The electronegativity of halogens decreases from fluorine to iodine while the electron affinity has the trend Cl>F>Br>I. The halogens are good oxidizers The oxidizing power of halogens in aqueous medium depends on their electron affinity, bond dissociation energy and heat of hydration. Basic character of their anions depends on their size and electronegativity. Similarly, the ionic character of the salts of different halides of the same metal depends on their electronegativity and size.
The heat of hydration and the basic character of halide ions follow the order: