1. Molecular Geometry
and
Bonding Theories

2. The properties of a molecule depend on its shape and
and the nature of its bonds. In this unit, we will
discuss two models.
(1) a model for the geometry of molecules
-- valence-shell electron-pair
repulsion (VSEPR) theory
(2) a model about WHY molecules form bonds
and WHY they have the shape they do
-- valence-bond theory

3. bond angles: the angles made by the lines joining
the nuclei of a molecule’s atoms
carbon dioxide
methane
formaldehyde
CO2
CH4
CH2O
180o
109.5o
120o

4. .. .. VSEPR electron domain: a region in which at least two
electrons are found
-- they repel each other because… they are all (–)
bonding domain: 2-to-6 e– that are shared by two
atoms; they form a… covalent bond
nonbonding domain: 2 e– that are located on a single
atom; also called a… lone pair
For ammonia, there are
three bonding domains and
one nonbonding domain.
NH3 N –H H– H ..
4 e– domains N H ..
Domains arrange themselves so
as to minimize their repulsions.

5. .. .. N The electron-domain geometry is one H
of five basic arrangements of domains.
-- it depends only on the total # of e– domains,
NOT the kind of each domain
The molecular geometry describes the
orientation of the atoms in space. ..
-- it depends on how many of each
kind of e– domain

6. Electron-Domain Geometry Possible Molecular Geometries
Total # of Domains
Electron-Domain Geometry
Possible Molecular Geometries 2 3 4 5 6
linear
linear (CO2)
trigonal
planar
trigonal planar (BF3), bent (NO2)
tetrahedral
tetrahedral (CH4),
trigonal pyramidal (NH3), bent (H2O)
“atoms – axial”
trig. bipyramidal (PCl5), linear (XeF2)
seesaw (SF4), T-shaped (ClF3)
trigonal
bipyramidal
octahedral
octahedral (SF6), sq. pyr. (BrF5),
square planar (XeF4)

7. [ ] .. .. .. .. To find the electron-domain geometry (EDG) and/or
molecular geometry (MG), draw the Lewis structure.
Multiple bonds count as a single domain.
Predict the EDG and MG of each of the following.
[ ] Sn
–Cl
Cl– .. Cl –
SnCl3–
EDG: tetrahedral
MG: trig. pyramidal
26 e– .. O –O O= .. O O– O= O3
EDG: trig. planar
18 e–
MG: bent
Cl–Se–Cl ..
SeCl2
EDG: tetrahedral
20 e–
MG: bent

8. [ ] .. .. .. .. .. .. .. C= O O– 2– CO32– EDG: trig. planar (res.)
[ ] C= O O– .. 2–
CO32–
EDG: trig. planar
(res.)
MG: trig. planar
24 e– .. S –F F– F
SF4
EDG: trig. bipyr. ..
MG: seesaw
34 e– I .. F –F F–
IF5
EDG: octahedral ..
MG: sq. pyramidal
42 e– Cl –F F– .. F
ClF3
EDG: trig. bipyr. ..
MG: T-shaped
28 e–