Lesson video

Hello, my name's Dr.

Warren.

I'm so pleased that you've decided to learn with me today.

Today's lesson is about metallic structure and properties, and it's part of the structure and bonding unit.

I'm here to help and guide you through the learning.

I will go through all those tricky parts together.

Our learning outcome for today's lesson is I can describe the properties of metals and relate these to a model of the structure of metals.

So this essentially means, we're gonna learn about what metals are like, what their properties are, and we're gonna learn about the structure of metals.

In today's lessons, we've got some key words for you, malleable, ductile, delocalised, conductor, and forces of attraction.

These are all important words for this topic.

And in a moment I'm going to show you these words In some sentences.

You may like to pause the video and note down these sentences because we're gonna be able to refer to them later on in the lesson.

When you are ready, just start play again.

In today's lesson, we have two parts.

The first part is all about the structure of metals, so that's kind of quite theoretical.

And the second part is about the properties and we'll be able to relate those properties to the structure.

So let's get started with the structure of metals.

In a pure metal, all the atoms are arranged in a regular pattern.

And you can see from this little animation that the ions or the metal ions, and I explained about them in a moment or two, are all lined up in rows and columns and they have this giant lattice structure.

Because all these atoms are so tiny.

Within the metallic structure, you will also see some what we call delocalised electrons.

Now you'll be familiar with the idea from previous learning that in an atom you have a nucleus and then you have shells of electrons going around them.

Well, in the outer shell there is one or two or maybe three electrons that shell is not complete.

And so in the structure, what actually happens is those outer shell electrons become what we call delocalised.

And that means that they can move throughout the structure.

And this is shown by the pink dots that seem to be going everywhere.

Now, the delocalised outer shell electron are often referred to a sea of electrons.

And that might sound like kind of a funny thing to do, but the idea is a sea is they can move throughout the structure a bit like the ocean can move and carries on moving.

They're not associated with one particular metal ion.

And that is why it is different.

So you can see here on the diagram we have our electrons, but we also have this kind of cloudy parts.

And this is the area that they can move in throughout the structure of metals.

Now the metallic bond is what keeps the metal together.

Otherwise these parts would kind of fly away.

There is a strong electrostatic force of attraction.

So remember, opposites attract a positive charge will attract to a negative charge.

And this is what holds the structure together.

You have a positively charged metal ion, in this case we're showing you sodium and a negatively charged delocalised electron, which can move throughout the structure, but it's still attracted to the metal lattice.

So, now let's go through this in a little bit more detail and remind ourselves.

So from previous learning, you've learned about the structure of the atom, and we can see that we have a sodium atom here, we have 11 electrons with one electron in its outer shell.

So what actually happens in the giant metallic structure is each atom forms an ion, it gives an electron away into the main structure and it becomes a plus one.

So there we have a sodium atom becoming a sodium ion plus an electron.

The metallic structure of sodium is shown in this diagram.

Here we can see the sodium ions, they are arranged in columns and rows making that great strong lattice structure.

The electrons are shown as blue dots and the sea of electrons is that area in which those electrons can move.

And what's really important to remember is that for every sodium ion, there is one electron in that sea of electrons and they can move throughout the whole giant structure.

So we're gonna have a look at another example now.

This time, calcium.

And we've got a picture of the calcium atom and we can see that there are two electrons in its outer shell.

So this time the giant metallic structure, we are going to have calcium ions being formed.

And each calcium ion has a charge of two plus.

So this means there are two electrons from the outer shell that are able to go into the sea of electrons.

So our structure is drawn like this and we can see that for every Ca2+ ion, there are two blue electrons, well really shown is blue.

They're not really blue, in the sea of electrons.

If we counterpart electrons, we'll find that there are 12.

And for every calcium two plus ion, those two electrons are delocalised.

They can move throughout the whole structure.

And this is really important when we come to understand when we come to at the different properties of the metals.

So now let's see how we're doing and check our understanding.

So we've got some statements here, which the following statements about the structure of a metal are correct.

The ions form a regular structure, the outer shell electrons become delocalised or a metallic bond is the force of attraction between the nucleus of a metal atom and its electrons.

Okay, well done if you picked A and picked B, because both of those are correct, the metal ions form that regular structure, The outer shell electrons become delocalised.

For C, that is incorrect because the metallic bond is a force for traction between the metal ion and the sea of electrons, not the nucleus.

Okay, we're gonna move on to our first task.

Some pupils have drawn some diagrams of the structure of a metal.

Now what I want you to do is to look very carefully at these diagrams and decide which diagram is correct and give an explanation for your answer.

Then I want you to suggest how the other pupils could improve their diagrams. So if you can pause the video and have a go at this task.

Well done if you had decided that Jacobs is the correct diagram.

We can see from Jacob's diagram it has a regular structure of positive metal ions and that's really important first of all, all lattices for metals are regular structure.

