Lecture Notes: Definitions for Acids and Bases

1. Bronsted-Lowry Definition

• Acids and Bases:

  • Bronsted-Lowry Acid: Proton donor
  • Bronsted-Lowry Base: Proton acceptor

• Proton Explanation:

  • Neutral hydrogen atom: 1 proton in nucleus, 1 electron outside
  • Removing electron: left with nucleus (H+), hence a proton

• HCl Example:

  • HCl donates a proton (H+) to water
  • Oxygen in water picks up proton forming Hydronium (H3O+)
  • Chlorine becomes Chloride anion (Cl-)

• Conjugate Acid-Base Pairs:

  • HCl and Cl- (1 H+ difference)
  • H2O and H3O+ (1 H+ difference)

• Reverse Reaction:

  • Chloride anion acts as a base, picks up proton from Hydronium
  • Conjugate base: Cl-
  • Conjugate acid: H3O+

2. Lewis Definition

• Acids and Bases:

  • Lewis Acid: Electron pair acceptor
    • Memory aid: 'A' in Acid and 'A' in Acceptor
  • Lewis Base: Electron pair donor
    • Memory aid: 'B' in Base turns to 'D' in Donor

• Boron Trifluoride Example (BF3):

  • Boron lacks octet (6 electrons), has empty p orbital
  • BF3 functions as Lewis acid
  • Water donates electron pair, functions as Lewis base
  • Bond forms between oxygen and boron

• Comparing Definitions:

  • Bronsted-Lowry applies to proton transfer
  • Lewis definition is broader, applies to electron pair transfer

• Application to HCl Reaction:

  • Water also a Lewis base (electron donor)
  • Proton in HCl can be considered a Lewis acid (electron pair acceptor)

Key Takeaways:

• Understand both definitions to analyze acid-base reactions fully
• Recognize conjugate acid-base pairs by proton difference
• Lewis definition helps where no proton transfer is evident.