Chemistry 101 : Chap. 9 Molecular Geometry and Bonding Theories (1) Molecular Shape (2) The VSEPR Model (3) Molecular Shape and Molecular Polarity (4) Covalent Bonding and Orbital Overlap (5) Hybrid Orbitals (6) Multiple Bonds

Molecular Shape  3-dimensional rendering of a molecule (example = CH 4 ) Structural Formula Ball-and-stick model Perspective drawing Space-filling model tetrahedral

Molecular Shape  Five fundamental shapes of AB n bond angle

Molecular Shape  Derivatives from the AB n geometries : Additional molecular shapes can be obtained by removing corner atoms from the basic shape

VSEPR Model Valence-Shell Electron-Pair Repulsion : The geometry around a central atom is determined by the number of bonding pair of electrons and non-bonding pair (lone pair) electrons surrounding the atom.

Electron Domain  Electron Domain: A region surrounding the central atom in which the electrons (bonding or nonbonding pair) are likely to be found VSEPR and Electron Domain : The electron domains in an atom get as far apart from each other as possible The best arrangement of electron domains is the one that minimizes the repulsions among them.

Electron Domain  Example : How many electron domains do NH 3 and O 3 have?

Electron Domain Geometry  Electron-Domain Geometry : The arrangement of electron domains about the central atom of a molecule or ion

Electron Domain Geometry

Molecular Geometry  Molecular Geometry : The arrangement of only the atoms around the central atom (1) If all the electron domains arises from bonding pair, electron-domain geometry = molecular geometry (2) If one or more electron-domains arise from nonbonding pairs, ignore such domain to predict the molecular geometry

Molecular Geometry  Procedure to determine a molecular structure (1) Draw a Lewis structure and count the total number of electron domains around the central atom (2) Determine the electron-domain geometry by arranging the electron domains to minimize the repulsions among them. (3) Use the arrangement of the bonded atoms to determine the molecular geometry

Molecular Geometry  Example : Use VSEPR model to predict the molecular geometry of O 3, H 2 O, and NH 4 +

Molecular Geometry  Effect of multiple bonding on bond angle Because multiple bonds contain higher electron-charge density than single bonds, multiple bonds represent larger electron domain  Effect of nonbonding electrons on bond angle Nonbonding pair experience less nuclear attraction  larger electron domain

Molecular Geometry  Example : Predict the geometry of IF 5 and SF 4