Group 7

• What are the elements in Group 7 called?

  Halogens
• What are some uses of halogens?

  Water purification and as bleaching agents
• Which halogen is used as a flame-retardant?

  Bromine
• What color trend is observed in Group 7 elements?

  Colors get darker going down the group
• What does volatility refer to?

  How easily a substance can evaporate
• What happens to the boiling points of Group 7 elements as you go down the group?

  Boiling points increase going down the group
• Which halogen is the most volatile?

  Fluorine
• What happens to the volatility of halogens as you go down the group?

  Volatility decreases going down the group

  
• What type of molecules are halogens?

  Diatomic molecules

  
• How are covalent bonds formed in halogens?

  By overlapping their orbitals
• What happens to bond strength as you go down Group 7?

  Bond strength decreases going down the group
• What is bond enthalpy?

  Energy needed to break one mole of covalent bonds
• Why does fluorine have a smaller bond enthalpy than chlorine and bromine?

  Significant repulsion between lone pairs

  
• What type of forces exist between diatomic halogen molecules?

  Weak van der Waals' forces

  
• How do instantaneous dipoles form in nonpolar molecules?

  Imbalance of electrons causes a dipole
• What happens to van der Waals' forces as you go down Group 7?

  They increase due to more electrons

  
• What is the trend of reducing power of halide ions down the group?

  Reducing power increases going down the group

  
• How do halogens act as oxidizing agents?

  By accepting an electron from metals
• What happens to the electronegativity of halogens as you go down the group?

  Electronegativity decreases going down the group

  
• What is the result of a more reactive halogen displacing a less reactive halogen?

  It can displace the less reactive halogen
• What is the ionic equation for chlorine displacing bromine?

  Cl (aq) + 2Br (aq) → 2Cl (aq) + Br (aq)
• How can halide ions be identified in a solution?

  By adding silver nitrate solution

  
• What is the purpose of nitric acid in the halide test?

  To prevent false positives from carbonate ions
• What precipitate forms when halide ions react with silver nitrate?

  Silver halide precipitate (AgX)

  
• What are the physical properties of Group 7 elements?

  • Distinct colors that get darker down the group
  • Increase in melting and boiling points down the group
  • Decrease in volatility down the group
  • Diatomic molecules with weak van der Waals' forces
• What are the chemical properties of halogens?

  • Act as oxidizing agents by accepting electrons
  • Reactivity decreases down the group
  • Displacement reactions with less reactive halogens
  • Halide ions act as reducing agents

  
• What is the process for testing halide ions?

  1. Dissolve in nitric acid
  2. Add silver nitrate solution dropwise
  3. Observe for precipitate formation

  
• What is the purpose of nitric acid in halide testing?

  To prevent false positives from carbonates
• How are halide ions identified in a solution?

  By adding silver nitrate solution dropwise

  
• What is the ionic equation for the reaction of silver ions with halide ions?

  Ag (aq) + X (aq) → AgX (s)
• What happens if halide ions are present in the solution?

  A precipitate of silver halide forms

  
• What color precipitate does silver chloride form?

  White precipitate
• What color precipitate does silver bromide form?

  Cream precipitate
• What color precipitate does silver iodide form?

  Yellow precipitate
• Why is ammonia used in halide testing?

  To differentiate between similar precipitates

  
• What does it indicate if a precipitate dissolves in dilute ammonia?

  The unknown halide is chloride
• What does it indicate if a precipitate dissolves in concentrated ammonia but not in dilute ammonia?

  The unknown halide is bromide

  
• What does it indicate if a precipitate does not dissolve in either dilute or concentrated ammonia?

  The unknown halide is iodide

  
• What happens to silver chloride and silver bromide in ammonia solution?

  They dissolve in ammonia solution
• What is produced when chloride ions react with concentrated sulfuric acid?

  Hydrogen chloride gas