Lesson video

Hello, my name is Mr. Gundry, and today we're gonna be looking at hydrocarbons from the unit Chemistry of Carbon.

I'm really excited to get started with you.

Today's lesson is gonna be focusing on the ideas of simple covalent structures and chemical compounds.

So the main aims for today's lesson are that you should be able to describe what alkanes are in the context of hydrocarbons.

To be able to name the first four alkanes of a chemical series and then be able to draw their chemical structures and write their chemical formula.

So the key words for today's lesson are hydrocarbon, feedstock, alkane, homologous series, and nomenclature.

All of these are defined on the next slide.

I'm not gonna go through them with you right now, but we will go through them as we get to them in today's lesson.

So this lesson is split into two parts.

The first part, we're going to look at what hydrocarbons are, and then we're going to talk about how there are these different groups of hydrocarbons that we can label homologous series.

So we're gonna look at hydrocarbons to begin with.

So hydrocarbons are a class of chemical compound.

They exist as simple molecular substances and are made up of only carbon and hydrogen atoms. They are a type of organic structure, as we can see, that they have this carbon backbone structure, and they are really important in chemistry because we use them either as fuels or as feedstock.

So feedstock being chemicals that are used as almost starting materials to make other chemicals.

Hydrocarbons are found mostly in a substance called crude oil or natural gas.

Most of the hydrocarbons though that we use come from crude oil.

And crude oil specifically is, well, sort of is the same as natural gas formed through similar processes formed through the decay of ancient organic matter, mostly from plants and similar structures like algae.

This process is a natural process.

It's part of the carbon cycle, and it's been going on for millennia.

So crude oil, then, is what's known as a mixture of hydrocarbons, and it's quite a complex one.

And so we have to, if we want anything useful out of it, separate it.

And the way we do that is through a process called fractional distillation.

Fractional distillation separates the different parts of the mixture by their boiling points, and that'll be covered later on in a later lesson.

So true or false? Hydrocarbons are not naturally occurring, i.

e.

, they are synthetically produced, so we have to make them in a lab somewhere.

True or false? Well, that is a false statement.

Below are provided two different justifications as to why that might be a false statement.

So I'm gonna give you a bit of time to pause and have a think about what you think is the correct answer.

And when you're ready, press play.

Well, the correct answer is B.

Hydrocarbons can be found in crude oil, which is formed through the decay of ancient organic matter.

So they are naturally occurring.

There are different types of hydrocarbon.

The first one we're gonna look at is known as alkanes.

These contain only single bonds between carbon and carbon atoms. And you might be thinking, well, carbon and carbon atoms. Well, we can see here some examples of some alkanes where we have some chains, like in the bottom left, we have in the middle a ring-like structure, and on the right-hand side we have this branch structure.

You can see that we are representing each of the covalent bonds between the carbons and the hydrogens as these single lines.

These represent our single covalent bonds.

Because there are only single covalent bonds, no double bonds, we call these saturated compounds.

That means that they have kind of the maximum number of hydrogen atoms that they can have within this structure, allowing carbon to have its four covalent bonds and hydrogen to form only one each.

True or false, then, hydrocarbons can only form straight-chain structures.

Thinking back to what we just saw on the previous slide, we hopefully know that that is false.

Why is it false? So have a look and read through these.

When you're ready, press play, but pause until you are.

So the answer is, in fact, B.

Hydrocarbons can form straight-chain, branched-chains or ring-like structures.

Another true or false for you, alkanes are referred to as saturated molecules.

True or false? Well, that is, in fact, true.

So have a read through these two justifications as to why, and when you are ready to move on, press play, but pause until you are.

Well, the answer is, in fact, B again.

And that's because saturated molecules contain only single bonds between carbon atoms. So we've got a multiple-choice question for you here, and I want you to select all the correct statements about hydrocarbon.

So have a read-through, and when you are kind of thinking about that, pause the video, and when you're ready to continue, press play.

Well, hydrocarbons aren't made of only carbon atoms. They're made of both carbon and hydrogen atoms. Hydrocarbons are organic molecules.

They have that carbon background structure.

Crude oil is a mixture of hydrocarbons, that's correct.

And alkanes are a type of hydrocarbons.

So remember, hydrocarbons are made up of carbon and hydrogen atoms only, as are alkanes.

So there are other types of hydrocarbons, not just alkanes.

So this includes alkenes.

So these have one or more double covalent bonds between carbon atoms, and there are also a type of chemical called alkynes.

