Group 7

• Which elements are gases at room temperature?

  Fluorine and chlorine
• Which non-metal element is the only liquid at room temperature?

  Bromine
• Which elements are solids at room temperature?

  Iodine and astatine
• Appearance of fluorine at room temperature:

  Very pale yellow gas
• Appearance of chlorine at room temperature:

  Pale green gas
• Appearance of bromine at room temperature:

  Dark red liquid
• Appearance of iodine at room temperature:

  Shiny black solid (but readily sublimes to form a purple vapour).
• State the trend in boiling points down group 7:

  Increases
• Why do boiling points increase down group 7?

  Molecules get bigger. Stronger van der waals forces between molecules. Needs more energy to overcome.
• State the trend in electronegativity down group 7:

  Decreases
• Why does electronegativity decrease down group 7?

  Molecules get bigger. Bonding electrons become increasingly shielded from nucleus. Weaker EFA between electrons and nucleus.
• What is an oxidising agent?

  Electron acceptor
• State the trend of halogens as oxidising agents down group 7:

  Decreases
• Why does the oxidising strength of the halogens decrease down group 7?

  Atoms get larger. Outer energy level is increasingly shielded from nucleus. Harder for atom to gain outer electron.
• Observation when bromide ions react with chlorine:

  Colourless solution to orange solution.
• Observation when iodide ions react with chlorine:

  Colourless solution to brown solution.
• Observation when chloride ions react with bromine:

  No visible reaction
• Observation when iodide ions react with bromine:

  Colourless solution to brown solution
• Observation when chloride ions react with iodine,

  No visible reaction
• Observation when bromide ions react with iodine:

  No visible reaction
• What is a reducing agent?

  Electron donor
• State the trend in the ability of a halide ion to behave as a reducing agent:

  Increases
• Which halide is the strongest reducing agent?

  Iodide
• Why does the ability of a halide ion to behave as a reducing agent increase down group 7?

  Ions get bigger. Less attraction between outer electrons and nucleus. Easier to lose electrons.
• What are the stages of halide ions behaving as reducing agents?

  Displacement and redox
• What can be added to a halide ion to produce a hydrogen halide?

  Concentrated sulphuric acid (H2SO4)
• How does concentrated sulphuric acid help produce a hydrogen halide?

  Donates a hydrogen ion to the halide ion.
• Write the equation for the production of a hydrogen halide:

  $NaX(s)+$$H2SO4(aq)\ \rightarrow\ NaHSO4(aq)+$$HX(g)$
• What will be observed when any hydrogen halide is formed?

  Misty fumes
• Why does the reaction stop when HF and HCl are formed?

  Fluoride and chloride ions are not strong enough reducing agents to reduce sulphuric acid.
• Why are other products formed when NaBr or NaI react with concentrated sulphuric acid?

  Bromide and iodide ions can reduce sulphuric acid.
• What is formed when bromide ions reduce concentrated sulphuric acid?

  Sulphur dioxide gas
• How is sulphur dioxide gas identified?

  Choking gas
• How is bromine identified?

  Brown gas
• What do iodide ions reduce concentrated sulphuric acid to?

  Sulphur dioxide, then to sulphur, and finally to hydrogen sulphide gas.
• How is sulphur identified?

  Yellow solid
• How is hydrogen sulphide gas identified?

  Rotten egg smell
• What is the final product when iodide ions reduce concentrated sulphuric acid?

  Hydrogen sulphide gas
• How is iodine identified?

  Purple vapour
• What is used to test for the presence of halide ions?

  Silver nitrate solution (AgNO3)