Lesson video

Hello, my name's Dr.

Warren.

I'm so pleased that you can join me today for this lesson on properties of giant ionic structures.

It's part of the structure and bonding unit and follows on from previous learning about ionic substances.

We're going to work through this lesson together today, and I'm here to support you with your learning all the way, especially through the tricky parts.

So let's get started.

Our learning outcome for today's lesson is I can describe the properties of ionic compounds and explain how they result from the ionic structure model.

We've got some key words for you.

Conductor, melting point, charge carrier, dissolve, and solubility.

And now we've got these keywords written in some sentences.

You may wish to pause the video and copy down the sentences so you can refer to them later on in the lesson.

A conductor is a material which transfers thermal energy easily, electrical conductors allow charge to flow through them.

The melting point of a substance is a temperature at which it changes from solid state to a liquid state.

A charge carrier is a particle that enables electrical conductivity, such as delocalized electrons or free-moving ions.

When a substance particle separate and spread out throughout the particles of a solvent resulting in it no longer being seen, it has dissolved.

Solubility refers to how well a solute is able to dissolve in a solvent to create a solution.

Pause the video and then when you're ready, press play and we'll get on with the lesson.

There are two learning cycles in today's lesson, changes of state and solubility.

So let's get started with learning about changes of state.

Sodium chloride is table salt, the stuff you put on your chips.

And sodium hydrogen carbonate is baking soda, which you might put into cakes to help it rise.

Both are examples of ionic compounds.

At room temperature, all ionic compounds are in the solid state.

And in the solid state, they do not conduct electricity.

In a giant ionic structure, there are strong electrostatic forces in all directions between oppositely charged ions.

This is the ionic bond and something we should be really familiar with by now as we've covered it in previous learning.

So the ions are in a fixed position in the arrangement of a solid.

And this means that they are not able to move.

They cannot act as charge carriers and therefore they cannot conduct electricity.

It's a really important point that we need to understand.

So let's just check our understanding before we go any further.

Ionic compounds in the solid state are good conductors of electricity.

True or false? Well done if you chose false, that is the correct answer.

But why? Is it A, charges carried around the circuit by the transferred electrons, or B, the ions are in a fixed position, so cannot act as charge carriers because they cannot move.

Well done if you chose B, that is the correct answer.

Okay, so let's move on.

When an ionic compound changes from a solid state to a liquid state, it melts.

And as you can see in this little animation, during melting, the energy is transferred to the ionic compound by heating.

This means that the ions gain energy, it breaks the electrostatic attraction between the oppositely charged ions in the lattice structure.

They are able to move.

The melting point is the temperature at which ions change from the solid state to a liquid state.

And that's a really important definition.

So ionic compounds always have a high melting point.

And here are some examples.

Sodium chloride melts at a 801 degrees Celsius.

We might think that's high, but how about comparing that to magnesium oxide, which is over 2,800 degrees.

In fact, it's almost 3,000 degrees Celsius.

Copper iodide and calcium carbonate are also ionic compounds with high melting points.

And the reason is we need a lot of energy to break those strong ionic bonds between the positively and negatively charged ions in the ionic lattice, so that the ions are free to move in the liquid state.

So when an ionic compound melts, it's in the liquid state, we've said that, and that means it can conduct electricity.

And if we put that molten ionic compound containing free ions into a circuit with some electrodes, we can see it will light up a light bulb.

This is because the ions are free to move and act as charge carriers.

The liquid can conduct electricity.

Okay, let's just check our understanding again.

The melting point of lithium fluoride is high, over 800 degrees centigrade.

True or false? Well done if you chose true.

Yes, it's an ionic compound.

It has a high melting point.

So let's justify your answer.

It takes a small amount of energy to overcome the strong ionic bonds, so the melting point is high.

It takes a large amount of energy to overcome the strong ionic bonds, so the melting point is high.

A or B? Well done if you chose B, that is the correct answer.

