Lesson video

Hello, my name's Mrs. Clegg, and today I'm looking forward to supporting your learning about groups of the periodic table.

In particular, today's lesson is going to be about Group 1.

We'll have a look at where they are on the periodic table and we'll look at some of their properties and electronic structure.

And here's the outcomes from today's lesson.

So we should be feeling much more confident about being able to describe the patterns in the properties of Group 1 elements and explain how those are determined by the electronic structure by the end of today.

Here are some of the keywords for today's lesson: alkali metals, density, and alkali metal hydroxides.

And here they are written into a sentence.

You might like to stop the video and make some notes that you can refer back to about the definitions here.

And so today's lesson is divided into three parts.

So first of all, we're gonna look together at the electronic structure of Group 1 elements, and then we're gonna look at their properties, and finally we'll look at the reactivity and some of the reactions of Group 1 elements.

Let's get started with electronic structure.

Here we've got a periodic table.

You can see the group numbers across the top there.

And Group 1 refers to the far left hand column in the periodic table here.

And the elements in Group 1, they're metals.

And from the top we've got lithium, sodium, potassium, rubidium, caesium, and francium there at the bottom.

They're also called the alkali metals because they produce metal hydroxides when they react with water, and metal hydroxides are alkalis.

So let's have a quick check.

Which symbols represent the elements from Group 1? Well done if you said sodium and rubidium.

Krypton, in the middle there, is actually one of the Group Zero elements.

Let's have another question.

So here's a statement.

The elements in Group 1 are lithium, sulphur, potassium, rhenium, caesium, and francium.

Is that true or is that false? It is indeed false.

And here's some statements to help you with that justification.

So this is a false statement because Group 1 elements do not include sulphur and rhenium.

Well done if you got that right.

Group 1 elements all have one electron in their outer shell, and that's an important fact to remember.

So Group 1 elements all have one electron in their outermost shell.

That's an easy way to remember it.

If you've got your periodic table, it might be worth having a look and finding lithium.

So you'll notice that lithium has an atomic number of three and that means it has three protons and three electrons.

And if we're going to represent this in an electronic structure diagram, it would look like this.

So there's two electron shells.

The first shell, the innermost one, is complete.

It has two electrons represented by the crosses, and then the outer shell has one electron.

Let's have a look at sodium, find that on your periodic table.

Again, sodium has an atomic number of 11, and so 11 protons and 11 electrons.

And if we represent that as a diagram, it would look like this.

So this time there are three electron shells.

We start in the centre, the first shell is full with two electrons, then we've got eight electrons, and then the final outer shell has got one electron, one outer electron.

Now we can also represent this by numbers.

And you'll see in the brackets at the bottom there, 2, 8, 1.

So we read from the inside.

So two electrons, eight electrons, one electron.

And that represents sodium.

So let's have a quick check.

which of these atoms could be elements that are in Group 1? B could definitely be an atom from Group 1 because it has one outer electron.

Just do a quick check and check all the others are complete, all the other shells are complete.

And they are.

C is also an atom which could be in Group 1 because it too has one outer electron.

Now A, if you have a look at A, it has three outer electrons, so that would not be in Group 1, and in actual fact it would be in Group 3.

So for Task A, these students are discussing Group 1 elements and they've said various things.

One of the four students is correct and the others are incorrect.

So what I'd like you to do, is first of all, decide who's correct and then amend the speech bubbles for the three students who are incorrect.

Pause the video and come back when you're ready.

Let's have a look at the answers.

The first student, we had to amend their idea.

So Group 1 elements are metals rather than non-metals.

The second student, again, we had to amend this one.

Group 1 is found on the far left hand side of the periodic table.

And we had to amend this one.

So they have one outer shell electron and are called the alkali metals.

And so the fourth student is correct with the potassium and sodium are Group 1 elements.

So we're now in the middle part of our lesson and we're gonna look at the properties of Group 1 elements now.

So Group 1 elements are all solids at room temperature.

Now francium is one of the least stable and most reactive elements in the periodic table.

It's quite spectacular.

