Welcome to today's lesson.

My name's Mrs. Clegg, and today we're gonna be looking at the reactions of the halogens, including the displacement practical.

Halogens, if you remember, are also called group 7, and they're non-metals.

This lesson is part of the unit Groups of the periodic table.

It's always useful to have a periodic table beside you to reference.

So if you need to go and get one, pause the video.

And here's the outcome for today's lesson.

By the end of it, we should be much more confident about writing word and symbol equations to show how group 7 elements react.

We've got some key words here to look out for: displacement, solution, and halides.

Think about those words, notice them in the lesson.

And here they are written into a sentence.

And if you need to make notes about what they are to refer back to, do that now.

I've split the lesson today into two parts.

The first part, we're going to look at how the halogens react with group 1 and group 2.

And in the second part of the lesson, we're gonna look at the displacement practical.

So let's get started with the first part of our lesson.

Here we've got the periodic table.

Group 7, the halogens, readily react with group 1, metals, and group 2, metals.

Let's just remind ourselves where they are on the periodic table.

So group 7 is here.

Fluorine, chlorine, bromine, iodine, astatine.

And group 1 is here.

Lithium, sodium, potassium, rubidium, and caesium.

And here's group 2.

Beryllium, magnesium, calcium, strontium, and barium.

Make sure you recognise those chemical symbols.

So I'm gonna do a quick check.

So using the periodic table that you've got beside you, match up the elements with the group that they belong to.

Pause the video and join when you're ready.

Let's look at the answers.

So lithium is in group 1 and potassium is in group 1.

Magnesium is in group 2, and calcium is also in group 2, which means we've got chlorine and bromine and iodine in group 7.

Fantastic if you got all those correct.

Now, the group number matches the number of electrons in an atom's outer shell.

So here we've got a diagram with an atom that has one electron in its outer shell.

That would be a metal in group 1.

And when it reacts, it is going to lose that outer electron and become positively charged because it's lost a negative electron.

So a little summary here.

When they react, group 1 and group 2 atoms lose their outermost electrons.

They obtain a full outer shell of electrons by doing that, and they become stable positive ions.

Now let's have a look what happens with group 7.

Halogens are in group 7, so that means they have seven electrons in their outer shell.

In the diagram we've got the outer shell of a halogen with seven outer electrons.

The blue circles are representing the electrons here.

And when this atom reacts, it needs to gain an electron.

And if you have a look carefully, you can see a black cross representing electron from a different atom.

So when they react, group 7 elements gain an outer electron.

They obtain a full outer shell of electrons by doing so and become stable negative ions.

Let's have a check.

So have a look at these three electronic structures.

Which atom here is from group 7? Well, let's have a look at the answers.

So the answer is B.

A, for example, has got one outer electron, so that would be an atom from group 1.

B has indeed got seven electrons on its outer shell, so that is from group 7.

And C, if you notice, has two electrons on its outer shell, so that would be from group 2.

Well done if you got that correct.

Group 7, the halogens, which are non-metals, readily react with group 1 metals to form ionically bonded halide salts, so sodium and fluorine.

Sodium is group 1 and fluorine group 7.

You know that because of the number of electrons on the outer shell.

And when they react together, an electron is transferred from sodium to fluorine and we form sodium fluoride.

The sodium ion is positively charged because it's lost a negative electron, and the fluoride ion is negatively charged because it's gained a negative electron.

So each group 1 atom transfers their outer electron to a group 7 atom.

They form stable oppositely charged ions, which electrostatically attract each other.

So sodium fluoride is a halide salt, and they are giant ionic lattices with strong uniform ionic bonds in all directions.

Sodium chloride, as we've shown here in the picture, is also a halide salt.

And you can see there the purple spheres represent the sodium ions, which are positively charged.

And the green spheres represent the chloride ions, which are negatively charged.

And we do wanna also look at the ratio of sodium to chloride ions, and we'll see it's one to one.

Quick check.

What compound would be formed when potassium reacts with bromine? So well done if you said potassium bromide.

