Lesson video

Hello, my name is Mr. Gundry and welcome to this lesson on Group 1 and 2 Metals from the unit: Patterns in the Periodic Table.

Today we're gonna be talking about Group 1 and 2 metals and there's a nice, a little experiment or demo involved later on in the lesson, which I'm really looking forward to going through with you and I hope you're excited to do as well.

The outcome for today's lesson is to be able to describe the pattern in reactivity of both Group 1 and Group 2 with their reactions with water and with acid, and to be able to compare the two groups' reactivity.

There are four keywords for this lesson.

They are: alkali, alkaline, group and period.

And whilst we are going to go through them in the lesson, if you'd like to pause the video and read the definitions on the next slide, that's fine too.

So this lesson is split into two parts.

The first one is about the alkali metals and the second one is about the alkaline earth metals.

And in the second half of the lesson is when you will get a chance to do that practical or watch a demo.

So let's start by looking at the alkali metals.

So we know elements in the same group have similar properties.

As we go down the group, we see that trend of properties kind of change throughout the group.

And let's start by looking at Group 1.

So we are referring to the left, far left hand side of the periodic table with lithium, sodium, potassium, rubidium, caesium and francium.

So that's highlighted here in purple.

We call these the alkali metals because when they react with water they form an alkaline solution.

So if we were to test that with pH paper or an indicator, we would see that it had a pH greater than seven, so it'd be an alkaline solution.

So Group 1 metals will dissolve in water to form alkaline solutions.

True or false? Well that statement is false.

I'd like to read through these two justifications and I'd like you to pause the video as you do so and press play when you think you know which one is the correct reason why that is false.

Well, the answer is B, they react with water.

They don't dissolve in the water, they react with it to form an alkaline solution.

So the Group 1 metals are a collection of metals that have very similar properties, and compared to most metals, they're actually quite soft.

They can be cut with a knife, which is quite interesting.

A lot of metals can't be.

They have quite low melting points, so they'll melt at a particularly low temperature compared to most metals.

They're very reactive.

Most metals are quite unreactive.

And they have much lower densities, which means that they float on water, whereas most metals will sink when put in water.

And as we've seen, Group 1 metals will react with water to form a metal hydroxide and hydrogen gas.

So down the group, let's talk about the trends then.

Down the group there are several trends you need to know about in physical properties.

So this includes density, so they become more dense as we go down the group.

And then melting and boiling points increase as you go down the group as well.

Remember, density is a measurement of a mass of a substance per unit volume.

So referring to how tightly packed substance's particles are in a particular space.

The Group 1 metals are all solids at room temperature.

And francium is one that we don't really know very much about.

It's one that's very unstable and it's thought to be the most reactive element on the periodic table.

However, because of its radioactivity, caesium generally holds that title.

So it's highly radioactive.

We know that it occurs naturally, but we can also synthesise it in a lab.

And its physical properties are predicted to be very similar to caesium's.

Compared to most metals then, which statements are true about the Group 1 metals? Have a read through them, pause as you do so and press play when you're ready for the answer.

Well the answers are that they are softer compared to most metals and they are more reactive.

They actually have lower densities and they have lower melting points as well.

True or false? Group 1 metals demonstrate a trend in properties throughout the group.

Well that statement is true, we've talked about that already.

That's the main theme of today's lesson.

I'd like you to have a think about which of these justifies that answer though.

So pause the video as you do so, press play when you're ready to continue.

So the answer is B, the melting point of the metals increases down the group.

The metals actually become more dense down the group.

Okay, so we've got a practical demonstration now.

Either you can watch the video shown or your teacher will demonstrate this for you in the room.

And as you watch the demonstration, I'd like you to fill in this table about the appearance of each of the different metals and how easy it is to cut them with a knife and then to describe what happens as the metals are added to water.

And then at the end of the video, we add universal indicator solution and I'd like you to comment on why the indicator changes colour.

So pause the video now whilst you do that, or what will happen now is the video will clip into that demonstration so you can watch it here or with your teacher.

And then we'll go through the answers together.

Okay, so the first thing that we're going to do is we are going to make sure all of the oil that is covering the Group 1 metals is removed.

So we're gonna dry them off and the metals are very reactive with oxygen and water in the air, so we need to make sure that we store them safely.

But we don't want that on there 'cause it's gonna stop its ability to react with the water in a second.

So here we've just cut the metal with a knife.

We can see it's quite straightforward to do that.

And we're gonna take a small piece and we're just gonna drop it into the water.

So we can see that the lithium is reacting.

It's fizzing, there's some as being produced, it's formed a nice spherical shape and it's floating on top of the water.

We've now added sodium.

So we can see sodium has done something very similar to lithium, but this time it is actually on fire, it's got an orange flame, so that's the helium gas that's burning.

But as it burns, it's burning the metal.

We've put some potassium in now, so potassium is much more reactive and we can see here that it has produced a lilac flame.

So here is the lithium being set on fire, and we can see for a very short period of time, as the hydrogen burns, it reduces a nice, kind of purpley flame for lithium, a nice crimsony, red, purpley flame.

