Which statement correctly defines a Lewis acid?

Which statement correctly defines a Lewis acid?

• A. A substance that donates electrons
• B. A substance that donates H+ ions
• C. A substance that accepts H+ ions
• D. A substance that accepts electrons

Answer: (D)

A Lewis acid is defined by its ability to accept an electron pair. In this framework, acids are electron-pair acceptors, while bases are electron-pair donors. This is why the statement describing a substance that accepts electrons is the correct definition. It also helps to keep straight the other notions: donating electrons corresponds to a Lewis base, while donating protons (H+) is the Arrhenius concept, and accepting protons is what a Brønsted-Lowry base does. A concrete example is boron trifluoride, which accepts a lone pair from ammonia to form a bond, illustrating how the acid draws in electron density from the base. Some species can act as either Lewis acids or bases depending on the reaction partner, highlighting the context-dependent nature of these definitions.

A Lewis acid is defined by its ability to accept an electron pair. In this framework, acids are electron-pair acceptors, while bases are electron-pair donors. This is why the statement describing a substance that accepts electrons is the correct definition. It also helps to keep straight the other notions: donating electrons corresponds to a Lewis base, while donating protons (H+) is the Arrhenius concept, and accepting protons is what a Brønsted-Lowry base does. A concrete example is boron trifluoride, which accepts a lone pair from ammonia to form a bond, illustrating how the acid draws in electron density from the base. Some species can act as either Lewis acids or bases depending on the reaction partner, highlighting the context-dependent nature of these definitions.