C121 11-3 lec20GL

C121 11-3 lec20GL - CHEM 121 The Other Half Dr Gary Leach...

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CHEM 121 – The Other Half Dr. Gary Leach office: TASC2 7072 tel: 778 782 8065 e-mail: [email protected] Office Hours: Wed, Fri 2-3 pm
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Lecture 20 October 26, 2011 Bonding: General Concepts Last Day: What is a chemical bond? (13.1) (a) Ionic bonds (13.4-13.5) Stability of Ionic Bonds Crystal Lattice Energy (L.E.) Born-Haber Cycle (b) Covalent bonds (c) Metallic bonds Today: (a) Ionic bonds (cont’d) Factors Affecting L.E . Trends in Ion Size (b) Covalent Bonding Nature of the Covalent Bond (13.1) Bond Dissociation Energy (13.7) Bond Energies and Chemical Reactions (13.8)
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M + + X - MX Recall, Ionic Bonds (Metal M --- Nonmetal X) Coulombic Interactions metal cations and non-metallic anions generally adopt noble gas electron configurations electrons are transferred from metallic to non-metallic elements due to large differences in electronegativity
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plotting the energy of interaction ( u H int ) as a function of the distance between the ions where u H int = u H attractive + u H repulsive dominated by attraction between oppositely charged ions p + /p + and e - /e - repulsion Energy (kJ/mol) Internuclear Distance (pm) Na + (g) Cl - (g)
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(b) in the solid state these strong electrostatic attractions occur in 3-D within the crystal lattice further stabilization consider the formation of solid NaCl lattice from the gaseous ions Lattice Energy (Enthalpy) defn: change in enthalpy that occurs when separated gaseous ions are packed together to form an ionic solid the more negative the lattice energy,the more stable the solid But… u H LE cannot be measured directly Na + (g) + Cl - (g) NaCl (s) UH LE = - 787 kJ/mol
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Born-Haber Cycle for the Formation of NaCl (s) design a cycle of reactions for which the enthalpy changes
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C121 11-3 lec20GL - CHEM 121 The Other Half Dr Gary Leach...

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