Well done.

Group 7 elements also readily react with group 2 metals pretty much in the same way as they do with group 1.

So we've got magnesium from group 2 and we've got chlorine from group 7.

Now, magnesium has two outer electrons, and each of the chlorine atoms there has seven outer electrons.

Magnesium needs to lose both of those outer electrons to gain this full outer shell.

And so that electron transfers to one of the chlorine atoms and the other one to the second chlorine atom.

So magnesium has now lost two electrons and so it is positively charged because it's lost two electrons.

And so you'll see there above the square brackets 2+ to show that it's lost two negatively charged electrons, so it's now positively charged.

And each of the chloride ions have gained an electron, and they are each negatively charged.

And the formula for magnesium chloride is one magnesium to two chlorine atoms, MgCl2.

So, a summary.

Each group 2 atom will transfer their two outer electrons to two separate group 7 atoms to form stable oppositely charged ions.

So magnesium, when we heat it, can react with chlorine gas to form magnesium chloride.

So here's magnesium, it's a silver metal, and chlorine, which is a green non-metal and it's a gas at room temperature.

And when they react together, you'll see a bright white flame and white smoke given off.

And what we form is a solid, which is magnesium chloride.

It's a white halide salt.

Here's the equation.

Magnesium plus chlorine gives magnesium chloride.

Don't forget to put in the state symbols there.

So magnesium's a solid.

Chlorine is a gas.

Magnesium chloride is a solid.

So chlorine gas is a toxic, green, non-metallic gas, which like other halogens forms an acidic solution with water.

So we can test chlorine gas using damp blue litmus paper.

It initially turns red and then it will bleach white all over.

So is this true or false? During reactions, group 1 and 2 metal atoms gain electrons to get a full outer shell and become stable.

Is that true or false? It is false.

And why is that? Why is it false? If you had to rewrite that sentence, what would you do? So which one of these justifications do you think is correct? And it would be the top one.

Group 1 and 2 metal atoms lose electrons to form positive ions with a full outer shell.

Well done.

So let's have a look at task A.

Complete the table below to show the name and formula of the halide salt formed, and your periodic table might be helpful here.

So we've got the reactants, then the product, and then the formula.

So pause the video and join us when you are ready.

Let's have a look at the answers.

So magnesium and bromine produce magnesium bromide.

Sodium and something make sodium astatide.

Now, astatide is the halide ion which comes from astatine, so sodium and astatine, which make sodium astatide.

And the formula for that is this.

We know sodium is in group 1, so it has one outer electron to transfer.

Astatine is in group 7, so that needs to gain one electron to complete its outer shell.

So we know the formula is one sodium to one astatine, NaAt.

Now, we know the product is caesium fluoride, so the reactant must be caesium.

When barium and chlorine react together, they'll form barium chloride.

So barium is in group 2, so it has two outer electrons to transfer.

Chlorine is group 7, so it needs to gain one electron to complete the outer shell.

So therefore there must be two chlorine atoms involved, and the formula is BaCl2.

Make sure you're getting the letters correct, where barium, for example, has two letters.

The first one is capital, and then the next one is a small letter, and make sure the numbers are clearly subscript here.

For the last one, we know the product is strontium iodide, so the reactants must be strontium and iodine.

And there's the formula.

Well done.

Our next task: complete and balance the following equation and then describe, in terms of electrons, what happens when lithium reacts with chlorine.

So have a go at that and pause your video and rejoin us when you're ready.

So let's check the answers.

And the description.

Several bullet points there.

Each lithium atom loses one electron to become a lithium ion with a full outer shell of electrons.

Each chlorine atom gains an electron to become a chloride ion with a full shell of outer electrons.

The lithium and chloride ions are electrostatically attracted together to form the halide salt lithium chloride.

Silver metallic lithium reacts with green chlorine gas to produce a white salt.

Well done.

Now we're on to the second part of today's lesson.

We're going to look at the displacement of the halogens.

So reactivity decreases as we go down group 7, with fluorine at the top, astatine towards the bottom.

