Hello, my name is Mr. Gundry, and welcome to this lesson on the Group 7 elements known as the halogens from the unit "Patterns in the Periodic Table".

Today we're gonna dive into looking at some more trends in the periodic table, specifically at the Group 7 elements.

And I'm looking forward to going through it with you.

There's a practical in this lesson which you may be doing either as a demo or on your own.

And that's at the end of this lesson, so we'll try and get to that as quickly as we can.

The outcome then of today's lesson is to be able to describe the pattern in reactivity of the Group 7 non-metal atoms, and then name the products of the reactions between metals and halogen.

So four keywords for today's lesson then: halogen, group, halide, and salt.

On the next slide are their definitions, so if you would like to read through those you can, but we're gonna cover them as we go through the lesson.

So the lesson is split into two parts.

We're gonna talk about the properties of the Group 7 elements, and then we're gonna talk about some reactions that they can do, and that's where you will find this practical/demo.

So let's start by talking about Group 7.

So Group 7 is a group of elements that have similar properties.

As we know, groups have similar properties within those elements, and there is also a trend of properties throughout that group as well.

And the Group 7 elements are no strange to that.

So the Group 7 elements include non-metals such as fluorine, chlorine, bromine, iodine, astatine, and tennessine.

Tennessine, one of the most recent elements to have been discovered.

Not very much is known about it, it's not very stable, and we're not really gonna talk about it in today's lesson.

So true or false? Group 7 elements are metals.

Well, the answer is false.

And I'd like you to justify the answer using the information below.

So pause the video, and have a read through, and press Play when you are ready to continue.

Okay, so the answer is A, they're all found on the right-hand side of the periodic table.

So the Group 7 elements are known as halogen, and they're called halogens because of what the word means.

It's a kind of a historic word.

It was devised because it meant salt maker, specifically because of their production of sodium salts at the time, but now we know they form lots of different salts.

Sodium chloride is an example of salt that we will have come across before, but it's not the only salt.

There are lots of other types of salt out there.

The Group 7 elements are non-metallic elements, they're non-metals, they have very similar chemical and physical properties.

One of their most well-known properties is they like to go around as molecules.

They go around kind of forming bonds with just one other atom of the same kind, so we get things like F2, Cl2, and Br2.

Each of them has a very distinct colour, and they're very highly reactive, but most importantly they're incredibly toxic.

So the trend in physical properties are that as we go down the group, their densities increase, and their melting and boiling points increase very similar to Group 1 metals.

And remember that density is a measurement of mass per unit volume.

So that's how tightly-packed a substance's particles are in a particular space.

So let's look at some physical properties then of the Group 7 elements.

One of the most intriguing parts about Group 7 is that they are all in different states at room temperature.

So fluorine and chlorine are both gases at room temperature.

Bromine is a volatile red-brown liquid.

So that means it will turn into a gas, it will vaporise into a gas very easily.

And you can see in that kind of image, we've got a kind of a reddish-brown gas kind of in that container, but a nice liquid at the bottom.

And then iodine at the bottom of the group is a solid, it's a purple-black solid, and it will go through sublimation, so we will skip the liquid phase at room temperature, and it will become a gas which is a very purple, it's very nice coloured gas.

So we go from yellow to green to reddish-brown to purple-black, and we go from gas to liquid to solid.

Astatine and tennessine are both very radioactive elements.

They are toxic, because all of the Group 7 elements are toxic, but we can also see we have this radioactivity sign as well.

Astatine is one of the rarest elements on Earth that's naturally occurring.

It's used to treat cancers, and it has a very high melting and boiling points.

Tennessine is synthesised, is a synthetic element, and decays very quickly.

So it has to last for at least one second to be recognised as an element, but it decays pretty quickly after that.

Its melting and boiling points are predicted, they are predicted to be higher than the rest of the group, and very little is known about tennessine, other than that we know that it can exist for a short period of time.

I'd like you to use the trend then that we saw of the Group 7 properties to predict the colour and state of astatine at room temperature.