Let's think about some of the facts we know about francium.

It's highly radioactive and it occurs both naturally and it can be synthesised.

Its physical properties such as melting point and density have been predicted, but we think they're going to be something similar to those of caesium.

So let's have a look at some of the trends for Group 1.

So we've got lithium at the top of Group 1 and francium at the bottom of Group 1.

And here are some of the trends.

So things that increase as we go down the group.

So the size of the atoms increases.

So lithium is the smallest atom in Group 1.

The mass of the atoms. So as the atoms get bigger, the mass increases.

And also the softness of the metal increases as we go down.

So the softest metal would be francium.

And then we've got decreases.

So we've got melting point and boiling point both decreasing as we go down the group.

So here's a quick check.

Going down the group, the size and the mass of the Group 1 elements does what? As you go down the group, what happens to the size and the mass? So the size and the mass of the atoms of Group 1 increases as we go down the group.

Although Group 1 elements are solid metals at room temperature, they're really soft and we can cut them with a knife.

So this softness is due to the weakness of the metallic bonds.

And here we've got a little video showing sodium being cut with a knife.

How easy is that? So we know they become softer as we go down the group because the metallic bonds become weaker.

And also look at the inside.

Once we've cut the metal, we can see it's much shinier inside.

Here we've got a bar chart looking at melting point.

So across the X axis we've got Group 1 elements, and on the Y axis we've got melting point.

And you can see as we go down the group, the melting points decrease.

So lithium has the highest melting point and caesium on this bar chart has the lowest.

And this trend is due to the weakness of the metallic bonding.

Let's look at this question.

So which Group 1 elements have melting points which are higher than that of potassium? It could be useful to have a periodic table here so you can look at the order of Group 1 elements.

And so the answers are sodium and lithium.

The weakening of the metallic bonds down the group is due to the fact that the metallic ions increase in size as we go down the group.

Look at the size of lithium there compared to potassium.

These are ions because they're charged particles.

You can see that because the lithium is a positive ion and you can see the positive there as well.

And sodium and potassium are positive ions too.

The electrostatic attraction between the negatively charged electron on the outer shell and the positive nucleus weakens as we go down the group.

Here we've got lithium ions, they're positively charged.

And here we've got the delocalized outer shell electrons.

So less energy is needed to overcome the weaker attraction as we go down the group.

Is this statement true or false? Group 1 elements have weak intermolecular forces between their metal ions and delocalized electrons.

Is that true or false? It's false.

And why is it false? Can you justify that answer? So which of these two would help? And it's false because Group 1 elements have electrostatic forces between their metal ions and delocalized electrons.

Group 1 elements also show a trend in density.

As Group 1 metals have weaker metallic bonding, their particles are less tightly packed together.

And here we can see sodium floating on the water there, scooting around.

Lithium, sodium and potassium are less dense than water and so they would float on the surface.

Here's a bar chart showing density.

We've got Group 1 elements along the bottom, and density on the Y axis.

And generally you can see there's an increase in density as we go down the group.

Lithium, remember, is at the top of the group and caesium is towards the bottom.

And the trend occurs because the mass of these atoms increases much more than the increase in atomic volume.

So that results in a higher mass per unit volume as we go down the group.

Remember if you want to make any notes throughout the lesson, just pause the video.

So let's have a look at Task B.

Here we've got a table of data, and what we're going to do is use our knowledge about the trends in some of these properties to predict the values for francium at the bottom.

And so we've talked quite a lot about what happens to atomic mass as we go down the group, and atomic radius.

PM means picometer, melting point and density.

So try and remember what those trends were to help you predict the values for francium.

Stop the video, have a go and come back when you're ready.

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

So you'll see that francium has a relative atomic mass of 223.

You could actually look that up on your periodic table.

And then in terms of atomic radius, remember that the atomic radius is getting bigger as we go down the group, it's increasing, so it's got to be more than 265.

And melting point, remember was decreasing down the group, so it's got to be less than 28 for caesium.

And density was increasing as we go down the group.