To overcome those strong ionic bonds, a lot of energy is required.

Okay, so when an ionic compound changes from a liquid state to a gas state, it boils.

And again, on this animation, you can see how the particles are gaining energy.

Energy is transferred to the molten ionic compound by heating.

And you can see the flame coming up there on the animation.

This means that the ions gain energy and the electrostatic attraction between the oppositely charged ions break.

They are moving a lot quicker.

The boiling point is the temperature at which the ions change from the liquid state into the gas state.

Again, an important definition.

So ionic compounds have high boiling points.

Again, we've got some data here looking at the similar compounds to before.

Sodium chloride boils at 1,465 degrees Celsius, whereas magnesium oxide this time is 3,600.

And you can see as well two other examples.

Copper oxide and calcium carbonate both have high boiling points.

Why? Similar argument, a lot of energy is needed to break the strong forces of attraction between the positively and negative charged ions in the liquid state so that the ions have enough energy to move around and be in the arrangement of a gas state.

Okay, so here are the boiling points of some ionic compounds.

Which substances are in the gas state at 1,500 degrees centigrade? So we're looking for substances in the gas state and we've got the boiling point.

So is it A, sodium chloride, B, magnesium oxide, C, copper iodide, or D, calcium carbonate? Okay, well done if you chose sodium chloride.

Its boiling points is 1,465 degrees centigrade, which is below 1,500 degrees centigrade.

So it must be in the gas state.

And the other one is copper iodide because it has a boiling point below 1,500.

So well done if you've got those two correct.

Okay, so now we come to our first task about changes of state.

So question one.

In terms of particles of an ionic compound and their changes of state, write down the meaning of A, melting point, B, boiling point.

When you've done that, move on to question two.

You've got a table here with some data.

You're given the melting point and the boiling point of two compounds, calcium carbonate and the copper iodide.

I want you to use that data to answer the question, what is the state of each compound? So is it a solid state, a liquid state, or a gas state at different temperatures, 500, 750, 1,500 or 3,000 degrees centigrade.

And can you give a reason for each answer? Question three, in terms of structure and bonding, so that's really important.

You need to think about the structure and bonding.

Explain why magnesium oxide has a high melting point of 3,600 degrees centigrade.

And finally, question four, what is an electrical conductor? And why does zinc chloride conduct electricity in the liquid state but not in the solid state? So pause the video, have a go at the questions, and then when you're ready, restart the video, and we'll have a look at the answers together.

So let's see how you got on.

So for question one, melting point.

Well, the melting point is a temperature at which the ions change from the solid state to the liquid state.

So well done if got that right.

And the boiling point is a temperature at which the ions change from the liquid state to the gas state.

Question two.

So what is the state of each compound at these temperatures? Right, well, A, both calcium carbonate and copper iodide are solids at 500 degrees centigrade because it is below the melting point of both of them.

B, copper oxide is a liquid at 750 degrees centigrade, because 750 is above its melting point but it's below its boiling point.

Calcium carbonate is a solid at 750 because it's below its melting point.

Okay, part C.

Copper iodide is a gas at 1,500 degrees centigrade because it's above its boiling point.

Calcium carbonate is a liquid at 1,500 degrees centigrade because that is above its melting point, but it's below its boiling point.

And finally, D, both are gases.

Both from the gas states at 3,000 degrees centigrade because it's above the boiling points.

So these are sorts of questions you often get.

You've got to look carefully at the information and then apply it to each situation.

So very, very well done if you've got all of those correct.

Question three, in terms of structure and bonding, explain why magnesium oxide has a high melting point of 3,600 degrees centigrade.

Well, first of all, think about it as a logical step through.

Magnesium oxide has a giant ionic structure, so that's the first point I'd make.

Second, there are strong or very strong electrostatic forces of attraction, which are the ionic bonds, so if you wrote ionic bonds that's fine, between the positively charged magnesium ions and the negatively charged oxide ions.

