized so some of the most common atoms that we're actually going to see that we're going to use I'll just highlight them real quick so definitely hydrogen that's gonna be something that's really known and we're gonna see that so much carbon is one of the most like used atoms I would say that we're going to use for lewis structures same goes with oxygen same goes with let's say nitrogen and then we probably are gonna see some fluorine chlorine sulfur and pretty much a lot of just the nonmetals because the whole concept here with lewis structures is the ones that we typically see are covalent Lewis structures meaning they share electrons and it's all nonmetals alright so if we remember that concept like going from ionic compound two covalent compounds ionic compounds consists of one metal and one nonmetal and then they're actually transferring electrons versus ion actually versus covalent compounds which are sharing electrons or and they also consists of just nonmetals okay so I think we're okay with that let's just start off with all the different steps of how to draw a lewis structure so first things first we're going to have to know every single valence electron so like carbon has how many valence electrons and then same with hydrogen and then we're gonna add all of that together so kind of going back from a memory or you can look at your periodic table how many valence electrons does carbon have fourth cool I'm gonna write it up here so carbon has four how many - I mean valence electrons does a hydrogen have perfect and then we would multiply this by 4 because this subscript is telling us that there are four hydrogen's in the structure so that would give us one times four so four and the next thing is just to add everything together so I would add just four plus four to give us eight valence electrons so first step is done all I have to do is calculate the total number of valence electrons we said it was eight the next thing is identifying which one is going to be the central atom so for the central atom I know this one's kind of like obvious because there's four hydrogen's so that has to surround the carbon but just to note carbon will typically always be or actually it will always be the central atom if it is in the structure okay so carbon number one that's always going to be in the center now if there wasn't carbon in the Lewis structure then it's going to be the least electronegative so the least electronegative atom would be your central atom if carbon isn't there okay so it doesn't it doesn't apply for this case because hydrogen is never an all so that's actually zoom in and out hydrogen will never be your central atom because it could only have one valence electron meaning it's only going to be able to create one bond just make it sound so far I know I'm like throwing all so yeah but when you say least electronegative like if we were comparing to and we're following that trend then the one opposite of the trend is that you're saying leave right work oh right like if I were to have something like around like like this and then you were asked like oh what's the central atom and I notice they're not gonna be giving this exactly but we'll do an example but from there you would say okay which one is the least electronegative compared to chlorine and fluorine well that would be chlorine so chlorine would be your central atom that makes sense oh yes because it goes Oh to the right yeah okay right but we'll see an example of that for now I just want you to kind of start to understand the steps so choosing our central atom that's gonna be carbon so okay I'll put that right in the middle next it's gonna be surrounded by four different hydrogen's so I'll put a hydrogen hydrogen and a hydrogen so that's done step 3 I do this a little bit differently so at first you're going to learn like the lewis dot diagram where you'd see like Oh carbon we said has four valence electrons so you're gonna draw it this way if it's just on its own and then hydrogen only has one so it could only make one bond so these would combine together to then form one bond so it would look something like like that and and then you'd still kind of see that whole approach here like if I were to actually put to show you this both carbons lewis dot diagram i would do the same thing i'm gonna do this in blue for hydrogen so just one valence electron one valence electron same thing here same thing here essentially what's happening is they're gonna form a bond because two electrons form a single blunt so instead of doing that each time because it's time consuming what I typically would just do is simply put a single bond already there because this is telling us that they're gonna bond regardless okay but does that make sense what would I'm what I'm explaining there yes like a lion yes yeah so and it's just because like we're basically connecting the dots here so it's gonna form a single bond either way so it kind of just saves you the step of drawing the Lewis dot diagram and then you know connecting everything I kind of like want you to understand that they're gonna form a bond regardless so that yeah right that would be the next step and then from there the very last thing part of step three is to just make sure that all of the electrons add up to what we did in step one so in step one we said that there are eight total valence electrons and we want to double-check that that's true so if I were to I'm going to draw this in red if I were to kind of recount these electrons I would see well remember one bond consists of two electrons so there's two so far so two four six and eight so yes