So it's got to be more than 1.

87.

Remember, these are predictions, so you might not have exactly the same values, but well done if you got those all correct.

Here's another couple of questions, read those questions and then pause the video while you have a go at them.

Atomic radius increases because the number of electrons increases as we go down the group.

And so the number of electron shells would increase, and so the radius would increase.

And our atomic mass increases for Group 1 elements because the number of protons and neutrons increases.

Let's think about melting point.

So we're told it decreases as we go down Group 1 and you've got to explain why.

So melting point decreases because the metallic ions increase in size, the electrostatic attraction between the negatively charged outer shell electrons and the positive nucleus weakens.

And so less energy is needed to overcome the weaker attraction as we go down the group.

And so melting point would decrease.

And the final part of our lesson is about the reactions and the reactivity of Group 1 elements.

So Group 1 metals are very chemically reactive and they need to be stored under oil.

And this is because they readily react with oxygen and water vapour present in the air.

If we have a look at sodium that's been left out in the air, it's tarnished, it's gone much duller than it was.

And that's because Group 1 metals react with oxygen and form oxide.

So on the surface there of the metal, it's formed sodium oxide.

And the balanced equation for that is this one.

So notice that oxygen, remember, is a diatomic molecule.

Just to remember when we cut the metal, it's shiny inside because it hasn't yet been able to react with oxygen in the air.

So reactivity increases as we go down Group 1.

And the reason for this increase in reactivity is due to the size of the atoms increasing.

So remember, sodium is larger than lithium and so on.

If we have a look here, lithium's got two shells, sodium's got three, potassium's got four shells there.

So the size gets bigger.

And so there's an increased distance between the outer electron and the positive nucleus.

And the outer electron, circled there in blue, is lost much more easily because it has a weaker attraction to the positive nucleus.

So is this statement true or false? Reactivity of the Group 1 metals decreases down the group.

True or false? It is, of course, false.

But why is it false? It's false because reactivity increases due to the weakened attraction between the outer electron and the nucleus, as we go down the group.

Group 1 metals react readily with Group 7 non-metals to form ironically bonded salts.

Now you might remember that Group 7, we often call the halogens, and Group 1, remember, the alkali metals.

So they react readily with each other to form ionically bonded salts.

Each Group 1 atom transfers their outer electron to a Group 7 atom.

And in doing so they form stable, oppositely charged ions that electrostatically attract each other.

So if we look at that in a diagram, we've got potassium here, the Group 1 metal, it's got one outer electron, the black cross, and fluorine, we're just looking at the outer shell here, and we're representing the electrons here with blue dots.

And if you count them up, there are seven in the outer shell.

So potassium and fluorine react together and form potassium fluoride.

The potassium ion is positively charged because it has lost an electron, and the fluoride iron is negatively charged because it has gained a negatively charged electron.

You can see that, the black cross there.

So both of them now have full outer shells.

Now potassium fluoride is an ionically bonded salt, and salts are giant ionic lattices with strong uniform ionic bonds in all directions.

Another salt is sodium chloride.

Sodium reacts with chlorine gas to form sodium chloride.

So sodium obviously is the silver Group 1 metal, very reactive.

And we've got chlorine, which is a gas, it's green, it's toxic or poisonous, and it's non-metal.

So sodium and chloride react together and form sodium chloride.

You would see an orange flame and white smoke happening during that reaction.

And sodium chloride is a white crystalline ionic salt.

It is the salt that we put on our food.

So it is edible.

Here's the balanced symbol equation.

Don't forget the state symbols.

Chlorine, remember, is a diatomic molecule.

Let's have a look at this question.

What would you see when sodium reacts with chlorine? You would see a white solid forming.

You would also see an orange flame and you would see white smoke.

Well done if you've got all three.

Now Group 1 metals react increasingly vigorously with water as we go down the group.

So we're gonna watch a clip now to see the reactions of lithium, sodium and potassium with water.

And what I'd like you to do is make some notes in a table about what you see.

So you might have drawn a table that looks something like this.