So these have triple bonds between the carbon atoms. That's the maximum number of bonds that we would expect to see between two carbon atoms. Carbon can form up to four bonds and generally does.

And so within this kind of setup, we can see ethene.

Each carbon atom has two single bonds to hydrogen and a double bond to the other carbon atom.

That's four bonds.

And in the alkyne on the left-hand side, we've got this carbon atom that has one bond to hydrogen and three bonds to another carbon atom.

That next carbon atom has three bonds to a previous carbon atom and then one bond to the next carbon atom.

So all the carbon atoms here are forming those four covalent bonds we would expect carbon to form.

So hydrocarbons have many uses, the main one being fuels.

We burn them to either generate electricity or power our vehicles.

We can use them as lubricants, so that's to reduce friction between mechanical moving components in machinery.

But we also use them for feedstocks, for other petrochemicals, where petrochemicals are the chemicals that are just produced through refining crude oil.

So we wouldn't be able to have them without crude oil.

Those useful products include things like pharmaceutical drugs, or polymers, or even solvents and materials that we use to clean things with, such as detergents.

So they were all incredibly positive things about hydrocarbon, things that we use daily.

However, hydrocarbons do have a negative side, and mostly that involves their role in pollution.

So one of the main types of pollutions we think of when it comes to fossil fuels and hydrocarbon specifically is their greenhouse gas emissions, so the release of CO2 through combustion.

However, there are other types of pollution, including oil spills, which cause significant damage to marine environments and can kill either organisms directly or indirectly by destroying the places that they live.

And this can cause multiple billions of pounds worth of damage, and it happens more regularly than you might think.

Not only is this a problem to the environment, this is also a problem for us in terms of the use of crude oil because crude oil is what's known as a finite resource.

This means that the reserves will eventually run out.

So humans are in search of sustainable alternatives.

So sustainability, if we remember, means the idea that we are not using up all of our resources so that they'll run out.

We want to keep the kind of the production of these resources or keep some of these resources available for future generations so that they can continue to use them as well.

So we're looking alternatives to hydrocarbons to either be used as fuels or feedstock.

One of the first ways that we thought of reducing our hydrocarbon consumption was to move towards hydrogen-powered vehicles.

And we can see here that in some parts of the world there are hydrogen-powered vehicles.

This is one of the first hydrogen-powered trains.

But another way we could move away from hydrocarbons is to use biofuels.

So they still have organic components, but rather than be generated through crude oil, these are either grown as plants or harvested from other organic material, which can then be turned into a fuel, such as kind of waste oils that we might use like vegetable oils at home.

This leads to less CO2 emission because the CO2 that is emitted from those fuels being burned will then be reabsorbed by plants when we grow them again to remake the biofuel.

This is similar to carbon neutrality, or being carbon neutral.

The idea that the carbon emissions that we produce are then reduced by another method.

In this case, just regrowing the plants.

Hydrogen as a fuel, though, is one of the kind of cleanest fuels that we can use because the only product from this reaction is water, and there's an abundance of water on the planet, and we need water to survive, not a pollutant.

True or false, then.

Crude oil is a renewable resource that can be easily replaced once depleted, true or false? Well, that is a false statement.

Have a read through these two justifications.

Pause the video whilst you do so, and when you are ready to hear the answer, press play.

Well, the answer is A.

Crude oil is a finite resource, and unfortunately, the current usage will eventually run out.

So there are some hazards associated with hydrocarbons.

The main one, obviously, is we use it as a fuel.

We burn it in combustion engines is that it is highly flammable.

That means we have to store it and handle it very carefully.

Not near open flames if we aren't obviously trying to burn it.

But there are three other hazards that are of major concern for some hydrocarbons.

Some hydrocarbons have incredibly dangerous health risks, such as if you inhale too much of it or any of it, for some of them, it can lead to respiratory problems, so that's lung and other kind of respiratory tract issues.

Or if we get it on our skin can lead to skin irritation.

So working with these chemicals has to be done in a well-ventilated area.

Generally, if we're doing things in a lab, we'll do it in a fume cupboard, and then, at the end of it, because of the hazard to the environment, we wouldn't just pour it down the drain, we have to dispose of the waste properly.

It has to go through specific waste removal processes.

So multiple choice.

What impact does the use of hydrocarbons have on the environment? Have a read through these three statements, there might be more than one that is correct.

Pause the video whilst you decide, and press play when you are ready to continue.

Well, the correct answer here is B.

They can cause multiple types of pollution as well as environmental damage.

