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Chapter 10

Chapter 10 – Chemical Bonding II Molecular Shape, Valence Bond Theory, and Molecular Orbital Theory

6 Pages
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Department
Chemistry
Course Code
CHMA10H3
Professor
Xiao- An Zhang

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Chapter 10 Chemical Bonding II: Molecular Shape, Valence
Bond Theory, and Molecular Orbital Theory
10.1 Artificial Sweetness: Fooled by Molecular Shape
- Taste of food depends on interaction between food molecules and taste cells on tongue 
main factors affecting the interactions are shape of molecule and change distribution within
molecule Food molecule will fit into active site of specialized proteins and when this
happens, changes in the protein structure= nerve signal to transmit
- Sugar molecules fit into active site of taste cell receptors called T1r3 protein receptor
proteins sugar molecule (key) entering active site (lock) = different subunits of T1r3
protein split apart ion channels open and nerve signal transmitted artificial
sweeteners fit into the T1r3 receptor making it stronger than sugar (sweeter)
- Properties of molecules depend on structure of molecule (factors include skeletal
arrangement of atoms, kind of bonding and shape of molecule)
- Molecule are 3-D objects (describe shape of molecule with terms that relate to geometric
figures, which have characteristics corners that indicate position of surrounding
atoms around central atoms, and bond angles)
- Lewis Theory predicts electron groups (regions of electron in an atom, some are
paired while other are unshared) these regions should repel one another (negative
charge) to predict shape of molecules (position is determined by where the bonding
electron groups are and will be determined by trying to minimize repulsion between
then)
- VSEPR Theory: Valence Shell Electron Pair Repulsion Theory because electrons
are negatively charged, they should be most stable when they are separated as far as
possible
10.2 VSEPR Theory: The Five Basic Shapes
- 5 basic arrangements of electron groups around a central atom (maximum 6 bonding
electron groups, though there maybe > 6 on very large atoms but is RARE)
- 5 basic arrangements result in 5 different basic geometries (in order for molecule shape
and bond angles to be perfect geometric figure, all electron groups must be bonds and all
bonds are equivalent, resonance does not matter)
1) Linear: 2 electron groups = occupy positions on opposite sides, bond angle = 180
www.notesolution.com
2) Trigonal Planar: 3 electron groups = occupy positions in shape of triangle, bond
angle = 120
3) Tetrahdral: 4 electron groups = occupy positions in the shape of a tetrahedron, bond
angle = 109.5
4) Trigonal Bipyramidal: 5 electron groups = occupy positions in shape of 2 terahedra
that are base-to-base, axial position (positions above and below central atom), equatorial
position (positions in the same base plane as the central atom), bond angle
between equatorial positions = 120, bond angle between axial & equatorial
position = 90
5) Octahedral: 6 electron groups = occupy positions that are base-to-base
with central atom in center of the shared bases, all positions are
equivalent, bond angle = 90
- The actual geometry may be different from the
electron
geometry (due to electron groups being
attached to different size, when bonding is
different)
10.3 VSEPR Theory: The Effect of Lone Pairs
- Lone pairs may also affect geometry lone pairs occupy more space on the central atom
(electron density is exclusively on the central atom rather than shared like bonding electron
groupa)
- Relative Size of Repulsive Force Interactions:
1) Bent (Derivative of Trigonal Planar): 3 electron groups (1 IS LONE PAIR), bond
angle < 120
www.notesolution.com

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Description
Chapter 10 Chemical Bonding II: Molecular Shape, Valence Bond Theory, and Molecular Orbital Theory 10.1 Artificial Sweetness: Fooled by Molecular Shape - Taste of food depends on interaction between food molecules and taste cells on tongue main factors affecting the interactions are shape of molecule and change distribution within molecule Food molecule will fit into active site of specialized proteins and when this happens, changes in the protein structure= nerve signal to transmit - Sugar molecules fit into active site of taste cell receptors called T1r3 protein receptor proteins sugar molecule (key) entering active site (lock) = different subunits of T1r3 protein split apart ion channels open and nerve signal transmitted artificial sweeteners fit into the T1r3 receptor making it stronger than sugar (sweeter) - Properties of molecules depend on structure of molecule (factors include skeletal arrangement of atoms, kind of bonding and shape of molecule) - Molecule are 3-D objects (describe shape of molecule with terms that relate to geometric figures, which have characteristics corners that indicate position of surrounding atoms around central atoms, and bond angles) - Lewis Theory predicts electron groups (regions of electron in an atom, some are paired while other are unshared) these regions should repel one another (negative charge) to predict shape of molecules (position is determined by where the bonding electron groups are and will be determined by trying to minimize repulsion between then) - VSEPR Theory: Valence Shell Electron Pair Repulsion Theory because electrons are negatively charged, they should be most stable when they are separated as far as possible 10.2 VSEPR Theory: The Five Basic Shapes - 5 basic arrangements of electron groups around a central atom (maximum 6 bonding electron groups, though there maybe > 6 on very large atoms but is RARE) - 5 basic arrangements result in 5 different basic geometries (in order for molecule shape and bond angles to be perfect geometric figure, all electron groups must be bonds and all bonds are equivalent, resonance does not matter) 1) Linear: 2 electron groups = occupy positions on opposite sides, bond angle = 180 www.notesolution.com
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