Lesson video

- Hello, I'm Ms. Barrett, your teacher for today's lesson on compounds.

This is part of the atoms and periodic table unit in Key Stage 3 with the Oak National Academy.

Make sure you've got a periodic table with you today because you're gonna need to use it.

Okay, in today's lesson, we are going to be defining a compound and looking at how compounds have their own unique properties.

And then we're going to write compound formulae and name compounds based on the atoms they contain.

So some key words that we need to know before we start today's lesson.

Some of these might be familiar from the start quiz if you had to go at that.

An element is a substance made from one type of atom.

If you did the last lesson, last lesson was all about elements, so you might remember that one.

An atom is the smallest unit of matter, and a molecule is two or more atoms bonded together.

So the outline for today's lesson, we're going to be defining compounds, then we're going to look at properties of compounds, then we're going to be naming compounds, and then we're gonna look at some formulae for compounds.

So we're gonna start with defining compounds.

Here we've got some particle diagrams. Have a look at what we've got on the left and what we've got on the right.

On the left, these are what we call compounds.

But on the right, these are not compounds.

So what can you see is different between these two sets of particle diagrams? How is the ones on the left different to the ones on the right? What do you think defines a compound? Perhaps you can see there that the ones on the left, that we are calling a compound, they contain two or more elements.

Whereas the ones on the right, these are all the same colour, so these just have one element in those molecules.

So is a compound a substance that contains two or more elements? Well, that is part of the definition, but that's not everything.

Have a look at these next pictures.

So what's the difference between the particle diagram on the left and the particle diagram on the right? The one on the left is a compound, but the one on the right is what we call a mixture.

What can you see is different here? Hopefully you can notice that the ones on the left, these ones are touching.

These particles, the green is touching the black, and the black is also touching the red, whereas the ones on the right, none of those particles are touching.

So the definition of a compound is a substance formed by the chemical bonding of two or more elements.

So we do need two or more elements, but they also need to be bonded together.

Just like you can see on the left.

When elements react together, they can form compounds.

So here's an example.

We've got a atom of carbon and then a molecule of oxygen.

Remember, a molecule is something where there is two or more atoms bonded together.

They don't necessarily have to be different, but just two or more atoms. So they react together.

What do you reckon they make, carbon and oxygen? You might have heard of this one.

This makes carbon dioxide.

Carbon dioxide, that's the gas that we breathe out from our bodies, and there's lots of carbon dioxide in the atmosphere that you might have heard about.

Carbon dioxide is a compound, whereas carbon and oxygen, these two are elements.

So remember, a compound is something where there are two or more different elements bonded together, just like you can see in carbon dioxide.

A further point to mention on the definition of a chemical compound is that the elements must be in fixed proportions within that compound.

So for example, here I've got a particle diagram of water, or H2O, you might have heard of water be called H2O before.

And here this is H202.

So they're made from the same things.

There's hydrogen there, there's oxygen there in both of them, but this one on the left is water, and the one on the right is not water.

This is actually something called hydrogen peroxide, a type of bleach.

You definitely don't wanna be getting those two modelled up, so it's really important that we make sure we know the formulas, and we know that the elements have to be in fixed proportions to be that particular compound.

Water is H2O.

Okay.

So we've looked at lots of pictures or diagrams of molecules so far, and all compounds are molecules, but not all molecules are compounds.

It's important to get this the right way round.

So have a look here.

On the left, we've got water, the H2O again, and this is a molecule and a compound.

Remember, a molecule is where there's two or more atoms that are bonded together, but it's also a compound because those two atoms that it contains, they're different.

They've got two different elements, they're chemically bonded together.

On the right here, we've got a molecule of hydrogen, H2, but this one's not a compound.

And remember, the reason why it's not a compound is because there's only one type of atom.

There's only hydrogen in there, there's nothing else.

That's only one element, so it's a molecule and not a compound.

All right, let's see what we've understood so far.

Have a look at this question.

Which term has this definition? Two or more elements chemically bonded together.

I'll give you a few seconds to think about that.

Is it atom, mixture, or compound? That definition is compound.

Of course, this is what this lesson is all about.

Did you get that one right? I hope you did.

Next question.

Which two diagrams show an element? So we've got four different particle diagrams here and only two of those show an element.

So remember what the definition of an element is, and I'll give you a few seconds to think about that one.

Okay.

So hopefully you have found that one and two are the ones that are elements.

