Group 7 3.8.2 Flashcards
Fluorine at RTP?
Pale yellow gas
Chlorine at RTP?
Pale green gas
Bromine at RTP?
Brown-Orange liquid
Iodine at RTP?
Grey solid
What is the trend of the boiling point down the group?
The boiling point increases because the london forces get stronger due to a greater number of electrons thus needing more energy to overcome the intermolecular bonds.
Trend of electronegativity?
The electronegativity decreases down the group because the atom gets larger and has more sheiling and a larger atomic radius so there is a less attraction between the postive nucleus and the outer electrons
Trend of reactivity?
It decreases as you go down the group because there is more sheilding and less attraction between the nucleus and the outer shell so there is less attraction to gain an electron.
Are halogens less or more oxidising agent as you go down a group?
Halogens are less oxidising as we go down the group. (Because the ability to gain an electron decreases as we go down the group)
How do you test for chloride, bromide and iodide ions?
Add dilute nitric acid (HNO3) then silver nitrate solution (AgNO3). The colour of the precipiate will help identify the ion.
Chloride ion present
A white precipitate of silver chloride (soluble in dilute ammonia solution)
Bromide ion present
Cream precipitate forms. Silver bromide (soluble in concentrated ammonia solution)
Iodide ions present
Yellow precipitate forms. Silver iodide (insoluble in dilute and concentrated ammonia solution)-
Specific order for tests to avoid false positives
Carbonate then sulfate test then halide test.
Reaction of Chlorine with Water
Cl2(aq) + H2O–> HClO(aq) + HCl (aq)
Reaction of chlorine with cold, dilute aqueous NaOH
Cl2(aq) + 2NaOH(aq)–> NaClO/bleach (aq) + NaCl + H2O (l)
What happens in Halogen-halide displacement reactions?
If the halogen added is more reactive than the halide present, then the halogen will displace the halide from the solution, halide will now be in halogen form: causing a colour change.
Cl2 + 2Br- –> 2Cl- + Br2
Why are iodine and bromine shaken in a non-polar solvent?
They are similar in orange-brown colour when in water so you add cyclohexane to tell them apart.
Halogen solutions colour in cyclohexane
Cl2- pale green
Br2- Orange
I2- Violet (but brown/orange in water)
What are the results of the halogen displacement reactions?
- Chlorine reacts with both Br- (forms orange layer) and I- (forms purple layer)
- Bromine reacts with I- only (forms purple layer)
- Iodine doesn’t react at all =least reactive
