Welcome to today's lesson.

Today we're going to be looking at melting and the particle model of melting.

It's from the unit solid, liquid, gas states and changes of state.

I'm Mrs Mightom-Smithson and today I'm going to help you use the particle model to explain why substances have got different melting points and use a thermometer to measure melting points.

Here are some keywords for today's lesson, melting, melting point, forces of attraction, regular arrangement, random arrangement.

On the next slide there's some sentences that include these keywords.

If you want to read them, press pause, and then press play when you're ready to start the lesson.

Today's lesson consists of four learning cycles.

Firstly, we're gonna do about the forces of attraction, then we're going to have a look at the particle model of melting, then we're going to look at how to use a thermometer and different types of thermometers, and then we're going to look at melting point.

Our first learning cycle is forces of attraction.

Let's get going.

Here we've got the diagrams for a solid state and a liquid state.

You can see that the particles are touching, and they're touching because they're held together.

They're held together by these things called forces of attraction.

They act in all directions.

So you can see here, these arrows are representing those forces of attraction holding those particles together.

All of the particles are attracted to all of the other particles, so all of these forces of attraction act in all directions.

This is a 2D representation, but there's also a three-dimensional aspect to this.

So if you imagine that there's layers and layers and layers and layers of particles and all of the forces of attraction are holding them together.

Each particle is attracted to the particles around it.

Right, a quick check.

Which statement is correct about the forces of attraction between particles? Do they act only in one direction? Do they act in all direction? Or are there no forces of attraction between particles? Pause the video now for some thinking time and press play when you're ready for the answer.

Well done if you said that they act in all directions.

The forces of attraction do indeed act in all directions.

Particles in a solid state are held in place and they do not have enough energy to overcome those forces of attraction between the other particles.

And that means that they're in a regular arrangement and they're kept fixed in position by those forces of attraction.

They can't move, however they do have enough energy to vibrate on the spot.

So they can vibrate on the spot, but they are fixed.

So we'll have a little look there, here's a little animation of the particles in a solid state vibrating.

Who do you agree with? Sam says in a solid state the forces of attraction are so strong that the particles are in a fixed position and can only vibrate.

Alex says there are no forces of attraction between particles in a solid state.

Jun says particles are free to move past each other in a solid state.

So, who do you agree with, Sam, Alex, or Jun? Pause the video now for some thinking time and press play when you're ready for the answer.

Well done if you said that Sam was right.

They said in a solid state the forces of attraction are so strong that the particles are fixed in position and can only vibrate.

Well done if you got that right.

Now here's a task.

Select the correct word or phrase from the list below to complete the sentences.

Words or phrases can be used more than once.

So, particles are held together by forces of.

Forces of, act in.

In a solid state, particles, by forces of.

The particles, enough energy to move past other particles.

So here's the phrases that you can select from.

Are not held in a fixed position, are held in a fixed position, have, do not have, one direction, all directions, attraction, repulsion.

So those are the words and phrases that fit into those gaps.

Pause the video now, complete the task, and then press play when you're ready for the answers.

How did you get on with that task? Well done for completing it.

So, particles are held together by forces of attraction.

Forces of attraction act in all directions.

In a solid state, particles are held in a fixed position by forces of attraction.

The particles do not have enough energy to move past other particles.

Well done if you got all those correct.

Remember that those forces of attraction are so strong that they're going to hold the particles in a fixed position and the only things that those particles can do is vibrate on the spot.

Well done.

Well done for completing the first learning cycle, forces of attraction, now we're going to have a look at the particle model of melting.

Then we'll go on to look at some thermometers, and then finally melting point.

Particles can lose or gain energy.

In a solid state, the particles have got some energy, but not enough energy to overcome those forces of attraction between particles.

So we've said that this holds them fixed in position.

When particles have got enough energy to overcome these forces of attraction, they can move over and around each other.

If you have a look at this diagram here, you can see the particles gain some energy and they move over and around each other.

If you have a look, you can see that they're still touching the other particles around them, there are no spaces between them, but the particles will be then free to move past each other rather than being fixed like in a solid.

They will be in a random arrangement, you can see that they are randomly arranged, there's no fixed pattern there, and that means that they will be in the liquid state.

So they're moving from a solid state into a liquid state.

So, when a substance in the solid state gains enough energy, it becomes a liquid, because the particles have got enough energy to overcome these forces of attraction and they can move over and around each other, and this process, you're probably familiar with it, is called melting.

So here's a picture of some wax that's melting.

