1. Chapter 10 Chemical Bonding II
Chemistry: A Molecular Approach, 1st Ed. Nivaldo Tro
Chapter 10 Chemical Bonding II

2. Exceptions to the Octet Rule
Incomplete Octets ---- Boron (6)
Expanded Octets Sulfur (sometimes), Iodine (12), Xenon (12), Phosphorous (10)
Practice:
BF3, ICl4, XeF4, PCl5

3. Structure Determines Properties
properties of molecular substances depend on the structure of the molecule
the structure includes many factors, including:
the skeletal arrangement of the atoms
the kind of bonding between the atoms
ionic, polar covalent, or covalent
the shape of the molecule
bonding theory should allow you to predict the shapes of molecules
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4. Molecular Geometry – Old News
Molecules are 3-dimensional objects
We often describe the shape of a molecule with terms that relate to geometric figures
Number of Bonds attached to the central atom
Number of Lone Pairs Around the Central Atom
Shape of Molecule 2
Linear 1
Bent 3
Trigonal Planar
Trigonal Pyramidal 4
Tetrahedral 5
Trigonal Bypyramidal 6
Octahedral
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5. VSEPR Theory
electron groups around the central atom will be most stable when they are as far apart as possible – we call this valence shell electron pair repulsion theory
since electrons are negatively charged, they should be most stable when they are separated as much as possible
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7. The Effect of Lone Pairs
lone pair groups “occupy more space” on the central atom
because their electron density is exclusively on the central atom rather than shared like bonding electron groups
this effects the bond angles, making them smaller than expected
As a result, there is a second type of geometry known as the electron geometry.
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8. Effect of Lone Pairs
The bonding electrons are shared by two atoms, so some of the negative charge is removed from the central atom.
The nonbonding electrons are localized on the central atom, so area of negative charge takes more space.
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9. Tetrahedral-Bent Shape
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10. Linear Shape
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11. Describing the Geometry of Methanol
Tro, Chemistry: A Molecular Approach

12. Polarity of Molecules in order for a molecule to be polar it must
have polar bonds
electronegativity difference - theory
bond dipole moments - measured
have an unsymmetrical shape
vector addition
polarity affects the intermolecular forces of attraction
therefore boiling points and solubilities
like dissolves like
nonbonding pairs affect molecular polarity, strong pull in its direction
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13. Molecule Polarity
The H-Cl bond is polar. The bonding electrons are pulled toward the Cl end of the molecule. The net result is a polar molecule.
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14. Molecule Polarity
The O-C bond is polar. The bonding electrons are pulled equally toward both O ends of the molecule. The net result is a nonpolar molecule.
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15. Molecule Polarity
The H-O bond is polar. The both sets of bonding electrons are pulled toward the O end of the molecule. The net result is a polar molecule.
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16. Molecule Polarity
The H-N bond is polar. All the sets of bonding electrons are pulled toward the N end of the molecule. The net result is a polar molecule.
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17. Molecular Polarity Affects Solubility in Water
polar molecules are attracted to other polar molecules
since water is a polar molecule, other polar molecules dissolve well in water
and ionic compounds as well
some molecules have both polar and nonpolar parts
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