So here we've got lithium being added to water again, but this time we've added some universal indicator solution and we can see the green represents the neutral water, but as the lithium reacts with water, it produces lithium hydroxide, which is soluble in water, which is causing the indicator to turn blue.

This is a very nice demonstration.

Okay, I've got some more questions for you then.

So I'd like you to describe the trend in the reactivity of the elements as you go down the group.

So we can use our results from that demonstration to explain that.

The Group 1 metals are actually stored in oil.

I'd like you to describe and suggest a reason why they're stored in oil.

I'd like you to describe the trend in physical properties, such as melting points and density, down Group 1.

And then I'd like you to write a word equation for the reaction between lithium and water.

Okay, so let's go through some answers now.

So here are the results from that demonstration.

So we can see that lithium, sodium, and potassium are all dull on the inside, but once we cut them we can see they're shiny on the inside.

It becomes easier to cut them as we go down the group.

So sodium was softer, the lithium and potassium was softer than sodium.

They all float on the water, they all form a sphere, they all fizz around.

But sodium produces a yellow flame, you might have been lucky to see that, but potassium produces a lovely lilac flame and sometimes may even spark depending on the piece of metal that is added.

When we add the universal indicator solution, it's green in neutral water but will turn blue in alkaline solutions.

And the metals become more reactive down the group, and they're stored in water because of how reactive they are because they can react with water and oxygen in the air.

So we don't want them to react, we want them to be pure metals so that we can do the reaction with them.

The trend in physical properties are that as they go down the group they become more dense and their melting and boiling points increase.

And the word equation for the reaction between lithium and water is lithium plus water makes lithium hydroxide and hydrogen.

So that's Group 1.

Now let's look at Group 2.

You are gonna either do a practical in this section or you are gonna watch your teacher do a demonstration for this.

So Group 2 refers to the second column of the periodic table containing metals like beryllium, magnesium, calcium, strontium, and barium.

We call these the alkaline earth metals because like the alkali metals, when they react with water, they also produce an alkali substance.

We call them the earth metals because of the products that they form.

So non-metallic substances that were insoluble in water were called earth substances, which is where that term comes from.

So Group 2 is a group of metallic elements that have very similar chemical and physical properties.

Compared to Group 1 though, they are harder, they're not as soft.

We might be able to cut them with scissors or with a sharp knife, but it's a bit more difficult.

They have higher melting points, they are less reactive and they are more dense as well compared to Group 1 elements in the same period.

So when we're comparing beryllium in Group 2 to lithium in Group 1, or magnesium in Group 2 to sodium in Group 1.

And when Group 2 metals react with acid, they form a salt and hydrogen gas.

So it's metal plus acid makes salt plus hydrogen gas.

So compared to Group 1 metals, Group 2 metals, then, read through these statements.

When you think you know the answer, press play, but pause as you read through them to begin with.

So Group 2 metals are less reactive than Group 1.

All the other descriptions are incorrect.

So you're gonna complete an investigation now where you are going to look at how reactive Group 2 metals are.

The first part looks at dilute acid, so you're gonna react the Group 2 metals with some dilute acid.

There's some instructions on the board here.

The second part looks at water.

So you're going to react the Group 2 metals with some water.

And again, the instructions are on the screen.

And here is a nice little diagram to show how you're gonna do this.

So you've got some test tubes in a test tube rack and some labels just to show you how to do this.

And then there's some questions underneath here.

I'd like you to record your results in a suitable table.

So you need to draw a suitable results table and I'd like you to then predict how Strontium would react based on the evidence that you have collected from calcium and magnesium.

And then I'd like you to write a equation for the reaction between calcium and dilute acid.

So pause as you do that.

It's probably gonna take you a bit of time.

And then when you're ready to see some results or when you want to go through the answers, press play and we'll go through that together.

Well, here are your results.

So you should have seen that there was some fizzing when magnesium was added to dilute acid, but when added to water, very little, kind of not very much happened.

You might have seen some fizzing, but very tiny, tiny amounts.

Whereas for calcium you should have seen that there was a lot more fizzing.

It was more vigorous for the reaction with dilute acid compared to magnesium.

And when calcium was added to water, you should have hopefully seen some fizzing, a lot more obvious than for magnesium.

Based on that trend then, we can predict that Strontium should react even more vigorously with water and dilute acid, as the trend is that they're becoming more reactive down the group.

And the reaction between calcium and hydrochloric acid gives you calcium chloride and hydrogen as your two products.

Thank you very much for learning with me today.

I hope you enjoyed today's lesson.

I thoroughly enjoy this type of, kind of practical-based chemistry.

The main themes of the lesson are that the properties of elements in each group in the periodic table change gradually down the group.

The Group 1 metals are all soft metals with lower densities than other metals and become more reactive down the group.

The Group 1 metals react with water to form alkaline solutions and hydrogen, which is why they're called the alkali metals.

And the Group 2 metals react with dilute acids to make a salt plus hydrogen gas.

Group 2 metals get more reactive as you go down the group, like Group 1, but they are less reactive than Group 1 compared to elements in the same period.

Thank you very much for learning with me today.

I look forward to seeing you soon.

Bye-bye.