10/12/2008 1 9.1 Molecular Shapes Lewis structures only provide the number and types of bonds between atoms Shapes of AB n molecules depend on the value of n. The shapes for AB 2 and AB 3 molecules are: Chapter 9 - Molecular Geometry and Bonding Theories In order to predict molecular shape, we assume that the valence electrons repel each other For molecules of the general form AB n there are 5 fundamental shapes:
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Chapter 9 - Molecular Geometry and Bonding Theoriesweb.uvic.ca/~chem101/BOYER/Chapter_9_notes.pdfGive the electron-domain and molecular geometries for ... 9.4 Covalent Bonding and
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9.1 Molecular Shapes
Lewis structures only provide the number and types of bonds
between atoms
Shapes of ABn molecules depend on the value of n. The shapes for
AB2 and AB3 molecules are:
Chapter 9 - Molecular Geometry and Bonding Theories
In order to predict molecular shape, we assume that the valence
electrons repel each other
For molecules of the general form ABn there are 5 fundamental
shapes:
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The shape of any particular ABn molecule can be obtained by
removing corner atoms from one of these basic shapes. Beginning
with a tetrahedron:
9.2 The VSEPR Model
What determines the shape of a molecule? Electron pairs, whether
bonding or nonbonding, repel each other.
Each nonbonding pair, single bond, or multiple bond produces an
electron domain around the central atom.
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The shapes of different ABn molecules or ions depend on the number
of electron domains surrounding the central A atom.
We can use the electron-domain geometry to help us predict the
molecular geometry.
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Effect of nonbonding electrons and multiple
bonds on bond angles
A nonbonding pair of electrons are physically
larger than bonding electron pairs.
Electrons in nonbonding pairs and in multiple bonds repel more
than electrons in single bonds:
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Molecules with Expanded Valence Shells
Atoms that have expanded octets have five electron domains
(trigonal bipyramidal) or six electron domains (octahedral) electron-
domain geometries.
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Shapes of larger Molecules
We can use the VSEPR model to predict the geometry around interior
atoms in complex molecules.
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Example
Give the electron-domain and molecular geometries for the following