Group 7: the Halogens

• What type of elements are the group 7 elements?

  Highly reactive non-metals
• Why do group 7 elements need to gain an electron?

  To form a 1- ion and achieve a full outer shell of electrons
• What happens to the atomic radius of group 7 elements as you move down the group?

  The atomic radius increases
• Why does reactivity decrease down the group 7 elements?

  Because the positive attraction of the nucleus is weakened by additional shielding
• What is the trend in first ionisation energy for group 7 elements?

  It decreases down the group
• What causes the boiling point of group 7 elements to increase down the group?

  The strength of van der Waals forces increases as the Ar of the molecule increases
• What is the state of fluorine at room temperature?

  Gas
• What is the state of iodine at room temperature?

  Solid
• How do halogens act as oxidising agents?

  They accept electrons from the species being oxidised and are reduced
• What happens to the oxidising power of halogens down the group?

  It decreases
• What are halide ions?

  Negative ions of halogens
• How do halide ions act as reducing agents?

  They donate electrons to the species being reduced and are themselves oxidised
• What trend is observed in the reducing power of halide ions down the group?

  It increases
• What are the redox reactions with H2SO4 that need to be known for halides?

  1. Fluoride and Chloride ions
  2. Bromide ions
  3. Iodide ions
• What is the purpose of acidified silver nitrate in testing for halide ions?

  It reacts to form different coloured precipitates depending on the ion present
• What precipitate is formed when chloride ions react with acidified silver nitrate?

  White precipitate (AgCl)
• What precipitate is formed when bromide ions react with acidified silver nitrate?

  Cream precipitate (AgBr)
• What precipitate is formed when iodide ions react with acidified silver nitrate?

  Yellow precipitate (AgI)
• What happens to the precipitate formed from chloride ions when dilute ammonia is added?

  The precipitate dissolves
• What happens to the precipitate formed from bromide ions when dilute ammonia is added?

  No change occurs
• What happens to the precipitate formed from iodide ions when dilute ammonia is added?

  No change occurs
• What happens to the precipitate formed from chloride ions when concentrated ammonia is added?

  The precipitate dissolves
• What happens to the precipitate formed from bromide ions when concentrated ammonia is added?

  The precipitate dissolves
• What happens to the precipitate formed from iodide ions when concentrated ammonia is added?

  No change occurs
• What do chlorine and cold water produce?

  Chlorate(I) ions (ClO-) and chloride ions
• What type of reaction occurs when chlorine reacts with cold water?

  Disproportionation reaction
• What happens to the oxidation state of chlorine in the disproportionation reaction?

  It goes from zero to both +1 and -1
• What does chlorine produce when it decomposes water in the presence of UV light?

  Oxygen and hydrochloric acid

  
• What is the role of chlorine in water treatment processes?

  To kill bacteria
• What is produced when chlorine is mixed with cold, aqueous sodium hydroxide?

  Sodium hypochlorite

  
• What is the test for sulfate ions (SO4^2-)?

  Using BaCl2 which reacts to form a white precipitate
• How can hydroxide ions (OH-) be identified?

  Using red litmus, which turns blue, or universal indicator, which turns blue-purple
• What happens when an acid is added to carbonate ions (CO3^2-)?

  Effervescence occurs and CO2 gas is given off
• How can carbon dioxide be confirmed after reacting with carbonate ions?

  By bubbling it through limewater, which will turn cloudy
• What are the flame test colors for Group 2 cations?

  • Calcium (Ca²⁺): Brick red
  • Strontium (Sr²⁺): Red
  • Barium (Ba²⁺): Pale green
• How can ammonium ions (NH4⁺) be tested for?

  By holding red litmus over the substance, which will turn blue if ammonium ions are present
• What is another method to test for ammonium ions?

  By adding NaOH to produce ammonia gas faster