Lecture Notes on Acids and Bases

Definitions of Acids and Bases

Bronsted-Lowry Definition

• Bronsted-Lowry Acid: Proton donor (e.g., HCl donates H+)
• Bronsted-Lowry Base: Proton acceptor (e.g., water accepts H+)
• Proton (H+): A hydrogen atom without its electron, essentially a hydrogen nucleus

Example: HCl and Water Reaction

• HCl:
  • Donates a proton (H+) to water
  • Turns into chloride anion (Cl⁻), gaining a negative charge
  • Acts as a Bronsted-Lowry acid
• Water (H2O):
  • Accepts the proton (H+) to form hydronium ion (H3O+)
  • Acts as a Bronsted-Lowry base

Conjugate Acid-Base Pairs

• HCl / Cl⁻: Conjugate acid-base pair with one H+ difference
• H2O / H3O+: Another conjugate acid-base pair, again with one H+ difference

Lewis Definition

• Lewis Acid: Electron pair acceptor
  • Remember: "A for acid, A for acceptor"
• Lewis Base: Electron pair donor
  • Remember: Flip "b" to "d" in "base" for "donor"

Example: Boron Trifluoride and Water Reaction

• Boron Trifluoride (BF3):
  • Lacks an octet, sp2 hybridized with an empty p orbital
  • Functions as a Lewis acid by accepting an electron pair
• Water (H2O):
  • Donates an electron pair to BF3, forming a bond
  • Functions as a Lewis base
  • Gains a +1 formal charge after bond formation

Application of Lewis Definition to Previous Reaction

• Water:
  • Acts as a Lewis base by donating an electron pair
• Proton (from HCl):
  • Acts as a Lewis acid by accepting an electron pair

Key Points

• Bronsted-Lowry: Limited to proton (H+) transfer
• Lewis: Broader definition, applicable to more reactions
• Understanding these definitions is crucial for analyzing different types of acid-base reactions.