How do you teach about the halogens?
I am in the middle of teaching about them and thought it was worth telling you how I introduce the topic. I do like this topic as it provides lots of opportunities to link together parts of the course.
Firstly, I will start with some theory, things such as the fact that the halogens are diatomic and are the only group whose members exist as solids, liquids and gases at room temperature.
This then leads into a discussion about the trend in melting and boiling point and the reasons for it (this links to topic 4 / 14).
We will then talk about reactivity—which is the most reactive halogen (and why, links to trends in the atomic radius and electronegativity)
I then like to show a few demos of the halogens.
[DISCLAIMER: WITH ANY LAB WORK OR DEMOS IT IS THE RESPONSIBILITY OF THE TEACHER TO THOROUGHLY TRY OUT BEFOREHAND AND RISK ASSESS THESE IDEAS].
All these demos take place in the fume cupboard due to the toxic nature of the halogens.
I start off with the least reactive, iodine, and will sublime a small amount of this in a fume cupboard. It is also good to show the students what solid iodine looks like—it has a lovely shiny grey colour to it.
I will then demo the reaction of bromine with iron wool. The bromine is in a gas jar. The iron wool heated and plunged into the gas jar…not much actually happens, showing (much to the disappointment of the students) that bromine is not very reactive.
I then move onto chlorine. This will react very readily and exothermically with iron wool producing lots of brown fumes of iron (iii) chloride—it is quite spectacular.
I will then finish with a video on fluorine, put together by our friends in the University of Nottingham in the UK:
This shows clearly how reactive fluorine is by showing its reaction with cold iron wool.
I have also shown the students how to prepare chlorine through the reaction of concentrated hydrochloric acid with solid potassium (vii) manganate—this is a great reaction to demo but please do try this in advance and make sure you use a fume cupboard:
Once the chlorine is made the usual tests for it (such as testing for it with blue litmus paper) can be shown.
How do you teach the halogens? As ever, I would love to hear your ideas so please feel free to post them below.