Charged nucleophile and SN1/E1/SN2/E2 reactions
Strong nucleophiles tend to undergo SN1/E1 reactions whereas weak nucleophiles tend to undergo SN1/E1 reactions.

An increase in electron density will make a nucleophile stronger. This effect can be clearly seen when conjugate bases of common nucleophiles are stronger than the nuclephiles themselves. For example: $\ce{NH_2^- &gt; NH_3} $.

In SN1/E1 reactions, the weak nucleophile can only attack the carbocation once the leaving group has left. This is precisely because it is a weak nucleophile.

IN SN2/E2 reactions, the strong nucleophile attacks the carbon before it can even form a carbocation. This forces the leaving group to leave. This is precisely because it is a strong nucleophile.