It's important when we talk about pollution that we don't just really use the word pollution on its own in an answer to a question.

We normally have to specify the type of pollution.

So, for instance, one of the main types of pollution that hydrocarbons cause is that we release greenhouse gases, but also we can damage ecosystems and habitats through oil spills.

Obviously not intentionally released, hopefully not intentionally.

Here's another multiple-choice question for you.

So I want you to have a read through these four statements.

I'd like you to select the ones that are correct statements about hydrocarbons.

So pause a video whilst you do that, and press play when you are ready to continue.

So this first statement, hydrocarbons are often feedstock for other petrochemicals.

That is a true statement.

Alkanes are the only type of hydrocarbon is not a true statement.

We know that there are alkenes and alkynes.

Burning hydrocarbons produces greenhouse gases.

We know that's true, we just talked about that on the previous slide.

And hydrocarbons aren't very flammable.

Well, that's incorrect.

We know that they are quite flammable, not all of them, but a lot of them are.

So we've got some extended tasks for you right now.

So there are three questions here.

The first one asks you to define the word hydrocarbon and decide whether the chemicals A, B, C, or D are actually hydrocarbons.

Question two says hydrocarbons are used as fuels, what are two other uses of hydrocarbons? And then question three are, what are the potential hazards of using hydrocarbons? So whilst you work through these tasks, pause the video, and when you're ready to hear the answers and move on, press play.

The first question asks you to define the word hydrocarbon.

And so the definition of hydrocarbons is presented.

Here they are simple covalent compounds made of carbon and hydrogen atoms only.

And all of the options that were available only methane and cyclohexane are hydrocarbons because they're the only ones that contain carbon and hydrogen atoms only.

The second question asks to give more uses of hydrocarbons.

So we've got lubricants, detergents, solvents, and feedstock.

So that's the idea that we can use them to then make more organic compounds that could be used in lots of other uses, including the ones listed.

And then the potential hazards of hydrocarbons are that they are highly flammable, they can cause skin irritation or some more serious health concerns like respiratory issues, and that they are often hazardous to the environment.

So that was our first half of the lesson.

We are now going to look at other types of hydrocarbons and organic molecules, and we're going to talk about how we can name them, draw them, and their chemical and physical properties.

So nomenclature refers to the name rules of chemical substances in chemistry.

And we can break that word down to literally mean the name calling, so the process of naming substances in chemistry.

And there is a body in the chemistry world called the International Union of Pure and Applied Chemistry, IUPAC for short.

And they've been the global authority on naming chemical compounds in chemistry for a very long time.

They also have a much wider role within the chemistry world.

They kind of set a lot of standards and so they're very important, but we don't need to worry too much about them now.

But just bringing it to your attention, if you were thinking about studying further chemistry, you'll hear about IUPAC quite a lot.

So the simplest alkane is a chemical called methane.

It contains one carbon atom and four hydrogen atoms. This is the gas, this is natural gas that comes through the gas taps in most science classrooms. And if you've got gas central heating or gas cooker at home, this will be the gas that's coming through those pipes.

It contains, as we've said, one carbon and four hydrogen atoms. And here are several ways that we can represent this molecule.

So we can represent it with a dot-and-cross diagram, which shows us how the electrons are shared between the atoms. We've got a ball-and-stick model which gives us a 3D representation of how these atoms are arranged, with kinda the sticks between the atoms representing the covalent bonds.

And then we've got a flat 2D displayed formula that shows again what we can see in the ball-and-stick model, but on a 2D plane.

Ethane is the next alkane in this series.

It contains two carbon atoms and six hydrogen atoms. And we can see that that's an increase of one carbon and two hydrogens compared to methane.

We've just slotted a CH2 group within this structure when we've moved up into the next compound.

Doing the same thing again, adding another CH2 group gives us propane C3H8, and doing that again to propane gives us C4H10, which it's butane.

My mnemonic to you to help you remember what the names of these first four hydrocarbons are in the alkane series, methane, ethane, propane, and butane is to take the first letter of each of them, M, E, P, B.

So one, two, three, four, M, E, P, B.

And we're going to remember the phrase, monkeys eat peanut butter.

And still to this day, when I forget and when I'm tired what the names are of these first four alkanes, I remember monkeys eat peanut butter.

Monkeys eat peanut butter.

M, E, P, B, one, two, three, four.

So one carbon, methane, two carbons, ethane, three carbons, propane, four carbons, butane.

Remember that, 'cause here is a question for you.