He's also remembered to make sure that there is an equal number of positive and negative charges.

So for every plus there, there is a minus and it shows the sea of delocalised electrons.

It's got that shading, so we can see where it goes.

So if you actually said that Jacob was correct, very, very well done.

Okay, so let's have a look at some of the other diagrams and see how good they are.

Well first of all, we've got Lucas's diagram and really he should remove the arrows from the electrons because we don't show that arrows in these types of diagram.

And we need to include the sea of delocalised electrons.

So he's got some idea of where they go.

Andeep, well, what he needs to do is remove some of the electrons.

If you count up Andeep's positives and negatives, they don't balance.

So that means that there are just too many electrons there and he also needs to include the sea of electrons.

Sofia, well she's got her idea of giving a metal metallic lattice for the positive ions, but what she's forgotten to do is to add her negative charges to balance out those positives.

So if you actually got all those explanations right for Lucas, and Andeep, and Sofia, you should be feeling absolutely fantastic because it's quite a difficult thing to do to really criticise other people's diagrams. So very well done.

So now we've completed our first learning cycle of the structure of metals, and we're gonna go on now and look at the property of metals.

So the properties of metals are kind of due to two main things.

First of all, the arrangement of ions in the lattice, and we can see a 3D picture of the ions in this diagram and the delocalised electrons that can move throughout the map metallic structure.

So it's really important.

Those are the two things that all our properties are gonna be related to.

The arrangement of metal ions and the fact that they can slide over each other and also the delocalised electrons.

A really important point to make here is that individual atoms don't usually have the same physical properties as the bulk material they form.

So that means that if we know that copper metal, for example, has that lovely bronzy coppery brownie colour, if we were to zoom right into the atomic level and have a look at one copper atom, it would not look like that.

So that's really important.

It's all the atoms joined together in the big metallic structure that gives it the properties that we are going to now have a look at.

So the first thing before we go on, we'll just check our understanding.

Aluminium has the same physical properties as it is individual atoms that make up its structure.

True or false? Well done if you picked false.

Now what's the reason why? Have a look at the two suggestions and choose one of them.

Very well done if you picked a, the properties of aluminium are due to the arrangement of aluminium atoms in the giant metallic structure.

Okay? The individual atoms don't have the same physical properties.

Really important point.

Okay.

So we're probably familiar with the idea that metals have high melting points and boiling points.

And you can see this in this table.

So let's take for example, gold, it melts at over a thousand degrees.

So that means we have to heat it up to 1064 degrees before it will melt.

That's degrees centigrade.

And if we want it to become a gas, we'll have to heat it even higher to over 2,830 because its boiling point is 2,836.

So you can see that all of these metals shown in the table have high melting points.

So what's the reason why? Well, think back to our model, there is a strong force of attraction between the metal ions and those delocalised electrons in the metallic structure.

So this means it takes a lot of energy to overcome those metallic bonds and disrupt that giant lattice because in a solid, if you remember, all the particles in this case, the metal ions are in that regular structure and it's only when they get to them melting point that they overcome the bonds, or forces of traction between them and take on the arrangement in a liquid.

Okay, let's have another check of our understanding.

The melting point of platinum is 1,768.

Now that's a high number.

Is that true or false? Well done if you picked true.

The melting points of platinum is a high number.

Now, let's have a think about why.

A or B.

Why is that platinum melting points so high? Well, very well done if you picked B.

It takes a large amount of energy to overcome the strong forces of attraction or the metallic bond between those positive ions and delocalised electrons.

So the melting point must be high.

Right.

Moving on, metals are malleable.

This means that they can be hammered into shape.

So if you hit a metal with a strong force, what actually happens is, the layers of ions can slide over each other resulting in a change of shape and it doesn't break.

Now, you might be familiar with this in the diagram we've got somebody who's heated up the metal a bit to help it move and it's banging it into shape, and this is how horseshoes, for example, are made.

You might also be familiar with the idea of hitting a metal with a strong force, or having an accent, or dropping something and it bending.

It doesn't break.

So, if we have a look at this diagram, remember our metal structure, our lattice, there's the ions.

If we put a force, it will be able to push along those metal ions, which means they can move, they can bend without breaking.

So metals are malleable.

That's a really important property.

Metals are ductile.

So malleable and ductile are kind of similar, but with ductile it means that they can be drawn or pulled into a wire.

And a lot of electrical cables are copper wire, for example.

And what happens is this time you put a force in either direction and you pull it, it's a bit like you might have some Play-Doh, you might have seen pull that.

And as you pull it, it gets thinner and thinner 'cause the diameter gets smaller.

What is actually happening here is the layer of ions are sliding over each other in opposite directions.

And then we just get a thinner and thinner and thinner piece of metal ending up with a wire with a small diameter.