Remember, an element is something where there is only one type of atom.

And in picture or diagram one, they're all exactly the same, and in diagram two, even though they're bonded together, so they're a molecule, they are still an element.

There is not two different types of atoms, so it must be an element.

Okay, which diagram shows a compound? I'll give you a few seconds to think about that one.

All right, remember, a compound is something where there are two or more different types of atoms that are chemically bonded together.

So the only one that fits into that definition is number three.

Well done if you got that one right.

Okay, final question on these diagrams. Which two diagrams show a molecule? So have a think about what molecule means.

I'll give you a few seconds to think about that one.

Okay, let's check your answers.

The correct answers for these were two and three.

That's because two or more atoms are bonded together.

It doesn't matter if they're the same, it doesn't matter if they're different, just the fact that there's two or more atoms that are stuck together or chemically bonded means it is a molecule.

All right, next question.

Which statement is true about the diagram? So this diagram down here, we've got a carbon that's bonded to four different hydrogens.

It is a molecule but not a compound, it's a compound but not a molecule, it is a compound and a molecule, or it is neither a compound or molecule.

Have a think about that one.

Okay, hopefully you identified the correct one, which was C.

It is a compound and a molecule.

It's a molecule because there's two or more atoms bonded together.

And because those two or more atoms are different, there's carbon and hydrogens, it must be a compound.

So this one was a compound and a molecule.

So we're gonna move on to the task now.

Now that you've had some practise and hopefully you're feeling really confident, that you know the difference between atoms, molecules, compounds, and elements.

So have a look at your worksheet or have a look on the screen and you'll see six boxes of particle diagrams. And for each of those six boxes, I want you to write two words for each one in the box to identify what those particles are.

For example, the particles could be molecules and elements.

So it has to be two words.

Pause the video here and have a go at that task.

Alright, let's go through that together.

Let's have a look at number one.

We've got some white particles, some black particles, some of those are stuck together.

So this one, what did you think that one was? That one was a molecule and a compound.

Remember that a molecule is two or more atoms bonded together, and a compound, two or more atoms bonded together when those atoms are different.

So all of those in box one are the same and they are all molecules and all compounds.

Well done if you've got that one right.

Let's move on to number two.

Number two, this one was atom and element.

All of the atoms are individual, none of them were bonded together, so they are just atoms, they are not molecules, and they are elements.

Some of those are one element, the white ones, and then we've got another element which are coloured by the black.

But just because they are two different elements doesn't mean it's compound because they're not bonded together here.

Number three, what did you think this one was? This one was a molecule and an element.

So a molecule because they are bonded together, but just an element because there's only one type of atom here.

Hopefully you're getting the hang of this now.

Number four.

This one was molecule and a compound.

So for the same reasons as number one, even though they look different, because there's two or more atoms that are different, chemically bonded together, it's a molecule and a compound.

Number five was a molecule and an element.

So again, similar to number three, even though they are a different element this time, 'cause they're a different colour, that's okay, they are still going to be a molecule and an element.

And number six, final one, this one was a molecule and a compound, so same as number one and four.

So it doesn't matter how many atoms are stuck together or are chemically bonded together, as long as there is more than two, it is a molecule.

And as long as some of those within that molecule are different, then it would be a compound.

Okay.

Onto the next part.

You've got two questions to answer.

Which boxes show mixtures? And then explain why the diagrams you selected are mixtures.

So pause the video and have a go at answering those two questions.

Okay.

Did you remember what a mixture was? A mixture is where there are different atoms, but they are not chemically bonded, they're just jumbled together, mixed around together.

There was two mixture boxes here.

First one was number two and the second one was number six.

If you have a look closely at number six, there was actually one molecule that was different to the rest, or two molecules that were different to the rest in fact.

Some of them had three, some of them had two, even though they're made from the same type of element.

This means that it's a mixture because not all of them were the same.

But those individual molecules, the twos, weren't stuck or chemically bonded to the threes.

They were separate, that means it's a mixture.

And box number two was a little bit easier.

You can see that there's two different types of atoms and none of them are stuck together.

That makes it a mixture.

So remember, a mixture, two different substances that are not chemically bonded together.

Well done if you got some of those right.

They can be a little bit tricky, so give yourself a big pat on the back even if you didn't get them all right.

All right, so we're gonna move on to the second part of the lesson.

Now we know what compounds are, we're gonna be looking at the properties of compounds.

So this means, what are they like? We're gonna look at this chemical reaction.

