Group 7 Flashcards
What is the trend in boiling points for the halogens?
Boiling points increase down the group due to the increasing strength of the van der Waals forces between the molecules.
What is the trend in electronegativity for the halogens?
Decreases down the group:
-Because as atoms get larger, the bonding pair of electrons in the covalent bond is further away and more shielded from the positive nucleus.
What is the trend in reactivity for the halogens?
When group 7 elements react, they gain an electron.
They get less reactive as you go down the group because the atom gets larger and there is more shielding. Therefore, the incoming electron is less attracted to the nucleus.
What is the trend in oxidising ability for the halogens?
a more reactive halogen will displace a less reactive halide. Oxidising ability decreases down the group.
What is the equation for the reaction between chlorine and cold, dilute, aqueous NaOH? what is this type of reaction called?
What is the observation?
Cl2(g) + 2NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l)
- Disproportionation reaction
- Green gas to colourless solution
What is NaClO used for?
- Bleach
- Disinfectant (kills bacteria)
What is the equation for the reaction between chlorine and water (not in the presence of sunlight)?
What happens to the equilibrium of this reaction as HClO kills microorganisms? What does this mean for the amount of Cl2 left?
Cl2 (g) + H2O (l) ↔ HCl (aq) + HClO (aq)
the equilibrium shifts to the right, so very little Cl2 remains once the HClO has done its job.
What is the equation for the reaction between chlorine and water in the presence of sunlight?
Why does this happen?
Cl2(g) + H2O (l) ↔ 2HCl (aq) + 1/2 O2 (g)
UV radiation from the sun breaks down HClO into HCl and O2.
Why is the F-F bond weak?
F atoms are very small, so in a molecule of fluorine, the atoms are held so close together that the lone pairs of electrons in each atom repel each other, weakening the bond.
At room temperature, what do each of the halogens look like?
- Fluorine is a pale yellow gas
- Chlorine is a green gas
- Bromine is a red-brown liquid
- Iodine is a grey solid
What is the trend in atomic radius for the halogens?
As you go down the group, the atomic radius of the halogens increase, because each halogen will have one more electron shell compared to the one above it.
What is a displacement reaction?
A chemical reaction in which one atom or group of atoms replaces another in a compound.
Explain the trend in reducing ability of the halides.
Reducing ability increases as you go down the group. This is because as you go down the group, the ionic radii of the halides increase, so the outer electrons are further away and more shielded from the attraction of the nucleus. This means it’s easier for the outer electron to be removed.
What is the general equation for sodium halides reacting with concentrated sulfuric acid to give a hydrogen halide to begin with?
NaX + H2SO4 → HX + NaHSO4
What is the general equation for the reaction between a hydrogen halide and concentrated sulfuric acid, where the sulfuric acid is reduced further?
2HX + H2SO4 → SO2 + 2H2O + X2
What is the reaction between NaF or NaCl with concentrated H2SO4 and what are the observations?
Why is this not a redox reaction?
What type of reaction is this?
NaF (s) + H2SO4 (l) → HF (g) + NaHSO4 (s)
NaCl (s) + H2SO4 (l) → HCl (g) + NaHSO4 (s)
Misty fumes of HF/HCl produced as the gas comes into contact with moisture in the air.
It’s not a redox reaction because the oxidation states of both the sulfur and halide stay the same (+6 and -1)
It’s an acid-base reaction.
What are the reactions between NaBr and concentrated H2SO4 and what are the observations?
What type of reactions are these?
NaBr (s) + H2SO4 (l) → HBr (g) + NaHSO4 (s)
2HBr (g) + H2SO4 (l) → SO2 (g) + 2H2O (l) + Br2 (g)
- Misty fumes of HBr as gas comes into contact with moisture in the air.
- Brown bromine gas.
- Colourless, choking gas of SO2
-First reaction= acid-base
-Second = redox
Reactions are exothermic
What are the reactions between NaI and concentrated H2SO4 and what are the observations?
What type of reaction is each one?
NaI (s) + H2SO4 (l) → HI (g) + NaHSO4 (s)
acid-base
2HI (g) + H2SO4 (l) → SO2 (g) + 2H2O (l) + I2 (g)
redox
6HI (g) + SO2 (g) → H2S (g) + 3I2 (s) + 2H2O (l)
redox
- Misty fumes of HI
- Rotten egg smell of H2S
- Colourless SO2
- Solid grey iodine (and maybe purple iodine vapour because the reaction is exothermic)
What can the silver nitrate test be used for?
To identify and distinguish between halide ions.
Describe how you would carry out the silver nitrate test for halide ions. What is the positive result for each of the halide ions?
what is the general ionic equation for the reaction that occurs?
- Add dilute nitric acid to the sample in a test tube, which will get rid of ions which may interfere with the test by producing a precipitate (e.g. carbonate ions, sulfite ions)
- Add a few drops of silver nitrate solution (AgNO3)
White precipitate= chloride ions
Cream precipitate= bromide ions
Yellow precipitate= iodide ions
Ag+ (aq) + X- (aq) → AgX (s), where X= Cl, Br or I
When carrying out the silver nitrate test, why can’t you acidify the silver nitrate with hydrochloric acid?
Because the HCl contains chloride ions, so the nitrate ions will react with the chloride ions and give a white precipitate.
Why does fluoride not produce a precipitate when acidified silver nitrate solution is added?
AgF is soluble in water.
What happens to AgCl, AgBr and AgI when dilute and concentrated ammonia is added?
AgCl dissolves in dilute ammonia
AgBr dissolves in concentrated ammonia
AgI is insoluble in concentrated ammonia
Which silver halide precipitate is the most soluble?
AgCl
