A Lewis base is a chemical species that can donate an electron pair to form a covalent bond. This concept is part of the broader Lewis theory of acids and bases, which defines acids as electron pair acceptors and bases as electron pair donors. Lewis bases are often molecules or ions with lone pairs of electrons, such as ammonia or hydroxide ions. In reactions, Lewis bases interact with Lewis acids, which are electron pair acceptors. This interaction is crucial in many chemical processes, including catalysis and complex formation. Understanding Lewis bases helps in predicting the behavior of substances in various chemical reactions and is fundamental in fields like organic chemistry and coordination chemistry.