And this is because it becomes much more difficult to gain an electron because the size of the atoms increases.

Trend in reactivity enables the halogens to undergo displacement reactions.

And here we're looking at a particular reaction.

So chlorine and potassium iodide react together to form iodine and potassium chloride.

These are all aqueous solutions.

And here we've got a more reactive halogen replacing a less reactive halogen in a halide salt compound.

You can see that because reactivity decreases down the group, iodine is below chlorine.

So chlorine is more reactive than iodine, and so it replaces the iodine in the halide salt compound.

Let's quickly check.

The reactivity of the halogens increases down the group.

Is that true or is that false? It's false.

Which one of those would help us justify the answer? And here we go.

The trend in reactivity is due to the size of the atoms increasing, so that makes it much harder to gain an electron.

Which halogens could chlorine displace from the halide salts shown below? Again, this is where it might be useful to just use your periodic table to help you.

And the answers are sodium bromide, and of course lithium iodide.

Chlorine is more reactive than bromine and iodine, so it can displace those from the halide salts.

Now, fluorine is more reactive than chlorine and so chlorine cannot displace the fluoride there.

And chlorine cannot displace itself.

So calcium chloride, there would be no reaction.

Solutions of halide salts are colourless, and halogen solutions are coloured.

And this is really helpful when we are doing experiments because we can see the displacement reactions actually happening.

So here we've got chlorine, which is yellow, being added to sodium bromide.

So chlorine is a halogen solution, so it's coloured.

Sodium bromide is a halide salt, so it's colourless.

We're adding chlorine to it and we're getting bromine and sodium chloride.

And we see an orange colour there because of the bromine solution.

Sodium chloride in there would actually be colourless.

So you're now going to do an investigation to look at the reactivity of the halogens.

We're gonna carry out a series of displacement reactions.

Here's the method to use.

Get a spotting tile and add two or three drops of each aqueous halogen to the correct rows as shown.

So here we're gonna put chlorine going across that way.

Then we're going to put the bromine solution across there and iodine across there.

Next, we're going to add two to three drops of each of the colourless halide salt solutions to the correct column.

So we're gonna go downwards here.

So we're gonna add two to three drops of potassium chloride to each of those three dimples.

And then we're gonna add potassium bromide to the next column and potassium iodide to the next one.

And then we'll record our results in a table like this.

And then we'll use our results to write a conclusion that includes two parts: the word and symbol equations for each of the displacement reaction that occurs, and an explanation as to why those reactions have actually occurred.

So your results might look something like this.

You'll notice there's a change there in the potassium bromide column and there in the potassium iodide column and there in the potassium iodide column too.

So your results table might look something like this, and you can see the changes in the table where we've just seen the colour changes there.

So our next part was to write the word and symbol equations for each of those reactions.

So chlorine and potassium bromide would produce bromine and potassium chloride.

And there's the symbol equation, including the state symbols.

Here's the second one and the third one.

You might have to pause the video to check your answers.

And the last part, we had to explain why these reactions occurred.

So those are the reactions we're interested in.

So why did they happen? They happened because as we go down the group, the halogen elements become less reactive.

Chlorine is more reactive, and so it reacts with both the potassium bromide solution and the potassium iodide solution.

Bromine is the second most reactive halogen we've got here, and it reacted with the potassium iodide.

Iodine is the least reactive halogen here, so it didn't react with any of the halide salts.

Again, it's useful to have your periodic table so you can see the order of the halogens.

And remember that as we go down the group, they become less reactive.

So we've come to the end of our lesson today.

Well done.

I hope you feel more confident in terms of the reactions of the halogens and displacement reactions.

So let's look at the summary.

This is what we've learned about today.

Group 7 elements react with group 1 and group 2 metals to form halide salts.

Halogens can be dissolved in water to form acidic solutions.

And the test for chlorine gas involves passing that gas over damp blue litmus paper, which will turn red and then it will bleach.

And a more reactive halogen will displace a less reactive one in a compound.

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