A Level Chemistry: Group 7

• Why does the boiling point increase down the group?

  As you go down the group, the molecules are larger with a higher Mr and more electrons so have stronger van der Waals forces between molecules
• Why is the ionic radius bigger than the atomic radius?

  The ion has the same number of protons but more electrons than the atom so the attraction is weaker
• Why does electronegativity decrease down the group?

  As you go down the group, there are more shells with more shielding, so the attraction between the nucleus and covalently bonded electrons decreases
• Why does first ionisation energy decrease down the group?

  As you go down the group, there are more shells with more shielding so the attraction between the nucleus and outer electrons is weaker
• Appearance of Cl₂ at room temperature

  Green gas
• Appearance of Br₂ at room temperature


  Red-brown liquid
• Appearance of I₂ at room temperature

  Black solid
• Colour of Cl₂ in solution

  Pale green
• Colour of Br₂ in solution

  Orange
• Colour of I₂ in solution

  Brown
• Why does the solubility in water decrease down the group?

  The number of electrons increase so stronger van der Waals forces between molecules which must be broken to dissolve it
• Observations and equation for the reaction between Cl₂ (aq) and KBr(aq)

  Solution turns orange as Br₂ is formedCl₂ + 2KBr → 2KCl + Br₂
• Observations and equation for the reaction between Cl₂ (aq) and KI(aq)

  Solution turns brown as I₂ is formed Cl₂ + 2KI → 2KCl + I₂
• Observations and equation for the reaction between I₂ (aq) and KBr(aq)

  No reaction (stays brown)
• Observations and equation for the reaction between I₂ (aq) and KCl(aq)

  No reaction (stays brown)
• Observations and equation for the reaction between Br₂ (aq) and KCl (aq)

  No reaction (stays orange)
• Observations and equation for the reaction between Br₂ (aq) and KI (aq)

  Solution turns brown (I₂ is formed)Br₂ + 2KI → 2KBr + I₂
• Define oxidising agent

  A substance that accepts electrons
• Why does a halogens ability to act as an oxidising agent decrease down the group?

  As you go down the group, there are more shells with more shielding so the nuclear attraction is weaker
• Define disproportionation

  A redox reaction in which the same element is simultaneously oxidised and reduced
• What happens when chlorine reacts with cold water?

  Cl₂ + H₂O ⇌ HCl + HClO
• What is the test for HCl?

  Turns blue litmus paper red
• What is the test for chloric (I) acid?

  Turns blue litmus paper red then white
• What happens when chlorine reacts with hot water or in sunlight?

  The chloric (I) acid decomposes 2 Cl₂ + 2H₂O → 4HCl + O₂
• What is the benefit of using chlorine to treat water?

  Kills bacteria
• What is the risk when using chlorine to treat water?

  Toxic in large quantities
• Write and equation for the reaction of chlorine with dilute sodium hydroxide and state observations

  Cl₂ + 2NaOH →NaCl + NaClO + H₂OThe green colour fades and smell is less pungent
• What is the test for halide ions?

  Add dilute nitric acid (to remove interfering ions eg CO₃²⁻), followed by silver nitrate solution
• What is the colour of silver chloride?

  White
• What is the colour of silver bromide?

  Cream
• What is the colour of silver iodide?


  Yellow
• Solubility of silver chloride in aqueous ammonia

  Soluble in both dilute and concentrated ammonia
• Solubility of silver (I) iodide in aqueous ammonia

  Insoluble in both dilute and concentrated ammonia
• Solubility of silver (I) bromide in aqueous ammonia

  Insoluble in dilute ammonia, soluble in concentrated ammonia
• Characteristic of SO₂

  Choking colourless acidic gas
• Appearance of S


  Yellow solid
• Appearance of H₂S

  Colourless gas, bad egg smell
• What happens in an acid base reaction between NaCl and H₂SO₄?

  Steamy white fumes of HCl are formed
• What happens in an acid base reaction between NaBr and H₂SO₄?

  Steamy white fumes of HBr are formed
• What happens in an acid base reaction between NaI and H₂SO₄?

  Steamy white fumes of HI are formed