hello class well we have talk about today is a a rule that helps us remember how many bonds atoms can form and we're going to look at the atoms that are most prevalent in organic chemistry and the rule is called the honk oh one two three four rule the honk1234 rule is H stands for halogens so those are just fluorine chlorine bromine and iodine and hydrogens so that what's the H stance we're in the honk and then that H corresponds to the one and that tells us one Bond so we could have examples like carbon hydrogen you can see that hydrogen only has one Bond when we look at halogens you can see that there's one Bond but with halogens what do we see we see three sorry three lone pairs one two three around the halogen why is that remember the octet rules which is simply telling us that for this atom here there needs to be eight electrons around it so if I look at a example like this let's look at this methyl bromide here when we take a look at the halogen we see that there's three lone pairs but how many electrons does it need well it needs to have an octet and that single bond that I had drawn right here that is a sigma Bond and that Sigma bond is represented by those two electrons there so when we look at and not only is this a sigma Bond it's a covalent bond and covalent bonds share electrons and so it shares all those electrons so when when you look at that pink circle that I drew how many electrons are in that Circle there's eight and so we have the octet rule is satisfied but when we take a look at carbon hydrogen bonds or anything bonded to hydrogen it's a little different in the fact that hydrogen can only have two electrons and so you can see that hydrogen right there only has two because it only has a 1s orbital that's all it has and in the 1s you can only have two electrons okay so that is the h any guesses on what o stands for anybody thinking oxygen that would be correct if that's what you're thinking so the O in the honk rule stands for oxygen all right and then o corresponds to 2 so that means that there's two bonds so we could have milk we could have oxygen atoms that look like this now how many lone pairs does it have it has two lone pairs why because the honkeral states that oxygen atoms forms two bonds there's our two bonds but it also needs to fulfill the octet rule so 2 4 6 8. so that's a valid structure we can also have an auction atom that looks like this a double bond to that oxygen atom and just like that so for example we could draw let's say a ketone what if we drew a ketone that looks like this okay there's a ketone that oxygen atom has two bonds and two lone pairs because we want to have the octet rule you can see that if you Circle that there's going to be eight electrons the next one nitrogen in nitrogen how many boss you think nicotine holds well the hawk rule tells us that it's three so three bonds so we would see a nitrogen species that looks like this we could do boom boom we could have three carbons attached to it three bonds but is that molecule fulfilling the octet rule when I count how many electrons are here I only count six it has to have eight so that means there has to be a lone pair so that nitrogen right there um fulfills octet has three bonds what if I had a nitrogen atom so it looked like this what about that that's three bonds one two three so it has to have a lone pair what if I had a nitrogen that had a triple bond attached to it let's go like that but if we had a molecule that looked like that we're focusing on the nitrogen it has three bonds that's what the honkeral says but how many lone pairs well there's six electrons here has to have eight so it has one lone pair and then the last one in the honk rule is carbon very very important because organic chemistry is all about carbons forming carbon-carbon bonds using carbons to change functional groups organic chemistry is all about the carbon so C stands for carbon and in the home curl it says it has to have four bonds so you could have a carbon with four bonds now how many lone pairs does the carbon have well let's think here Each Bond right here represents two electrons right so there's eight electrons around it so it fulfills the octet that's good that's done there's no lone pairs what if we had a carbon with a double bond right there what do we have this carbon has a double bond and we'll put make it look like a real molecule here I'm focusing on this carbon right here one two three four five six seven eight no lone pairs what if we had a carbon with a triple bond so I'm focusing on this carbon right here and we could draw another methyl coming off of that so this carbon right here how many bonds does it have one two three four that means it has eight electrons around it so no lone pairs okay what if we had a carbon that looked like this foreign looking at this carbon in the center how many bonds does that carbon have carbon has one two three four does it have any lone pairs no you did take any one of these molecules here and put a lone pair let's let's look at this one right here if I did put a lone pair there what mistake did I make we'll just count the electrons one two three four five six seven eight nine ten I violated the octet rule the octet rule says eight I have ten that's not possible not possible so that would be incorrect no lone pairs on the carbons now this is very important to know and remember that this honk curl only works when the the molecules are neutral they have to be neutral in order for this molecule for this honkeral to work the moment you make these molecules have a formal charge like a plus charge or you could draw a molecule with a negative charge the honk rule does not apply that is very very important to remember when you're using the Hong Pearl only when the molecule is neutral