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

Nucleophilicity, the ability of a species to donate electrons to form a chemical bond, generally increases up the periodic table in aprotic solvents due to the nature of these solvents and their interactions with nucleophiles.

Aprotic solvents do not have hydrogen atoms attached to electronegative atoms, which means they do not participate in hydrogen bonding. This absence of hydrogen bonding allows nucleophiles to remain more "free" and reactive, as their electron density is not heavily shielded. In the case of aprotic solvents, nucleophilicity is influenced primarily by the charge density and size of the nucleophile. As one moves up the periodic table, for example from iodide to fluoride, larger atoms tend to hold onto their electrons more loosely, making them more effective nucleophiles in a medium that does not interfere with their reactivity.

In contrast, protic solvents stabilize nucleophiles through hydrogen bonding, particularly for larger anions. This stabilization can impede their nucleophilicity because the solvent creates a solvation shell around the nucleophile that can hinder its ability to approach the electrophile and share its electrons.

Non-polar solvents do not facilitate nucleophilic reactions well because they lack polarity, which is necessary for sol