..
..
..
[
–
]
..
Cl
..
..
..
36 e–
..
ICl4–
Cl
.. ..
Cl–
.. I –Cl
..
EDG: octahedral
MG: sq. planar
For molecules with more than one central atom,
simply apply the VSEPR model to each part.
Predict the EDG and MG around the three interior
atoms of ethanoic (acetic) acid.
CH3COOH
PORTION
EDG
MG
H O
..
H–C–C–O–H
..
H
–CH3
tetra.
tetra.
C=O
trig. plan.
trig. plan.
..
tetra.
bent
–OH
..
Nonbonding domains are attracted to only one nucleus;
therefore, they are more spread out than are bonding
domains. The effect is that nonbonding domains
(i.e., “lone pairs”) compress bond angles. Domains for
multiple bonds have a similar effect.
e.g., the ideal bond angle for the tetrahedral
EDG is 109.5o
H
H
H2O
N
O
..
C
H
109.5o
H
H
H
H
COCl2
124.3o
H
O=C
124.3o
107.0o
104.5o
..
Cl
..
..111.4
Cl
..
..
NH3
o
..
CH4
H
EDG = trig. plan.
ideal = 120o
Polarity of Molecules
A molecule’s polarity is determined by its overall
dipole, which is the vector sum of the dipoles of
each of the molecule’s bonds.
Consider CO2 v. H2S...
bond dipoles
O=C=O
bond dipoles
S
H
H
overall dipole = zero
overall dipole =
(NONPOLAR)
(POLAR)
Classify as polar or nonpolar:
BCl3
..
..
..
Cl
B
..
..
26
e–
..
PCl3
.. .. ..
Cl–
.. P–Cl
..
Cl
..
..
24 e–
Boron can be extracted by
the electrolysis of molten
boron trichloride. Boron is
an essential nutrient for
plants, and is also a primary
component of control rods
in nuclear reactors.
polar
nonpolar
Valence-Bond Theory: merges Lewis structures
w/the idea of atomic orbitals
(2s, 3p, etc.)
Lewis theory says… covalent bonding occurs when
atoms share electrons
V-B theory says… covalent bonding occurs when
valence orbitals of adjacent
atoms overlap; then, two e–s
of opposite spin (one from
each atom) combine to form
a bond
V-B theory is like Velcro: “No overlap, no bond.”
Consider H2, Cl2, and HCl...
(unpaired e– is in 1s orb.)
H
Cl
[Ne]
H2
(unpaired e– is in 3p orb.)
Cl2
HCl
= orbital overlap region
(responsible for bond)
There is always an optimum distance between two
bonded nuclei. At this optimum distance,
attractive (+/–) and repulsive (+/+ and –/–) forces
balance.
Energy
0
H2 molecule
optimum dist.
(min. PE)
H–H distance