[Music] welcome to this video that's gonna discuss topic ten be the halogen or alkanes this is the second part of the unit to our damaged chemistry section partly is just the general principles so I haven't made a video on that it's literally just two pages just going through all the different terminology that we need to know for example oxidation reduction elimination substitution that's something that's fairly simple for you to be able to do yourself what we're gonna focus on today is the hello general alkanes and we're gonna look at a number of different learning outcomes and look at some past papers towards the end so we need to be able to go over the nomenclature and you need to be able to draw the structures of our halogen or alkenes we have to be able to classify the different halogen Americans looking at their reactions and some mechanisms as well as looking at the relative rates of hydrolysis of our primary secondary and tertiary or our chloro bromo or i old or alkenes there are two core practicals with on this topic core practical five and core practical sex I will not cover these unless particular video you can find more information on most core practicals and the core practical video that will be uploaded into the es chemistry playlist so please find there what you need in order to understand those practicals so we're gonna start off by looking at the halogen or alkenes these are a homologous series of compounds and they are have the general formula cnh2n plus 1x now of course we do not classify these as hydrocarbons because they do have this halogen here and the halogen could be a floater chloro bromo or i or doe we tend just to focus on these three the chloro bromo or i although sometimes fluid or can be there and we very very rarely talk about astatine we also sometimes can simplify the formula of a halogen allow Kim to just simply R X R meaning an alkyl group so for example me fail or if a and B X as our halogen atoms are floating according bromine or iodine when we are naming these halogen elkins we name them very similar to our branched alkanes and alkenes if we have more one halide more than one halogen atom then they're listed alphabetically so for example if we take the center molecule here we've got a carbon with two hydrogen's and a brownie connected to a carbon with two hydrogens connected to a carbon with two hydrogen's and the coating so both be coming before C and the alphabet this becomes carbon number one this then becomes carbon number two and this becomes carbon number three and our halogen alike an ends up being called one bromo 3 Coral propane we can also have some other examples as you can see on the table I'll let you try and draw them and name them yourself so the second thing that we have to be able to do with the halogen arguments we have to be able to classify them now you have seen the terms primary secondary and tertiary classifications before when you were discussing carbo cations back in topic 5 we will also discuss Trainmen a secondary and tertiary classifications when we do alcohols and that will be in another video so what do we mean by primary second giant actually works all to do with how many alkyl groups they have attached or you can look at it as how many hydrogen's they have attached so if we take for example that his first one if we look at just the end portion of our molecule here so we have carbon connect two hydrogen's and the bromine which is connected to an R group because we only have one R group we're gonna call this Simon a halogen origin when we look at the second one here I have a carbon connected the bromine that is connected to to our groups and one hydrogen so we call this a secondary color general alkane because it's connected to those two alkyl groups whereas the third one you can see is connected antistick our cow grips and we call this a tertiary collagen or our kin it's very important that we can distinguish between these three things that has become depending on the classification can depend on what sort of reactions we're going to get so we need to understand why haulage low alkanes are reactive as we consider hydrocarbons hydrocarbons have only carbon and hydrogen atoms and they contain very similar electronegativities two point five and two point two because they have such similar electronegativity their bonds are almost nonpolar that means that the electrons are very nicely shared we don't get any overall dipoles so it's not particularly reactive to other molecules such as positive or negative ions or dipoles or even lone pairs this is why we require things like UV light in order for a substitution of an alkene to happen when we compare this to the halogen or alkanes they have a much larger difference in electronegativity and their carbon halogen bond we already know that the halogens are the most electronegative atoms and the entire periodic table so because of this we get polar bonds now how does that have an effect well it basically causes the carbon to have its electrons pulled away from it and they will set a little bit closer to the bromine similar to the diagram here and that causes the bromine to be a tail to negative and it causes the carbon to be Delta positive now the same thing will happen with floating codeine or iodine they will just have different levels of dipole activity so one way we can modulate the negative at slightly positive them the other and we'll come back to that later on so if this happens it causes VES carbon and the center to become electron deficient so that actually means that attracts a nucleophile and then you could well is something that was attracted to an area of electron of law electron density because they are going to attract nucleophiles they can undergo nucleophilic substitution reactions and we're going to look at a couple of them elected on in this body stretch reaction that we're going to look at is called a hydrolysis reaction now hydrolysis as you can see from the bottom bullet point it can be split into two words of the hydro meaning water and the lesss meaning to split so this is basically the splitting up of a molecule using water how this works is we have a delta negative oxygen on the water because of course they have lone pairs and these are going to be attracted to our slightly positive carbon of the halogen allow kim and we make an alcohol and a hydrogen halide now we can write this hydrogen