1. Atomic Size: Iodine has a larger atomic size than bromine. As the atomic size increases, the distance between the nucleus and the outermost electrons also increases. This results in a decrease in the effective nuclear charge experienced by the outermost electrons. As a result, the outermost electrons in iodine are more loosely held and less reactive compared to bromine.
2. Polarizability: Polarizability is the ability of an atom or molecule to deform its electron cloud in response to an external electric field. Iodine is less polarizable than bromine. This means that the electron cloud of iodine is more tightly held and less susceptible to distortion. As a result, iodine is less reactive towards electrophiles (species that are attracted to electrons) compared to bromine.
3. Bond Dissociation Energy: The bond dissociation energy of iodine is greater than that of bromine. This means that more energy is required to break the I-I bond in iodine compared to the Br-Br bond in bromine. As a result, iodine is less likely to undergo homolytic bond cleavage, which is a common reaction pathway for many chemical reactions.
In summary, the larger atomic size, lower polarizability, and higher bond dissociation energy of iodine contribute to its reduced reactivity compared to bromine.