Which of these three structures have the correct names under those IUPAC nomenclature rules? So pause now whilst you decide, and when you're ready, press play.

Well the answers are, in fact, both A and C.

Propane.

That's monkeys eat peanut.

That's number three.

It should have three carbon atoms, which it does.

Ethane is monkeys eat.

That's two, that's not what B shows.

That should be methane.

And then the final one, monkeys eat peanut butter.

That's the fourth one.

Should have four carbon atoms, and we can see that is butane.

So did we notice anything about the naming of methane, ethane, propane, and butane? Well, they all end in ane, that's the kind of suffix that we give to this naming system.

And they get that because they are all part of what's known as a homologous or a homologous series, where homologous stands for kind of the same proportion.

So what that means is, is that there is actually a proportionality to the carbon and hydrogen atoms within this structure.

And we call that a general formula.

So for alkanes, this is known as CnH2n+2.

That means for every one carbon atom, there are double the number of hydrogens plus another two.

And so we can see that in this nice table where we've got methane, ethane, propane, and butane.

Each time we're going up by one carbon atom, that's N.

So we've put one for methane, two for ethane, and so on.

And then, where we have our 2n+2, that tells us how many hydrogens there are in the structure.

We can see for methane, two times one, 2n is two, plus another two is four.

So that gives us the formula CH4.

For ethane, we've got two times two, where N is two, 'cause that's how many carbon atoms there are.

So two times two is four plus another two, which gives us six.

So that's C2H6.

And we can see that that pattern continues for both propane and for both.

Sorry for both propane and for butane.

True or false, the general formula for alkanes is CnH2n+2.

Well, we know that's true, we've just seen that.

So here are two reasons why it might be true.

Pause the video whilst you read through them, and when you're ready to hear the answers and move on, press play.

So whilst the first answer might be tempting because in methane, CH4, where there is one carbon atom, there are four times the number of hydrogen atoms. That's not what the general formula tells us.

It tells us for every one carbon atom, there are double the number of hydrogens plus another two.

So in the context of ethane, ethane has two carbon atoms. So two times two is four plus that extra two, which is six.

So we can start to write a definition of a homologous series.

They are a family of compounds, and we'll do more on that later in more organic chemistry lessons.

They have the same general formula, and they are neighbours within this series that differ by CH2 groups.

Now, not all homologous series have a difference by CH2, although all of the ones that you are gonna learn about in this course do.

So, for example, we've got methane, ethane, extra CH2, propane, extra CH2, and then butane, the next CH2.

We've only been looking at the straight-chain alkane so far, but as the number of carbon atoms increases, there's a potential to form different chains.

Remember we talked about branched chains earlier.

And so butane has this molecular formula of C4H10, so that's number of carbons and hydrogen atoms that it has, but that is equivalent to this structure on the right, methylpropane.

We can see here, rather than all the carbon atoms be it in one long line, we've decided at the second carbon atom to kind of have this extra branch coming out.

This new chain, which we're calling that methyl group.

You don't need to know how to name these branched chains, but you need to be aware that they are these different chemical structures called isomers.

So, a bit like isotopes, which are different forms of the same atom.

So if you think of chlorine as an example, you have chlorine 35 has a mass of 35, chlorine 37 has a mass of 37.

They are both chlorine atoms, but they have different masses.

Isomers are the same chemical structures in terms of their molecular formula, but the atoms are arranged differently.

So we can see here butane and methylpropane.

Because they're arranged differently, that means they have different chemical and physical properties.

We're gonna recap what chemical and physical properties are a little bit later on.

Here's a multiple-choice question, quick-fire one for you.

What group often differentiates one compound from its neighbour in a homologous series? Is it CH2, CH3, or CH4? Well, we talked about it a bit so far, so hopefully you've realised it's CH2.

So as the carbon chain length increases throughout homologous series, the properties of the substance change.

So some physical properties then are the melting and boiling points increasing.

Viscosity, so that's a measure of how much a substance kind of flows or it's resistance to flow.

So we can see here a demonstration that we're pouring some crude oil.

It's incredibly viscous, it's kind of taking a long time to pour.

It's not a substance that flows very well.

Volatility is another physical property that we need to talk about.

So that's how easy they can evaporate or kind of vaporise, turn into a gas.

And so as we increase the carbon chain length, our melting and boiling points of our hydrocarbons, our alkanes increases, the viscosity also increases, they become these thicker liquids, and their volatility decreases so they don't evaporate easily.

All three of these physical properties are linked to the fact that as we increase the carbon chain length, as these molecules get larger, there are more forces of attraction between molecules.

