Transcript Section 15.1 & 21.2 Power Point Presentation

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
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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)
Chemistry 1011 Slot 5
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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
Chemistry 1011 Slot 5
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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
Chemistry 1011 Slot 5
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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 BronstedLowry 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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