bond line structures that'll be the topic of this lesson and we've just covered condensed structures and after this we'll move on to talking about functional groups and resonance so but the topic of this one's gonna be bond line structures also called line angle structures as well and so we're in the second chapter of molecular representations and resins in my brand new organic chemistry playlist i'll be releasing these lessons weekly throughout the 2020-21 school year so if you don't want to miss one subscribe to the channel click the bell notifications you'll be notified every time i put one of these up all right so a bond line structure obviously they call it a bond line structure because every bond is going to be represented by a line okay not so bad so but these are kind of the epitome of organic chemistry laziness or really truth be told organic chemistry efficiency so because we draw carbons and hydrogens so ubiquitously so in organic molecules so again it's all based on carbon but the truth is we often have more hydrogens than carbon atoms well the solution to being the most efficient as we can be in drawing structures is to just not draw in all the carbons and hydrogens and you're just supposed to know where they are based on some rules here so so the first part is we typically don't draw in any carbon atoms in a bond line structure so the way it works in a bond line structure is every vertex in your structure is a carbon atom and so in this case from this structure right here we can see that we have one two three four and a fifth carbon right up here this one's got one two three carbons this one's got one two three carbons this one's got one two carbon so any vertex that's not labeled by default is a carbon atom now the second rule talks about hydrogen knobs we don't typically draw all the hydrogens either and specifically don't draw the hydrogens that are bonded to carbon we'll see one exception for an aldehyde functional group but outside of that we don't draw hydrogens that are attached to carbon atoms that are bonded to carbon atoms cool now not all hydrogens are bonded to carbon atoms so we'll see that hydrogens that are bonded to anything other than carbon we specifically do draw those so however we don't draw lone pairs on all those atoms and oftentimes we'll call those heteroatoms meaning different atoms other than carbon and hydrogen carbon and hydrogen are found in almost all organic molecules but whether you find nitrogen or oxygen or halogens you know those just vary from organic molecule to organic molecule so sometimes outside of carbon and hydrogen we just label everything else is heteroatoms so but in this case we do draw hydrogens that are attached to these heteroatoms but we often typically don't show the lone pairs now i say that a good a typical bond line structure or line angle structure doesn't have to put lone pairs on those heteroatoms however you should be careful typically your instructions on any exam you're likely to see this year especially in the first semester are going to say you should draw all lone pairs on every structure you draw including bond line structures so it's technically not required for a bond line structure but we usually acquire it of all of our undergraduates to make sure they know where all these lone pairs go and stuff so let's kind of see how this works so in this first structure we're going to turn this into a lewis structure and this vertex right here represents a carbon and that carbon has no formal charge so if it had a formal charge we'd have to list it like on these two so it's got no formal charge and when carbon doesn't have a formal charge he's going to typically have four bonds almost always in fact so in any example you're likely to see any time soon so in this case this carbon right here is bonded to let's just set up the skeleton of carbons here a carbon right there that carbon right there is bonded to a carbon up here that carbon up here is bonded to a carbon over here and that carbon over here is bonded to a carbon over there and that's kind of the carbon skeleton here so and none of these carbons have a formal charge so we know they all have filled octets then so and that means they're going to have four bonds for a neutral carbon and so we're just going to add hydrogens because those aren't drawn in either until it's got four bonds so like this carbon right here only has one bond showing and that means he must have three bonds two hydrogens same thing with this carbon up here he's only got one bond showing so he must have three bonds to hydrogens now this carbon right here he's got one two three bonds showing so to get a filled octet he's only going to need one bond to hydrogen this carbon right here's got two bonds showing so he's going to need two bonds to hydrogens and finally this last carbon has only one bond showing so he's going to need three more bonds to get to four and a filled octet and there indeed is our corresponding lewis structure now cool notice i've showed angles here a little bit to more accurately reflect the geometry here now a lewis structure lewis usually made everything look like 90 or 180 so this might not quite look like a typical lewis structure used to seeing so but i tried to represent it in the molecular geometry here now these bond line structures are also called line angle structures because we also in addition to representing every bond with a line we try to represent the angles the bond angles accurately as possible and that's why i've kind of tried to represent this lewis structure as much like the bond line structure as possible as well we'll do the same thing here so in this one we've got three different vertexes that are not labeled so that's going to represent that we've got three carbons so and in this case once we set up our carbon skeleton we're gonna worry about that last one because he's got a positive formal charge we want to figure out what in the world that means but the ones on the ends here they're neutral and