1. The Covalent Chemical Bond: A Model

2. Models
Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world.
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3. Fundamental Properties of Models
A model does not equal reality.
Models are oversimplifications, and are therefore often wrong.
Models become more complicated as they age.
We must understand the underlying assumptions in a model so that we don’t misuse it.
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4. The Localized Electron Bonding Model

5. Localized Electron Model
A molecule is composed of atoms that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms.
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6. Localized Electron Model
Description of valence electron arrangement (Lewis structure).
Prediction of geometry (VSEPR model).
Description of atomic orbital types used to share electrons or hold long pairs.
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7. Lewis Structures

8. Lewis Structure
Shows how valence electrons are arranged among atoms in a molecule.
Reflects central idea that stability of a compound relates to noble gas electron configuration.
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9. Lewis Structures Sum the valence electrons.
Place bonding electrons between pairs of atoms.
Atoms usually have noble gas configurations.
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10. React 8 Draw a Lewis structure for each of the following molecules: H2
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11. React 9 Draw a Lewis structure for each of the following molecules:
NH3
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12. React 10 Draw a Lewis structure for each of the following molecules: CO
CO2
CH3OH
BF3
C2H6O
PCl5
NO3-
SF6
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13. Molecular Structure: The VSEPR Model

14. VSEPR Model
The structure around a given atom is determined principally by minimizing electron pair repulsions.
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15. Predicting a VSEPR Structure
Draw Lewis structure.
Put pairs as far apart as possible.
Determine positions of atoms from the way electron pairs are shared.
Determine the name of molecular structure from positions of the atoms.
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16. VSEPR
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17. VSEPR: Two Electron Pairs
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18. VSEPR: Three Electron Pairs
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19. VSEPR: Four Electron Pairs
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20. VSEPR: Iodine Pentafluoride
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21. React 11
Determine the shape for each of the following molecules, and include bond angles:
HCN
PH3
SF4 O3
KrF4
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22. React 12
To determine the shape of a molecule, what is always the first step?
How do we treat multiple bonds in VSEPR theory?
If more than one atom can exceed the octet rule, where do the extra electrons go?
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23. React 13
True or false:
A molecule that has polar bonds will always be polar.
-If true, explain why.
-If false, provide a counter-example.
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24. React 14 True or false: Lone pairs make a molecule polar.
-If true, explain why.
-If false, provide a counter-example.
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