here laid out in two ways we can either write it as just HS or we can write as the ions that are present each positive and X positive that really doesn't make a difference because our main focus actually as this part here the alcohol this is a way to make an alcohol from a hydrogen halide start from a halogen allow kim by the end of this organic topic you should be able to build a map that will show you all the different organic reactions but we'll come back to that a little bit later now the hydrolysis reaction is actually very very useful to us because what it can actually do is it can help us determine the relative reactivity of these halogens and the way that we do this as we compare either Coral a bromo or an iota alkane or we look at primary a second ray or at actually structure the basal tend to be bromo alkanes but it doesn't matter you can use a coral or diode or if you wish this is a core practical this is core practical five there I'm not going to go into the details of how we carry out core practical five you will find that information and a different video on the es chemistry playlist please feel free to check that out actually made it we're gonna look at what information this actually tells us then the his problem with this particular reaction is that the products that are formed when we add on water are both colorless liquids so we can't actually see when the reaction is finished without having to do a test and we've been that we can't time that so the we need to be able to overcome this because in order to time the reaction and get a writ we need to physically see a change happening whether that be a color change or a mass change or something or effervescence now what we're gonna focus on or what we're going to use to our advantage is we're gonna use color change and we're gonna achieve this using silver nitrate now you've seen silver nitrate before back in GCSE and it was one of our chemical tests now I'm hoping that you can remember what the chemical test was but if you can I'm gonna help you out and the silver nitrate when it comes into contact with a halide it's gonna form a silver halide to precipitate and of course we get different colors of the precipitate so we can't tell them apart as well the only thing that we do need to be aware of here is that we have to dissolve the silver nitrate and ethanol that just helps us get over any miscibility issues because our halogen or alkyne and our equation are not going to MEK spectacularly well because oh we have a little bit all nonpolar and polar substance trying to mix together and we already know that like dissolves like so there's gonna be a bit of a problem there so if we dissolve it and to the ethanol it's just gonna be a little bit easier for us so the first reaction that we're going to look at is we're going to be comparing our I adore and promote and our coral bit in it does not matter what I'll count grips at you use the es chemistry core practical advises you to use 15 compounds but it does not really matter most like leaving you to boot in because these are also all going to be liquids and they are quite small molecules so we don't get too many interacting and two molecular forces so what we see from this is that we get iow tin as fastest followed by bromo brutal followed by coral bitten one of our objectives of this topic is to be able to understand the reason why it's very simple for us just to remember the they order but that would be something like GCSE available it is all about the wire and the wire is actually a very very simple answer and it is all to do what the bond enthalpy if we look at the difference in the bond enthalpy between carbon and iodine carbon and bromine and carbon and chlorine we can see that the carbon and iodine has the smallest bond enthalpy this means that as the weakest bond the weakest bond is going to be the one that has broken the most easily when the weakest bond breaks in this case our carbon iodine we're gonna form iodide ions these iodide ions will very quickly Maxon with our silver and we will form a silver iodide precipitate that's gonna happen very quickly when we get the bromine and will continue to happen of course and we will make that silver bromide and we will also make silver colloids but silver chloride has the strongest bond therefore it takes the most amount of energy and therefore the most amount of time so this we can use bond enthalpies to explain why the I order butane is the fastest okay the carbon fluorine bond is so strong that it is very very rarely used and these hydrolysis experiments because you can be timing for quite some time and still not see any precipitate being formed when we test the different structural isomers the pattern is that Terry as the quickest followed by secondary followed by prime in it now the good thing for a s label students is that you do not need to understand the reasons behind best trend because it actually requires very much a deeper understanding of the reaction mechanism and this is something that is going to be discussed and topic 11 it comes down to the fact that the territory and the primary undergo two different mechanisms that will an effect on their weight but when we discussed that when we get into your 30 so we need to know four key reactions of the hello generations and you have to be able to draw the mechanisms for reactions number two and number four so that's number two and number four now I'm not going to go into any more detail about reaction number one because this as simply the hydrolysis reaction that we have just been looking at so we're going to jump straight to reaction number two and this is known as a nucleophilic substitution reaction and this just means that we're getting a substitution of an atom or a group of atoms and undergoes via a nucleophile okay so reaction number two is to heat the halogen or alkene with aqueous potassium hydroxide under the flux and this is another way that we can make an alcohol now our attacking nucleophile and this kiss has the orange and an example here as our coral prop in one quarter propane being formed farming so I hope an one or plus AK or eight iron the mechanism for this particular reaction begins with the donation of a lone pair of electrons from the switch to our electron deficient carbon remember all of these are going to go through our electron deficient carbon that is our site of our nucleophilic