Summary of Halogen Group (Group VIIA) Trends:
- The ionic compounds MX become progressively less ionic as the relative atomic mass of X increases, because of the decreasing electronegativity of he halogens. Iodine has the greatest tendency to form cationic species, e.g. I2+, I5+, because it has the lowest ionization energy. The cation Br2+ is known in Br2+Sb3F16- and Br5+ has been reported.
3. The atoms also form strong covalent bonds with other non-metals. The mean bond enthalpies for E-X bonds are particularly large for fluorine and therefore a wide range of molecular fluorides are known and fluorine is particularly effective at bringing out the highest valencies of the non-metals and highest oxidation states of the metals.
7. The halogens form many interhalogen compounds with the less electronegative halogen surrounded by the more electronegative halogens. Neutral, anionic, and cationic interhalogen compounds are known. ICl and IBr are widely used in organic synthesis and are commercially available.
- The most extensive series of compounds exists for iodine, e.g. IF7, IF5, ICl4-, ICl2-.Fluorine does not form any interhalogen compounds where it occupies the central position within the molecule.
8. Oxygen fluorides are extremely strong and reactive oxidants and have been explored as potential rocket fuels, the oxides become less reactive down the column and more numerous. Iodine forms a particularly wide range of oxides.
- Br> I > Cl
- And results in the formation of the corresponding +5 oxoanions,
- ClO4- + 2e- = ClO3- E° = 1.20 V
- BrO4- + 2e- = BrO3- E° = 1.85 V
- IO4- + 2e- = IO3- E° = 1.63 V
- The hypohalite ions disproportionate according the equation:
- 2XO- = 2X- + XO3-
- the equilibrium constants are 1027 for ClO-/Cl- :(the reaction is slow at room temperature), 1015 for BrO-/Br-, and 1020for IO-/I-. HOF has been prepared from ice + F2 but is very reactive, decomposing to HF + O2.