Bronsted-Lowry acid base theory

Bronsted-Lowry: The proton tug of war

This model rests on the transfer of protons. The theory treats acid base properties in terms of a tug of war between particles. The proton is the "object" in this tug of war. Situation where acids and bases are defined based on the how well protons are held by a species.

Acids attract protons less than bases.

Bases attract protons better than acids.

Strong bases are electron rich and have a strong attraction for protons. Usually bases have a large negative charge like -1, -2 0r -3.

Acids are proton donors. This means that an acid must contain an H atom that has a weak covalent bond.

Examples of acids: HCl, HBr, H₂SO₄, HNO₃, H₃PO₄

The designation of an acid and base is actually specific for reactions.

Bases are proton acceptors.

The theory widens the kinds of compounds that are considered bases. Anything with an unshared electron pair can act as a base. This means any anion can act as a base.

Examples of bases: H2O, NH3 and S 2-

An acid in this theory transfers a proton to another molecule or ion. The residue from the acid is called a conjugate base. All acids can be considered to be a "conjugate acid". It is an acid formed when a base picked up a proton. The reaction of an acid with a base really involves two acids and two bases.

conjugate acid1 conjugate base2 conjugate acid2 conjugate base1

HNO3 (aq) + H2O(l) --à H3O1+ (aq) + NO31- (aq)