Chem 161 Chapter 9 Molecular Geometry Worksheet - Shape Determines Function Page 12
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409.5 SHAPES AND BONDING IN LARGER MOLECULES
Geometry of Molecules with More than One Central Atom
– Overall geometry of entire molecule cannot be described
instead describe the shape around each central atom in molecule
→
– e.g. CH
OH
3
Lewis structure
H
H
C
H
H—C—O—H
O
H
H
H
tetrahedral around C and
bent around O
bond angle = 109.5°
bond angle = <109.5°
Ex. What is the geometry around each central atom in acetic acid, CH
COOH?
3
H
O
st
1
C: shape = __________________, bond angles = _______
nd
2
C: shape = __________________, bond angles = _______
H—C—C—O—H
O: shape = _____________________, bond angle = _______
H
Sketch the 3D shape
(with approximate bond
angles) for acetic acid
at the right:
9.3 POLAR BONDS AND POLAR MOLECULES
Bonding electrons are not always shared equally
– If two atoms bonded together have different electronegativity (EN) values
→ separation of charges = dipole
..
. .
→ more EN atom gains a partial negative charge
H―F
→ other atom gains a partial positive charge
..
– molecules that have a dipole are polar molecules
– A dipole is indicated with an arrow pointing to more EN atom.
– The more polar the molecule, the greater its dipole moment, the quantitative
measurement of the separation of positive and negative charges in the molecule.
For diatomic molecules:
– nonpolar molecules: when the 2 atoms have equal EN values → no dipole
– polar molecules: when the 2 atoms have different EN values → dipole
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