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Chemistry 1011

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). 15.1/21.2 Lewis Acids and Bases. YOU ARE EXPECTED TO BE ABLE TO: Identify Lewis acid-base reactions

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Chemistry 1011

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  1. 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) Chemistry 1011 Slot 5

  2. 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) Chemistry 1011 Slot 5

  3. 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 Chemistry 1011 Slot 5

  4. 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 Chemistry 1011 Slot 5

  5. 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 Chemistry 1011 Slot 5

  6. 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 Chemistry 1011 Slot 5

  7. 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 Chemistry 1011 Slot 5

  8. 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 H3N:BF3 Base Acid • NH3 is the electron pair donor • BF3 is the electron pair acceptor Chemistry 1011 Slot 5

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