A nucleophile is a chemical species that donates an electron pair to form a chemical bond in a reaction. Nucleophiles are typically negatively charged or neutral molecules with lone pairs of electrons, allowing them to attack positively charged or electron-deficient areas in other molecules. Common examples of nucleophiles include water, ammonia, and halide ions. In organic chemistry, nucleophiles play a crucial role in nucleophilic substitution and addition reactions. During these reactions, nucleophiles interact with electrophiles, which are electron-deficient species, leading to the formation of new bonds. Understanding nucleophiles is essential for predicting reaction mechanisms and outcomes.