Module 3: Group 7 (The Halogens) Flashcards
What is the trend in boiling points down group 7 & why?
- Increases.
- Increasing strength of Van der Waals forces as atomic radius & relative mass of molecules increases.
- More energy is required to break the bonds.
- Observed in changes of physical state from fluorine (gas) to iodine (solid).
What is the trend in electronegativity down group 7 & why?
- Decreases.
- Atom radius & shielding increases.
- Less attraction between outer electrons & protons in the nucleus.
What are the four halogens?
- Fluorine
- Chlorine
- Bromine
- Iodine
What is the appearance of flourine?
- Very pale yellow gas.
- Highly reactive.
What is the appearance of chlorine?
- Pale green gas.
- Poisonous in high concentrations.
What is the appearance of bromine?
- Red-brown liquid.
- Produces dense brown or orange poisonous fumes.
What is the appearance of iodine?
- Shiny grey solid.
- Sublimes to a purple gas.
Are the halogens oxidising or reducing agents?
- Oxidising.
- They can accept electrons & be reduced.
- E.g. F2 (g) + 2e- –> 2F- (aq)
What is the trend in oxidising power down group 7 & why?
- Decreases.
- Atom radius & shielding increases.
- Outer electrons are less attracted to the nucleus.
What is the trend in reducing power down group 7 & why?
- Increases.
- Atomic radius & shielding increases.
- Electrons are less attracted to the nucleus so more readily lost.
What is the trend in displacement reactions down group 7?
- A halogen will displace a halide from solution if the halide is below it in the periodic table.
- E.g. chlorine can displace bromide ions, but chloride ions are displaced by flourine.
What happens when potassium chloride reacts with iodine?
No visible reaction.
What happens when potassium bromide reacts with chlorine?
- Orange solution is formed (Br2).
- Cl has displaced Br.
- Cl2 (aq) + 2Br- (aq) –> 2Cl- (aq) + Br2 (aq)
What happens when potassium bromide reacts with bromine?
No visible reaction.
What happens when potassium bromide reacts with iodine?
No visible reaction.
What happens when potassium iodide reacts with chlorine?
- Brown solution is formed (I2).
- Cl has displaced I.
- Cl2 (aq) + 2I- (aq) –> 2Cl- (aq) + I2 (aq).
What happens when potassium iodide reacts with bromine?
- A brown solution is formed (I2).
- Br has displaced I.
- Br2 (aq) + 2I- (aq) –> 2Br- (aq) + I2 (aq).
What happens when potassium iodide (KI) reacts with iodine?
No visible reaction.
What can H2SO4 act as?
An acid or an oxidising agent.
What occurs when H2SO4 is acting as an acid?
- Converts the sodium salts of the halides into hydrogen halides.
- E.g. H2SO4 (l) + NaX (s) –> NaHSO4 (s) + HX (g)
What occurs when H2SO4 is acting as an oxidising agent?
- Sulfuric acid can be reduced to SO2, S or H2S.
- E.g H2SO4 + 2H+ + 2e- –> SO2 + 2H2O
- E.g. H2SO4 + 6H+ + 6e- –> S + 4H2O
- E.g. H2SO4 + 8H+ + 8e- –> H2S + 4H2O
What is the equation for the reaction of H2SO4 with NaF?
NaF (s) + H2SO4 (l) –> NaHSO4 (s) + HF (g)
What is observed during the reaction of H2SO4 with NaF?
White, steamy fumes of HF.
What is the equation for the reaction of H2SO4 with NaCl?
NaCl (s) + H2SO4 (l) –> NaHSO4 (s) + HCl (g)
