Arrhenius, Bronsted-Lowry, and Lewis concepts

1. Arrhenius Concept

  1. Introduced by Svante Arrhenius in 1884.
  2. Defines an acid as a substance that increases the concentration of H+ ions (protons) in aqueous solution.
  3. Defines a base as a substance that increases the concentration of OH− ions in aqueous solution.
  4. Example of acid: HCl → H+ + Cl−.
  5. Example of base: NaOH → Na+ + OH−.
  6. Limitations:
    • Only applicable to aqueous solutions.
    • Does not account for acid-base reactions in non-aqueous solvents.

2. Bronsted-Lowry Concept

  1. Proposed by Johannes Bronsted and Thomas Lowry in 1923.
  2. Defines an acid as a proton (H+) donor.
  3. Defines a base as a proton (H+) acceptor.
  4. Example: HCl + H2O → H3O+ + Cl−.
  5. Water acts as a base by accepting a proton to form H3O+.
  6. Applicable to aqueous and non-aqueous systems.
  7. Introduces the concept of conjugate acid-base pairs.
  8. Example of conjugate pairs:
    • HCl (acid) and Cl− (base).
    • NH4+ (acid) and NH3 (base).
  9. Limitations:
    • Does not include reactions where protons are not involved.

3. Lewis Concept

  1. Proposed by Gilbert N. Lewis in 1923.
  2. Defines an acid as a species that can accept an electron pair.
  3. Defines a base as a species that can donate an electron pair.
  4. Example: BF3 + NH3 → F3B−NH3.
  5. BF3 acts as a Lewis acid by accepting an electron pair from NH3.
  6. Applicable to a wide range of reactions, including those that do not involve protons.
  7. Introduces the concept of acid-base adducts.
  8. Broadens the definition of acids and bases beyond the Arrhenius and Bronsted-Lowry theories.

4. Comparison of Acid-Base Theories

ConceptDefinition of AcidDefinition of Base
ArrheniusProduces H+ in waterProduces OH− in water
Bronsted-LowryDonates a proton (H+)Accepts a proton (H+)
LewisAccepts an electron pairDonates an electron pair

5. Key Points 

  1. The Arrhenius concept is limited to aqueous solutions and does not account for non-aqueous reactions.
  2. The Bronsted-Lowry concept introduces proton transfer and conjugate acid-base pairs.
  3. The Lewis concept extends the definition to include electron pair acceptors and donors.
  4. Examples of Lewis acids: BF3, AlCl3, H+.
  5. Examples of Lewis bases: NH3, OH−, Cl−.
  6. Understanding these concepts is essential for solving problems in acid-base chemistry.
  7. All three theories provide complementary perspectives on acid-base behavior.
Category
Concepts of Acids and Bases
Acids, Bases, and Salts
Chemistry