Group 7

• What are the elements in Group 7 called?

  Halogens
• What are some uses of halogens?

  Water purification and bleaching agents
• How do the colors of halogens change down the group?

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

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

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

  Fluorine
• What type of molecules are halogens?

  Diatomic molecules
• How does atomic size affect bond strength in halogens?

  Bond strength decreases as atomic size increases
• What is bond enthalpy?

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

  Lone pairs cause significant repulsion in fluorine

  
• What type of forces exist between halogen molecules?

  Weak van der Waals' forces

  
• How do van der Waals' forces change down the group?

  They increase due to more electrons

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

  Volatility decreases going down the group

  
• What do halogens act as when they react with metals?

  Oxidising agents
• What happens to the oxidation number of metals when halogens react with them?

  It increases
• How does the oxidising power of halogens change down the group?

  It decreases going down the group
• What is the relationship between electronegativity and atomic size in halogens?

  Electronegativity decreases as atomic size increases

  
• What is a displacement reaction in halogens?

  A more reactive halogen displaces a less reactive one
• What happens to the reducing power of halide ions down the group?

  It increases going down the group

  
• Why do halide ions lose electrons more easily down the group?

  Outermost electrons are held less tightly
• What does the term 'halogen' mean?

  Salt-maker
• How can halide ions be identified in a solution?

  By adding silver nitrate solution dropwise

  
• Why is nitric acid added when testing for halides?

  To prevent false positives from carbonates
• What is the ionic equation for halide ion reaction with silver ions?

  Ag (aq) + X (aq) → AgX (s)
• What is the purpose of the state symbols in the ionic equation?

  To indicate the physical states of substances
• 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 Group 7 elements?

  • Act as oxidising agents
  • React with metals to form salts
  • Displacement reactions with other halide ions
  • Halide ions can act as reducing agents
• What is the process for testing halide ions?

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

  
• What is the meaning of the Greek word from which "halogen" is derived?

  Salt-maker
• What is the process for testing halide ions in a solution?

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

  
• Why is nitric acid added when testing for halide ions?

  To prevent false positives from carbonates
• What is the ionic equation for the reaction of silver ions with halide ions?

  Ag (aq) + X (aq) → AgX (s)
• 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

  
• How can ammonia be used to identify halide ions?

  • Dilute ammonia dissolves silver chloride
  • Concentrated ammonia dissolves silver bromide
  • No dissolution indicates silver iodide

  
• Which silver halide precipitate is insoluble in ammonia?

  Silver iodide
• What happens when halide ions react with concentrated sulfuric acid?

  • Produce toxic gases
  • Reactions should be done in fume cupboard

  
• What is the general reaction of halide ions with concentrated sulfuric acid?

  H$_2$SO$_4$ (l) + X (aq) → HX(g) + HSO$_4$ (aq)

  
• What gas is produced when concentrated sulfuric acid reacts with sodium chloride?

  Hydrogen chloride gas