The Brønsted-Lowry Acid-Base Theory

Here’s how the Brønsted-Lowry theory defines acids and bases:

✓ An acid is a proton (H+) donor

✓ A base is a proton (H+) acceptor

The base accepts the H+ by furnishing a lone pair of electrons for a coordinate-covalent bond, which is a covalent bond (shared pair of electrons) in which one atom furnishes both of the electrons for the bond. Normally, one atom furnishes one electron for the bond and the other atom furnishes the second electron . In the coordinate-covalent bond, one atom furnishes both bonding electrons. Figure 1-1 shows the NH₃/HCl reaction using the electron-dot structures of the reactants structures and products.

Figure 1-1: Reaction of NH₃ with HCl.

HCl is the proton donor, and the acid and ammonia are the proton acceptor, or the base. Ammonia has a lone pair of nonbonding electrons that it can furnish for the coordinatecovalent bond.