that checks out and because that's correct because that checks out we're done that is the correct lewis structure so those are i'd say like the main three steps for a typical Weaver structure that's what we would apply questions here now that makes sense perfect moving on to the octet rule so we just your i structure and if we saw there's actually there was eight valence electrons that's what we sit that's what we said so this actually follows the octet rule and what the octet rule is saying is that the central atom prefers to have eight valence electrons surrounding it like it's stable it's happy and we always want to make that central atom happy so we can look at this again and I'm just looking at the central atom so carbon and I'm saying that there's two of us electrons here so two four again six and eight because there are eight valence electrons surrounding that carbon then I know yep this follows the octet rule it's it's stable what's happy once again the structure is correct so I'm going to keep applying this okay I'm going to keep applying one the octet rule and the steps that we went through to draw a lewis structure so once again let's just start with the first part where we're calculating the total number of valence electrons how many valence electrons does phosphorus have sorry yes what about coin second good and then we'd multiply by 3 because there are three chlorines so 21 we'd add these together so 5 plus 21 is 26 electrons so Chuck next we have to choose our central atom what would be our central atom in this case phosphorus yes and then another way to when when I said like Oh the least electronegative atom is gonna be your central atom that that will help you a lot when you have like larger structures so like when there's typically like more than one central atom which we'll go over but that's something that we're gonna see for this case we could have just seen that phosphorus is by itself and the fact that there is a three subscript that tells us that there's going to be three chlorine surrounding the phosphorus oh yes you know yeah right right okay it makes ice are essential is phosphorus and then next I'm just going to place a bond so I said that there's three chlorine surrounding phosphorus and then I'm already gonna say hey this is gonna this is going to add up so there's a bond here bond here now I also want to talk about the different lone pairs so lone pairs just mean that they are these are lone pairs there are electrons that are not like on a bond so they're still on that atom but but they're not actually within a bond so let me show you this again just in the very beginning I will draw the actual link Lewis dot structure so for chlorine we said there are seven valence electrons so I'll say there's one two three four five six and seven and I would do the same thing for every single one now if we realize there's always going to be one here that's being shared with whatever element it's bonded to and then there's going to be two electrons on on every we'll sign essentially so there's going to be six electrons or six yeah six electrons three lone pairs that makes sense like these are lone pairs these are the three lone pairs on the chlorine just making sense of four okay cool and I would basically do this all throughout for every single one just showing you that there are seven valence electrons on that chlorine and then now I would look and see okay well is this phosphorus does phosphorus have five valence electron well no it doesn't because here's one two three now I need a lone pair five so I could have seen it that way or I could have done what I preferred you which is kind of like the faster way so the faster way of doing this and I'll show you again was just to simply start withdrawing the bond then from there I see well actually from there I'm going to actually draw the lone pairs on fluorine and then something to know every single basically any single like halogen same with our like our oxygen sulfur and so on those are going to also have like lone pairs like this you're gonna see a pattern so typically with I'm pretty much just going to say for our halogens you're gonna constants constantly see a pattern with this where there's going to be three different lone pairs on that atom so that's why I already know that okay I just have to put all the lone pairs in put a bond and I'm almost done the last step is then to know that well one this has to follow the octet rule and it doesn't right now because there's only one two three four five six valence electrons on our central atom it wants to have eight so I add two more on phosphorous another thing that kind of done to also check this which is the end part is saying if all of the electrons add up so I can really I can just count this again so I can say one two three four five six seven eight nine ten in 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 okay I could do that if I truly wanted to or I could also do this a little bit faster here and just saying that this is eight valence electrons there's three here so three times eight gives us 24 plus the additional two here I know there's so many things that I'm throwing but this is essentially the concept of of drawing Lewis structures yeah no that makes sense perfect okay you get the point and it looks something like this I just want to leave it cool maybe not all right so we saw that we can put lone pairs on the central atom and then now we're going to go into just the different types of bonds so just recall that when two electrons combine that forms a single bond when four electrons combine that forms a double