being neutral we should expect those carbons to have four bonds so any bonds they're missing so far after we've set up our skeleton should be hydrogen so this carbon right here only has one bond showing to get to a total of four bonds we're going to need to draw three hydrogens in same thing with the other one on the other side we've only got one bond showing so we're going to need to draw in three more bonds but that one in the middle you might look at this and be like chad he needs two more bonds and don't draw this in yourself just yet because i'm about to erase one of these but we might be intended to do something like this but if this was the case this carbon would have four bonds which is normal and he would not have a formal charge so we would take four the normal number of valence electrons for carbon and subtract one two three four so four lines no dots so four minus four is zero no formal charge but we're supposed to have a positive formal charge what that means then is we're going to take erase one of those hydrogens and now we do 4 minus 1 2 3 and that would be a positive formal charge so this is an example of a carbon with no filled octet so he's not making his normal number of four bonds he's only making three so and often times to reflect the geometry a little better so this guy's actually going to be sp2 hybridized which means he's trigonal planar bond angles are 120 and so oftentimes we draw that third hydrogen here to reflect that trigonal planar geometry so we'd also represent that formal charge on the carbon like so similar to the way it looks in the bond line structure cool so we call this a carbocation by the way we'll revisit these a little bit down the road so but a carbocation is just a carbon with a positive formal charge and generally you're going to see those pretty frequently in this course and they're going to have three bonds and no lone pairs to end up with that positive formal charge now this next one here's a carbon with a negative formal charge and once again we'll set up the carbon skeleton so three unlabeled vertexes those are all carbons once again the ones on the ends have no formal charge so to get them to four bonds for both of them we'll add three hydrogens and again if we did the same thing with this guy and gave him two hydrants that he'd have four bonds well then he'd have no formal charge but we've got to have a negative formal charge and so in this case the question is how do we get to a negative formal charge well in this case we can't go over the octet rule or anything but we are going to erase one of those hydrogens and in its place put a lone pair of electrons and if you again notice carbon's normal valence is four and we'll subtract the dots and lines and he's got two dots three lines and four minus one two three four five is negative one four minus five is negative one and that's how we get a negative formal charge we call this again a carbon ion so we had carbocation over here carb anion over here which is just a carbon with a negative formal charge and to accomplish that you should file it away in your head because we'll see these on a regular basis throughout the the course of the year as well so you're gonna have a carbon with three bonds and a lone pair of electrons oh and i forgot to draw a couple of hydrogen let's just get those in because that just looks horrible otherwise cool we've got one last bond line structure to do here and so this is a functional group we'll learn about in the next lesson called an amide and in this case we've only got two vertexes that are not labeled so we've got a and let's do this down low here so carbon carbon nitrogen oxygen and we can see that even that's a double bond okay so we'll start off with those carbon atoms and again we need to add hydrogens to those carbons and this carbon right here so it has no formal charge in the structure so he's going to have four bonds and in this case to have four bonds we need to add three more hydrogens but this carbon right here already has one two three four bonds he's good he doesn't have any hydrogens whatsoever cool notice we did have to draw a couple hydrogens in here and that's the thing i want to point out with this example is put a couple heteroatoms in there and i wanted to point out that if they're bonded to hydrogens those actually have to be included in the bond line structure only the hydrogens on carbons that are not going to be included all right now what's not included though are lone pairs of electrons now if oxygen and nitrogen don't have formal charges then we got to be like okay well nitrogen usually gets three bonds he's got three oxygen usually gets two bonds he's got two but if we don't show their non-bonding pairs of electrons then how do i know they to fill octet and stuff so in this case we're going to add those lone pairs in and in our case with oxygen we're going to have to add four electrons because we only had four around him now he's got a filled octet and he's got eight around him nitrogen here's got two four six around him he's going to need a pair on him as well and now he's got a filled octet and so for hetero atoms we generally add lone pairs until they got a filled octet when you're going from the bond line structure to the lewis structure cool so you got to typically draw hydrogens in on carbons and you've got to typically draw lone pairs in on all the rest of the atoms all right so now we've learned how to turn bond line structures into lewis structures well in the last lesson we learned how to turn condensed formulas into lewis structures as well and the truth is we got to be able to interconvert between all three we've got lewis structures we learned in chapter one and something learned back in gen chem and now we've also learned how to draw condensed formulas and bond line structures and how to convert them back and forth with lewis structures but now you've got to convert them back and forth with each other so you've got to be able to turn condensed formula into bond line