Group 7 - Halogens Flashcards
What happens to the boiling and melting point of the halogens as you go down the group? And why?
They increase, due to the increasing strength of the van Der vaals forces as the size and relative mass of the atoms increase.
What word is used to describe the negative ion (X-) of group 7
Halide
What word is used to describe the atom or molecule of group 7?
Halogen
What happens to reactivity down group 7, and why does this happen?
Halogens get less reactive down the group. The atoms react by gaining an electron in their outer shell. As you go down the group, atoms become larger so the outer electrons are further from the nucleus. The outer electrons are also shielded more from the attraction of the positive nucleus because there are more inner electrons. This makes it harder for larger atoms to attract the electron needed to form an ion, so larger atoms are less reactive.
What is the oxidisation number of a halide ion?
-1
What is the oxidisation number of a halogen?
0
What happens to a halogen (in terms of redox) when it reacts?
It acts as an oxidising agent. It oxidises another substance and gains an electron, therefore it is reduced.
What is a displacement reaction?
Halogens displace less reactive halide ions from solution.
Give an example of a displacement reaction.
If you mix bromine water (halogen) with sodium iodide (halide solution) , the bromine will displace the iodide to form sodium bromide with iodine . The bromine oxidises the iodide.
How can you see if a displacement reaction has taken place? And how can this be clearer?
There would be colour changes. Iodine water is brown, and bromine water is orange. However by adding an organic solvent such as hexane a coloured layer would appear, a violet/pink colour would show the presence or iodine and an orange/red solution would show the presence of bromine. A very pale yellow/green shows the presence of chlorine.
What test can you use to test for halides, and how can this test be confirmed.
Add dilute nitric acid to a solution to remove ions that might interfere with the test. Then add silver nitrate solution. A precipitate is formed. The colour indicates the halide. If it is white, it is silver chloride. If it is cream, it is silver bromide. If it is yellow, it is silver iodide. This can be tested again by adding ammonia solution. Silver chloride will dissolve in dilute NH3. Silver bromide will dissolve in concentrated NH3. Silver iodide is insoluble.
What do you see when potassium iodide is added to bromine water?
The bromine would displace the iodide ions to create potassium bromide and iodine.
Write an ionic equation for the reactive n between iodine solution and sodium astatine (NaAt)
I2 + 2At- ➡️ 2I- + At2
What are the main properties of the first four halogens?
Fluorine, F2, pale yellow, gas
Chlorine, Cl2, green, gas
Bromine, Br2, red-brown, liquid
Iodine, I2, grey, solid