So a lot of energy is needed to break the strong ionic bonds between the oppositely charged ions so that they can move and take on the arrangement of a liquid.

So very well done if you got that right.

Finally, what is an electrical conductor? Well, electrical conductor is a substance that allows charge to flow through it easily.

And zinc chloride can conduct electricity in the liquid state but not the solid state.

Well, in the solid state we start with that first.

The zinc and chloride ions are in a fixed position in the giant lattice structure.

So the ions are not free to move, they cannot act as charge carriers, therefore, zinc chloride cannot conduct electricity.

Let's compare that to the liquid state, where zinc and chloride ions are free to move, therefore, the ions can act as charge carriers, so the liquid zinc chloride can conduct electricity.

So if you've got that right, very, very well done.

Excellent work.

Okay, so that brings us to the end of our first learning cycle on changes of state.

We are now going to move on and have a look at the second learning cycle, which is all about solubility.

Most ionic substances can dissolve in water.

Okay, water is a solvent, and we can see a little image here of a beaker with some water in.

And we're putting in the solid sodium chloride and it is dissolving.

So we can no longer see that solid white at the end.

So what we have got is we have got a solution.

So keywords here to remember is the water's a solvent, ionic compounds are soluble in water because they dissolve, and a solution is formed.

So what happens? Well, as a substance dissolves, its particles start to spread out throughout the solvent, so you can't see them anymore.

So if we look at this animation, we can see some sodium chloride particles in the solid state going into our solvent, which is the water, and they're starting to spread out.

And as they spread out, we cannot see the individual particles anymore, but they are still there.

So ionic compounds are soluble in water.

So what actually happens is the water molecules are attracted to the ions in the lattice because water is special.

It's a very special compound, and its the compound that allows life to exist on Earth, it is slightly different.

So those water molecules are attracted to the ions in the lattice.

And you can see the water molecules in the diagram, all the red oxygens with two white hydrogens.

The ionic forces of attraction are overcome and the substance dissolves.

Effectively what happens is the water particles can pull away the positive and negative ions.

And this is what happens during dissolving.

So let's check our understanding.

Which diagram shows potassium bromide solution? Is it A, B, or C? Well done if you chose B.

In solution, there are the positive ions, the negative ions, and the water molecules.

A, we have just got positives and negatives.

The regular structure has been broken down, so that is potassium bromide in the liquid state.

And C, we have a regular structure of positive and negative ions, so that will be potassium bromide in the solid state.

Okay, the solubility of an ionic compound in water indicates how well it will dissolve at a particular temperature.

So here we've got some data.

We've got three ionic compounds, lithium chloride, sodium chloride, and potassium chloride.

And we've given you their solubility at 20 degrees centigrade.

So what does this tell us? Well, it tells us that lithium chloride is much more soluble than sodium or potassium chloride in water.

Because if we look at that data, we can see that 83.

5 grammes of lithium chloride will dissolve in 100 grammes of water, but only 35.

7 of sodium chloride will dissolve and only 34 of potassium chloride will dissolve.

So that's really important word.

Solubility gives an indication of how well it dissolves.

Okay, let's check our understanding again.

Which ionic compound is the most soluble in water? Is it A, magnesium chloride, B, potassium chloride, C, sodium chloride, and D, calcium nitrate? Look carefully at the numbers given in the question.

Well done if you chose D, that is the correct answer.

129 grammes of calcium nitrate will dissolve in 100 grammes of water, but with the others it's a lot less.

So good work, well done.

Okay, so when an ionic compound dissolves in water, the ions are free to move and this is why it will conduct electricity.

So as you can see here in this little setup, if we have an ionic compound solution and we put some electrodes in it, we can see that the electric circuit will light up a light bulb, so it is conducting electricity.

Now why? The ions can act as charge carriers and so they can move around the circuit and the solution can conduct electricity.

Okay, so let's check our understanding.

Copper chloride solution can conduct electricity.

