Solubility : Halogens, being non polar in nature do not readily dissolve in a polar solvent like water. however, fluorine reacts with water vigorously even at low temperature (exothermally) forming a mixture of ozone and oxygen

2F₂ + 2H₂O ———> 4 HF + O₂

2F₂ + 3H₂O ———> 6 HF + O₃

Chlorine and bromine are fairly soluble but iodine is very little soluble in water. chlorine, bromine and iodine are more soluble in organic solvents like CCl₄.CS₂ or CHCl₃ and produce coloured solutions. Thus Cl₂.Br₂ and I₂ give yellow, brown and violet colour respectively. It is believed that in non-polar solvents, halogens exist as free molecules just as in the gas phase.

In nucleophilic (electron donating) polar solvents like alcohols, ketones or liquid SO₂ , halogens produce brown solution. This colour is due to the complex formation (solvent —> halogen) which are charge transfer compounds.

The solubility of iodine (I₂) in water increases with addition of KI or NaI due to the formation of polyhalide (triiodide, I₃^– ) ion, KI + I₂ KI₃

However, this solution behaves as a simple mixture of KI and free I₂ and contains K⁺ and I^– ions and free I₂ molecules. It has a brown color. The solution of iodine in water (due to its very little solubility) is also brown.

Oxidizing power : All the halogens acts as strong oxidizing agents since they have a strong tendency to attract electrons and have positive values of electrode potentials (E^o). The oxidizing power, however, decreases as we move down the group from F to I . i.e., F₂ > Cl₂ > Br₂ > I₂

Since F₂ is the strongest oxidizing agent, it will oxidize all other halide ions to halogens.

Similarly, Cl₂ will displace Br^– and I^– ions from their solutions while Br₂ will displace I^– ions only.

Cl₂ + 2X^– ————> 2Cl^– + X₂ (X = Br, I)

Br₂ + 2I^– ————> 2Br^– + I₂

Hence F₂ is the strongest and I₂ is the weakest oxidizing agent. This is also indicated by the decrease in the electrode potential (E^o) for the reaction X₂(aq) + 2e^– ————> 2X^– (aq) on moving down the group.

The electron affinity of fluorine is less than that of chlorine but still it is the strongest oxidizing agent. This is because of its low bond dissociation energy (158 kJ mol^–1) and high heat hydration (158 kJ mol^–1) as compared to chlorine (for which the values are 243 and 372 kJ mol^–1 , respectively).