As there are more forces, therefore, more energy will be required to overcome those forces as they either move apart or as they turn into a gas.

So that's physical properties.

How do the chemical properties change, if they change at all? Well, all of the molecules in the same homologous series take part in the same types of chemical reactions.

For example, a combustion reaction.

The larger the molecule, though, the less flammable it is.

And that's partly due to its volatility because they become less likely to turn into a gas as we go through the group.

The combustion energy per molecule increases with chain length, and that's because we are breaking more carbon and hydrogen bonds as the molecules get larger.

So we can now update our definition of homologous series.

And so we've got the same three statements as before, but now we're saying that they have similar chemical properties, but they show trends in their physical properties.

And I've given an example here that, as carbon chain length increases, the boiling point also increases.

Multiple-choice question for you, then.

The term homologous series refers to compound as that what? Give you some time to read through these, pause as you do so, and then press play when you're ready to continue.

Well, the only statement that's correct here is that they have the same general formula.

True or false, then.

The boiling point of compounds in the same homologous series increases with the length of carbon chain.

The answer is true.

And here are two statements as to why that might be true.

Pause now to have a read through them, and press play when you're ready to know which one is the correct option.

Well, the correct option is B.

Larger molecules have more forces of attraction between them, so therefore more energy is needed to overcome those forces.

Right, the final set of tasks, then.

So the first part of this task is to complete the table.

So you've been given some names of alkanes, some molecular formula, and then the displayed formula.

I'd like you to fill in the blanks, and when you are ready to hear the answers, you can kind of unpause the videos.

Until that point, press pause, and when you're ready to continue, press play.

Well, here are the answers.

So we've got methane, ethane, propane, and butane.

Each one is increasing by CH2 group each time.

Well done if you've got those correct.

Here are some more kind of written-answer questions, though.

So task two asks you to define what is meant by the term homologous series.

Task three asks you to look at the three chemicals provided.

These are types of chemical called alcohols.

What about their structures shows you that they are in the same chemical homologous series? And then for the question number four, cyclohexane is a ring structure shown on the left there.

It belongs to the homologous series called cycloalkanes.

Why does it not belong to the series alkanes? And give a similarity between cyclohexane and other alkanes like ethane.

Pause the video now as you do that, and then when you're ready to hear the answers, press play.

A homologous series then is a family of compounds that have the same general formula, where each neighbour of the series often differs by a CH2 group.

Each compound has similar chemical properties, and there is a trend in physical properties.

The structures that were shown to you were all alcohols.

What about them showed that they were part of the same homologous series? Well, each of the neighbouring molecules differed by a CH2 group.

They also had the same general formula.

Well done if you were able to to work out what that was.

But you could have just said that they have the same general formula.

There was no expectation that you worked it out.

For those of you that are interested, we can see here that the formula is CnH2n plus 1OH.

So that means for every one carbon atom, there are two times the number of hydrogens plus an extra one.

And then somewhere in the molecule, there's also this OH group.

And so that's that final statement there.

They contain what's known as a functional group, a hydroxyl group.

That's what makes them an alcohol, and how and why kind of they have the chemical properties they do.

That's a bit above and beyond what we are covering in this lesson.

So those of you that are kind of interested in that, that's gonna come up in a later lesson in a different unit.

And then question four, cyclohexane is a ring-like structure, is a hydrocarbon as well, but it belongs to the series cycloalkanes.

Why is it not an alkane? Well, it doesn't follow the alkane general formula of CnH2n+2.

It actually has a different general formula of CnH2n, and that's because it doesn't have an end to the molecule.

So if you think about what we've done is we've just wrapped a straight-chain alkane into a circle.

And to do that, we've had to lose a hydrogen from one end of the molecule and hydrogen from the other end to be able to connect the molecule together.

And we're asked here to give a similarity between cyclohexane and other alkanes.

Well, there are only single bonds between the carbon atoms, so it's a saturated molecule like an alkane.

In summary then, hydrocarbons are simple covalent compounds made of hydrogen and carbon atoms only.

Hydrocarbons are found in crude oil and are used as fuels and feedstock for other materials.

Alkanes can either be chains or ring structures.

And alkanes are a type of homologous series of hydrocarbons that have the same general formula and a trend in physical properties.

And that general formula for alkane is CnH2n+2.

I've really enjoyed learning this with you today.

Well done on the tasks that you've completed, and I look forward to seeing you in the next lesson.

Thank you very much.

Goodbye.