You can see that there's some wax still left in the solid state.

So those particles in that wax will be fixed in position.

And the wax in the liquid state, that means that those particles are able to move past each other.

Those are the particles that have melted.

Here's a quick check for understanding.

True or false? It doesn't matter how much energy particles have, they will always stay in a fixed position, in a regular arrangement.

So I want you to say true or false for that, then I want you to justify your answer, by choosing one of these two statements.

If particles have enough energy they can move past other particles.

Or, the forces of attraction are so strong that particles always remain in a fixed position.

Pause the video now for some thinking time, press play when you're ready for the answer.

Well done if you said that that statement was false.

If particles have got enough energy, they can move past other particles.

So the particles don't always stay in a fixed position.

Well done if you got that right.

Here's a picture of that wax that's being melted on heating.

Which statement best describes melting? The particles move apart.

The wax around the particles melts.

The hard, solid particles change into runny, liquid particles.

The particles start to move around and over each other, whilst still touching.

Pause the video now for some thinking time and press play when you've got the answer.

Well done if you said D, the particles start to move around and over each other, whilst still touching.

Now we've got task B.

So what I want you to do here is it's a match up, so I want you to match up the sentences on the left to the sentences on the right to explain what happens to the particles in a solid state when a substance melts into a liquid state.

So, in a solid state, forces of attraction between particles.

When particles gain enough energy, they can.

Melting happens when the particles.

In the liquid state, particles are held together.

I want you to match these up with one of these.

Gain energy to overcome some of the forces of attraction holding them in a fixed position.

But have enough energy to overcome the forces of attraction to move around and over each other.

Overcome the forces of attraction holding them in a fixed position.

Hold them in place in a fixed position, they can only vibrate.

Pause the video now, complete the task, and press play when you're ready for the answers.

In the solid state, forces of attraction between particles hold them in place in a fixed position, they can only vibrate in that fixed position.

When the particles gain enough energy, they can overcome those forces of attraction that are holding them in a fixed position.

And melting happens when they gain energy to overcome some of the forces of attraction holding them in place.

And finally, in the liquid state, particles are held together but have enough energy to overcome the forces of attraction to move around and over each other.

Well done if you got that correct.

Well done for working hard so far in this lesson, we've completed forces of attraction, particle model of melting, and now we're going to move on to using a thermometer before finally doing the melting point learning cycle.

Most people are familiar that we use thermometers to measure the melting temperature of substances.

You might've already used one.

In the UK, we measure temperature in degrees Celsius, so the little degrees sign is that little tiny circle.

You might be familiar from maths with this meaning degrees, but it must always have a capital C after it to represent Celsius.

Other countries might use different units to represent temperature, but in the UK, in your science lab, you're going to be using degrees Celsius.

There are different types of thermometers and you might recognise some of these.

So here we've got a mercury-filled thermometer.

You can see the mercury, the silver liquid metal, at the bottom of this thermometer.

We've got some alcohol-filled thermometer.

This could be, in this case it's red, but sometimes it is green or blue.

We've got a digital thermometer.

This one's turned off, but you can see that there's a silver probe and a digital reader.

And also, this is an infrared thermometer and you can see that this has got a digital display.

Now we're going to look at the good things about thermometers, so here's a positive feature.

So, thermometers are often long and that makes it easier for you to read the scale because there's larger gaps between the markings.

The liquid in the thin glass bulbs, the bottom of the thermometer is called a bulb, and that reacts quickly to the temperature changing.

Some thermometers are more accurate than other thermometers.

This alcohol-filled thermometer can measure to the nearest one degree C, some thermometers can only measure to the nearest two degrees C, because they only have markings every two degrees C.

If you have a look, you can see that these markings, you've got the 40 and there's 10 little lines between the 40 and the 50, so each one of those represents one degree C.

The digital thermometer can measure to the nearest 0.

1 degrees C and it's more accurate than the alcohol-filled thermometer.

You can see the display here is measuring 47.

6 degrees C, so that is more accurate.

What I want you to do is identify the most accurate thermometer.

So thermometer A reads to the nearest 0.

1 degrees C, thermometer B reads to the nearest one degrees C, and thermometer C reads to the nearest two degrees C.

Pause the video now, have a think, and then press play when you're ready for the answer.

Well done if you said that A, that digital thermometer, is the most accurate because it measures to the smallest amount, in this case it's 0.

1 degrees C.

Well done.