So pause as you have a think, and then press Play when you think you know the answer.

Well, the answer is D, a black solid.

That makes sense, hopefully, because as we saw, as we go down the group, they go from gas to liquid to solid, so it can't be A or B, 'cause they're both liquids and gases.

And we also saw the colours getting darker.

So we wouldn't expect the colour of the solids to be purple, because it was already kind of a greyish kind of black colour for astatine, sorry for iodine, so we would expect then astatine to be an even darker colour of black.

So black solid makes the most sense.

True or false? Group 7 elements do not demonstrate a trend in properties throughout the group.

Hopefully, we know that this answer is false, and I'd like you to read through these two justifications as to why that might be false, and pick the one that makes the most sense.

Press Pause as you do that, and press Play when you're ready to continue.

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

We know that there are trends in properties.

The one above is just an incorrect trend, so the elements become more dense down the group.

So a task for you now.

There are two questions, two tasks to do.

I'd like you to explain why halogen are called halogen, and what does that name reflect about their chemical properties.

And then I'd like you to describe how the colour and physical state of the halogens changes from the top to the bottom of the group.

And I'd like you to provide examples for each of the halogens mentioned.

So that's fluorine, chlorine, bromine, and iodine.

Pause as you do that, and press Play when you're ready to see the answers.

Well, the halogen phrase, the name means salt maker.

That means they readily form salts with metals.

That's a chemical property, 'cause we're talking about a chemical reaction.

Fluorine is a pale yellow gas, whereas chlorine is a pale green gas, bromine is a red-brown liquid, and iodine is a purple-black solid at room temperature.

The melting and boiling points increase down the group, which is why we see this change in state at room temperature, because more energy is required to overcome forces of attraction between those molecules as we go down the group.

So more energy means higher melting and boiling points.

So the Group 7 then, the halogens.

And we've covered some information on their physical properties, and a little bit on their chemical properties.

We're gonna talk now about some more reactions of the halogen, so we're gonna talk more about their chemical properties.

So we talked about salts, we talked about table salt a little bit earlier.

In chemistry, when we refer to a salt, we're talking about a substance that forms when a metal reacts with a non-metal.

These reactions produce normally solid substances, and sometimes they're soluble in water.

Not always, but most of the time.

The ones that we are gonna look at in kind of school, they normally are soluble, but not all of them are.

Salts are formed generally when acids react with bases through a neutralisation reaction, where salt and water is formed.

And we know that halogen can form salts when they react with metals, because halogen are non-metals.

True or false? Table salt, sodium chloride, is the only salt.

Well, that is false.

I'd like you to read through these two statements.

Pause as you do so, and press Play when you know which one justifies why it's false.

Well, the answer is B.

Sodium chloride is just an example of a salt.

Compounds that contain halogen atoms are not the only compounds that could be classed as salts.

So Group 7 elements are quite reactive, and they're very toxic, so their toxicity is linked to their reactivity.

So examples of useful compounds that can be made with Group 7 elements are kind of fluoride, so sodium fluoride, I don't know whether that's the one that's used in toothpaste, but fluoride salts are used in toothpaste.

Chlorine, not as a compound necessarily, but as a gas is added to sterilise drinking water.

But chlorine is added in compound forms as chloride into swimming pools to sterilise.

And iodine, again, just as iodine as an element is used to treat wounds because of its toxicity.

But the concentrations that we use is not toxic to humans, but it is toxic to microorganisms which we're trying to sterilise and kill.

When halogens react with the metals to form compounds, they form what is known as a halide salt.

So when metals and halogen react, they form metal halide.

Some examples shown here that when sodium reacts with chlorine, we form sodium chloride.

And when magnesium reacts with iodine, we form magnesium iodide.

Which of the following then are considered to be halide salts? Thinking about what we've just discussed.

Pause as you have a read through, and then press Play when you are ready for the answers.

Well, the answers are A and C.

They both include halogen atoms in their structures.

