Procedure for Predicting
Molecular Geometries:
1. Draw the Lewis Structure for
the Molecule:
Example
Predict the molecular
geometry and bond
Predict the molecular geometry and
angles of PCl3
bond angles of ICl4
PCl3 has 26 valence
electrons
Example
-
-
ICl4 has 36 valence electrons
Cl
Count valence e-s; Follow octet
rule if possible
Cl
Cl
P
Cl
I
Cl
Cl
Cl
2. Determine the total number
of electron domains around the
central atom*
The central atom has 4
electron domains
The central atom has 6 electron
domains
3. Count the number of bonding
and nonbonding domains
around the central atom:
There are 3 bonding
domains and 1
nonbonding domain
There are 4 bonding domains and 2
nonbonding domains
Cl
Cl
e- domain geometry depends on
total number of e- domains
Molecular geometry depends on
number of bonding and
nonbonding domains
Cl
P
nonbonding domain
(lone pair)
The electron domain
geometry is
4. Use the table on other side
(or in book) to determine the
electron domain geometry and
the molecular geometry
Tetrahedral (4 edomains). The
molecular geometry is
Trigonal Pyramidal (3
bonding/1 nonbonding
domain).
Because of the lone pair on the
central atom, the bond angles in
PCl3 are slightly less than the
ideal angles for the tetrahedral
electron domain geometry
Bond Angles
Cl
I
nonbonding domains
(lone pairs)
Cl
Cl
<109.5º
Cl
The electron domain geometry is
Octahedral (6 e- domains). The
molecular geometry is Square
Planar (4 bonding/2 nonbonding
domains).
Cl
Cl
P
Cl
Cl
Cl
I
Cl
Cl
90º
*Remember that a single bond, double bond, triple bond or lone pair each counts as ONE electron domain.