does this work so that leads us into carbons that have charges with them so let's erase this honk rules and look at carbon atoms with charges on them so before we start looking at the charges what if I drew a molecule that looked like that how many carbons would you say you have here hopefully you're all saying that there are four carbons how many hydrogens three six nine and one coming off here 8 10. now when we take a look at this carbon in the center do you see how it has four bonds it's following the honk rule so if I draw it out we would have it looks like this ch3ch3 and then a hydrogen coming off that follows the honk rule right because it has four bonds but what if I take that same molecule here like this and I draw a positive charge and when we have a positive charge on a carbon atom we call that a carbo cation now carbocations are telling us hey we have a positive charge here and so that positive charge is telling us that we are missing one of the four bonds and so when we look at this carbon we see that we have three bonds so what is the What bond is missing well it's going to be this hydrogen atom that's missing so this carbocation has a chemical formula of C4 H9 because it's missing that hydrogen here now there are different types of carbocations this carbocation is a tertiary carbocation and tertiary carbocations are this positive charge or this formal charge is attached to this Center carbon and whenever I draw a formal charge I want you to sir I Circle it so if it's a positive one a positive 2 negative 1 negative 2 doesn't matter what the charge is I Circle it and that's going to tell me and you that that is a formal charge and so we'll know what we're talking about so that is a tertiary carbocation because when you look at that Central carbon that the formal charge is attached to you can count that it has one two three carbons directly attached to that Center carbon so that is a tertiary carbocation now if I drew a structure like this and placed a positive charge on that right there when I'm looking at this carbon right here it's telling me it has a positive charge and the honk rule says if it's neutral the carbon would have four bonds but because it's positively charged it's telling me I'm missing one of those four and so what we have is we are missing one of the carbon hydrogen bonds so I'm going to actually take this positive charge here and draw it below and let's just contrast it real quick with the neutral if we are looking at this carbon right here how many hydrogens does this carbon have well it has two hydrogens right there because this carbon right there in the center needs four bonds right but we have a carbocation now the and so we're going to lose one of these so now we only have one of those hydrogens and so this carbon right there has how many bonds one two three so another way that you can look at it if a carbon atom has three bonds it's going to be positive one now this is a formal charge do you remember calculating formal charges in general chemistry if you don't highly recommend going back and learning that we will talk about it and ref and I'll help refresh your memory but it's better that you go back and learn it and make sure you understand it because you learned it before okay but I will help you re remind yourselves so now when we take a look at this carbon or this carbocation what degree of carbocation is it is it a tertiary well when we look at that Central carbon how many carbons are directly attached to it there's one two so that makes this carbocation a secondary carbocation and I'm not going to spell out the whole carbocation huh now we could draw another molecule and draw a positive charge for that carbon there let's contrast it to a neutral one so this carbon right here we can see that there's one carbon-carbon Bond but then it has three carbon hydrogen bonds that are not shown so that's the neutral form oh but this guy's positively charged so that means it can only have three bonds so we could see one and let's let's move this positive charge here out of the way for a moment [Music] let's put it right there do you see how there's three hydrogens now there's only two okay so when I redraw this without the hydrogens it looks like this so these two molecules right here are the exact same now we see that there's this Central or this carbon here that's what the positive charge is attached to how many carbon atoms are directly attached to that guy right there there's it's just that guy only one so that makes this right here a primary carbocation and it's very important that you're able to see that the different degrees of carbocations because in the future depending on the carbocation it will determine what type of reaction it can undergo so understanding and be able and being able to identify the degrees of these carbocations will help you understand reactivity and be able to predict reactivity that's the skill set that you want to have in organic chemistry because you cannot memorize all the reactions that we're going to go through you need to understand the principles that I'm teaching you here and this is one of those very important principles looking at the degree of the carbocation so we've taken a look at carbocations but we can also have something called a carbo anion so if we look at the same molecule that we've looked at before we'll keep that neutral so the honkroll says that there's going to be a hydrogen here we just looked at if we have a positive charge that means the hydrogen is missing and that's a carbocation but what if we had a lone pair and a negative charge that right there is called a carbo carbo anion or sometimes we just say it really fast and say a carbanion what we have here now is when we take a look at this Central Carbon Let's