hello everyone and welcome to this lesson in this lesson we're going to be exploring the alkanes alkenes and alkynes a little bit more in detail in the last couple of lessons we've just been spending time identifying the different types of molecules but now we're going to look at what these things actually are so let's start up with the alkanes so here we have a couple of alkanes on the screen now alkanes are the simple ones they literally just consist of carbons and hydrogens and they are only single bonds that's it carbons and hydrogen so we give those a name we call those hydrocarbons by the way in the last couple of videos i've been talking about alkanes alcohols aldehydes ketones esters and things like that those things are called the homologous series okay so we can say that an alkane is a type of homologous series so in one of the videos i called them families but the proper technical name that your teacher is going to say in class is homologous series so we are looking at the alkanes which are a type of homologous series you get other types like alcohols ketones aldehydes but we're looking at alkanes okay so they are hydrocarbons they also have some really cool thing happening check this out if you count the number of carbons in this first molecule they are one two three four five then if we count the hydrogens there will be one two three 4 5 6 7 8 9 10 11 12. okay so kevin what's so cool about that well i'm just going to write that down for now so i'm going to say that there are five hydrogens and i mean five carbons and twelve hydrogens let's do the next one so there's one two three four five six seven eight nine carbons and then i'm not going to waste your time but if you had to go count all of those hydrogens you'd see that there are 20. don't believe me pause the video check it out and so we can see that we have c9 h20 then this one over here has one carbon and four hydrogens now there's a pattern emerging i know it might not look really obvious right now but check this out the pattern is the following if you times the number of carbons by two and then you add two you will get the number of hydrogens that they are meant to be so for example if there are 9 carbons if you times that by 2 that's 18 plus 2 that gives you 20. and guys this isn't rocket science check this out for this for each of the carbons that are in the main chain they always have two hydrogens like definitely see that and then the two on the end they have an extra one and that's where that's why i said you can take the number of carbons multiply that by two because they all have two hydrogens and then just add two to the answer for the two hydrogens that are on the end and so we can say that the general formula for hydrocar or for alkanes will be cn h then you say 2n plus 2. so if we have 10 carbons then you say c10 and then the h's will be 2 times 10 plus 2. so that will be h22 and so there we have it guys the general formula is cnh2n plus 2. so you need to get used to that because i could for example in an exam they could say okay so we've got this molecule c5h12 give the homologous name now you might say alcohol aldehyde but if you realize hey it's only got carbon and hydrogen so that could be an alkane and the ratio is two n plus two so you say five times two which is ten plus two is twelve oh that's an alkane all right so here's a very random question what do we use a towel for you know a towel that you use when you get out the shower get out the bath that's that tau is used to soak up water from your body okay but let's say you working in the kitchen for example and you spill a huge bucket of water all over the kitchen floor because we all work with buckets of water in the kitchen don't we now if you were to use a towel to try and clean up that water or try to soak up that water i'm sure you've done this before you'd realize that that towel does not have enough uh what could we call it water retaining ability okay it can't it can't collect all the water eventually the towel becomes full or the proper scientific word is saturated and then you can't add any more water to that towel that's usually when you'd have to go squeeze the towel so that all the water comes off and then you could use the towel again to try soak up some more water so in chemistry we're going to talk about the word saturated and when something's saturated it means you can't add anything more to it so what i want you to do is quickly look at each of these carbons they have one two three four bonds i can show you any of them check here one two three four and so those carbons are saturated we know that carbon can only form a maximum of four bonds and so alkanes are saturated we will look at alkenes next and we'll see what unsaturated means okay so the next important thing you need to know about alkanes is that they are saturated and that's about it really we'll look at alkanes at a later stage when we start looking at the naming but for now those are your arcanes i hope you're feeling a lot more comfortable with them next will be the alkenes now the alkenes are the guys that have the double bond okay that's what that's what's important for them so this will be a lot faster than the alkanes because straight away we see that there's only carbon and hydrogen and so these are also called hydrocarbons and guys the word hydrocarbon it's self-explanatory hydro for hydrogen carbon for carbons there's only hydrogens and carbons aha next we need to look at their general formula oh and by the way their homologous name is alkenes okay so remember that is a type of homologous name or homologous series i know it's a weird word homologous who comes up with that but that that's what that's the group of molecule it's called the alkenes okay and remember there's nine different types nine different