Chemistry 1011

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Chemistry 1011

• TOPIC
• Acids and Bases
• TEXT REFERENCE
• Masterton and Hurley Chapter 4.2 (Review), 13,
  14.1, 15.1 (page 427), 21.2 (page589)

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15.1/21.2 Lewis Acids and Bases

• YOU ARE EXPECTED TO BE ABLE TO
• Identify Lewis acid-base reactions
• Identify substances that can behave as Lewis
  acids or bases
• (Textbook pages 427 and 589)

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Complex Ions

• Transition metal ions in crystals and in solution
  are bonded to water molecules
• Copper II Sulfate consists of
• Cu(H2O)42 ions and SO42- ions
• The copper ion is the central metal ion
• The water molecules are ligands
• The number of atoms bonded to the central metal
  ion is the coordination number in this case the
  coordination number is 4

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Other Ligands

• If ammonia solution is added to an aqueous
  solution of copper II sulfate, ammonia molecules
  will replace the water ligands
• Cu(H2O)42(aq) 4NH3(aq)
  Cu(NH3)42(aq) 4 H2O(l)
• Ammonia molecules are now the ligands. The
  coordination number remains 4

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Bonding in Complex Ions

• When complex ions are formed, the ligands bond to
  the central atom. The electrons required for the
  bonds come from the ligands
• In Cu(H2O)42 or Cu(NH3)42 a lone pair of
  electrons from the water or ammonia molecule is
  shared with the central atom, which uses unfilled
  d-orbitals to form a bond
• Any molecule or ion that has an unshared pair of
  electrons can donate them to a metal ion to form
  a covalent bond

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Lewis Acids and Bases

• The Lewis model of acids and bases is an
  extension of the Bronsted-Lowry model
• The Bronsted-Lowry model sees acid-base reactions
  as the exchange of hydrogen ions
• The Lewis model sees acid-base reactions in terms
  of the giving or receiving of electron pairs
• A species acts as a Lewis acid when it accepts a
  pair of electrons
• A species acts as a Lewis base when it donates a
  pair of electrons

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Lewis Acids and Bases

• Bronsted-Lowry bases will be Lewis bases
• The base can accept a proton because of the
  availability of an electron pair
• NH3(aq) H2O(aq) NH4(aq)
  OH-(aq)
• In complex ion formation
• Ligands such as NH3 and H2O are acting as Lewis
  bases
• The central metal ion acts as a Lewis acid

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Lewis Acids and Bases

• Substances such as transition metal ions and
  electron deficient molecules (eg BF3) can act as
  Lewis acids but will not be Bronsted-Lowry acids
• In the reaction between NH3 and BF3
• NH3 BF3 H3NBF3
• Base Acid
• NH3 is the electron pair donor
• BF3 is the electron pair acceptor