ap chemistry chapters 9. vocab (ch 9) vsepr- valence shell e- pair repulsion bonding pair non...
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AP Chemistry
Chapters 9
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Vocab (Ch 9) VSEPR- Valence Shell e- Pair Repulsion bonding pair non bonding pair – lone pair of electrons electron domain – regions around a central atom
where e- are likely to be found. molecular geometry- the arrangement of atoms in
space electron domain geometry- the arrangement of e-
domains about the central atom of a molecule The Molecular geometry is a derivation of the
Electron-Domain geometry See Table 9.2 (page 309)
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Electron Domains
The e- in a multiple bond constitute a single e- domain.
# of e- domains = (# of atoms bonded to the central
atom) + (# of non bonding pairs on the central atom)
Page 306
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Molecular Shapes Website
See VSEPR table handout for molecular shapes
http://www.molecules.org/VSEPR_table.html
See B& L page 307-309
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Effect of Non bonding e- and multiple bonds on Bond Angles
e- domains for non-bonding e- pairs exert greater repulsive forces on adjacent e- domains and thus tend to compress the bond angles
e- domains for multiple bonds exert a greater repulsive force on adjacent e- domains than do single bonds.
Page 310
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Molecules with Expanded Valence Shells These shapes generally contain axial and
equatorial positions See B&L pg. 312 Variations of the trigonal bipyramidal shape
show lone electron pairs in the equatorial position
Variations of the octahedral shape show lone electron pairs in the axial positions
Page 311
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Molecules With More Than One Central Atom
You can use the VSEPR theory for molecules with more than one central atom, such as, CH3NH2.
Pages 313-314
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Bond Polarity Bond Polarity is a measure of how equally the
e- in a bond are shared between the 2 atoms of the bond.
Polarity is used when talking about covalently bonded molecules.
If the molecule has only 2 different atoms, such as, HF or CCl4 you can calculate the electronegativity difference and determine the type of covalent bond (polar or non-polar).
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Polarity and Bond Type
Electronegativity Difference
Bonding Type
<0.5 Non-polar covalent
0.5 – 1.9 Polar covalent
> 2.0 ionic
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Dipole Moment Dipole Moment – the measure of the
amount of charge separation in the molecule.
For a molecule with more than 2 atoms, the dipole moment depends on both the polarities of the individual bonds and the geometry of the molecule.
The overall dipole moment of a polyatomic molecule is the sum of its bond dipoles.
See B&L page 315 figure 9.9
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Dipole Moment For each bond in the molecule, consider
the bond dipole (the dipole moment due only to the 2 atoms in that bond)
The dipole “arrow” should point toward the more electronegative atom in the bond
The overall dipole moment of a polyatomic molecule is the sum of its bond dipoles. (Consider the magnitude and direction of the bond dipoles)
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Different Theories VSEPR Theory (using Lewis Dot Structures) Valence Bond Theory (using hybridization) Molecular Orbital Theory (shows allowed states
for e- in molecules)
Go to the following web-site for a compare and contrasting of the 3 different theories
http://www.chem.ufl.edu/~chm2040/Notes/Chapter_12/theory.html
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sp Hybrid Orbitals
See section 9.5 pages 318-320
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sp2 and sp3 Hybrid Orbitals
See section 9.5 pages 320-322
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d Orbital Hybridization
See section 9.5 pages 322
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Multiple Bonds and Hybridization
See section 9.6 pages 324-326
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Delocalized π Bonding
See section 9.6 pages 327-330
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Sigma Bonds ( σ )
Sigma bonds occur when the e- density is concentrated between the 2 nuclei.
These are single covalent bonds. Sigma bonds can form from the
overlap of an s orbital with another s orbital, an s orbital with a p orbital, or a p orbital with a p orbital.
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Pi Bonds ( π )
Overlap of 2 “p” orbitals oriented perpendicularly to the inter-nuclear axis
This overlap results in the sharing of electrons.
The shared electron pair of a pi bond occupies the space above and below the line that represents where the two atoms are joined together.
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Hybridization
An atom in a molecule may adopt a different set of atomic orbitals (called hybrid orbitals) than those it has in the free state.
See B&L pages 319-322 for explanation and diagrams of electron promotion
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Multiple Bond A multiple bond consists of one sigma
bond and at least one pi bond. A double bond consists of one sigma
bond and one pi bond. A triple bond consists of one sigma
bond and two pi bonds. A pi bond always accompanies a sigma
bond when forming double and triple bonds.
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Sigma and Pi Most of the bonding that you have seen
so far has bonding e- that are localized. σ and π bonds are associated with the
2 atoms that form the bond (and NO other atoms)
Delocalized bonding can occur in molecules that have π bonds and more than one resonance structure.
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Molecular Orbital Diagram Energy Level Diagram (Molecular Orbital
Diagram) The H2 molecule is the easiest molecule
to plot on the molecular orbital diagram Whenever 2 atomic orbitals overlap,
2 molecular orbitals form (one is a bonding orbital and one is an anti-bonding orbital).
This is not on the AP exam
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Paramagnetism
Molecules with one or more unpaired electrons are attracted into a magnetic field
The more unpaired electrons in species, the stronger the force of attraction
This behavior is called paramagnetism
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Diamagnetism
Substances with no unpaired electrons are weakly repelled from a magnetic field
This property is called diamagnetism
Diamagnetism is much weaker than paramagnetism
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Problems to Try Ch 9 # 5-13, 15, 23, 27, 31, 32, 34, 40, 43, 44 (a
and c), 63 AP Exam Problems to Try
1999 # 82000 # 7 (last section)2002 # 62003 # 82004 # 7 & # 8