Chapter 9 Chemical Bonding I: Lewis Theory

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Chapter 9Chemical Bonding I Lewis Theory

• Outline
• Lewis Theory
• Types of Chemical Bonds
• Ionic
• Born-Haber Cycle
• Lattice Energy
• Covalent
• Electronegativity
• Lewis Structures
• Bond Energy
• Bond Length
• Metallic

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Potential Energy versus Distance
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Where is the electrostatic potential most
energetically favorable?
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How are bonds classified?
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How are bonds classified?
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What happens when sodium metal and chlorine gas
are placed in the same reaction flask?
Tro Chemistry A Molecular Approach, 2/e
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Lattice Energies
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Chapter 9 Examples Formation of Ionic
Compounds

• Calculate the enthalpy of formation of sodium
  chloride from its elements. Given
• Na (s) ? Na (g) 107.3 kJ/mol
• Na (g) ? Na(g) 1 e- 495.8 kJ/mol
• ½ Cl2 (g) ? Cl (g) 122 kJ/mol
• Cl (g) 1 e- ? Cl- (g) -348.6 kJ/mol
• Na (g) Cl- (g) ? NaCl (s) -787 kJ/mol
  

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Chapter 9 Examples Formation of Ionic
Compounds

• Calculate the energy released in kJ/mol when
  sodium iodide is formed.
• Na (s) ½ I2 (s) ? NaI (s)
• The energy of vaporization of elemental sodium
  is 107 kJ/mol. The ionization energy of sodium
  is 486 kJ/mol. The sum of the enthalpies of
  dissociation and vaporization of elemental iodine
  is 214 kJ/mol and the electron affinity of iodine
  is -295 kJ/mol. The lattice energy of sodium
  iodide is -704 kJ/mol.

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Chapter 9 Examples Formation of Ionic
Compounds

• Calculate the energy released in kJ/mol when
  lithium hydride is formed. The heat of
  vaporization of elemental lithium is 161 kJ/mol,
  the ionization energy of lithium is 520 kJ/mol.
  The dissociation energy of hydrogen gas is 436
  kJ/mol and the electron affinity of a gaseous
  hydrogen atom is -73 kJ/mol. The lattice energy
  of lithium hydride is -917 kJ/mol.

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Chapter 9 Examples Formation of Ionic
Compounds

• Determine the energy of formation of magnesium
  bromide. Given
• Mg (s) ? Mg (g) 147.7 kJ/mol
• Mg (g) ? Mg(g) 1 e- 737.7 kJ/mol
• Mg(g) ? Mg2 (g) 1 e- 1,450.7 kJ/mol
  Br2 (g) ? 2 Br (g)
  193 kJ/mol
• Br (g) 1 e- ? Br- (g) -325 kJ/mol
• Mg2 (g) 2 Br- (g) ? MgBr2 (s) -2,440 kJ/mol
  

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How does atomic size affect lattice energy?
Metal Chloride Lattice Energy
LiCl -834 kJ/mol
NaCl -787 kJ/mol
KCl -701 kJ/mol
CsCl -657 kJ.mol
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How does ionic charge affect lattice energy?
Ionic Compound Lattice Energy
NaF -910 kJ/mol
CaO -3414 kJ/mol
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Bond Polarity
NaCl
Cl-Cl
HCl
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Bond Polarity
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Bond length - the optimum distance between nuclei
in a covalent bond.
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Chapter 9 Examples Bond Energy

• Approximate the ?Hrxn for the production of
  ammonia by the Haber process
• N2 (g) 3 H2 (g) ? 2 NH3 (g)

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Chapter 9 Examples Bond Energy

• Approximate the ?Hrxn for the combustion of
  methane
• CH4 (g) 2 O2 (g) ? CO2 (g) 2 H2O (g)

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Chapter 9 Examples Bond Energy

• Approximate the ?Hrxn for the halogenation of
  acetylene gas
• C2H2 (g) 2 Cl2 (g) ? C2H2Cl4 (g)

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Metal Bonding