And this again, is really useful because metal wires are used for all sorts of different things.

And I'm sure you can think of different sort of like wire netting, for example, that you have on fences sometimes.

Let's just check our understanding before we move on any further.

When an iron railing, so iron that's a type of metal is hit with a very strong force, it will bend, true or false.

Well done if you picked true, it will bend, it won't break.

Now have a read of the other two, A and B to decide why.

What is the reason? Well done if you picked a, the layers of metal ions can slide over each other easily, so the shape of the metal will change.

If those metal lines were in a fixed position so they couldn't move and the shape of metal wouldn't change and we would not be able to bend metal into different shapes for all those different properties, those different uses of metals that depend on it being malleable and also ductile.

So very, very well done if you got that correct and you've got the correct reason as well.

Right.

We're gonna move on to a different property now.

Metals are good electrical conductors.

Now, a conductor is a material that will allow energy or charge to transfer through it, and it's due to the delocalised electrons.

So remember, each metal atom donates its outer electrons into the metallic structure and they are free to move.

And this means that they can carry an electric charge.

So if you make up a circuit and we've got one here just being shown a very simple electric circuit with a piece of metal in, and as soon as it's connected, you can see that that light bulb lights up.

The delocalised electrons can move throughout the metal wires carrying electric charge.

And this is really important because you know we want to put on the electric lights or lamps or anything like that, or ring a doorbell that needs electric current to pass through it.

And it is due to that delocalised electron that can act as a charge carrier.

So as well as being good electrical conductors, metals are also good thermal conductors.

Remember, each metal atom donates its outer electron to that metallic structure, making it free to move.

And it's these moving delocalised electrons that can carry energy as well as carrying charge.

So, we're very familiar with this idea because we've got here something boiling away, a lot of our cooking is done by boiling up a liquid.

Now the reason we need a container, source pans are often and usually made of metal because we're a good thermal conductor.

So we can put our food into the source pan, we can put on the energy source, which might be electric or it might be gas.

And we can cook our food because it's a good conductor.

So when these delocalised electrons collide with the metals, they transfer energy faster than in insulators.

So here we are going to carry out our tests.

So we're gonna put an iron, hot iron on the ends of the rod to actually be our source of heat.

And then what we need to do is watch that black thermochromic paper to see a changing colour.

Just takes a few minutes to get going, but what you can start to see is it changing colour.

And what we found is, copper was the only substance that changed the colour of the thermochromic paper.

Because it is a good thermal conductor, those delocalised electrons can carry thermal energy throughout the structure.

So, let's check our understanding again.

A silver spoon has been connected into electric current into an electric circuit.

When switch is closed, the bulb lights up.

Which of the following properties of silver explain why? Silver is ductile, Silver is a good electrical conductor, silver is malleable, silver is a good thermal conductor.

Well done if you chose B.

Silver is a good electrical conductor and that is why the light bulb lit up.

And now we've come to our second task, task B about the properties of metals.

And first of all, what we'd like you to do is look at this diagram that a student has drawn and label it.

Label A, B, and C.

So just pause the video while you do that and then we'll have a look at the answer together.

Okay, so the first one is a sea of delocalised electrons.

We then have a positive metal ion.

So well done if you've got those.

And finally we have a delocalised electron.

So if you've got all those labels right, very well done.

We're gonna move on to our next couple of questions in this task.

So question two, I want you to explain why metals are used to make different things, why they used to make electrical wires, jewellery and pans, and think about their structure and their properties as you answer this question.

And finally, for questions three, we want to explain why the atoms usually do not have the same properties as the bulk material they form.

We've talked about how they're different.

See if you can actually answer that question.

Okay, so let's have a look at the answers.

First of all, electrical wires.

The electrical wires are made from metals because they're ductile.

We can pull them into a long wire, which is really important.

And also they're good electrical conductors.

This is due to their delocalised electron.

Metals are used to make jewellery because they're malleable.

We can basically bang them into shape and it might be the shape of a cross, or a heart or any other object that you might want to have on that jewellery.

And finally, metals are used to make pans because they're good thermal conductors, they will heat up our food.

And question three, while the properties of bulk materials are due to the way that atoms are bonded to each other in the structure of the materials.

So remember in metals we have our giants structure of metal ions bonded to the delocalised electrons and this gives them the properties.

So it's very different from the properties of atoms that they're made from because they don't have that metallic bond.

So now let's have a look at what we've learned in today's lesson.

Metals are good electrical and thermal conductors.

Metals can be stretched into wires, or bent or hammered into shape.

Individual atoms do not have the physical properties of the bulk material they form.

Metal structures consist of positive ions and delocalised outer electrons.

And finally, the electrostatic forces of attraction between metal ions and delocalised electrons bind them together in a giant metallic structure.

I hope that you have enjoyed this lesson today and look forward to learning with you again.