structures and bond line structures back into condensed formula and usually i recommend students start off by using the lewis structure as the intermediate or the intermediary between the two so what i mean by that is this so here we've got a condensed formula so back in the last lesson we learned how to convert this condensed formula into this lewis structure now we want to convert this lewis structure into the corresponding line angle formula and the way you do this you just kind of look at your longest chain all the way through in this case it's one two three four five carbons and you're just going to start zigging and zagging it doesn't really matter if you zig up or down first so and the key is don't count the number of lines you're drawing count the number of vertexes one two three four five notice five vertexes only needed one two three four bonds that's why i mean don't count the number of bonds count the number of vertexes so one two three four five to match up with one two three four five in this case we don't draw any of the actual carbons they're they're they're uh by default as the vertexes that are not labeled and then we don't have to draw any of these hydrogens in because those sort of hydrogens are all bonded to carbon this actually is the entire bond line structure second example i want to look at is also one from the last lesson in fact uh the next several we're going to do are all from last the last lesson we converted such condensed formulas into these lewis structures and that's why i'm just kind of taking this by default you probably already have this in your notes from the last lesson so the question is now how do we turn this into a bond line structure well once again you want to find your longest carbon chain going right across so one two three four five i just drew a long bond so we could line things up here so but one two three four five and so we'll just do some zigging and zagging again so one two three four five and i'm counting my vertex is one two three four five and on the second one in i need a bromine now one thing you should realize we've got two different areas coming off this carbon we've got this little area down here and we've got this big area up there when you start drawing in additional bonds on a bond line structure don't draw any more into this little area always put them into this big area here so i like to think these two atoms right here or these two bonds i should say form an arrow pointing up and it's up where you put the additional bonds whereas these two right here once again you've got this little area right here you've got this big area right here and again if we have to draw additional bonds coming off that carbon we're going to draw them in this big area here so again these two bonds right here form an arrow pointing down and that's we're going to draw the next bonds if we had to draw any additional bonds here so let's look for this second carbon in we do have to draw an additional bond to a bromine and so we'll draw that up here not down below we'll get those out of there as best i can and on the next carbon over we've got a ch3 to draw in and so in this case that's going to go down here now we don't actually have to draw anything except an unlabeled vertex because that unleveled vertex is a carbon and it's bonded to as many hydrogens as it needs in this case three to get that filled octet so that's all we draw in right there i'll erase this as best i can without looking too terrible cool and then we move on and the that was the third carbon in the chain the fourth carbon in the chain is there and the fifth one is right there and that is the entire bond line structure all right these next two structures are also from the last lesson on condensed formula so uh we already turned these condensed formulas back into lewis structures back in the last lesson so i'm kind of taking that we've already done that so far so but if i ask you to turn this condensed formula into a bond line structure the first thing you'd probably want to do at this stage of the game is turn it into a lewis structure and then once you've got that lewis structure you can turn that into a bond line now eventually you'll get pretty good at this and whether you brought in the condensed formula or the bond line you'll pretty much be pretty good in all likelihood at converting those back and forth without having to go through the lewis structure but for now i would highly recommend going through the lewis structure to get back and forth between the content structure uh and the bond line structure all right so if you want to turn this lewis structure that came from this condensed formula into a bond line structure you look for your longest carbon chain one two three four five and we'll zig and zag here five times one two three four five i should say we'll zig and zag four lines but five vertexes so and now that we've got our five vertexes we'll go back in and we realize that between our third and our fourth we've got to put a double bond right there cool so this would be one way to demonstrate this so it turns out this is not the most specific although we could say it is and maybe i actually haven't drawn the right one but it turns out that double bonds cannot rotate when you've got sideways overlap of p orbitals if you try to rotate that bond so it's just not possible you'd have to break the pi bond so you'll learn a little more about this in the next couple of chapters so but it turns out there's one other possible way to represent this with that double bond and instead so we'll still put that double bond in there but instead of having this zag down or zig down we can have a zag up or something along those lines and it turns out we'll find out that these are examples what we call cis and trans isomers so and that's not important for now super not a big deal if you didn't see one of these coming i'm just trying to cover all my bases at this stage of the game whether or not you drew this one or this one both are pretty