Chapter 12 Chemical Bonding II.ppt

Chapter 12 Chemical Bonding II II. Valence-Bond Theory Hybridization Bonding in NH3 sp2 hybridization sp hybridization sp3d hybrid Orbitals sp3d2 hybrid Orbitals * I. Bonding Theory A covalent H-H bond is the net result of attractive and repulsive electrostatic forces. When bringing together two atoms that are initially very far apart. Three types of interaction occur: (1) The nucleus-electron attractions (blue arrows) are greater than the (2) nucleus-nucleus and (3) electron-electron repulsions (red arrows), resulting in a net attractive force that holds the atoms together to form an H2 molecule. If the hydrogen atoms are too far apart, attractions are weak and no bonding occurs. A zero of energy when two H atoms are separated by great distances. A drop in potential energy (net attraction) as the two atoms approach each other. When the atoms are optimally separated, the energy is at a minimum. A minimum in potential energy at particular internuclear distance (74pm) corresponding to the stable H2 molecule and the potential energy corresponds to the negative of the bond dissociation energy. If the atoms are too close, strong repulsions occur. A increase in potential energy as the atoms approach more closely. A graph of potential energy versus internuclear distance for the H2 molecule. bond formation by overlapping orbitals: A description of covalent bond formation in terms of atomic orbital overlap is called the valence bond theory. It gives a localized electron model of bonding: core electrons and lone-pair valence electrons retain the same orbital locations as in the separated atoms, and the charge density of the bonding electrons is concentrated in the region of orbital overlap. 2) hybridization of atomic orbitals: How do a carbon with a s orbital and three p orbitals combined with four hydrogen (s orbitals) form four bonds and all four bonds are found to be 109.5?? In 1931, Linus Pauling proposed that the wave functions for the s and p atomic o