bond and then when six electrons combine that forms a triple bond so I'm going to do the same sort of concept here again let's just identify the total number of valence electrons so I'll start with carbon how many are there there are four good what about oxygen six perfect and I'll multiply those by two giving us 12 so 4 plus 12 gives us 16 electrons and then what's our central atom kirb yep that's surrounded by two oxygens and then again I'm just going to place the bonds already there so I did all this so far now I'm just placing a bond in a bond and then I also know that oxygen is going to have these electrons surrounding it okay these lone pairs so if we notice carbon isn't happy okay because it doesn't have a full octet so it does have 8 valence electrons surrounding it so far there's only one two three and four so what we have to do is we actually have to form a larger bond or a double bond so how we do that is by actually moving electrons to then give us that double bond so we're not adding an additional amount of electrons because this has to give us 16 and if we notice this already has 16 so like 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 yep I can't add any more electrons to that central atom so instead I have to form a double bond and when I do this I'm essentially taking these electrons and moving it to form that double bond so there's no longer three lone pairs there's now just two and then this is something else to note is that if this were something that was just bonded to something that was a single bonded to an atom then I would have three lone pairs if this was double bonded I would just have two lone pairs that this was triple bonded I would just have one lone pair okay yeah definitely be aware of that just because I have seen this where you add too many electrons or too many lone pairs and you do get the answer wrong unfortunately okay so okay perfect and then we can check again and just see yes this does obey the octet rule because here's 1 2 3 4 5 6 7 & 8 that's happy and then we didn't add any additional electrons it's still 16 all right this is another one that's a little bit larger I'd say so for this one we're going to have multiple central atoms and I would how I would approach this is just by seeing well there are there are several hydrogen's right there's four hydrogen's in the structure but our central atom could never be hydrogen since that could only form one bond since it only has one valence electron so our central atoms can only be carbon and oxygen but before I do that I have to figure out how many valence electrons there are in total so carbon has how many valence electrons oh good what about oxygen oh six perfect and then we have and then hydrogen we know has one theirs don't forget about actually counting them all so this is three plus an additional one at the end so there are four hydrogen's one times four is four we'll add everything up four plus six plus 4 gives us 14 electrons and then we said that our carbon and our oxygen were our central atoms so I'm going to draw it this way now if you were curious and you weren't sure how do I draw this like how do I know where the hydrogen's go like what is it bond - well this is typically written in the form that it wants you to draw the structure so this already is telling us that there are three hydrogen's on this carbon so I would I would surround this as follows and then same goes for the next one this is already telling me oh that Oh H that H is going to be together so that's how I would put a bond for everything and I'm not done yet so then I would then look at the octet rule and see its carbon happy does it had eight valence electrons on the central atom and I would see that yes it does because here's one two three four five six seven eight that checks out our other central atom is oxygen and now that has to also have eight valence electrons following the octet rule and it does not because this only has one two three and four so instead we would have a lone pair two lone pairs actually to give us eight valence electrons now this is complete questions no that makes sense perfect next one okay so with this one this one was actually on one of your slides or in class assignments and just a note they did give you a hint they did tell you that the it was the oxygen was bonded to this carbon so just so no because I know I just said for the last one that they typically will give you like this is already written out the way you should bond it to like these hydrogen's go with this carbon this hydrogen goes with this oxygen this one actually had to tell you that this oxygen goes with this carbon yeah that's not just like you know you're magically going to no no they they would have to explain that so once again let's just calculate how many valence electrons we have so you know I know you know the certify now but you're gonna see this a lot these are probably the most common atoms that we're going to see our carbon hydrogen and oxygen carbon reset has four there are two carbons in this case so eight and then four hydrogen's here this says there's three here plus this additional one so there's one valence electron times the four hydrogen so four and then there's only one oxygen so six so I would add this all together so eight plus four plus 6 gives us 18 valence electrons and then now now looking at this what's our central atoms so we're gonna have two two central atoms what do you think are the central atoms so carbon is one of them good can we have carbon again yes we can perfect yes we can and if if you were trying to actually this goes back to the rule I