Whereas B, chlorine, is not a salt, that's just an element, chlorine.

And D doesn't involve any halogen atoms at all.

Okay, one of the most interesting properties that we can observe with the halogens is known as their displacement reactions.

So displacement reactions involve a reaction where a more reactive element will replace another element within a compound.

So we can see here an example where A is being reacted with a compound of B and C, but A is more reactive than B, so it kicks B out of the compound.

So A has now formed a chemical bond with C instead.

The halogens can do this to each other.

So the more reactive halogens will replace the less reactive halogens in salts.

True or false? Displacement reactions involve a less reactive element replacing another element in a compound.

Well, that statement is false.

And here are two justifications as to why only one is correct.

Pause as you have a read through them, and press Play when you would like to know the answer.

Well, the answer is B.

A is kind of correct, it does involve elemental swapping, but it involves specifically a more reactive element replacing another one from a compound.

You are gonna have a go at doing a practical, or you're gonna watch a demo now, of the the displacement reactions between the chlorine, bromine, and iodine solutions, and their salts.

So you can see here we've got a spotting tile set up, and you're gonna put a little bit of each of the aqueous halogen, the chlorine water, the bromine water, or the iodine water into the rows, and then you're gonna add a little bit of the salts in the order shown on the screen.

You're then gonna record your results in this table.

And once you've collected your results, you can then order the halogens based on most reactive to least reactive using your results to explain your decision.

You can then describe how the reactivity changes through Group 7.

And then you're going to write a word equation for all of the displacement reactions that occurred.

Some of these are not going to cause a reaction to occur, because we're gonna be adding less reactive elements to compounds.

So only for the ones that cause a reaction to happen.

Pause the video now once you do that.

That's gonna take you a bit of time.

And once you are ready to then move on and see the results, press Play.

So we should have seen when we added sodium chloride to chlorine, bromine, and iodine solutions that no change happened.

When we added sodium bromide to chlorine, we saw the colour change to a slightly darker colour, but no change to bromine and iodine.

And the colour change should have turned darker for sodium iodide being added to chlorine and bromine, but no change when it was added to iodine.

Now that makes sense.

If we're adding chlorine to sodium chloride, or bromine to sodium bromide, or iodine to sodium iodide, we wouldn't expect to see any change because any reaction that might occur would be swapping chlorine with chlorine, bromine with bromine, or iodine with iodine.

So we can draw almost like a straight line straight through the middle there.

So our conclusions show that chlorine must be the most reactive, because it reacted with two of the three substances.

Bromine is the second most reactive, 'cause it only reacted with one of the substances.

And iodine is the least reactive, because it reacted with none of them.

An incorrect results would be to assume that sodium iodide, therefore iodine was the most reactive, because when that was added to two different substances, a chemical reaction occurred twice.

However, what's actually happening is the iodine is being removed from that compound.

So sodium iodide is releasing iodine, which is why the colour turns darker, 'cause iodine is a slightly darker colour, and the chlorine or the bromine have kind of made a new bond with the sodium.

So it's become sodium chloride, or sodium bromide, because chlorine and bromine are more reactive than iodine, and chlorine is more reactive than bromine.

That means we can write a general statement that down the group, the Group 7 elements become less reactive.

And this is shown by the lower elements not being able to displace the higher-up elements.

And so there are only three displacement reactions that occurred: sodium bromide and chlorine to make sodium chloride and bromine, sodium iodide and chlorine to make sodium chloride and iodine, and sodium iodide and bromine to make sodium bromide and iodine.

That's a nice little practical.

Well done for having a go at that.

So in summary then the elements in Group 7 are all non-metals that have coloured vapours, but most of which are toxic.

The state of the elements at room temperature changes from gas to solid down Group 7.

The reactivity decreases down in Group 7.

And the halogen react with Group 1 and 2 metals to form metal halides, which are generally soluble in water.

I've really enjoyed going through this lesson with you, and I look forward to seeing you again soon.

Bye-Bye.