substitution at the same time as this happens our carbon bromine bond is going to break and we're going to have a chollet accession meaning that the electrons are going to go off one of the atoms not worth two of them if the electrons are split between two that's homiletic fashion and we get free radicals first time we're getting hit accession because we're forming ions and this is going to form an alcohol and a bromide ion as our products so let's have a quick look at the mechanism for this so we have our hydroxide that contains two lone pair two electrons and a lone pair they are going to attack using a curly arrow of course to show the movement of the electrons they're going to attack our electron deflection carbon and the electrons from the carbon bromine bond are going to go onto the bromine the bromine to form a bromide ion and we're going to form a new bond between our carbon and our oxygen group here to form our alcohol we get alcohol then a bromide i've reaction number three as a reaction over halogen or alkene again by heating under reflux last time we are heating it with potassium cyanide and ethanol and we're gonna make a nitrile now we do not need to know the mechanism for this reaction again this will be touched on later and you're thirteen and they are gammac sections what we do need to know is that the attacking nucleophile is the CN I am and an example of what happens as a reaction here so we have a bromo Ethan being attacked by the CN and we're gonna form that a nitrile group what you may notice is that this first reagent has two carbons whereas our product has three carbons this is actually a very useful way of lengthening a carbon chain which is very very useful in organic synthesis organic synthesis is a topic that isn't again in year 13 and topic 20 and you will come back to this particular reaction as a way to lengthen our chin in order to make a new product then we can look at reaction number four which is the heating of a halogen or arcane West ammonia solution under pressure and assume chip to make a primary amine now we do need to do this under pressure and assume trip because we are using ammonia gas and of course if we don't have a unless you trip the gas will escape so our attacking nucleophile as our ammonia molecule please remember that ammonia contains a lone pair so it can act as a nucleophile that lone pair will attack and - our molecule in an example of our reaction as shown here where we make our primary amine which is this here and we also make a hydrogen halide the biggest difference what this particular reaction is that the hydrogen iodide is an acidic substance so it's going to react with the basic organic molecule so our aiming in order to form a salt now we don't want result to be formed so what we actually do is we use a very high excess of ammonia and that avoids the salt to be formed this would be the salt that would be formed and we as we said we want to avoid that so what we do is we add on this excess of ammonia and we end up making an ammonium salt plus our primary amine and we can combine them into this equation down here that as we've said previously you do need to know the mechanism for this particular reaction that can come up and an exam you could be asked to read adjuster final is very straightforward and comparison to some of the other mechanisms and it does fall very similar patterns that we've seen so we start with our ammonia a nucleophile that has its lone pair and the curly arrow will travel from the lone pair on the nitrogen to the electron deficient carbon and then our electrons between the carbon coating bond I'm going to travel on to our core eight iron and we're going to form this kool-aid and we're going to form an intermediate here then what happens when we have our excess because these two things would form our salt and we do not want that so we have our excess ammonia being added and then basically we get this lone pair again this time attacking the hydrogen and our electrons from the nitrogen hydrogen bond here go on to the nitrogen of course getting the nitrogen back its lone pair and forming an ammonium then this ammonium will join up with escorting and we will form ammonium chloride salt now the last reaction that we need to know about before we look at some past papers are an element as an elimination reaction so if we have reaction number two being carried out and ethanol ik reactions then just a remainder that was the addition of the potassium hydroxide and aqueous whose reaction number two if we have that's happening and ethanol conditions so being dissolved into ethanol we get a different reaction happening under these reactions are all which actually acts as a base instead of a nucleophile and what happens it causes our hydrogen atom next to an electron deficient carbon to be removed as water so we're actually eliminating an atom and this particular reaction and what we do is we get water being formed and we form an alkene so this is a way that on organic reactions map this is a way for us to go from a halogen allow Kim back to an alkene you can see here that we lose so the potassium bonds and with the bromine and then this hydrogen bonds with the o H and we get water and potassium bromate and we form our double bond here because we've lost an atom from each of these two and carbons so let's have a look at a passed paper question for best or a number of different questions and looked at some multiple choice as well as I've still length questions to the paper that I've taken these from is the January 2018 paper so the first one is looking at the properties of our liquid Codel 2-butene so let's just draw out real quick so the built in is gonna give us four carbons its second carbon Cotto's on and then we draw hydrogens for all the rest so in terms of solubility and water well we know that with it being cold or butane and with it being mostly on organic molecule we're going to have insoluble substance and water so we can automatically discount C and D no we just need to look at what effect does it have on charged rod with it out so I wash it with a charge rods have on the stream of liquid now because we have this carbon to chlorine bond here which is very polar it does give a slight polarity and the molecule so that's gonna have an effect on our childhood and actually it's gonna cause extreme to be directed so the answer to this question as a