was talking about where if I'm trying to decide if carbon or oxygen is like the other central atom we would say well is which one is the least electronegative oxygen is the most electronegative carbon is the least electronegative so I know that the other carbon also will be our central atom okay perfect and then next I'm just going to see that these hydrogens go to that carbon so I'll place them around that carbon this originally told us that this oxygen will be bonded to that carbon so I'm just going to put that on top and then I'll put the hydrogen next to the carbon and then it once again I'm just going to build this just by adding single bonds all throughout okay and then from there I'm just going to double check if we have one if we have 18 wheels electrons and if this obeys the octet rule so for carbon this does obey the octet rule because this has two four six and eight valence electrons next for this carbon it does not because this only has two four and six valence electrons so what I would need to do and something the note was just remember this oxygen has three lone pairs so if carbon isn't happy meaning it doesn't have eight valence electrons it's not following the out tet role it wants to have a greater bond so it wants to have a double bond so I would just move one of these electrons here to form that double bond okay now this is complete so would it be wrong if you just decided to add a lone pair to the carbon itself yes yes it would why because Oh adding electrons exactly then we have 20 valence electrons exactly so you always want to have the total number of valence electrons that's why that's the first step and then another thing like yeah that's actually like the main reason we always want to just kind of like we're moving around the electrons and just to get the best structure like that's essentially what lewis structures are like we're just trying to build the best most favorable structure okay cool and there's exceptions of course so I know but luckily these aren't that terrible okay there's gonna be two main exceptions to the octet rule so we could have an incomplete octet meaning there's going to be less than eight valence electrons on the central atom and I'll tell you how you can just easily tell so the ones that will have an incomplete octet are basically going to be the atoms that don't have four valence electrons to begin with so remember carbon has four valence electrons please had three these had two so what I'm looking at is I'm literally just looking at the groups that do not have four valence electrons and the reason why I just highlighted boron and beryllium is because those are the most common ones so those are typically the exceptions to the octet rule that you will see that's pretty much it so I literally would say those are the main ones that they always use but just knowing that they're always going to have less and four valence electrons to begin with that's how you know it's going to be an income incomplete octet okay and I'll show you an example so how many valence electrons does boron have three good what about flying seven perfect so seven I'm going to multiply this by three because there's three of them so three plus twenty-one that gives us 24 electrons what's our central atom I born perfect I'm going to surround this by three fluorines putting our single bonds already putting the lone pairs knowing that halogens will always have those three lone pairs and then now I'm just going to double check that I do have 24 electrons so how I could easily do this is just by seeing that this is 2 4 6 8 so this is 8 this is also 8 8 8 times 3 does give us 24 so that checks out but I know that this is an incomplete octet because there's only two four and six valence electrons on that central atom but it's happy it's totally fine so we would just leave it like that that is the best structure that is the correct structure okay so the exception meaning that I give your sentence so it's less okay cool yes exactly and then the other one is the opposite way there's more so it's an expanded octet there's more than eight valence electrons on the central atom I'll explain or what that would be so the place that it's going to actually start is going to be the third row so this is the third row but specifically it's going to be here so the third row and then below so in your book it's probably gonna say the third row and above and though that's correct mentally we don't that doesn't make sense because this is this is Row three right and we're thinking oh this is wrote the three it would be above it right three and above and that's not what you're gonna think about it right so I like to think about it as it's Row three and like physically below way more sense because I would totally be thinking that but are they saying that because like based on the energy like the energy levels of being like a four-car okay exactly that's how they're basing it yet so but I just prefer to kind of box it up and say these are the main ones just know that these are your exceptions and so I typically say yeah three and physically on the periodic table below you know so the main ones that I'm actually that I always see and I wrote that down so the example is that you're probably always going to see our phosphorus let's see all of these whole time and sulphur is one of them as well these are probably the most common ones that are going to be used now something that I want to make a point here these all have the possibility or potential to form an expanded it doesn't mean that every single time they will and I'm gonna highlight back to one of the ones