Oxoacids and interhalogens

• Due to high electronegativity and small size, fluorine forms only one oxoacid, HOF known as fluoric (I) acid or hypofluorous acid
• The other halogens form several oxoacids
• Most of the halogen oxoacids cannot be isolated in pure state
• Halogen oxoacids are stable only in aqueous solutions or in the form of their salts
• Halogen oxoacids


  • Table 7.10
  • Fig. 7.8
• Interhalogen compounds


  Compounds formed when two different halogens react with each other
• General compositions of interhalogen compounds

  • XX'
  • XX'3
  • XX'5
  • XX'7
• Interhalogen compounds


  • X is halogen of larger size and X' of smaller size
  • X is more electropositive than X'
  • As the ratio between radii of X and X' increases, the number of atoms per molecule also increases
• Iodine (VII) fluoride should have maximum number of atoms as the ratio of radii between I and F should be maximum
• Iodine (VII) fluoride


  Formula: IF7
• Preparation of interhalogen compounds

  1. Direct combination

  2. Action of halogen on lower interhalogen compounds
• The product formed depends upon some specific conditions
• Interhalogen compounds


  • Covalent molecules
  • Diamagnetic in nature
  • Volatile solids or liquids at 298 K except ClF which is a gas
  • Their physical properties are intermediate between those of constituent halogens except that their m.p. and b.p. are a little higher than expected
• Interhalogen compounds


  More reactive than halogens (except fluorine)
• Reason for higher reactivity of interhalogens

  X–X' bond in interhalogens is weaker than X–X bond in halogens except F–F bond
• Hydrolysis of interhalogen compounds

  Gives halide ion derived from the smaller halogen and a hypohalite (when XX'), halite (when XX'3), halate (when XX'5) and perhalate (when XX'7) anion derived from the larger halogen
• Molecular structures of interhalogen compounds

  Explained on the basis of VSEPR theory
• Molecular shapes of interhalogen compounds

  • XX3 compounds have bent 'T' shape
  • XX5 compounds have square pyramidal shape
  • IF7 has pentagonal bipyramidal structure
• Molecular shape of BrF3

  1. Central atom Br has seven electrons in the valence shell

  2. Three of these form electron-pair bonds with three fluorine atoms leaving behind four electrons

  3. There are three bond pairs and two lone pairs

  4. According to VSEPR theory, these will occupy the corners of a trigonal bipyramid

  5. The two lone pairs will occupy the equatorial positions to minimise lone pair-lone pair and the bond pair-lone pair repulsions

  6. The axial fluorine atoms will be bent towards the equatorial fluorine in order to minimise the lone-pair-lone pair repulsions

  7. The shape would be that of a slightly bent 'T'