We've had a look at some of the positives about using thermometers, now we're going to have a look at some of the negative features of using a thermometer.

So, one of the problems, and you might have come across this or maybe even done it yourself, is where the glass bulb at the end is quite delicate and it can break if it's roughly handled.

So, what you need to do, is you need to handle it gently and not use it as a stirrer.

If you use it as a stirrer, you're more likely to hit the sides of the beaker or whatever you're mixing with it and then it might break.

A broken bulb can be an issue, particularly if you've got a mercury thermometer because you can see here the poisonous mercury has escaped and formed these little silver balls.

This is very dangerous to the environment.

They're long and they're round and they can easily roll off of a table-top.

So you've put your thermometer down and it might roll off.

So one of the things that I would recommend that you do is always place the thermometer in the middle of the table.

That way it won't accidentally roll off to the end, and there's also these things called anti-roll tops.

You might have seen these, but not really realised what they're used for.

So here's an anti-roll top and all this does is it just stops the thermometer rolling off of a table.

A quick check about your knowledge about thermometers.

It is good lab practise to place a thermometer down where you have been using it.

Is this true or is this false? Well done if you said that that is false.

Then I want a reason for this, a reason why that statement is false.

So, glass can smash when dropped, thermometers are made of glass.

Or, thermometers are long and thin which makes them strong.

So pause the video now for some thinking time and press play when you've made up your mind.

Well done if you said A, glass can smash when dropped, so thermometers are made of glass.

So if you place your thermometer down where you've been using it, that might be at the edge of a table.

If it rolls off, then it's going to smash because it's made of glass.

We're going to look at some everyday temperatures.

So the human body temperature is approximately 37 degrees C, room temperature is considered to be around 20 degrees C, it might be a little bit higher if you like it a bit warmer, or a bit cooler if you like it a bit cooler.

Freezer temperature recommendation is -19 degrees C, so this is less than freezing temperature of water, which is 0 degrees C.

Select the correct statement.

Human body temperature is 37 degrees C.

Room temperature is 37 degrees C.

Human body temperature is 100 degrees C.

Pause the video now, have a think, press play when you've got an answer.

Well done if you said human body temperature is 37 degrees C.

We're going to have a look at how to read a scale on a thermometer.

So if you take a look at this scale, the first thing you need to figure out is what each small mark represents.

So I can see that each big mark is numbered 60 and 70, halfway between that is a slightly bigger mark but that's not labelled up with a number, that's number five.

So if we then start at 60 and then we go upwards you can see, 61, 62, 63, 64, 65 is that mark that's not labelled up that's a bit bigger, 66, 67, 68, 69, and 70.

So this thermometer measures 70 degrees C and each little mark represents one degree C.

Let's have a look at this.

So we can see now that we have a look at the nearest whole mark, so that's 20, and then we're just going to count up knowing that each little mark represents one degree C.

So 20, 21, 22, and 23.

This thermometer measures 23 degrees C.

The human body temperature is 37 degrees C.

Which thermometer reads 37 degrees C? Is it A, B, or C? Pause the video now, press play when you've got an answer.

Well done if you said A.

A reads 37 degrees C.

B reads 44 degrees C and C reads 33 degrees C.

Well done if you got that right.

Here's task C now.

Lucas has got some homework about thermometers and he needs to do the following, name at least one type of thermometer, state the units used to measure temperature in UK classrooms. So what units do we write for temperature? Describe a safety precaution that should be taken when using a thermometer.

So how are you gonna keep yourself safe when using a thermometer? The bulb of the thermometer is made of thin glass, I want you to give me a positive about the bulb being made of thin glass, so a good thing, and give a negative about the bulb being made of thin glass, so a bad thing.

Pause the video now, complete the task, press play when you're ready for the answers.

Your answers should be similar to Lucas' answers.

So thermometers can be digital thermometer, a mercury-filled thermometer, or an alcohol-filled thermometer.

Any of those three would be a correct answer.

Temperature in UK classrooms is measured in degrees Celsius, so if you've written degrees Celsius or a little circle with a capital C please, that's brilliant.

A safety precaution should be, so you could've chosen to have an anti-roll cap or that plastic cap on the top and don't place it near the edge of the lab bench, handle it gently, and don't use it as a stirrer.

So then we've got the bulb of the thermometer, we're going to look at that, that's made of thin glass.

A good thing about is it measures changes in temperature quickly.

A bad thing about it is it's fragile and it can break easily.

Well done for completing that task.

Now we're onto our final learning cycle.