Sodium reacts with chlorine gas to produce sodium chloride.

So here I've got my particle diagram of sodium, sodium is an element that reacts with chlorine, which is also an element, you'll find both of these on your periodic table, and that makes sodium chloride, which looks a little bit like this.

Now, this is our compound.

So elements will react together to make compounds.

So how would you describe sodium and chlorine? I've got a picture of sodium here and I've got a cartoon picture of chlorine.

How would you describe those? I would describe sodium as metallic.

Sodium is a metal, it's on the left hand side of the periodic table, it's grey.

Whereas chlorine, this one is a non-metal.

We find that on the right hand side of the periodic table, and it is a gas.

And in fact, it's a yellow green gas.

So that's the properties of sodium and chlorine, the elements.

And when they react together, what would you predict the properties of sodium chloride to be? Some people would predict that the properties of sodium chloride would be a combination of the two.

So perhaps sodium chloride is a metallic yellow green gas, but in fact that's not actually the case.

So sodium chloride is actually table salt.

So if you are ever adding salt onto your chips, you are adding sodium chloride to your chips.

So hopefully you know what sodium chloride looks like, it's a white crystalline solid, it's not a metal.

And as you can see, this looks very, very different to sodium, and it looks very, very different to chlorine, and it's definitely not a combination of the properties of sodium and chlorine.

So the properties of compounds are different from the properties of the elements that they are made from.

And that's really important for us to remember.

Okay.

True or false.

Iron sulphide will have similar properties to iron and sulphur.

Give you a few seconds to think about that.

So that one is false.

And as we said just now, that is because the compounds have different properties to the elements that they are made from.

Iron is a metal, sulphur is a non-metal, and in fact is yellow.

Iron sulphide is a grey solid.

Doesn't look like iron and it doesn't look like sulphur.

All right, so we're gonna move on to the second task now.

That section was nice and quick.

Magnesium reacts with oxygen gas to produce magnesium oxide.

On your sheets or just on a bit of paper, I'd like you to write a paragraph about the reaction stating whether each substance is an element or a compound and describe their different properties.

So just like we did for sodium and chlorine and sodium chloride, I want you to do the same in your own words for magnesium, oxygen, and magnesium oxide.

As a little point, this oxygen container, this is what we call a gas tube.

So little clue there that oxygen is a gas.

Pause the video, have a go, and come back and check your answers in a minute.

Alright, how did you get on? Hopefully you didn't find that too difficult.

And here I've got some answer points for you to check against what you have written.

Magnesium is an element, oxygen is an element, and magnesium oxide, the product of the reaction of those two elements, is a compound.

Magnesium is a metal, it's on the left hand side of the periodic table.

And as you hopefully you can see from that cartoon, it's a silvery solid.

Oxygen is a non-metal and a colourless gas, and magnesium is a white powder.

As you can see, magnesium oxide, the compound, has different properties.

It looks very different to magnesium and oxygen that it was made from.

All right, so we're onto the third part of the lesson.

We're going to look at naming compounds.

All compounds have a name and a formula.

Firstly, we're gonna look at names.

This is water, it's formula is H2O.

And this is sodium chloride, we looked at this earlier, also known as salt, and it's formula is NaCl.

So most of the time, the name matches the formula and the words that we use in the product table.

Water is a little bit of an exception.

Some people might call that di-hydrogen oxide, but actually we just call it water.

How do we name compounds? Most compounds have a two-word name, and there are three rules that we need to follow.

Rule one, first rule, the element furthest to the left on the periodic table comes first in the name.

So this here, we've got calcium bonded to oxygen, this is called calcium oxide, not oxide calcium.

And there's a little bit of a clue to the next rule there.

Rule two, if the compound is made of two elements, then the name ends in -ide.

So whatever it is that it's bonded to, and the second part of the name, we change the ending to -ide.

So this is calcium oxide, not calcium oxygen.

Sometimes we use prefixes to determine how many atoms of each element are present in the compound.

So for example, here we've got carbon monoxide because this is carbon bonded to one oxygen.

And on the right here, we've got carbon dioxide, hopefully you've heard before that di means two.

So we've got one carbon bonded to two oxygens, so that's why it's called carbon dioxide.

And here's a little table to help you understand.

So mon- means one, di- is two, tri- three, tetra- four, penta- five, hexa- six.

We don't tend to use naming really above tri- very much at Key Stage 3, but just in case you come across those, there they are.

