Chem 161 Chapter 9 Molecular Geometry Worksheet - Shape Determines Function Page 16
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409.4 VALENCE BOND THEORY
Localized Electron Model
– a molecule is a collection of atoms that share electrons between their atomic orbitals
– “localized” because the electrons are assumed to exist between the atoms
Valence Bond (VB) Theory
– assumes electrons in molecules occupy atomic orbitals of individual atoms in a bond
– accounts for changes in PE as distance between reacting atoms changes
– incomplete picture of all aspects of bonding but gives some insight
Basic Theory
– a covalent bond consists of a pair of electrons in atomic orbitals
1
Ex. 1 H atom has the electron configuration:
1s
H atom has the atomic orbital diagram:
↑
1s
Lewis formula for H
molecule: H—H
2
Each H in a H
molecule has the atomic orbital diagram:
↑↓
2
1s
S orbitals are spherical, so two 1s orbitals for the two H atoms in H
bond by
2
having an overlapping region where the two electrons are shared.
2
2
5
Ex. 1
F atom has the electron configuration:
1s
2s
2p
F atom has the atomic orbital diagram:
.
.
.
↑↓
↑↓
↑
2p
.
↑↓
F atoms forming F
molecule:
2s
2
↑↓
••
••
••
••
•
•
1s
• •
•
•
•
F
+
F
F F
→
•
•
•
•
•
••
••
••
••
CHEM
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C hapter
9
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