draw it out like this so so when I take a look at that Central carbon how many electrons around that Central atom well there's two here two there two there so that's six seven eight so that Central carbon there has eight electrons in it so it has fulfilled the octet but here's my question to you do you think that there is still this hydrogen is it on the carbala anion what do you think well think about it and just draw it out now if I have the hydrogen there how many electrons are around the central carbon 2 4 6 8 9 10. that violates the octet rule so that guy it doesn't work there's too many electrons so what we have here is a carbo anion it is missing that hydrogen but it does have a lone pair so when we take a look at these three different anions let's that's not correct because they're not all anions is that these three different structures here we have a neutral carbon a positive carbon and a negative carbon how do I know this is a plus one and that's a minus one back to the idea of calculating formal charges now if you go back to General chemistry and review your notes your instructors would have taught you how to do it their way and a textbook would teach you how to calculate formal charges you could go on YouTube and they have ways to do it also I have my way of doing it and I hope it works for you but if not find a way that works for you so what we're going to do is we are going to look at just these Central carbons and calculate the formal charge on each one of those and the formal charge has to match what we have here so the first thing that you do here is you need to calc you need to go to your periodic table and find out how many valence electrons the atoms have and let's see I'm going to grab my book here so I have my textbook right here and I'm just looking at a periodic table and when you look at your periodic table you see that the elements have different groups and those groups are the vertical columns okay and when you look at those vertical columns carbon has a number of 14 above it and nitrogen has a number of 15 oxygen has 16 and fluorine has 17. so it looks like this so carbon nitrogen oxygen fluorine and it has a group number of 14 15 16 17. when I look at that I'm only paying attention to this last digit here and that number in that last digit four five six seven is telling me how many valence electrons that element has in its neutral state that's the trick these numbers here tell us how many valence electrons an atom has in its neutral state so when I look at this molecule I am going to find this number so I'm going to see okay what Atom am I looking at and I'm like I'm the arrow is pointing to a carbon so I come here look at my periodic table okay so that means carbon has four valence electrons now I need to subtract how many electrons that carbon atom owns so I'm going to come over here or I'm going to actually erase this I'm going to draw it out so we can visually get an understanding of what's going on here like this now if I take a look at this Central carbon these Sigma bonds or covalent bonds they just are representing like this right so this molecule right here is this molecule now we are going to say when we look at this molecule here because these are covalent bonds that means it shares the electrons so when we look at these two okay they're sharing so carbon's only going to worry about this one there's two here carbon's only going to worry about this one over here so it's only sharing half of the electrons in those bonds so I'm going to circle the electrons carbon owns it only owns four of them four of the eight so those electrons there I minus and then that's going to equal the formal charge so this is the formal charge so 4 minus 4 is 0 which means it's neutral so the formal charge for this carbon is zero and when the formal charge is zero or neutral we just don't write write it down it's just completely neutral now if we take a look at this carbocation we are going to have to erase this guy we're going to have to put in the formal charge and so that means this guy no longer exists and so now I that this green force it's the same all across the board because the first number in this calculation is how many valence electrons does the carbon atom supposed to have so we're looking at this carbon here we go to our periodic table we see that it's a carbon we don't care what the formal charge is just ignore that for right now how many valence electrons does a carbon atom have four that's that number minus how many electrons it has around it or owns so this is what it looks like we can then translate this Lewis structure into this if we'd like and we can see that there's one two three electrons so we are going to erase this guy and go three so four minus 3 is a positive one so you could go just a plus that means positive one or if you want to do a little bit more work you could go plus one but really now that I'm thinking about it you don't do it that way that's just not how it's really done drawing that plus tells us it's a plus one charge right now if we do the same process here with this anion what do we have here we have a carbon okay this is a minus minus one so that means it has a lone pair and so that lone pair is going to be right here so we can just go that's a carbon atom how many valence electrons does that Central carbon have four how many electrons does it have around the central carbon one two three four five four minus five is a negative one that's why we have our negative charge there so you can see that's how do it a little bit more time drawing out all the structures and so there's just a quicker way to do this and the way I do it is when I look at the structure I write down how many valence electrons it's supposed to have minus and then I count how many