Strength of Halogens as Oxidizing Agents: F₂ > Cl₂ > Br₂ > I₂
This section explores the trend in the oxidizing ability of the Group VII elements (the halogens) – fluorine, chlorine, bromine, and iodine. We are going to look at the ability of one halogen to oxidize the ions of another one and how that changes as you go down the Group.
Background:
A substance that has a tendency to accept one or more electrons is said to show oxidizing property. The halogens, due to high electron affinity values, have a great tendency to accept electrons and hence act as strong oxidizing agents. The oxidizing property of a halogen molecule, X2, can be represented by:
X2 + H2O → HX + HOX
It has been observed that the values of standard electrode potentials (Eo) decrease from F2 to I2. This means the oxidizing power of the halogens also decreases in the same direction, i.e., the oxidizing power of halogens follows the order F2 > Cl2 > Br2 > I2 (weakest oxidizing agents). Since F2 is the strongest oxidizing agent in the series, it will oxidize other halide ions to halogens in solution or when dry. For example, F2 displaces other halogens from their corresponding halides.
Examples:
Fluorine Displacement Reactions:
F2 + 2X– → 2F– + X2
Here, F2 displaces Cl–, Br–, and I– ions from their solutions to form F– ions and X2 (where X can be chlorine, bromine, or iodine).
Chlorine Displacement Reactions:
Similarly, Cl2 will displace Br– and I– ions from their solutions:
Cl2 + 2X– → 2Cl– + X2
Bromine Displacement Reactions:
Bromine, Br2, will displace I– ions from their solutions:
Br2 + 2I– → 2Br– + I2
Understanding the Trend:
Fluorine (F2): The strongest oxidizing agent due to its high electronegativity and small atomic size, which leads to a high tendency to gain electrons.
Chlorine (Cl2): Weaker than fluorine but still a strong oxidizing agent. It can oxidize bromide and iodide ions.
Bromine (Br2): Weaker oxidizing agent than chlorine but can still oxidize iodide ions.
Iodine (I2): The weakest oxidizing agent among the halogens listed. It does not have enough oxidizing power to displace other halogens.