we just did so phosphorus has the potential to form an expanded octet if it needs to but as we saw previously with this example I didn't have to write this had already what two four six eight this obeyed the octet rule and that was fine however if I needed to if I needed to add like if there was five chlorines then I would I would see okay this does have that possibility of having that expanded octet if it's so needed to so it's based on whatever atoms are attached to it okay okay we'll do some examples there verses like let's say boron or beryllium they're always gonna be incomplete like it's not saying that they have the possibility no those for sure are incomplete they're not gonna obey the octet rule so here's an example for an expanded octet rule so let's just look at how many valence electrons we have again so for xenon how many valence electrons does that have good what about fluorine perfect good under me to add these together so a nice I just found the four from here so 28 plus eight that would give us 36 electrons okay what's our central atom okay we know this is gonna be surrounded by four fluorines so I could draw it like this for now I'll put our single bonds and then of course any sort of halogen is gonna have three lone pairs so just putting them all perfect and then we're gonna count and see does this have 36 electrons so this has eight right two four six eight that's eight times four of them so eight times four you 32 we need more so this right now only has two 32 valence electrons we need 36 so because of that we need to add 4 electrons so that means we're going to add it to lone pairs on the central atom so that's something to note is whenever you basically put all of the electrons on the elements that are like surrounding it or on the outside and you if you don't have enough valence electrons then you come back to the central atom and add more ok then that's how in this case we do have 36 we will see that this is going to be an expanded octet because this has 2 4 6 8 10 and then 12 so this actually has 12 valence electrons surrounding it but that's completely fine because it is part of the exception right here okay we're going to keep going and we're going to see Lewis structures of ions so now we're adding a charge so this is basically going to be the same sort of concept where remember that cations were actually going to lose an electron meaning we're going to subtract an electron and then anions the negative charge we're actually going to add an electron so we're gonna we're gonna add so in this case since we have that positive charge or a cation we're actually going to have to subtract one electron at the end so the first thing we're gonna do is just identify how many valence electrons do we have so how many are there for nitrogen there are five for nitrogen and one for hydrogen we're multiplying by four those so there's more good so five plus four and then we would subtract one based on this one plus one charge so subtract one and then instead of having let's see instead of having nine we're actually going to have eight and then that's something to also note you're not going to be having like in an odd number of valence electrons because that would mean that we wouldn't have a pair like a lone pair so if you were to see that there's I'd say double-check most likely there is a charge that you're forgetting to apply so that's why in this case we had to have this charge to reduce that number from nine to an actual even number of eight what is our what's our actually we're here what's the central item go ahead nitrogen good I'm going to surround that by four hydrogen's placing a single bond all throughout and then I'm just going to double check if this just gives us what we wanted so let's see this is 8 so 2 4 6 8 yep that checks out the last thing so the only difference now is that we have to actually place the entire structure in brackets and place the charge on top this is whenever it's a charged or an ion essentially whenever this is an eye on it you have to put the Lewis structure in brackets and put the charge on the outside it would be marked wrong if you didn't okay do the same thing for the sex 1 so now we have an anti on and I know that I'm actually going to add in the electric so go ahead and and let's figure out again how many valence electrons we have so how many valence electrons for chlorine chlorine has 7 and oxygen has 6 good and then multiply that by 4 ok and then I'm going to add one more electron so 7 plus 24 plus this one let's see what does that give us so ordered to do this gives us 8 24 plus 8 32 but I'll have you do you know I'm gonna have you do practice problems after but that's fine you can use your calculator to calculate it that's that's not a problem so what's our essential item in this case chlorine yes perfect and then we're just going to place oxygen surrounding it and placing our bonds you know the oxygen can have three lone pairs all throughout and then we'll double check the amount of electrons so in this case I have again this is 8 8 times 4 does give us 32 that checks out the last step is to just place this in brackets and then our charge on the outside so perfect keep practicing those steps to drawing Lewis structures that we covered take notes and really just give this all you got because we're kind of in the middle of the semester right now and you know what I know you can do this I know you don't want to repeat the con and quite frankly you're capable of doing this and you know it too you just really need to believe in yourself so keep going try out the next questions in the next video