CHEM 150 1nd Edition Chapter 9 : Molecular Geometry and Bonding Theories Lecture 31Outline of Last Lecture • Polar bonds and Polar molecules• bond dipole• Dipole moment• valenece bond theory• overiap• sigma bond Outline of Current Lecture • A covalent bond is produced by the overlap of orbitals in the region between the two atoms the greater the overlap, the stronger the bond.• Problem: The atomic orbitals do not always point in the right directions to produce the shapes that we know the molecules have. • To explain this, it is assumed that the atomic orbitals are mixed to produce ‘hybrid’ orbitals that point in the correct direction.• Hybrid orbitals are named from the orbitals that contribute to them: sp2 are a combination of one s and two p orbitals • The orbitals that are mixed must come from the same shell (same value of n)Current Lecture-The total number of orbitals is unchanged[There will be two sp orbitals, three sp2 orbitals, four sp3 orbitals, etc.]Each type of hybrid orbital is associated with a specific electron geometry# of e- groups (SN) Geometry Hybridization2 Linear Sp3 trigonal planar Sp24 tetrahedral Sp35 trigonal bipyramidal Sp3d6 Octahedral Sp3d2-Single bonds are formed by the overlap of orbitals in the region between the atoms. Suchbonds are called sigma (ó) bonds.-Double and triple bonds also contain a ó-bond but the second (and third bond) cannot form directly between the atoms (there is already a pair of electrons there)-The additional bonds are formed by unhybridized p-orbitals that overlap in the areas to either side of the ó-sigma bond. Such bond are called pi bonds.-A double bond consists of a ó-bond and a pi-bond.A triple bond consists of a ó-bond and two
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