acceptable and they're in fact drawing both will be the most complete and most correct answer but it's not usually something we're expecting of you at this point until we teach you about cis trans isomer isomerism a couple chapters down the way so if you didn't come up with one of these no problem it's not going to be required you at this stage i just want to cover my bases in case some of you drew this one and some of you drew this one and you didn't know what's going on so they're both acceptable all right this next one here same kind of thing we've got our longest carbon chain so again this is also again from that last lesson so we've already got the lewis structure and then we'll take and convert the lewis into our bond line structure so one two three four five so and we'll draw a five carbon chain and again i start by zigging up but you could have just as well started by zigging down instead doesn't matter totally arbitrary so not one right way to draw that and draw this in that respect so but i'm gonna do it like so and again all the rest we got five vertexes which stands for five carbons and the rest of this is all hydrogens and so we might just think well just get that triple bond in there and we're done but we have one major problem so again these bond line structures we try to actually get the bond angles correct so again sometimes they're called line angle structures and so if you look back here like this angle right here well this is an sp3 hybridized carbon and so the bond angles around it are all 109.5 and if you look at that i'm not going to pull out my protractor or anything but that kind of looks like 109.5 cool now these two carbons right here are just sp2 hybridized and so the bond angles are 120. well notice the difference between 109.5 and 120 it's not a big difference and if you look at this i'm like i could pull up the protractor and maybe i'm off by a little bit one way or another but whether it's 109.5 or you know 120 whatever it's close cool but we don't have that here so here this is a triple bond these two carbons right here are sp hybridized and sp hybridized carbons are have 180 degree bond angles and i can look at that and i don't know if that's 109.5 or 120 but i know it ain't 180. and so when you've got a triple bond in your chain you want to make sure you get your bond angles correct and so what we often have you do is start with the triple bond so this is technically wrong don't want you to draw this exactly like so but start with that triple bond so and these are both carbons right here and you've got one more carbon coming off to the right and then you've got two more coming off the left you want to make sure the first one comes off at 180 degree bond angle and whether this one zigs up or zigs down is totally up to you but again this represents one two three four five carbons a lot of students have a little trouble with this one not recognizing that that vertex right there is a carbon and that vertex right there is also a carbon and we have one two three four five carbons in the chain but with a triple bond make sure the two bonds coming off the sp hybridized carbons are coming off at 180 degree bond angles all right these last two examples once again also from the last lesson on condensed formulas in the last lesson we turned each of these condensed formulas into these two lewis structures and again the goal here is to turn these two condensed formulas into the corresponding bond line structures which again i highly recommend you do by drawing the lewis structures first but we already did this in the last lesson so i'm not going to repeat that but now we're going to take these condensed formulas which we turned into lewis structures and now turn them into bond line structures and again find your longest continuous chain so in this case one two three four five carbons and so once again we'll zig and zag till we've got five vertexes so one two three four five and then we'll go back and between carbons one and two we're good but between two and three so that's carbon two carbon three here from the end we'll put a double bond and then coming off carbon four from the left we'll put a double bond to oxygen and from there everything else are hydrants that are bonded to these carbons that aren't going to get drawn in and this is your bond line structure and once again so we've got a double bond and once again you could have drawn that potentially one other way just cover my bases whether you draw one or the other you're probably okay at this stage of the game oh i don't need lone pairs technically either so and you could have drawn it like this as well but again this is based on you guys understanding system and translucentism which again we'll get to later so i don't really care if you came up with one of these or the other so it wouldn't necessarily be required of you to come up with both at this stage but that's coming a couple chapters down the road one thing to note if you were converting this lovely condensed formula into these on your likely organic chemistry first semester exams they're going to say oh by the way make sure to draw all lone pairs and so even though a proper bond line structure doesn't actually need lone pairs on your exams you're probably going to need to include them and so you're going to want to get in the habit even though your professor is likely to not draw them in because they're not required for bond lung structure you're going to want to get in the habit of including them always because it's in all likelihood going to be required of you on your exams all right last example here so this was that carboxylic acid and again we've got this condensed formula we've already converted into a lewis structure in the last lesson and now we want to convert it into the bond line structure and we've got one two three four and we can even call this a fifth even though it's not a carbon we'll label it appropriately so zigzag till we've got five atoms in the longest chain but the last atom on the