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Halide Reactions

01Halide Reactions

Reducing power

This section covers the increase in reducing power of halide ions down Group 7 and explains the trend using ionic size and shielding.

Halide ions as reducing agents

A reducing agent donates electrons to another species and is itself oxidised. Halide ions can act as reducing agents by losing electrons to form halogen molecules.

2 XX−→XX2+2 eX−\ce{2X- -> X2 + 2e-}

The reducing power of the halide ions increases down Group 7:

FX−<ClX−<BrX−<IX−\ce{F- < Cl- < Br- < I-}

Explaining the trend

  • Halide ions become larger down the group.
  • The outer electrons become further from the nucleus.
  • Additional inner electron shells increase shielding.
  • The attraction between the nucleus and an outer electron therefore becomes weaker.
  • The ions lose electrons more readily, so their reducing power increases.
F−Cl−Br−I−ionic radius increasesshielding increaseselectron loss becomes easierreducing power increases

The increasing reducing ability is demonstrated by the reactions of solid halide salts with concentrated sulfuric acid.

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