Question

Which is a better nucleophile $\mathrm{Br}$ or $\mathrm{I}$?

Answer 1

1. Nucleophiles are species which tend to lose their electrons in a certain organic reaction.
2. The strength of the nucleophile is determined by nucleophilicity.
3. In the periodic table, nucleophilicity increases as we go from top to bottom in a group.
4. Considering the case of $\mathrm{Br}$and $\mathrm{I}$, the size of ${\mathrm{Br}}^{-}$ is lower than ${\mathrm{I}}^{-}$ and the valence electrons will be held more tightly as compared to ${\mathrm{I}}^{-}$.
5. Thus ${\mathrm{I}}^{-}$ will tend to lose electrons more easily than ${\mathrm{Br}}^{-}$ making iodine a better nucleophile than bromine.