So lithium, sodium, potassium, you would see that they all float on water, they all move quite rapidly across the surface of the water, but actually potassium moves the most rapidly across the water.

They seem to disappear once they've reacted.

And there's a fizzing.

And potassium burns with a lovely lilac flame.

So here's a summary.

You might want to pause the video and make some notes if you haven't got all of those observations.

Let's think about the explanations for those observations we've just noticed.

Why do they float? Because the metal is less dense than water.

Why do they move so rapidly across the surface of the water? Because a gas is being made.

Why do they seem to disappear? That's because the Group 1 metals are reacting with the water, producing a colourless solution and a gas.

And what's the fizzing? That's because the Group 1 metals are reacting with the water and producing a gas.

And in the case of potassium, we've got this lovely lilac flame as they ignite.

The general reaction for Group 1 metals reacting with water is this: alkali metal plus water gives alkali metal hydroxide plus hydrogen.

So if we think about lithium, lithium reacts with water to produce lithium hydroxide and hydrogen gas.

And here we've got the balanced symbol equation underneath.

Don't forget the state symbols, lithium's a solid, water's a liquid, lithium hydroxide is aqueous, and hydrogen is a gas.

Now lithium hydroxide is a colourless, soluble alkali and it'll turn universal indicator blue or purple.

And this is why Group 1 are known as the alkali metals.

If we collect the hydrogen gas, it will produce a squeaky pop when it's exposed to a flame.

So here's a task for you to do.

On the first column we've got Group 1 metals reacting with oxygen.

And so what I'd like you to do is complete the word equation and then the balanced symbol equation underneath.

Watch out for any missing state symbols and add those in.

And then on the right hand side we've got Group 1 and Group 7 reacting together.

So alkali metals and the halogens, and do the same thing, complete the word equation and then balance the symbol equation.

Pause the video and join us when you're ready.

Here's the answers.

So you might like to pause the video while you check yours off.

Well done if you've got all of those correct.

Here's another couple of questions.

So the first question is asking you to describe the trend in reactivity.

And the second question is asking you to explain why we see this trend in reactivity.

So pause the video and come back when you're ready.

Let's have a look at the answers.

So the trend is that reactivity increases as we go down Group 1.

Why do we see this trend? We see that reactivity increases down Group 1 because the size of the atoms increase, remember.

And the distance from the positive nucleus to the outer negative electron shell increases.

And so the negative outer electron can be lost much more easily due to the weaker attraction to the positive nucleus.

Task C.

Let's have a look at this question.

So this is about the reaction of lithium, sodium, and potassium with water.

We've got the observations that we made there, and what I'd like you to do is complete the explanation column.

And then 3b, complete the word equation and then the symbol equation.

Pause the video and come back when you're ready.

And here are the answers.

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

And here's the summary.

These are the things that we've learnt today.

So Group 1 metals are very reactive, and reactivity increases as we go down the group.

As we go down the Group 1 metals, atomic mass and density increases, but melting point decreases.

In chemical reactions, atoms of Group 1 metals lose one outer electron, leaving a full electron shell.

As we go down the Group 1 metals, the attraction of the outer electron to the atomic nucleus weakens.

So Group 1 metals react with water to produce alkaline solutions.

Remember the video that you watched and seeing green universal indicator solution turn blue or purple, and these were the metal hydroxides being formed during the reaction.

So we've come to the end.

Well done.

I hope you're feeling a lot more confident now about the properties of Group 1 elements, and I look forward to working with you next time.

Metals are very reactive and their reactivity increases down the group.

As we go down the group, atomic mass and density increase while melting point decreases.

In chemical reactions, atoms of Group 1 metals lose one outer electron to leave a full electron shell.

Going down the Group 1 metals, the attraction of the outer electron to the atomic nucleus weakens.

And Group 1 metals react with water to produce alkaline solutions.

And if we use universal indicator, it will turn a purple to blue colour.

So we've come to the end.

Well done.

I hope you feel a lot more confident about the properties of Group 1 metals, the trends, and how they react with water.

Well done, and I'll see you next time.