Okay.

So the last rule, rule three, is that when the compounds are made of three different atoms and one of them is oxygen, the name ends in -ate.

So it changes a little bit.

So sodium carbonate means it's made of sodium, carbon, and oxygen.

Potassium sulphate means potassium, sulphur, and oxygen.

Lithium nitrate is lithium, nitrogen, and oxygen.

So we don't call it something sulphur oxygen or oxide anymore, the whole thing just becomes sulphate or nitrate.

And the last one, calcium sulphate.

Have a think about what do you think this one is made from.

I'll give you a few seconds.

Okay, so hopefully you've realised that one is made from calcium, sulphur, and oxygen.

Okay.

All right, let's see what we have learned so far.

So a compound contains magnesium and oxygen.

What is the name of this compound? Give you a few seconds to think about that one.

Did you work it out? That one is magnesium oxide.

Well done if you've got that one right.

Next, a compound contains beryllium, nitrogen, and oxygen.

What is the name of this compound? Again, I'll give you a few seconds to think about that one.

All right, so that one, beryllium, nitrogen, and oxygen, that becomes beryllium nitrate.

If there was no nitrogen, then it would be beryllium oxide.

And beryllium nitrogen oxide, that's just wrong.

We end up combining the nitrogen and oxygen to be called nitrate when both of them are present.

Okay, carbon trioxide is composed of how many carbons, how many oxygens? Have a little think.

All right, that one was one carbon and three oxygen atoms. 'Cause remember that tri- means three oxygens.

Not three carbons, it has to be next to the word that is the element, so trioxide, tri- three oxygens.

Well done if you got that one correct.

Iron carbonate is composed of? Have a little think.

Okay, did you work that one out? That one is iron, carbon, and oxygen.

Remember, carbonate means carbon and oxygen together.

Good job if you got those right.

Next, hopefully you've got a little bit more confidence in naming compounds now.

We're gonna move on to task three.

So in this task, you are going to be firstly, identifying the elements present in the compounds.

And once you've completed this table, come back and we're gonna go through the answers together.

All right, how did you get on? Hopefully you didn't find those too difficult at the moment.

The next part might be a little bit more tricky.

The elements present in lithium nitride, this was lithium and nitrogen.

In aluminium bromide, aluminium and bromine.

Remember that it's bromine not bromide.

It's only -ide when it's bonded to something else in a compound.

Iron carbonate is iron, sorry, iron, carbon, and oxygen.

And cobalt fluoride is cobalt and fluorine.

And the last one, zinc nitrate, this one was zinc, nitrogen, and oxygen.

Remember, the -ate tells us that it's got oxygen in it as well.

All right, well done if you got those.

We're gonna move on to a slightly harder task.

So part B, this time, I've given you the elements that are present and you are going to name them.

So the opposite to what we just did.

So pause the video here and have a go.

Okay, hopefully you didn't find those two tricky.

But don't worry if you did, we're gonna go through those together and work at how we got those names.

You've gotta remember your rules of namings.

We've got three rules that we need to remember.

The first rule, the element on the left, most left of the periodic table comes first in the name.

The second rule, if it's got two elements in the compound, then it gets called -ide on the end.

And if it's got three elements and one of those oxygen, it's -ate on the end.

So let's see how we go on.

Magnesium and oxygen, this is magnesium oxide.

Copper and oxygen, copper oxide.

Silver, nitrogen, and oxygen, silver nitrate.

Potassium and nitrogen, potassium nitride.

So not nitrate 'cause there's no oxygen there, it's nitride.

Calcium, sulphur, and oxygen, calcium sulphate.

So give yourself a tick if you've got them right.

And if you did, really, really well done because those can be quite tricky.

There's lots to remember there, so really well done if you got those correct.

All right, so we're gonna move on to the last part of the lesson.

Well done for getting this far 'cause it's been a lot to learn today, so really good job.

The final part of today's lesson is the formula of compounds or the formulae of compounds.

This can be a little bit tricky, so make sure that you've got your head screwed on.

All right.

The formula of compounds, a chemical formula, uses the chemical symbols to show the elements that are present in the compound, and also the number of atoms of each element that are present.

So remember, last lesson we looked at chemical symbols, these are the one or two-letter symbols you find on the periodic table, and we're gonna use those today to make the chemical formula.

Here, I've got carbon monoxide.

So remember, mon- means one, so carbon monoxide is CO.

