group 7

• What are the 5 halogens?

  Fluorine, Chlorine, Bromine, Iodine & Astatine
• Why isn't astatine studied?

  Because it's very radioactive and can't exist for more than a few seconds before decaying.
• What oxidation state are the G7 elements usually found in?

  -1, found as X-1 ions (known as halide ions)
• Appearance of G7 elements: Fluorine

  Very pale yellow gas, highly reactive
• Appearance of G7 elements: Chlorine

  Pale green gas, poisonous in high concentrations
• Appearance of G7 elements: Bromine

  Red liquid, gives off dense brown or orange poisonous fumes
• Appearance of G7 elements: Iodine

  Shiny grey solid that sublimes to a purple gas
• Appearance of G7 elements: Astatine

  Black solid, is radioactive
• Trends of G7: Boiling point as you go down the group

  Increases

  -Number of VDW forces increase between molecules as they're larger

  -More energy is needed to break the bonds
• Trends of G7: Electronegativity

  Decreases

  -Atomic radius increases

  -Shielding increases

  -Less attraction between the outer electrons and the protons in the nucleus
• Are the halogens oxidising or reducing agents?

  Oxidising

  -They can accept electrons and are reduced

  F2(g) + 2e- --> 2F-(aq)

  Cl2(g) + 2e- --> 2Cl-(aq)

  Br2(l) + 2e- --> 2Br-(aq)

  I2(aq) + 2e- --> 2I-(aq)
• Trends of G7: Oxidising power

  Decrease

  -Atoms become larger

  -Shielding increases

  -Outer e-'s are less attracted to the nucleus
• Are halides oxidising or reducing agents?

  Reducing

  -They can lose electrons and can get oxidised

  2F-(aq) --> F2(g) + 2e-

  2Cl-(aq) --> Cl2(g) + 2e-

  2Br-(aq) --> Br2(l) + 2e-

  2I-(aq) --> I2(aq) + 2e-
• Trends of G7: Reducing power

  Increase

  -Atoms larger

  -Shielding increases

  -Electrons aren't attracted to the nucleus as strongly so they're more easily lost
• Trends of G7: Displacement reactions

  The more reactive halogens (strongest oxidising agents) will displace the more reactive halides (strongest reducing agents) from solutions of their ions
• What happens when: potassium chloride reacts with chlorine?

  No reaction
• What happens when: potassium chloride reacts with bromine?

  No reaction
• What happens when: potassium chloride reacts with iodine?

  No reaction
• What happens when: potassium bromide reacts with chlorine?

  A yellow solution is formed, Cl has displaced Br.

  Cl2(aq) + 2Br-(aq) --> 2Cl-(aq) + Br2(aq)
• What happens when: potassium bromide reacts with bromine?

  No reaction
• What happens when: potassium bromide reacts with iodine?

  No reaction
• What happens when: potassium iodide reacts with chlorine?

  A brown solution is formed, Cl has displaced I

  Cl2(aq) + 2I-(aq) --> 2Cl-(aq) + I2(aq)
• What happens when: potassium iodide reacts with bromine?

  A brown solution is formed, Br has displaced I

  Br2(aq) + 2I-(aq) --> 2Br-(aq) + I2(aq)
• What happens when: potassium iodide reacts with iodine?

  No reaction
• Sulfuric acid can act as..?

  An acid or an oxidising agent
• Sulfuric acid acting as an acid

  Can convert the sodium salts of the halides into the hydrogen halides

  H2SO4(l) + NaX(s) --> NaHSO4(s) + HX(g)
• Sulfuric acid acting as an oxidising agent

  Can be reduced to either SO2, S or H2S.

  H2SO4 + 2H+ + 2e- --> SO2 + 2H2O

  H2SO4 + 6H+ + 6e- --> S + 4H2O

  H2SO4 + 8H+ + 8e- --> H2S + 4H2O
• Sulfuric Acid Reactions: Fluorine & Chlorine

  No redox reactions, only acid-base reactions.

  NaF(s) + H2SO4(l) --> NaHSO4(s) + HF(g)

  White steamy fumes of HF are produced.

  NaCl(s) + H2SO4(l) --> NaHSO4(s) + HCl(g)

  White steamy fumes of HCl are produced.
• Sulfuric Acid Reactions: Bromide


  Br- ions are stronger reducing agents and after the acid-base reaction, they reduce the sulfur

  NaBr(s) + H2SO(l) --> NaHSO4(s) + HBr(g)

  White steamy fumes of HBr are produced

  2HBr(g) + H2SO4(l) --> Br2(g) + SO2(g) + 2H2O

  Red fumes of bromine are evolved and SO2 (a colourless acidic gas)
• Sulfuric Acid Reactions: Iodide

  The strongest reducing agent of the halides

  NaI(s) + H2SO4(l) -->NaHS(s) + HI(g)

  White steamy fumes of HI evolved

  2HI(g) + H2SO4(l) --> I2(s) + SO2(g) + 2H2O(l)

  Black solid and purple fumes of iodine are produced, as well as SO2

  6HI(g) + H2SO4(l) --> 3I2(s) + S(s) + 4H2O

  A yellow solid of Sulfur

  8HI(g) + H2SO4(l) --> 4I2(s) + H2S(g) + 4H2O(l)

  Hydrogen Sulphide gas is produced (gas with a pungent egg smell)
• Silver Nitrate Reactions: Process

  Make a halide solution and acidify with dilute nitric acid. Add silver nitrate solution and treat any excess with dilute ammonia solution. If there is still a precipitate, treat with concentrated ammonia solution
• Silver Nitrate Reactions: Chloride

  White precipitate formed, soluble in both concentrations

  Dilute: AgCl(s) + 2NH3(aq) --> [Ag(NH3)2]+(aq) + Cl-(aq)
• Silver Nitrate Reactions: Bromide

  Cream precipitate formed, insoluble in dilute ammonia but soluble in conc. ammonia

  Conc.: AgBr(s) + 2NH3(aq) --> [Ag(NH3)2]+(aq) + Br-(aq)
• Silver Nitrate Reactions: Iodide

  Yellow precipitate formed, insoluble in both concentrations
• Why acidify with nitric acid?

  Reacts with any carbonates present to prevent formation of the precipitate Ag2CO3, which would mask the desired observation

  2HNO3 + Na2CO3 --> 2NaNO3 + H2O + CO2
• What is disproportionation?


  A reaction where an element oxidises and reduces simultaneously
• Disproportionation of: Chlorine with water

  CL2(aq) + H2O(l) --> HOCl(aq) + HCl(aq)
• Disproportionation of: Chlorine with water in sunlight

  2Cl2(aq) + 2H2O(l) --> 4H+ + 4Cl- + O2
• What will happen when U.I (Universal Indicator) is added to chlorine and water solution?

  It will turn red due to the acidity of both products, it will then turn colourless as the HClO bleaches the colour
• Uses of chlorine


  Water treatment to kill bacteria, it can treat drinking water and swimming pool water.