Nucleophilicity in Polar Aprotic Solvent Why is it that fluoride is more nucleophilic than iodide in an aprotic solvent? The Clayden textbook suggests that lower-row elements of the periodic table are more nucleophilic since their valence electrons are in higher energy levels and are therefore more reactive. However according to the slides from my lecture class, the order of nucleophilicity for halides in an aprotic solvent goes from F- > Cl- > Br- > I- which is opposite from what is stated in the Clayden textbook. Can someone please explain this?

Thank you
It's because of the anion stability. Fluoride is less stable than iodide, therefore more likely to donate electrons. 
In protic solvents, the fluoride was stabilised by the partially positive hydrogen end. Therefore, it is less nucleophilic then iodide.