properties halogens

• Characteristic properties of halogens

  • Form diatomic molecules in free elemental state to complete their octets by sharing single unpaired p electrons
  • React by gaining an additional electron to form halide ions or sharing single unpaired p electrons to form single covalent bonds
• Halogens


  • High electronegativity values
  • High tendency to attract an additional electron to achieve stable octet electronic configuration
  • Highest among elements in the same period
• Halogens


  • Negative values of electron affinity
  • High tendency to attract an additional electron to form respective halide ions
• Melting point and boiling point


  Increase progressively from fluorine to astatine due to increasing strength of van der Waals' forces holding halogen molecules together
• Electronegativity


  Decreases going down the group due to increasing atomic size and number of electron shells, creating greater shielding effect
• Electron affinity


  Increases from fluorine to chlorine, then decreases from chlorine to astatine due to increasing atomic size and number of electron shells, decreasing effective nuclear charge
• Fluorine has abnormally low electron affinity due to very small atomic size, requiring energy to overcome repulsion between additional electron and electrons in shell
• Halogens are strong oxidizing agents due to being one electron short of octet, having high electronegativity and highly negative electron affinity
• Reactions of halogens with sodium

  1. Fluorine reacts explosively

  2. Chlorine reacts violently

  3. Bromine and iodine burn steadily in vapours
• Disproportionation of chlorine in water and alkalis

  Cl2 is simultaneously oxidized and reduced to form NaCl and NaOCl
• Relative oxidizing power of halogens

  F2 > Cl2 > Br2 > I2

  
• Reactions of halide ions with halogens

  1. F2 displaces all other halogens

  2. Cl2 displaces Br2 and I2

  3. Br2 displaces I2 only
• Reactions of halide ions with halogens

  • Cl2 with Br- and I-
  • Br2 with I-
• Bromine and iodine dissolve more readily in organic solvents than water
• Chlorides, bromides and iodides have similar solubilities in water, but fluorides have anomalous properties
• Silver chloride, silver bromide and silver iodide are insoluble in water, but silver fluoride is soluble
• Reactions of aqueous halide ions with silver nitrate

  Form precipitates of silver halides (except fluoride)
• Formation of silver halides

  • Silver chloride
  • Silver bromide
  • Silver iodide
• Action of acidified silver nitrate on halides

  • Chloride: white precipitate of AgCl, solution turns grey, precipitate dissolves in ammonia
  • Bromide: pale yellow precipitate of AgBr, solution turns yellowish grey, precipitate slightly dissolves in ammonia
  • Iodide: yellow precipitate of AgI, solution remains yellow, precipitate does not dissolve in ammonia