Chemistry 101 : Chap. 9
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Transcript of Chemistry 101 : Chap. 9
Chemistry 101 : Chap. 9Chemistry 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 ShapeMolecular Shape
3-dimensional rendering of a molecule (example = CH4)
Structural Formula
Ball-and-stick model
Perspective drawing
Space-filling model
tetrahedral
Molecular ShapeMolecular Shape
Five fundamental shapes of ABn
bond angle
Molecular ShapeMolecular Shape
Derivatives from the ABn geometries :
Additional molecular shapes can be obtained by removing
corner atoms from the basic shape
VSEPR ModelVSEPR 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 DomainElectron 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 DomainElectron Domain
Example : How many electron domains do NH3 and O3 have?
Electron Domain GeometryElectron Domain Geometry
Electron-Domain Geometry : The arrangement of electron
domains about the central atom of a molecule or ion
Electron Domain GeometryElectron Domain Geometry
Molecular GeometryMolecular 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 GeometryMolecular 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 GeometryMolecular Geometry
Example : Use VSEPR model to predict the molecular geometry of
O3, H2O, and NH4+
Molecular GeometryMolecular 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 pairexperience less nuclear attractionlarger electron domain
Molecular GeometryMolecular Geometry
Example : Predict the geometry of IF5 and SF4