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 = CH4)
Structural Formula
Perspective drawing
tetrahedral
Space-filling model
Ball-and-stick model
Molecular Shape
 Five fundamental shapes of ABn
bond angle
Molecular Shape
 Derivatives from the ABn 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 NH3 and O3 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
O3, H2O, and NH4+
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 IF5 and SF4