Chapter 09 notes S10

Chapter 09 notes S10 - Chapter Nine Chemical Bonding I 1...

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1 Chapter Nine Chemical Bonding I
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2 The Ionic Bond and Lattice Energies
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3 Consists of atomic symbol surrounded by 1 dot for each valence electron in the atom Only used for main group elements # valence electrons = group number Lewis Dot Symbols
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4 Electrons are transferred from 1 atom to another Metal atoms: Lose electrons to form cations Nonmetal atoms: Gain electrons to form anions Electrostatic force bonds ions into an ionic compound Form an ionic salt with repeating structure: NaCl, LiF Ionic Bonds follow the octet rule Atoms lose or gain valence e- to make an octet (8e-) 8 valence e- = Noble gas configuration Ionic Bonding 1s 2 2s 1 1s 2 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 Li Li + + e - e - + F F - F - Li + + Li + F -
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5 The Born Haber Cycle Formation of a salt can be tracked by individual steps Enthalpies associated with each step are additive Lattice energies are exothermic: salt is more stable than ions ( Δ H) associated with gaseous atoms, so convert to gas Ionization energies: Electron loss Electron affinity: Electron gain Lattice energy: Energy released when forming a crystal Formation energy ( Δ H f ) not based on gaseous atoms Energy associated with forming 1 mole of a compound from its elements in their normal states Sum of energy transfers called “Born-Haber cycle” Can use the cycle to the enthalpy of any step in cycle
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6 Energy Changes in the Born-Haber Cycle Li (s) b Li(g) Δ H subl = +155 kJ 1/2 F 2 (g) b F(g) Δ H diss = +75 kJ Li (g) b Li + (g)+ e - Δ H IE = + 520kJ F(g) + e- b F - (g) Δ H EA = - 328 kJ Li + (g) + F - (g) b LiF (s) Δ H lattice E = ? kJ Li(s) + 1/2F 2 (g) b LiF(s) Δ H ° f = - 594 kJ Hess’s Law: Δ H ° f = Δ H subl + Δ H diss + Δ H IE + Δ H EA + Δ H lattice E -594kJ =155kJ + 75kJ + 520kJ - 328kJ + Δ H lattice E Δ H lattice E = -1016kJ
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7 Lattice Energies of Common Salts
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8 The Covalent Bond and Electronegativity
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This note was uploaded on 02/25/2010 for the course CHM 101 taught by Professor Geldart during the Spring '07 term at Rhode Island.

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Chapter 09 notes S10 - Chapter Nine Chemical Bonding I 1...

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