Use the following data to estimate Hf for magnesium fluoride. Lattice energy 2913 kJ/mol First ionization energy of Mg 735 kJ/mol Second ionization energy of Mg 1445 kJ/mol Electron affinity of F 328 kJ/mol Bond energy of F2 154 kJ/mol Enthalpy of sublimation for Mg 150. kJ/mol
Resonance structures Molecules and ions with more than one distinct but equivalent (by rotation or reflection etc.) Lewis structures can occur. The real structure is an average of these different resonance forms Failures of the Lewis model Anumber of molecules with odd numbers of electrons exist (no octet) e.g. NO An atom may not have enough electrons to complete its octet without having ridiculous formal charges e.g. BF 3 Acentral atom may clearly have more than 8 electrons e.g. SF 6 O is paramagnetic!! 2 VSEPR Valence Shell Electron Pair Repulsion theory is a useful tool for predicting the geometrical structures of main group compounds Based on the idea that pairs (or groups) of
