The elements of Group are referred to as the halogens. Their elemental form is a diatomic molecule. The most common Group ions are the halides. Formulae for halogens and halides are given in the table.
Halogens most commonly react with other elements or compounds to give halides. Thus all halogens are oxidants. Fluorine is the strongest oxidant and iodine is the weakest.
2Cl– . The reverse reaction can also occur where the halide ion donates its electrons to form the halogen. Thus all halide ions are capable of acting as reductants. As shown above, the reductant strength of halides varies from moderate (I–) to VERY weak (F–).
Be careful not to get the halogen and the halide ion mixed up. Remember that the element has the ending -ine, and that the negative ion has the ending -ide (similar to the negative ions oxide and sulfide).
All reactions having elements as reactants or products involve transfer of electrons between atoms.The electron acceptors are oxidants (oxidising agents).
The electron donors are reductants (reducing agents).
The electron donors are reductants (reducing agents).
| Oxidant strength | Elemental form | Most common ion | Reductant strength |
very strong moderate | F2 (fluorine) | F– (fluoride) | very weak moderate |
| Cl2 (chlorine) | Cl– (chloride) | ||
| Br2 (bromine) | Br– (bromide) | ||
| I2 (iodine) | I– (iodide) |
Halogens most commonly react with other elements or compounds to give halides. Thus all halogens are oxidants. Fluorine is the strongest oxidant and iodine is the weakest.
It should be noted that despite iodine being a much weaker oxidant than fluorine, iodine is widely used as an oxidant.
The reaction of a halogen to accept electrons can be written as an equation: Cl2 + 2e– 2Cl– . The reverse reaction can also occur where the halide ion donates its electrons to form the halogen. Thus all halide ions are capable of acting as reductants. As shown above, the reductant strength of halides varies from moderate (I–) to VERY weak (F–).The strongest oxidant (F2) has a halide ion (F–) that is a very weak reductant because of the strong tendency for the reaction F2 + 2e– 2F– to proceed in the forward direction. The tendency for the forward reaction to occur is lower for the other halogens. This is accompanied by an increase in the tendency for the reverse reaction to occur and an increase in reductant strength for the lower halides.
2F– to proceed in the forward direction. The tendency for the forward reaction to occur is lower for the other halogens. This is accompanied by an increase in the tendency for the reverse reaction to occur and an increase in reductant strength for the lower halides.