bonds there's one two three four so I know that carbon is neutral when I take a look at this guy I know it's four valence electrons minus how many bonds one two three equals plus one now this one it is four valence electrons minus and this is how I count it count the bonds one two three and any lone pair you count both electrons so let's do this again let's look up bonds one two three four five and that would be equal a negative one so you count the electrons the lone pairs and then you count bonds and I know that may be different than what you were taught in general chemistry in general chemistry you had a formula that you type in the info or enter in the information to figure out your formal charges if that works for you use it that is great I've just come up with this method because it just goes fast for me right so with that let's apply this principle to something else other than carbon so let's draw an alkoxide well something that looks like what I want to figure out is what is the formal charge of this auction atom when I go to the periodic table I see it's in group 16. so that means this oxygen atom has has or should have six valence electrons and now using my trick you count how many bonds and how many electro how many electrons that are in Lone pairs so I have one two three four five six seven equals a negative one so the formal charge on this auction atom is a negative one what would the formal charge be on this ether if I see an auction atom so it has to have six valence electrons minus one Bond two Bond three four five six equals zero so that is a neutral auction and we already know that's neutral why because the honk rule if oxygen has two bonds it's neutral and it has two lone pairs all right so looking at let's take a look at a nitrogen species real quick oh no no let's let's talk about this for a little bit so you will see structures all right like this I could draw a structure just like this on the exam or practice homework and you should know you know that this oxygen only has one covalent bond three lone pairs that has to be negative one charge I may not draw in the formal charge if you can see that I'm drawing in the lone pairs then you already know what the formal charge should be if I draw the same structure like this do you see how I'm omitting the lone pairs but I gave you the formal charge and so that formal charge of negative one is going to tell you that there are three lone pairs even though I may not draw them in so if I take a another species like let's see here let's draw a amine here I draw just like that what is the formal charge of that Amine what does the honk rule tell us and if we can't if you're someone like me you just have to write it out for some reason the honk one two three four rule okay so that means nitrogen has to have three bonds okay so that doesn't have three bonds so right off the bat I know that is not neutral because it that rule is broken so now I just got to go figure out go to my book find out what group number nitrogen is in and nitrogen is in group 15 so that means there has to be five valence electrons and I see this nitrogen how many bonds one two three four five six so that nitrogen right there has to have a formal charge of negative one or when they're ones you never type put in the number that's a minus one what if you had a nitrogen with four bonds attached what would you think same rules five minus one two three four one so that would be a plus one Amine okay let me just reiterate and emphasize how important it is to know how to do formal charges it's going to help you know reactivity and predict reactivity it will help you understand if the reaction is even probable very very important so a challenge that we have as organic chemists it's a minor challenge but it's the fact that when we try when we attempt to draw molecules on a two-dimensional plane of glass or chalkboard we have we have to understand that molecules are not two-dimensional but a lot of molecules not all a lot of molecules they have they're not flat they have three-dimensional shape to them and so we need to devise a way to unders draw a molecule on a board but still represent that three-dimensional shape that a molecule has so remember that a carbon with four bonds isn't just a carbon with four bonds in the same plane and flat but it is tetrahedral to remember in general chemistry that we have tetrahedral shapes and so to represent that tetrahedral shape we also have to understand that look the way I drew this what is the bond angle the way I drew it that is 90 degrees but a tetrahedral molecule does not have bonds that are 90 degrees from one of one another it's 109.5 degrees and so what we have to do here is represent that uh actual angle the way that we demonstrate the tetrahedral geometry of that molecule is by using wedges and dashes so now do you see how that Bond angle there is greater than 90 degrees and we want to represent it as 109.5 because this is tetrahedral one of these bonds is going to be a wedge and the other is going to be a dash and so what this is telling us is that this wedged Bond is coming out of the plane or out of the board at you so if I'm looking at this molecule these two bonds right here are in the plane of the board or the plane of the glass and this Bond right here is sticking directly out of the glass and then this dashed bond is pointing in the opposite direction of the wedge going out of the board in that direction so what we're going to have to be able to do is get your hands on a modeling kit and you're going to see when you build this molecule with your modeling kit that one bond is going to be pointing out of the board and the dash it can be pointing into the board and so that's what how we represent the bonds in uh tetrahedral carbons