Topic 3.2 of the periodic table deals with periodic trends. In particular, under the applications and skills section, we are told to ‘discuss the similarities and differences in the properties of elements in the same group, with reference to the halogens (group 17).’

In this month’s blog, I thought I would share with you my way of teaching this particular aspect of the course.

It goes without saying that the halogens are toxic, poisonous and in general pretty nasty. You the teacher are responsible for ensuring that you thoroughly risk asses things before trying out any of these experiments yourself.

It’s always good to demo how chlorine is produced by using concentrated hydrochloric acid and potassium (VII) manganate:

Once you have made your chlorine, you are ready to use it.

Chlorine reacts readily with iron wool. A piece of iron wool can be heated in a Bunsen flame and then plunged into the chlorine:

If you are feeling daring, why not react some sodium with chlorine gas as well, although I would not taste the salt!

I always show that as you move down the halogen group, they get less reactive. To show this I will react bromine with iron wool. The bromine reacts but is not so dramatic as with the chlorine:

Because of this, students get the wrong message about bromine but If you do want a dramatic reaction, try bromine and potassium:

(But not as dramatic as chlorine and bromine!):


In terms of how it reacts, Iodine is a little tamer but should still be treated with respect. You can show your students what happens when it sublimes:

Or what happens when it reacts with iron wool (finishing off the trend in reactivity of the halogens and iron):

As with bromine, if you do want to show your students a vigorous reaction, show them the solid – solid reaction of iodine and aluminium:

A halogen that you will not demonstrate it fluorine (if you do, I will be very very impressed!). The website has a great clip on fluorine, showing the colour of it and some of the reactions of it, also including its reaction with iron wool (linking in with the trend covered above):

So that’s how I do it, now it’s over to you. As a teacher, how do you address this particular part of the course? I’d love to hear from you.