Chemistry 242 - Inorganic Chemistry II
Chapter 20 - The Halogens: Fluorine, Chlorine Bromine, Iodine and Astatine


Occurence and Isolation, and Properties of the Elements






They can be made by:
  1. Direct reaction. In the case of fluorine, particularly, high oxidation states can be reached.

  2. Reaction with an oxide.

  3. Halogen exchange reactions.

  4. By dehydration of hydrated halides.

Molecular Halides

As a class of compounds, the halides illustrate the distinction between ionic solids, network solids and molecular compounds (which can be solids liquids or gases). This section deals with all three, its heading notwithstanding!

The particularly high electronegativity of fluorine leads to some special properties in its compounds:

Halogen Oxides

Fluorine forms two oxygen compounds:

  1. Oxygen Fluoride, OF2 a yellow gas produced by:

    F2   +   NaOH(aq)      OF2

  2. Dioxygen difluoride, O2F2 a yellow-orange solid produced by:

    F2(g)   +   O2(g)      O2F2   (Electric discharge through the reactants)

Chlorine does not react directly with oxygen, but forms a dangerously exposive paramagnetic oxide ClO2 in the following reaction:

NaClO3   +   SO2   +   H2SO4      2ClO2   +   2NaHSO4

It is used as a chlorinating agent in organic synthesis well diluted with air!

Iodine forms one important oxide, I2O5, by dehydration of HIO3:

HIO3      I2O5   +   H2O   (240 oC)

Its use is as a reagent for quantitative analysis for carbon monoxide:

5CO   +   I2O5      I2   +   5CO2

then the iodine is titrated as triiodide with thiosulphate:

I2   +   I-      I3-

S2O32-   +   I3-      3I-   +   S4O62-   (starch as indicator)

Oxo Acids


Organic Compounds of Fluorine

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