Chapter 8 Concepts of Chemical Bonding - John Bowne High School：8章概念的化学键-约翰邦恩高中.ppt

Chapter 8Concepts of Chemical Bonding November 15Chapter 8 – Chemical Bonding Section 1 and 2 Bonding types Lewis Structures Ionic bonding HW: 1,3,4,7 to 19 odd ,24,25 There will be a quiz any day on hw questions Chemical Bonds Three basic types of bonds: Ionic Electrostatic attraction between ions Covalent Sharing of electrons Metallic Metal atoms bonded to several other atoms Ionic BondingElectron Transfer Energetics of Ionic Bonding As we saw in the last chapter, it takes 495 kJ/mol to remove electrons from sodium. Energetics of Ionic Bonding We get 349 kJ/mol back by giving electrons to chlorine. Energetics of Ionic Bonding But these numbers don’t explain why the reaction of sodium metal and chlorine gas to form sodium chloride is so exothermic! Energetics of Ionic Bonding There must be a third piece to the puzzle. What is as yet unaccounted for is the electrostatic attraction between the newly formed sodium cation and chloride anion. Lattice Energy This third piece of the puzzle is the lattice energy: The energy required to completely separate a mole of a solid ionic compound into its gaseous ions. The energy associated with electrostatic interactions is governed by Coulomb’s law: Energetics of Ionic Bonding By accounting for all three energies (ionization energy, electron affinity, and lattice energy), we can get a good idea of the energetics involved in such a process. Born-Haber CycleApplication of Hess’s Law Vaporize the metal (enthalpy of vaporization) Na (s) ? Na (g) Break diatomic nonmetal molecules (if applicable) (bond enthalpy) ? Cl2 (g) ? Cl- Remove electron(s) from metal (ionization energy) Na (g) ? Na+ (g) + e- 4 Add electron(s) to nonmetal (electron affinity) Cl (g) + e- ? Cl- (g) 5 Put ions together to form compound (lattice energy) Na+ + Cl- ? NaCl (s) Overall Reaction: Na (s) + ? Cl2 (g) ? NaCl (s) This is useful because all quantities are directly measurable except lattice energy. The Born-Haber cycle can