Group 7 / Halogens

• What is the physical state and color of fluorine (F2)?

  Very pale yellow gas
• What is the physical state and color of chlorine (Cl2)?

  Greenish, reactive gas
• What is the physical state and color of bromine (Br2)?

  Red liquid
• What is the physical state and color of iodine (I2)?

  Shiny grey solid
• What is the trend in melting and boiling points of halogens down the group?

  • Increase down the group
  • Larger molecules have more electrons
  • Larger van der Waals forces require more energy to break
• What is electronegativity?

  Relative tendency of an atom to attract electrons
• How does electronegativity change down the halogen group?

  • Decreases down the group
  • Atomic radii increases due to more shells
  • Nucleus less able to attract bonding electrons
• What happens to the reducing power of halides down the group?

  • Increases down the group
  • Larger ions donate electrons more easily
  • Outer electrons are less tightly held by the nucleus
• What will chlorine displace in a reaction with halide ions?

  Both bromide and iodide ions
• What color indicates the presence of chlorine in solution?

  Very pale green solution
• What color indicates the presence of bromine in solution?

  Yellow solution
• What color indicates the presence of iodine in solution?

  Brown solution
• What are the half-equations for the displacement reactions of halide ions?

  1. \(2Br^-(aq) \rightarrow Br_2(aq) + 2e^-\)
  2. \(Cl_2(aq) + 2e^- \rightarrow 2Cl^-(aq)\)
• What is the role of nitric acid in the silver nitrate test for halides?

  • Reacts with carbonates
  • Prevents formation of Ag2CO3 precipitate
• What precipitate do chlorides produce in the silver nitrate test?

  White precipitate
• What precipitate do bromides produce in the silver nitrate test?

  Cream precipitate
• What precipitate do iodides produce in the silver nitrate test?

  Pale yellow precipitate
• How can silver halide precipitates be differentiated?

  • Silver chloride dissolves in dilute ammonia
  • Silver bromide dissolves in concentrated ammonia
  • Silver iodide does not react with ammonia
• What is the overall reaction of bromide ions with concentrated sulfuric acid?

  1. Acid-base step: \(NaBr(s) + H_2SO_4(l) \rightarrow NaHSO_4(s) + HBr(g)\)
  2. Redox step: \(2H^+ + 2Br^- + H_2SO_4 \rightarrow Br_2(g) + SO_2(g) + 2H_2O(l)\)
• What is the overall reaction of iodide ions with concentrated sulfuric acid?

  1. Acid-base step: \(NaI(s) + H_2SO_4(l) \rightarrow NaHSO_4(s) + HI(g)\)
  2. Redox steps:

  • \(2H^+ + 2I^- + H_2SO_4 \rightarrow I_2(s) + SO_2(g) + 2H_2O(l)\)
  • \(6H^+ + 6I^- + H_2SO_4 \rightarrow 3I_2 + S(s) + 4H_2O(l)\)
  • \(8H^+ + 8I^- + H_2SO_4 \rightarrow 4I_2(s) + H_2S(g) + 4H_2O(l)\)
• What is disproportionation in chemistry?

  • Reaction where an element is both oxidized and reduced
  • Example: Chlorine with water
• What happens when chlorine reacts with water in sunlight?

  Produces oxygen gas and chloride ions
• What is the reaction of chlorine with cold dilute NaOH solution?

  • \(Cl_2(aq) + 2NaOH(aq) \rightarrow NaCl(aq) + NaClO(aq) + H_2O(l)\)
  • Used as bleach and disinfectant
• How are chlorates and sulfates named in IUPAC convention?

  • Named with oxidation numbers in Roman numerals
  • Example: NaClO is sodium chlorate(I)
• What is the oxidation state of sulfur in K2SO4?

  +6
• What is the oxidation state of sulfur in K2SO3?

  +4