A Lewis acid is a chemical species that can accept an electron pair from a Lewis base during a chemical reaction. This interaction forms a coordinate covalent bond, which is essential in many chemical processes, including catalysis and complex formation. Lewis acids are often metal ions or molecules with an incomplete octet, making them electron-deficient. Common examples of Lewis acids include aluminum chloride and boron trifluoride. These substances play a crucial role in organic chemistry, particularly in reactions like Friedel-Crafts acylation and alkylation. Understanding Lewis acids helps chemists predict reaction pathways and design new compounds.