And here, carbon dioxide.

You might be able to work out what's coming next.

That is CO2.

And you might have actually heard of that one before.

It's much quicker and easier to write the formulas rather than writing out the words.

So that's chemistry, a little bit lazy, and that's why we use formulas instead, it makes life a lot easier.

There are again some rules we need to follow.

Rule one, the symbol for the element furthest to the left of the periodic table is written first.

So that's the same as when we write the name, it also needs to come first when you're writing the formula.

So here we've got lithium and fluorine bonded together.

This is LiF, not FLi.

So lithium fluoride.

And the second rule, when there is more than one atom of the same element present, we use subscript numbers after the corresponding element.

So here we've got a particle diagram.

You might remember this one was water.

Can you remember the formula? Water's formula is H2O.

So it's not O2H and it's important that that two is not as large as the rest of them.

We write it little after the letter of the element that it corresponds to.

So it's H, little two, O.

Here we've got two hydrogen atoms bonded together in a molecule.

So this is just H2.

So again, the number comes after, not before, and it has to be little, H2.

So there are the rules so we can move on and check our understanding now.

A compound has two atoms of aluminium and three atoms of oxygen.

Think really carefully about this one.

What is the chemical formula? Pause the video here if you need to 'cause you might need a few seconds to work out.

Okay, how did you get on with that one? Did you remember the rules? So remember, the most left element on the periodic table comes first.

That rules out C and D because aluminium has to come first, and then we need to make sure we include the numbers of the atoms. So that one is Al2O3.

That tells it has two aluminums and three oxygens.

Okay, next question.

A compound has two lithium atoms, one sulphur atom, and four oxygen atoms. What is the chemical formula? Again, if you need to pause the video, that's fine.

All right, so another tricky one here.

Remember that lithium has to come first 'cause that is actually in group one on the periodic table on the most left, that rules out option D.

And now we need to think about sulphur and oxygen.

Well, the sulphur comes first as they all are in A, B and C, but now we need to think about those numbers.

We're told there's one sulphur atom and four oxygen atoms, so that one must be C.

Did you get that one right? Good job if you did.

That one was pretty tricky.

Okay, the structure of a compound is shown.

What is the chemical formula? So this time I've drawn it for you, you need to tell me what the formula is.

Remember the rules.

Remember what order to put them in.

Okay.

Hopefully you've worked this one out.

This one is COCl2.

So they're in the order that they are on the product table from left to right, and the only thing that's got two is the cl, so we write little two after the cl.

COCl2.

Good job if you got that one.

Okay, I think you're doing really, really well and I think you're pretty confident now to be moving on to your final task of the lesson.

You've got another table to complete.

This time I'm giving you the atoms that are present, and you're going to name them and then write the formula as well.

So this might take you a while, use your periodic table to help you work out what the formulas or the chemical symbols are, and I will see you when you're back.

Okay, how did you find that one? That one could be a little bit tricky, so don't worry if you found it hard.

We're gonna go through it together now.

I gave you one example.

One lithium and one bromine is lithium bromide, and we would write one Li and one Br.

LiBr.

Next one we've got one potassium and one fluorine.

So that one would be called potassium fluoride, and the formula would be KF.

There's just one of each.

Next, we've got one calcium and two iodine, that's calcium iodide, CaI2.

Next, we've got two cesium and one oxygen.

This is cesium oxide, and cesium's chemical symbol is Cs, so it's CS2O.

Now we've got one nitrogen and two oxygen.

This is nitrogen dioxide and NO2.

And the last one, one iron and three chlorine is iron chloride, FeCl3.

If you've got those right, even if you've got some of those right, you've done really, really well 'cause they can be really tricky, especially for Key Stage 3, so really, really good job.

That is the end of the lesson.

We have learned loads of new chemistry today, so give yourself a pat on the back.

We're gonna just summarise what we've learned today.

So today we looked at compounds, and a compound is a substance formed by the chemical bonding of two or more elements.

A mixture is two or more elements that are not chemically bonded together.

The properties of compounds are different to the properties of the elements that they are made from.

Remember our examples with iron sulphide and also with sodium chloride salt.

They look very different to the elements that they were made from.

And compounds can be represented by names and formulae, and we've had a go at writing both of those.

So have a go at the Exit quiz, see how you got on.

And again, a really, really well done for getting through this lesson 'cause that was a lot to learn here, and I hope to see you next time.

Thank you for using the Oak Academy.