CHEM 101 Chapter Notes - Chapter 9: Orbital Hybridisation, Pi Bond, Chemical Polarity
Chapter 9 Notes
9.1 Molecular Shapes
• The shape of a molecule is determined by its bond angles – the angles made by the lines joining
the nuclei of the atoms in the molecule
• The bond angles with the bond lengths define the shape and size of the molecule
• Linear
o AB
o Bond angle = 180°
• Bent
o AB
o Bond angle ≠ 8°
• Trigonal Planar
o AB
o Bond angle = 120°
• Tetrahedral
o AB
o Bond angle = 109.5°
9.2 The VSPER Model
• A bonding pair of electrons defines a region in which the electrons are most likely to be found
(electron domain)
• A nonbonding pair of electrons defines an electron domain that is located principally in one
atom
• Each multiple bond in a molecule also constitutes a single electron domain
• In general, each nonbonding pair, single bond, or multiple bond produces a single electron
domain around the central atom in a molecule
• The VSPER model is based on the idea than electron domains are negatively charged and
therefore repel one another
• The best arrangement of a given number of electron domains is the one that minimizes the
repulsion among them
• Two electron domains orient linearly
• Three electron domains orient in a trigonal planar
• Four electron domains orient tetrahedrally
• The shapes of different ABn molecules of ions depends on the number of electron domains
surrounding the central atom
• The electron domain geometry is the arrangement of electron domains about the central atom
of an ABn molecule or ion
• The molecular geometry is the arrangement of only the atoms in a molecule or ion
• Applying the VSPER model to Determine Molecular Shapes
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