In which type of solvent does nucleophilicity generally increase down the periodic table?

Nucleophilicity refers to the ability of a species to donate a pair of electrons to form a chemical bond. In the context of solvent effects, the behavior of nucleophiles can vary significantly depending on the solvent type.

In protic solvents, which have hydrogen bonds (for example, water and alcohols), nucleophilicity generally increases down the periodic table due to the lower electronegativity and larger atomic size of the nucleophiles. As we move down a group, the nucleophilicity of elements like the halides (F-, Cl-, Br-, I-) increases because larger atoms have more diffuse electron clouds, making it easier for these nucleophiles to share their electron pairs.

In protic solvents, stronger intermolecular interactions (like hydrogen bonding) can stabilize the anions. However, as you go down the group, the nucleophiles become less solvated due to their larger size. For example, iodide ion (I-) is less solvated than fluoride ion (F-) in protic solvents, allowing I- to be a stronger nucleophile although it is less electronegative. Thus, in protic solvents, nucleophilicity increases down the periodic table.

This behavior contrasts with aprotic