1. Lewis Acid and Base Theory
Ivan Gradjansky and Jack Zigler

2. Definition
Any atom/ion/molecule that donates or accepts an electron pair to form a covalent bond
Suggested by G. N. Lewis, the namesake of the Lewis structure, in 1923

3. Lewis Acid
Any atom/ion/molecule that ACCEPTS an electron pair to form a covalent bond
Applies to any ‘species’ that can accept an electron pair and form a covalent bond with another
Includes any compound where central atom has 3 valence electrons and 3 covalent bonds
Applies in any phase

4. Lewis Base
Any atom/ion/molecule that DONATES an electron pair to form a covalent bond
Anions are Lewis acids when forming a covalent bond by donating a pair
Applies in any phase
Lewis Acid-Base Reaction: Formation of a covalent bond between a Lewis acid and a Lewis base

5. Relation to Other Definitions
Broadest definition of acids and bases, and only one to not emphasize bare protons (hydrogen ions), though it can include them
Often overlaps with other theories: Brønstead-Lowry bases are often Lewis bases as well

6. Acid
Base
Arrehnius
H+ or H3O+ producer
OH- producer
Brønstead-Lowry
Proton (H+) donor
Proton (H+) acceptor
Lewis
Electron-pair acceptor
Electron-pair donor

7. Examples H+ + NH3 → NH4+ Ag+ + 2NH3 → Ag(NH3)2 BF3 + F- → BF4-
BF3 + NH3 → BF3:NH3