Lesson video

Hello, everyone.

How are you today? I hope you're feeling really good.

My name is Ms. Afzal and I'll be your teacher for this lesson.

I'm feeling very pleased about that because I think we've got quite an interesting topic ahead.

Today we're looking at melting.

Our lesson is called "Melting: Particle Model" and it comes from the unit of work, "Solid, Liquid, Gas States and changes of state." So, I hope this all sounds interesting to you, and if you are ready with some focus, energy, and enthusiasm, we'll begin our lesson now.

The outcome for today's lesson is I can use the particle model to explain why substances have different melting points and use a thermometer to measure melting points.

I hope that sounds interesting to you.

We have some keywords in our lesson.

I'd like us to go through them one at a time, saying them out loud.

Melting, melting point, forces of attraction, regular arrangement, random arrangement.

Good to hear those keywords.

And now I'd like you to tell someone nearby, do you know the meaning of any of these keywords? Thanks for sharing your ideas.

Let's find out the definitions.

Melting is when a substance changes from a solid state to a liquid state.

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

Forces of attraction hold particles together.

In a solid state, the particles are in a regular arrangement.

In a liquid state, the particles are in a random arrangement.

These are our keywords, melting, melting point, forces of attraction, regular arrangement, and random arrangement.

Let's look out and listen out for them.

Let's think carefully about them, they'll be coming up in today's lesson.

Our lesson is called "Melting: Particle Model," and it has four learning cycles, forces of attraction, particle model of melting, using a thermometer, and melting point.

Let's begin by exploring forces of attraction.

In a solid state and liquid state, particles in a substance are held together by forces of attraction.

These forces of attraction act in all directions so that we can see the solid state and the liquid state, and we can see how these forces of attraction act in all directions.

Let's get straight into a check for understanding.

Which statement is correct about the forces of attraction between particles? Select from these options, a, act in one direction only, b, act in all directions, c, there are no forces of attraction between particles.

Pause here while you decide which statement is correct about the forces of attraction between particles.

Well done if you selected option b.

Indeed they act in all directions.

The particles in the solid state do not have enough energy to overcome the forces of attraction between other particles.

Particles in a solid state are an a regular arrangement and kept in a fixed position by the forces of attraction.

They cannot move around, only vibrate, and then we can see a model of a solid.

Let's have a check for understanding.

Who do you agree with? Here's Sam, "In a solid state the forces of attraction are so strong that the particles are in a fixed position and can only vibrate." Alex, "There are no forces of attraction between particles in a solid state." And Jun, "Particles are free to move past each other in the solid state." Pause here while you decide who you agree with.

Well done if you selected Sam.

Sam's statement is true.

And now it's time for your first task.

I would like you to select the correct word or phrase from the list below to complete the sentences.

The words/phrases can be used more than once.

Here's our first sentence, 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.

And here are the words or phrases needed to complete the sentences.

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

So, pause here while you select the correct words or phases to complete the sentences.

I'll see you when you're finished.

It's good to be back with you.

So, how did you get on with that task? Let's read through these sentences with the correct words added.

Number one, particles are held together by forces of attraction.

Two, forces of attraction act in all directions.

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

And four, the particles do not have enough energy to move past other particles.

Well done if you completed the sentences in this way.

And now we are onto our next learning cycle, particle model of melting.

Particles can gain or lose energy.

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

In a solid state, particles are in a regular arrangement, as we can see in this model of a solid.

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

They'll still be touching the particles around them.

The particles will be free to move past each other, will be in a random arrangement, will be in the liquid state.

When a substance in a solid state gains enough energy, it becomes a liquid.

The particles then have enough energy to overcome the forces of attraction, move around and over each other.

This process is called melting.

And there we can see some water melting.

Water in the liquid state, water in a solid state.

Let's have a 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.

Pause here and decide, is this statement true or false? Well done if you selected false.

and now I'd like you to choose from one of these two statements to justify your answer.

A, if particles have enough energy, they can move past other particles, or b, the forces of attraction are so strong that particles always remain in a fixed position.

Pause here while you select which statement justifies your earlier answer.

Well done If you selected statement a.

Let's have another check for understanding.

This picture shows water that has melted.

Which statement best describes melting? Choose from this selection.

A, the particles move apart, b, the water around the particles melts, c, the hard, solid particles change into runny liquid particles, or d, the particles start to move around and over each other while still touching.

Pause here while you decide.

Which statement best describes melting? Well done if you selected statement d.

Indeed, the particles start to move around and over each other while still touching.

This statement describes melting.

And now it's time for your next task.

I would like you to match up the sentences to explain what happens to the particles in a solid state when a substance melts into a liquid state.

So, here at our sentence starters, 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.

And here are the endings of the sentences.

Gain energy to overcome some of the forces of attraction holding them in a fixed position, but having 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, and hold them in place in a fixed position, they can only vibrate.

So, pause it while you match up the sentences to explain what happens to the particles in a solid state when a substance melts into a liquid state.

Let's see when you've completed this.

So, how did you get on with that task of matching up the sentences to explain what happens to the particles in a solid state when a substance melts into a liquid state? Perhaps you matched the sentences in this way.

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

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

Melting happens when the particles gain energy to overcome some of the forces of attraction holding them in a fixed position.

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 matched the sentences in this way.

And now onto our next learning cycle, using a thermometer.

We can use a thermometer to measure the melting temperature of substances.

We measure temperatures in degrees Celsius, or degrees C in the UK.

There are different types of thermometers, mercury filled thermometer, alcohol filled thermometer, digital thermometer, and digital display.

Pause here and share with someone, have you seen or used any of these kinds of thermometers? Thanks for sharing.

Positive features of a thermometer.

They're long, so easy to read the scale due to larger gaps between markings.

