CHAPTER 9: MOLECULAR
GEOMETRY AND
BONDING THEORIES
Dipole Moment, μ, is a
measure of the polarity of
a molecule.
A species is polar if:
1) it has polar bonds and
2) the arrangement of the
polar bonds does not
result in cancellation
We can use the dipole
moment result to help
predict the shape of a
molecule
Predict the shape of
CO2 ( μ=0), SO2 ( μ≠ 0)
NH3 ( μ≠0), BCl3 ( μ=0)
H2O( μ≠0)
CH4( μ=0)
Structures of Covalent
species can also be
predicted from their Lewis
structures and
Valence Shell Electron Pair
Repulsion theory.
VSEPR-the structure of a
molecule is determined by
placing the electron pairs
(domains) around a central
atom as far apart as
possible.
pairs of e (num. elec. pair
of atoms) geometry
2
linear
3
trigonal planar
4
tetrahedral
5
trigonal
bipyramidal
6
octahedral
electron pair (domain)
geometry - the
arrangement around a
central atom of all bond
pairs and lone pairs of
electrons.
molecular geometry - the
arrangement around a
central atom of the bond
pairs of electrons. (The
true shape of a molecule)
For central atoms without
lone pairs:
Elec. Pair Geom. = Mol.
Geom.
BeCl2, BCl3, CH4, PF5, SF6
For central atoms with lone
pairs:
Elec. Pair Geom ≠ Mol.
Geom.
NH3, H2O, SF4, XeF4
Predict the shape of
molecules with double or
triple bonds:
CO2, C2H2, CH2O, O3
Tables 9.1, 2, 3, 4
summarize all info. on
shape and hybridization.
Valence Bond Theory- a
bonding theory in which a
covalent bond is formed by
overlapping orbitals
(atomic or hybrid) from two
different atoms. Normally
each atom contributes 1 efor a single bond, 2 for a
double, and 3 for a triple
bond.
hybrid orbital - a bonding
orbital made by mixing two
or more atomic orbitals of
the same atom. (sp, sp2,
sp3, dsp3, d2sp3)
pairs elec. pair
of e geometry hybrid
2
linear
sp
3 trigonal planar sp2
4
tetrahedral sp3
5
6
trigonal
dsp3
bipyramidal
octahedral d2sp3
Sigma bond- ( σ ) a bond
formed by head to head
overlap of orbitals in which
the electron density is
along the internuclear axis.
Pi bond ( π) a bond formed
by sideways overlap of "p"
orbitals in which the
electron density is above
and below the internuclear
axis.
single bond is 1σ
double bond is 1σ and 1π
triple bond is 1σ and 2π
Give the number of bonds
(sigma and pi),
hybridization and bond
angle for the examples in
9.60 and 9.61
Bonding Theories:
-VBT, Valence bonding
theory, overlap of
orbitals (atomic or
hybrid on different
atoms)
-MOT, Molecular orbital
theory, placing electrons
into Molecular Orbitals,
MO, made by combining
atomic orbitals on
different atoms.
Electrons are added to
follow Pauli Ex clusion
Principle, PEP, and
Hunds rule
Bonding orbitals ale lower
in E and Antibonding
orbitals are higher in E.
Bond Order =1/2 (#
bonding e-#antibonding e)
Diamagnetic- a substance
with no unpaired electrons,
repelled by a magnetic
field
Paramagnetic- a substance
with unpaired electrons,
attracted to a magnetic
field.