these wedges and these dashes now when we take a look at a zigzag structure like this so that's a pretty good zigzag structure now I want you to contrast this zigzag structure to this one in blue and one more you clearly see a difference right now why is the blue one down here wrong and this one up here correct well it has to do with this Bond angle right there you are trying the best that you can to represent that 109.5 degrees here that angle between there clearly not 109.5 so this zigzag structure is incorrect and will result in loss of points if you're going to draw zigzag structures like this you need to have that beautiful 109.5 Bond angle and that's why we draw zigzag structures we're representing this angle and so then when we have a zigzag structure how do we represent the wedges and the dashes well the wedges and the dashes are quite simple here we see let's number the carbons one two three now when you take a look at Carbon two do you see how it's Apex pointing up and then when you look at Carbon three the Apex is pointing down so you're going to find that Apex and you simply draw a wedge and a Dash like that you do not if I'm calling this Carbon 2 that's carbon one carbon three if this one right here is carbon two you do not draw the wedges and dashes like that this is a no-nose don't do that you find the Apex and you draw the wedge and the dash now students may ask and it's a very valid question if this is carbon two is there a difference between that so we have a molecule on my left to molecule on my right is there a difference between those two and the answer is no there's no difference whatsoever why because this wedge right here is saying it's coming out this wedge almost knocked my book over here this way I just saying the exact same it's coming right out this Dash is saying it's going into the board this Dash is going into the board so what you can say is that if you trace the green skeletal backbone here these blue bonds are just perpendicular to the green bonds the green bonds are in the plane of the glass and these blue bonds are out of the plane so it's kind of the way I look at is if I could take my eyeball and look down this green backbone so I'm just like looking at it and I'm just looking and I can see the green backbone right through the plane and then I see these spawns right here they're outside of the plane so it's kind of like looking if right down the center of my chest if that's the green backbone the blue bonds right here are on either side of that green backbone kind of like handlebars on a bike so those if I leave these wedges drawn as is what do I have here I have a methyl group and a methyl group if I want those to be hydrogens I'm going to have to draw them in when you draw your wedges and your dashes so if you ever just draw a wedge like that that's legit but there is a methyl group do I have to draw in the dashed hydrogen no I don't if I don't want to draw on my hydrogens I don't have to because we are organic chemists so that is a valid wedge yeah so if you have if you're only going to draw one wedge or one dash it can go right in the middle like that but the moment you have to put two uh groups on that Carbon Let's look at this one you have to put a wedge in a dash they have to be opposite there's the wedge there's the dash you can see why do I want it like that because I'm looking for whoa that 109.5 so that 109.5 angle is for every single one that's why we draw the zigzag that is why we draw the wedges and dashes all right another thing students do that's kind of a pain and not actually correct if they draw something like this they'll have your zigzag and they'll draw a wedge there and it's dashed down like that incorrect don't do it you find the Apex I'm going to say it one more time I know I'm now a broken record if we're looking at this carbon right here we put the Apex is pointing down so that means the wedge comes here and the dash goes like that and then you type you put in what elements there are if that's a hydrogen put in a hydrogen if that's a chlorine put in a chlorine all right now as we progress through the course we're going to be able to look at cyclohexane rings and even on a ring you can have a wedge and a Dash and we are going to look at all different sorts of structures okay your book talks about those early on I'm not going to spend too much time on that right here but you can read about it and looking at all the different ways we can draw molecules but these this wedges wedges and dashes to represent tetrahedral carbons is super super important right so looking at the time we will I'm going to stop here so the next topic that we're going to take a look at is another topic that you learned in general chemistry it's called resonance and you need to review that I'm going to go through some the basic rules of it again but it's something that is so important for your success in organic chemistry because resident structures are going to be a thing from here until the end of orgo2 and it's going to go into biochemistry it is a principle that never goes away you cannot approach this hey let's learn the bare minimum just so I can pass the test and think you're going to be okay because you're not you have to understand this to be successful in the future topics and in orgo too and so if you find this a difficult topic you're right resident structures are a lot of students struggle with it because it's so new and it's just in it's just it's just what it is but I just want to make you aware that it's so important that if you're finding yourself struggling with that you need to get the help that you need so look to the ta's office hours anything just to get this down pat it's super important okay so let me know if you guys need anything and need any help