Is that true or false? Well done if you chose true, that is the correct answer.

But why? So in a solution, the ions are not in a fixed position and cannot act as charge carriers.

Or B, in a solution, the ions are free to move and act as charge carriers.

Well if something is gonna conduct electricity, we have to have charge carriers present, so B is correct.

Well done if you chose that answer.

Okay, so now we come to our second task, task B.

For our first question, we want to draw a line from the property to its explanation.

So we've got two properties.

The first one, most ionic compounds are soluble in water.

And the second one, ionic compounds conduct electricity when dissolved in water.

So down the other side by the bullet points, we've got some explanations.

Electrons are free to move.

No charged particles are free to move.

Charged ions are free to move.

Bonds are strong.

Bands are weak.

Water molecules are attracted to ions and the ionic forces of attraction are overcome.

Pause the video and have a go at this question.

Then when you're ready, we'll look at the answer together.

Okay, for our first one, most ionic compounds are soluble in water.

Well, this is because water molecules are attracted to the ions and the ionic forces of attraction are overcome.

That's the single most important thing about why ionic compounds are soluble.

For our second one, ionic compounds conduct electricity when dissolved in water, charged ions are free to move.

And if we don't have those charged ions moving, acting as charged ions, nothing will happen.

So excellent work if you've got those correct.

Right, we're gonna move on to our second question.

So this time I want you to write down the meaning of solubility.

And then for part B, list the ionic compounds in order of decreasing solubility.

So look carefully at the information in that table.

And then for part C, in terms of structure bonding, explain why most ionic compounds will dissolve in water.

So need to think through a logical answer to that one.

Question three, we want to label the diagram showing the particles of sodium chloride in solution.

And then go on to explain why sodium chloride solution can conduct electricity.

Pause video and have a go at these questions.

And when you are ready, we'll look at the answers together.

Okay, so the meaning of solubility.

It's the ability of a substance to dissolve in a particular solvent creating a solution.

It tells us how well a solute dissolves in a solvent at a particular temperature.

So well done if you got that right.

Part B, listing the compounds in order of decreasing solubility.

So we want to start with the highest number on the table first.

So that is lithium chloride is the most soluble at 83.

5 grammes per 100 grammes of water, followed by potassium nitrate, copper sulphate.

And then finally, calcium carbonate, which is barely soluble at all because only 0.

018 grammes would dissolve in 100 grammes of water.

So well done if you got that right.

So in terms of structure and bonding, explain why most ionic compounds dissolve in water? Okay, remember that logical step.

So ionic compounds have a giant ionic lattice structure.

That's the first thing I would say.

Secondly, there are very strong electrostatic forces of attraction or ionic bonds between the positively charged ions and the negatively charged ions.

And the water molecules are attracted to the ions in the lattice.

Finally, we can talk about the strong electrostatic forces of attraction are broken and the substance to solves.

So well done if you've got all of those points.

And you really want to try and get them in the right sequence to give a really good explanation.

Okay, so let's have a look at the labels on this diagram.

We've got an Na plus ion or a sodium ion, we've got a Cl minus ion or a chloride ion, and we've got a water molecule.

So well done if you've got those correct.

Why can sodium chloride conduct electricity? Well, we've just shown from the diagram above, the ions are free to move and act as charge carriers so they can conduct electricity.

So very well done if you've got the answer to that right.

Okay, so that brings us to the end of this lesson.

So let's just summarise what we have learned.

In a giant ionic structure, there are strong electrostatic forces in all directions between oppositely charged particles.

Ionic compounds have high melting points and high boiling points because strong ionic bonds need a lot of energy to be broken.

Most ionic substances can dissolve in water.

The ions of an ionic compound dissolved in water are free to move around and the solution can conduct electricity.

The ions of an ionic compound are in the liquid state and are free to move around and the liquid can conduct electricity.

I hope you have enjoyed today's lesson and I look forward to learning with you again very soon.