right is not a carbon it's an oxygen so we've got to label it so before i put that oxygen and drew that in that looks a whole lot like a carbon an unlabeled vertex but once i label it as an oxygen now i know it's not a carbon so we've got one two three four carbons and then an oxygen so one two three four carbons in an oxygen this carbon's also double bonded to another oxygen atom this oxygen is also bonded to a hydrogen but the rest of these hydrogens are all bonded to carbons and they're not going to show up in the bond line structure and once again this is the correct bond line structure but once again you should include your lone pairs and get in the habit of doing so putting those lone pairs on the heteroatoms cool but there's your bond line structure with lone pairs of electrons drawn in all right last thing i want to do in this lesson is we want to take some bond line structures and turn these back into lewis structures and technically they could even ask you to turn them back into condensed formula but i just want to go back to lewis structures i'm confident that you guys now know how to convert between condensed formula and lewis structures back and forth but i would definitely want to take an example or three examples here of converting bond line structures back into lewis structures so if we look at this first one we've got four vertexes that are not labeled so that's going to be a four carbon chain so in this case the only one that's got a formal charge is this carbon right here so we'll worry about him last but the rest of these we just need to add enough hydrogens in to get them filled octets so this carbon here only has one bond showing so we have to draw in three hydrogens this carbon right here has only got two bonds showing so we've got to draw in two hydrogens and the carbon on the right has only got one bond showing so we've got to draw in three hydrogens now this carbon right here has a positive formal charge and i'm gonna rely on the fact that earlier in the lesson we learned that for carbon to end up with that positive formal charge he's gonna only have three bonds not four and no lone pairs and so in this case instead of giving him two hydrogens i'm only going to give him one and whether i put it on top or bottom is totally irrelevant so but normal valence electrons for carbon is 4 minus dots and lines well he's got 3 lines and no dots and so 4 minus 1 2 3 is indeed plus 1. that's how we end up with that positive formal charge cool move on to the next one we've still got the same four carbon chain so and in fact the three carbons that don't have a formal charge are identical in both these structures so i'll just repeat what we did there but now we've got this one here with a negative formal charge and again earlier in the less we pointed out for carbon end up with a negative formal charge he needs to only have three bonds not four but in addition to those three bonds have a lone pair of electrons that way when you go calculate formal charge again carbon's normal valence is four four minus the dots and lines in this case he's got two dots and three lines so four minus one two three four five is indeed negative 1. that's how we get carbon negative formal charge and there's our corresponding lewis structure now this last example this is the first example where we've seen a dot and a lot of students don't recognize that as anything more than a dot but that is like this except there's only one un you know one uh electron their non-bonding electron when you've got one non-bonding electron we obviously don't call it a lone pair we just call it a radical it turns out when you hear the term like free radicals are you know giving me cancer and things of this sort free radicals just mean you have an unpaired electron somewhere now uh back in chapter one i actually lied to you i was totally wrong i said you're never going to encounter a situation where you have a violation of the octet rule we have an odd number of electrons actually i was wrong no we're going to see radicals every once in a while in this course but we're not going to usually look at them in in the context of the octet rule so technically i was wrong in chapter one but you're not going to see an example we have to analyze this in the context of the octet rule so if we look at this though we have the same kind of thing we've got these three carbons match up with this those same three carbons on these other structures so first one here so it's got three hydrogens the next one only having two bonds showing it's going to have two hydrogens and then again the one on the end so with no formal charge one bond showing and he should have three hydrogens as well now this one right here is the one with the unpaired electron they had to show that unpaired electron so but in this case there's no formal charge he's not positive like this one he's not negative like this one he's still got a zero formal charge he's neutral but he's a radical he's got an unpaired electron but in this case i can't give him two hydrogens notice there's not room i'd have to go over the octet rule but in this case he gets three bonds and just has that unpaired electron there's no charge and again if we do the normal formal charge rule so four is the normal valence for carbon and in this case it's got one dot three lines so four minus one two three four is indeed zero and so we'll find out this is another example of a neutral carbon so but you can distinguish it from a neutral carbon like this because we have to show that unpaired electron as part of the structure whether it's on the bond line or whether it's on the lewis it's going to show up in both otherwise we can't distinguish the two now if you found this lesson helpful consider giving me a like and a share and if you've got questions feel free to leave them in the comments section below now if you're looking for the study guides that go with this lesson or if you're looking for practice materials check out my premium course on chadsprep.com