 Each atom in a molecule can be thought of as having a Formal Charge  Formal Charge = difference between the number of valence electrons on the free atom minus number of valence electrons assigned to the atom in the molecule

 Atoms in molecules try to achieve formal charges as close to zero as possible  Example: Based on the two Lewis structures for sulfate, which is the best representation for the molecule?

 Energy, in kJ, required to break a bond in 1 mole of a compound  Bond energies given in Table 8.4 (pg. 374)

 Bond energies can be used to calculate an approximate energy of reaction   H can be thought of as the energies required to break old bonds plus the energies released when new bonds are formed  H =  D(bonds broken) -  D(bonds formed)

 Use bond energies to calculate the  H for the reaction of methane with chlorine and fluorine to give freon (CF 2 Cl 2 ) CH 4 + 2Cl 2 + 2F 2  CF 2 Cl 2 + 2HF + 2HCl