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 include water, ammonia, and halide ions. In organic chemistry, nucleophiles play a crucial role in nucleophilic substitution and addition reactions. Their ability to seek out electron-deficient centers makes them essential in forming new bonds and driving chemical transformations. Understanding nucleophiles is fundamental for predicting reaction mechanisms and outcomes.