The liquid in the thin glass bulb at the end reacts to temperature change quickly.

Some thermometers are more accurate than other thermometers.

This alcohol filled thermometer can measure to the nearest one degree C.

It's more accurate than measuring to the nearest two degrees C.

This digital thermometer can measure to the nearest 0.

1 degrees C.

It is the most accurate thermometer shown.

Let's have a check for understanding.

Identify the most accurate thermometer.

A, b, or c? Well done if you selected a.

This is the most accurate thermometer.

Let's take a look at some of the negative features of thermometers.

They're delicate.

The glass bulb can break easily if roughly handled.

We need to handle them gently.

They can break if used as a stirrer.

They're long and round, so can easily roll off the tabletop, so we need to place them in the middle of the table and use anti-roll tops.

An anti-roll top stops the thermometer rolling off the table.

Let's have a check for understanding, true or false? It is good lab practice to place a thermometer down where you have been using it.

Pause here and select, is this statement true or false? Well done if you selected false, and now I'd like you to justify your answer by choosing from one of these statements.

A, glass can smash when dropped, thermometers are made of glass, or b, thermometers are long and thin, which makes them strong.

Pause here while you decide.

Well done if you selected answer a.

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

This justifies your earlier answer.

Some everyday temperatures include human body temperature at approximately 37 degrees C.

Room temperature is considered to be 20 degrees C, and freezer temperature, recommendation is minus 19 degrees C.

Let's have a check for understanding.

Select the correct statement.

Choose from the following, a, human body temperature is 37 degrees C, b, room temperature is 37 degrees C, c, human body temperature is 100 degrees C.

Pause here while you select the correct statement.

Well done if you selected statement a.

Indeed, human body temperature is 37 degrees C.

Reading a scale on a thermometer.

Look at the scale and see what each small mark represents.

Pause here and share with someone, what is the reading on this thermometer? It's 70 degrees C.

And pause here and share with someone, what is the reading on this thermometer? It's 23 degrees C.

Let's have a check for understanding.

The human body temperature is 37 degrees C.

Which thermometer reads 37 degrees C, a, b, or c? Well done if you selected thermometer a, this reads 37 degrees C, which is human body temperature.

And now it's time for your next task.

Lucas has some homework about thermometers.

He needs to name at least one type of thermometer, state the units used to measure temperature in UK classrooms, describe the safety precaution that should be taken when using a thermometer.

The bulb with the thermometer is made of thin glass.

Give a positive about the bulb being made of thin glass, give a negative about the bulb being made of thin glass.

So, pause here while you have a go at completing this homework alongside Lucas.

I'll see you when you're finished.

It's good to be back with you.

So, your answers should be similar to Lucas's answers.

Thermometers can be digital, mercury filled, alcohol filled.

Temperature is measured in UK classrooms in degrees Celsius.

A safety precaution should be to have an anti-roll cap/plastic cap on the top.

Don't place near the edge of the lab bench.

Handle gently.

Do not use as a stirrer.

And the bulb of the thermometer is made of thin glass.

A positive is that we can measure changes in temperature quickly.

A negative is that it makes them fragile and they can break easily.

Well done if you had answers similar to Lucas's.

Now we're onto our next learning cycle, melting point.

The force of attraction between particles will vary depending on substance.

The stronger the force of attraction, the more energy is needed to overcome the force.

Increasing energy is needed to overcome the force as the force of attraction is stronger.

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

This is the temperature at which the particles in a solid state have enough energy to overcome the forces of attraction and move around and over the other particles transitioning to the liquid state.

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

The melting point of water, ice, is zero degrees C.

Any temperature lower than zero degrees C, the water will be in the solid state, ice.

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

Any temperature higher than zero degrees C, the water will be in the liquid state, liquid water.

Let's have a check for understanding.

Which two substances are above their melting points? Choose from these selections, a, b, c.

Well done if you selected a and b.

These two substances are both above their melting points.

Let's take a look at some common melting points.

Water melts and becomes liquid at zero degrees C.

Chocolate melts and becomes molten, melted chocolate at approximately 32 degrees C.

And candle wax melts and becomes molten, melted wax at approximately 67 degrees C.

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

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

The melting point of gold is 1,064 degrees C, and the melting point of silver is 962 degrees C.

In these examples, the forces of attraction are the strongest between gold particles and weakest between gallium particles.

Let's have a check for understanding.

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

Who do you agree has the best explanation of why iron melts at a higher temperature than wax? Here Aisha, "The attraction between iron particles is stronger." Lucas, "Iron particles are closer together than wax particles." Jun, "Iron is a better conductor of heat." And Izzy, "Iron is harder and stronger than wax." Pause here while you decide whose explanation you agree with.

Well done if you selected Aisha.

This is a great explanation, "The attraction between iron particles is stronger." And now it's time for your final task.

I would like you to choose one of the words or phrases in brackets to complete the sentences.

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

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

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

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

So, pause here while you choose one of the words or phrases in brackets to complete the sentences.

I'll see you when you're finished.

It's good to be back with you.

How did you get on with that task? Let's read through the completed sentences.

Particles are held together by forces of attraction.

Different substances have different strength forces of attraction between particles.

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.

Also acceptable, the lower the melting point, the less energy is needed to overcome the forces of attraction between the particles.

Well done for having to go at this task and completing these sentences.

In our lesson "Melting: Particle Model," we've covered the following.

In a 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 zero degrees C, room temperature is about 20 degrees C, and body temperature is about 37 degrees C.

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

Well done, everyone, for joining in with this lesson.

It was so great to explore melting and a particle model with you, exploring solid states, liquid states, how we move between them, and investigating thermometers.

I hope you've enjoyed this lesson.

I really enjoyed teaching you and I'm looking forward to seeing you again soon.

Until then, stay curious.