Chemistry 1011 Slot 51 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 /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 53 Complex Ions Transition metal ions in crystals and in solution are bonded to water molecules Copper II Sulfate consists of Cu(H 2 O) 4 2+ ions and SO 4 2  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 54 Other Ligands If ammonia solution is added to an aqueous solution of copper II sulfate, ammonia molecules will replace the water ligands Cu(H 2 O) 4 2+ (aq) + 4NH 3(aq) Cu(NH 3 ) 4 2+ (aq) + 4 H 2 O (l) Ammonia molecules are now the ligands. The coordination number remains 4

Chemistry 1011 Slot 55 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(H 2 O) 4 2+ or Cu(NH 3 ) 4 2+ 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 56 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 57 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 NH 3(aq) + H 2 O (aq) NH 4 + (aq) + OH  (aq) –In complex ion formation: Ligands such as NH 3 and H 2 O are acting as Lewis bases The central metal ion acts as a Lewis acid

Chemistry 1011 Slot 58 Lewis Acids and Bases Substances such as transition metal ions and electron deficient molecules (eg BF 3 ) can act as Lewis acids but will not be Bronsted- Lowry acids In the reaction between NH 3 and BF 3 :NH 3 + BF 3 H 3 N:BF 3 Base Acid NH 3 is the electron pair donor BF 3 is the electron pair acceptor