So we've looked at forces of attraction, particle model of melting, how to use a thermometer and different types of thermometers now we're gonna move onto melting point.

We know that all particles are held together by forces of attraction, but the force of attraction between those particles will vary depending on what substance it is.

The stronger the force of attraction, the more energy it's going to need to overcome that force.

So here you can see we've got two particles held together by a force of attraction.

This substance is different, it's a little bit bigger arrow, so representing a stronger force of attraction, an even bigger arrow representing a greater force of attraction.

So this shows that increasing energy is needed to overcome the force as the force of attraction is stronger.

The melting is the temperature at which a substance will change from being in a solid state to a liquid state.

And this is the temperature at which the particles in a solid state have got enough energy to overcome those forces of attraction and then they can move over and around each other to the liquid state.

A substance that has a temperature below the melting point will be in the solid state.

So the melting point of water as ice is 0 degrees C.

So any temperature lower than 0 degrees C, the water will be in the solid state, so it's going to be ice.

A substance that is heated above its melting point will be in the liquid state.

For example, if water is in a temperature, any temperature higher than 0 degrees C, the water will be in the liquid state, so we'll have liquid water.

Let's have a look at these pictures.

Which two substances are above their melting points? A, B, or C? Pause the video, have a think, press play when you've got your answer.

For this, all we needed to do was see which ones were in the liquid state.

So we've got the melted ice cream, which is A, and that's actually liquid mercury, which is B, you can see it's being poured from that bottle into the bowl.

Well done if you got those right.

So common melting points for you to think about, ice melts and becomes liquid water at 0 degrees C, chocolate melts and becomes molten, so that's melted chocolate at approximately 32 degrees C, and candle wax melts and becomes molten wax at approximately 67 degrees C.

Different substances have got different melting points, as the energy needed to overcome the forces of attraction between the particles in a substance are different.

So each substance has got a different melting point because those forces of attraction are different.

For example, the melting point of gallium is 30 degrees C.

Here's a little picture of gallium melting in somebody's hand.

So the body temperature's about 37 degrees C, so something that melts at 30 degrees C will melt in your hand.

Melting point of gold is significantly higher at 1064 degrees C.

Melting point of silver is 962 degrees C.

So in this example, the forces of attraction are strongest between the gold particles, and weakest between the gallium particles.

Some students have been discussing this question.

So iron must be heated to a higher temperature than wax before it melts.

Who do you agree with has the best explanation of why iron melts at a higher temperature than wax? So wax melts at 67 degrees C, iron melts at 1538 degrees C.

Aisha said the attraction between iron particles is stronger.

Lucas says iron particles are closer together than wax particles.

Jun says iron is a better conductor of heat.

Izzy says iron is harder and stronger than wax.

Who do you agree with? Pause the video for some thinking time and press play when you've got an answer.

Well done if you said Aisha.

Aisha says the attraction between iron particles is stronger.

So it's stronger than the attraction between the wax particles.

Well done if you got that right.

Now you're going to complete task D.

Choose one of the words or phrases in brackets to complete the sentences.

So there's going to be four sentences and you're going to select the correct words in the brackets to make those sentences make sense.

Particles are held together by, forces of attraction or no forces.

Different substances have different or the same strength forces of attraction between particles.

The stronger or weaker the force, the more energy is needed to overcome this force.

And finally, the higher or lower the melting point, the more or less energy is needed to overcome the forces of attraction between particles.

Pause the video now and complete the task.

Press play when you're ready for the answers.

Well done for completing task D.

We're going to go through the answers now.

So particles are held together by forces of attraction.

Different substances have got different strength forces of attraction between the particles.

That means the stronger the force, the more energy is needed to overcome this force.

The higher the melting point, the more energy is needed to overcome the forces of attraction between the particles.

You could've also written this, the lower the melting point, the less energy is needed to overcome the forces of attraction between the particles.

So to get that last sentence right, you either need to have higher and more or lower and less.

Well done for working hard and getting those right.

Here's a summary of today's lesson.

In the solid state, forces of attraction between particles hold them in fixed positions.

In the liquid state, particles are held together but have enough energy to overcome the forces of attraction to move around and over each other.

The stronger the force of attraction between particles in a substance, the higher its melting point.

Water melts at 0 degrees C, room temperature is about 20 degrees C, and body temperature is about 37 degrees C.

The bulb of a thermometer is made of very thin glass and is delicate.

Well done for working hard throughout this lesson, I hope to see you again soon.