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 that gives off dense brown/orange poisonous fumes
• What is the physical state and color of iodine (I2)?

  Shiny grey solid that sublimes to purple gas
• What is the trend in melting and boiling points of halogens down the group?

  • Melting and boiling points increase down the group
  • Larger molecules have more electrons
  • Larger van der Waals forces require more energy to break
• What is the trend in electronegativity of halogens down the group?

  • Electronegativity decreases down the group
  • Atomic radii increase due to more shells
  • Nucleus is less able to attract bonding electrons
• What is the relationship between oxidizing strength and halogens?

  • Stronger oxidizing agents displace weaker ones
  • Oxidizing strength decreases down the group
  • Chlorine displaces bromide and iodide ions
• What color solution indicates the presence of chlorine in a reaction?

  Very pale green solution (often colorless)
• What color solution indicates the presence of bromine in a reaction?

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

  Brown solution (sometimes black solid present)
• What are the half-equations for the displacement reactions of halide ions by halogens?

  1. \(2Br^-(aq) \rightarrow Br_2(aq) + 2e^-\)
  2. \(Cl_2(aq) + 2e^- \rightarrow 2Cl^-(aq)\)
• What is the test for halide ions using silver nitrate?

  • Acidify with nitric acid
  • Add silver nitrate dropwise
  • Fluorides: no precipitate
  • Chlorides: white precipitate
  • Bromides: cream precipitate
  • Iodides: pale yellow precipitate
• What is the reaction of chlorides with silver nitrate?

  Produces a white precipitate of AgCl(s)
• What is the reaction of bromides with silver nitrate?

  Produces a cream precipitate of AgBr(s)
• What is the reaction of iodides with silver nitrate?


  Produces a pale yellow precipitate of AgI(s)
• 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 reaction of halide salts with concentrated sulfuric acid?

  • F- and Cl-: acid-base reactions only
  • Br-: reduces sulfur from +6 to +4
  • I-: strongest reducing agent, reduces sulfur to +4, 0, and -2
• What is the observation when NaF reacts with concentrated sulfuric acid?

  White steamy fumes of HF are evolved
• What is the observation when NaCl reacts with concentrated sulfuric acid?

  White steamy fumes of HCl are evolved
• What is the observation when NaBr reacts with concentrated sulfuric acid?

  White steamy fumes of HBr and orange fumes of bromine are evolved
• What is the observation when NaI reacts with concentrated sulfuric acid?

  White steamy fumes of HI, black solid and purple fumes of iodine, and a colorless gas SO2 are evolved
• What is disproportionation in chemistry?

  • A reaction where an element is simultaneously oxidized and reduced
  • Example: Chlorine with water
• What is the reaction of chlorine with water?

  Cl2(g) + H2O(l) ⇌ HClO(aq) + HCl(aq)
• What happens when chlorine is bubbled through water in sunlight?

  Produces O2 and the greenish color of chlorine water fades
• What is the reaction of chlorine with cold dilute NaOH solution?

  Cl2(aq) + 2 NaOH(aq) → NaCl(aq) + NaClO(aq) + H2O(l)
• What are the names of chlorates and sulfates in IUPAC convention?

  • NaClO: sodium chlorate(I)
  • NaClO3: sodium chlorate(V)
  • K2SO4: potassium sulfate(VI)
  • K2SO3: potassium sulfate(IV)