homologous series let's look at the general formula now so if we look at this first one it's got one two three carbons okay so i'm going to say c3 then if you count the hydrogens there would be six for the next one one two three four carbons and if you count the hydrogens one two three four five six seven eight okay so look at the pattern now the hydrogen is always double the number of carbon so let's see how this makes sense these alkenes are the same as alkanes but they have a single double bond okay oh by the way if an alkene has two double bonds we haven't looked at something like that yet but you can easily get a molecule that does something like this when there's more than one of those double bonds then these formulas don't work okay i've never really seen them do that too much in an exam but just remember that those general formulas only work if there is one double bond so as i was saying these are the same as the alkene alkanes which have the general formula h times two n plus two but we need to understand how a double bond is formed so if we have a carbon carbon with hydrogens okay so the important thing is look at how many bonds are surrounding each carbon there is one two three four and then one and then four for that one now that always has to be like that for carbon so what's going to happen is the following if we want to form a double bond we can put a little double bond over there but now you've created a bit of a problem now each of your carbons have one two three four five that that double bond consists of two bonds hence it's called a double bond so we have a bit of a problem so what we're gonna do unfortunately we're gonna have to kick away some hydrogen sorry hydrogens on either side now have a look at each carbon so this carbon on the left now has one two three four so now everything makes sense carbon is happy again it is bonded to four it has four bonds surrounding it and so notice what we had to do we had to knock off those two hydrogens okay and so that is why we are going to lose this part and so this part here was for alkanes but alkenes just do this they lose that plus two and so that is the general formula for alkenes now i need to look at the concept of saturated and unsaturated these molecules these alkanes they are not saturated that means that they are like a towel that can still collect more water the reason i say that is the following if i had to come along so i come along here i come along here and i break this bond over here then if i enlarge this part of the molecule it's going to look like this you've got a carbon and then you've got a hydrogen and then you've got a carbon and a hydrogen and a hydrogen i've broken one of those double bonds and so there's only a single bond now okay oh and then this one was bonded to a carbon what's happened now is that each of these two carbons are only surrounded by three molecules or three atoms and so if you break that double bond which is fairly easy to do in chemistry you can then to complete carbon's requirement for having four bonds you can then add another hydrogen that's like adding more water to your towel so if you ever see a double bond or a triple bond you must remember that those are unsaturated meaning that they can still have more things added to them because once again if i come along because over here i can't do anything i can't break a single bond a single bond um it's very stable a double bond you can break it so you break this one over here now all of a sudden this carbon only has three things surrounding it and so does this carbon so what we can then do to fix that is we could add a hydrogen to each thing and so notice that we can still add more atoms to this molecule and so we call it unsaturated and lastly the alkynes i promise this one's going to go a lot quicker the all kinds are very teachers barely ever test these ones but they are pretty much the same as alkanes except that they have a triple bond so it makes sense that there's no hydrogens attached here because if i had to attach a hydrogen over here then if you had to look at this carbon it would be surrounded by three bonds here four and then five so remember carbon can only be surrounded by four bonds at a time not three and not five so quick summary they are hydrocarbons meaning there's only hydrogen and carbon their general formula i'm going to go through that so if we we can imagine that these ones have even less hydrogens let's quickly look here one two three four carbons and then if you quickly count that up that's going to be six hydrogens that's c4h6 this one here is one two three carbons and the hydrogens will be four the formula for these ones is you multiply the number of carbons by two and then you subtract two okay so four times two is eight minus two is six so their general formula is c n h then you times that by two but then you minus two so notice that the alkanes which have the most hydrogens they were cnh2n plus two then the alkenes they subtracted that and then the oh oh that's two n and then the alkynes minus another two so it starts off at plus two then goes to two n so they take away two and then they take away another two and so their general formula is the following and then lastly guys these things are unsaturated why they are like a towel that can still hold more water because if i have to break these bonds then i can open up more bonding positions and then more hydrogens can come and attach meaning more water uh if i'm thinking about the towel my towel can hold more water so these are unsaturated and that's it guys i hope you really learned the difference between alkanes alkenes and alkynes they're all hydrocarbons we looked at their general formula and we looked at what saturated and unsaturated means thank you very much see you in the next video