first question 13 we're looking at the organic elimination products from 2-bromobutane so this is very much the kind of their last topic that we're just looking at there so let's just draw it again so we have to draw more bit in now we will obviously remove this bromine but the question that we can't work out of the question that we have is that what say does the hydrogen come from it can either come from the site or it can come from this site now we can't actually control this we do get a major and a Mainer product depending on the carbo cations but we don't need to go into enough detail about that what we do need to be aware of is that we can make at least two different products here so we can end up having the double bond between carbons 1 & 2 or we can have the double bond between carbons 2 & 3 know that you may then think the answer is going to be two however we do need to consider that be it to teen can have e-z Paesanos you can get e butyrin and Zed beauty in so now we have one isomer from our big one in and our two geometric isomers so the answer to this is actually three don't get caught by saying turn thinking that we can only get one geometric isomer I mean you do need to remember that you can have more than one okay let us look at a full-length question on this so we're gonna have the question about the trepidation and the properties of I or don't fit in so I order gluten can be prepared by warming a mixture of damp red phosphorus with iodine to produce phosphorus iodide unless reacts with Britain one out perform the IO don't fit in we want to complete the balanced equation for the formation of the one iota butane we do not need to state symbols now let's may look at first glance quite confusing but actually all the information that we need is all in the question so we know that we're gonna form c4h9 hi we have our other product well the other product is going to be the phosphorus reacting with the oxygens and the waters that are being removed from the alcohol here now we do need to take into account that we have got this difference and our number of iodine's so if we have pi/3 a phosphorus 3 iodide we're gonna be having to use all three of our iodine's and our kyoto butan Batman gives us also having to balance out that we need to start with 3 so our reaction reads as 3 butan one''ôs plus phosphorus the iodide gives us 3 one iota greetin's plus h 3 p o3 now the one I adore Britain as we said has been formed but we can actually draw four different structures structural isomers of this there will and previous one talking about the herald orbiting but we can also of course have it as different structural isomers so the first one is going to be very simply so we've got carbons one two three four connected to an iodine we can then also have a branch again another branch and we can form our basic two iota butan so remember whenever we're drawing any structural isomers the first thing that you should do is look at the possession of the iodine atom and then look at the chain length and all you do is you either move the possession of the iodine or you keep the iodine where there's and you reduce the chain length until you get all four iyslah's if you've got two or three connect you we get one mark if you get all four connect you we get to Mike's now you can do them and displease our structural formula I've chosen to do that and scale to formula because of course that's what the question asked for if you do use displayed or structural formula you do however still get one mark so let's move on to another question where we're looking at the iOW team being dissolved and ethanol with the hot liquid silver nitrate to form a yellow precipitate okay this reaction is going to involve two steps well this is going back to our reaction number two which is the reaction with our hydroxide and so this is come back to reaction number one which is our reaction with our hydrolysis okay so our attacking reagent endless kiss is going to be water and we're looking at the lone pair that is on the water and the type of mechanism well it is going to be a nucleophile that is attacking so we're gonna have a nucleophilic reaction and they always four halogen or alkenes are going to beat substitution reactions then we have to look at the ionic equation for the formation of the yellow precipitate and of course it's going to ask us to include state symbols here be very very careful that you always include the states and ones when they are asked for this is only for one marked if you don't include the state symbols you are going to throw that away so the ionic equation is going to be our silver which is a twist reacting with our iodide which is also a twist to form our silver iodide precipitate which of course is going to be solid never gonna look at our final question what is the looking at the reaction between the iota butane and excess ammonia so that is going back to reaction number four which is the excess ammonia and we're going to form two products okay it says and we can identify them by name or by formula well if we have butan has our alkyl group we are going to have a butyl alien being formed and that is simply the name that we use is Brito aiming we can also write one amino butyric hi their answer would be accepted now that is just one of our products of course what the excess ammonia we know that we're also going to make some form of salt and the salt is always going to be an ammonium so we just have to double-check what is our halogen and we're going to form ammonium iodide my one piece of advice for this particular question with the best part here the name and the formula assert the name or in the formula you can write both that is absolutely acceptable however if one of them is wrong you lose that mark so if you're not sure on the formulas or you're not hundred percent sure on the name do not to rate them right one or the other pick the one that you are most confident with now you can of course check all of your answers and the Mark skins that you can find at the end of the presentation and you can go back and check through each of the questions that you have answered that is everything for the halogen or alkanes I hope that you have found this video useful and that you've been able to understand all the reactions that we need check back later for some additional videos on the organic section and I hope to see you coming back soon [Music]