CHEM 150 1nd Edition Chapter 9: Molecular Geometry and Bonding Theories Lecture 29Outline of Last Lecture • Exceptions to the octet rule:• Li, Be, and B sometimes form compounds in which they have fewer than eight valence electrons.Outline of Current Lecture • The AXE type of a compound can be found from a valid Lewis structure• AXnEmn= # of bonding groups* on the central atomm = # of lone pairs on the central atom*Any type of bond (single, double or triple) is one bonding group.• The steric number determines the Electron Geometry (Geometry)Current Lecture-n+m = the number of electron groups on the central atom. Our text calls this the steric number (SN)-Valence Shell Electron Pair Repulsion Theory (VSEPR)-Groups of valence electrons around an atom will tend to get as far apart from each other as possible.-The steric number determines the Electron Geometry (Geometry)-The electron geometry determines the ideal bond angles (“approximate bond angles”)-Electron geometry and the number of lone pairs determines the Molecular Geometry (Molecular Shape)-The Molecular Shape, the bond polarities, and the formal charge distribution determine the Molecular Polarity. -Polar molecule: a molecule with an imbalance of (partial) charge. -Polar molecules have a distinct negative side and positive side.-Polarity is determined by molecular symmetry (molecular geometry, shape): The molecule will be polar unless the polar bonds are arranged so that the polarities cancel.-A numeric measure of the polarity of a molecule is its dipole moment (m). The more polar the molecule, the larger its dipole
View Full Document
Unlocking...