Group 7 Flashcards
What happens to atomic radius as you go down the group?
It increases due to increased shielding
What is the trend in boiling point down group 7? Why?
Increases
Because: size of atom increases as more occupied electron shells → stronger van der Waals forces of attraction between
molecules, take more energy to break
What is the trend in
electronegativity down
group 7? Why?
Decreases
Because: more occupied electron shells → greater atomic radius and outer electrons are further from the positive charge of the nucleus → lower force of attraction between the nucleus and electron pair in the covalent bond
What do you use to test for halide ions?
Acidified AgNO3
Why do you add HNO3? Why not HCl?
To remove CO₃2-
Adding HCl would add Cl- ions, giving a false positive result
Result and equation for Cl- test?
white ppt
Ag+ + Cl- → AgCl (s)
What is the result and
equation for the test for Br-?
Cream ppt
Ag+ + Br- → AgBr (s)
What is the result and
equation for the test for I-?
Yellow ppt
Ag+ + I- → AgI (s)
What happens to silver chloride when dilute/conc NH3 is added?
AgCl- dissolves in both dilute and conc
AgCl (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Cl
What happens to silver bromide when dilute/conc NH3 is added?
AgBr- only dissolves in conc
AgBr (s) + 2NH₃ (aq) → [Ag(NH₃)₂]+ (aq) + Br
What happens to silver iodide when dilute/conc NH3 is added?
AgI- will not dissolve in either
What is the trend in
oxidising ability down the group? Why?
Decreases down group
Because: Cl has fewest occupied electron shells, greatest force of attraction between outer electrons and nucleus, easiest to gain electrons and be reduced → best oxidising agent
Write the equation for Cl2 oxidising 2I-
Cl₂ + 2I- → 2Cl- + I₂
What is the trend in
reducing ability of the
halides down the group?Why?
Increases down group
Because: I- has the most occupied electron shells, so outer electrons are further from the nucleus, weakest force of attraction between outer electrons and positive charge of
nucleus → easiest to be oxidised and lose electrons → best
reducing agent
Why is chlorine added to drinking water? Why is it safe?
Forms ClO- ions which oxidise (kill) all microorganisms in water. Once it has done its job, little remains, and the health benefits outweigh the risks of use.
What are potential risks of adding chlorine to drinking
water?
Chlorine is toxic and damages the respiratory system in large enough quantities; can form
carcinogens with hydrocarbons
Why is ozone not used to purify water in the UK?
More expensive than chlorine, evaporates from water more quickly
What is the equation for the reaction of Cl2 with water?
Cl₂ (g) + H₂O (l) → HClO (aq) + HCl (aq)
What type of reaction is the reaction of chlorine with water?
Disproportionation; chlorine is both oxidised and reduced
What are the two forms of the chlorate ion?
ClO- is chlorate (I)
ClO₃- is chlorate (V)
What is the equation for making bleach?
Cl₂ + 2NaOH → NaCl + NaClO + H₂O
NaClO is bleach
Give the equation for the reaction of chlorine and water in the presence of sunlight
2Cl₂ + 2H₂O → 4HCl + O₂ (g)
What is desalination?
Converts saltwater into clean, potable water
Either by reverse osmosis (using a smart membrane) or by vacuum distillation at low pressure and low temperature
What are the advantages of desalination?
safe, clean, drinkable water produced in places
where it might not otherwise be available
What are the disadvantages of
desalination?
uses lots of energy, reverse osmosis has
low efficiency, can disturb marine ecosystems
