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5. The Halogens and the Noble Gases eLearn.Punjab

The oxidizing power of halogens decreases with increase in atomic
number. Fluorine has the highest oxidizing power and iodine the least.
The order of decreasing power as an oxidizing agent is F2 > Cl2 > Br2 > I2

The oxidizing power of halogens depends upon the following
factors:
1. Energy of dissociation
2. Electron affinity of atoms
3. Hydration energies of ions
4. Heats of vapourization (for Br2 and I2)

If a halogen has a low energy of dissociation, a high electron affinity and
a higher hydration energy of its ions, it will have a high oxidizing power.

Oxidizing power of F2 is higher, because it has low energy of
dissociation and higher hydration energy of its ions. Due to the
relative strength as oxidizing agents, it is possible for each free
halogen to oxidize the ions of other halogens next to it in the
family. Standard electrode potential measures oxidizing power.

Standard reduction potential. Eo (V) F2 CI2 Br2 I2
+2.87 +1.36 +1.07 +0.54
XX2++22ee- → 2X-

Fluorine can oxidize all the halide ions to molecular halogens.
(A reaction will occur if the value of E°is positive) Iodine being
a weak oxidizing agent cannot oxidize chloride or bromide ion.

F2 + 2e- → 2F- Eo =2.87V
2Cl- →Cl2 +2e- Eo = -1.36V
Eo =+1.51V
F2 +2Cl- →Cl2 +2F-

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