When there are six electron groups around the central

•
When there are six electron groups around the central atom, and two are
lone pairs, the result is called a square planar shape .
–
The bond angles between equatorial positions are 90°.

Practice Problem on Molecular Geometry and Electron Groups

Using VSEPR to Predict Molecular Geometries
The steps:
1. Draw the Lewis structure.
2. Determine the number of electron groups around the central
atom.
3. Classify each electron group as a bonding or lone pair, and
count each type.
–
Remember, multiple bonds count as one group.
4. Determine the shape and bond angles.

Practice Problem on Predicting Molecular Geometries
Predict the molecular geometry and bond angle of ClNO
Predict the molecular geometry of ICl
4
−

Representing Three-Dimensional Shapes on Paper
•
is difficult.
•
How to draw a 3-D representation of molecule on paper:
–
By convention, the central atom is put in the plane of the paper.
–
Put as many other atoms as possible in the same plane and indicate
with a straight line .
–
For atoms in front of the plane, use a solid wedge .
–
For atoms behind the plane, use a hashed wedge .

Illustrations of Molecular Geometries of Molecules
Using 3-D Notations

Multiple Central Atoms and Their Geometries
•
Many molecules have larger structures with many interior
atoms.
–
Think of them as having multiple central atoms.
•
For multiple center molecules:
–
Each center atom has a designated shape.
The shape around the:
•
N atom is trigonal pyramidal
•
Left C is tetrahedral
•
Right C is trigonal planar
•
O is bent

Practice Problem on Predicting Molecular Geometries for Multi-Centered
Molecules
Predict the geometry about each interior atom in each:
Make a sketch of each of the molecules
CH
3
CH
2
CH=CHCH
2
CH
3

Polarity of Molecules
•
For a molecule to be polar, it must have the following:
–
Polar bonds
•
Electronegativity difference
•
Bond dipole moments—measured
–
An unsymmetrical shape
•
Vector addition
•
Polarity affects the intermolecular forces of attraction.
–
Example:
•
Boiling points and solubilities
–
Like dissolves like
•
Nonbonding pairs affect molecular polarity, a strong pull in its direction.

Molecule Polarity
•
The bond between the H atom and Cl atom in HCl molecule is
polar.
•
The bonding electrons are pulled toward the Cl end of the
molecule because Cl is more electronegative (EN) than the H atom.
–
The net result is a polar molecule.

Molecule Polarity
•
The bond between the C atom and O atoms in CO
2
molecule is
polar.
•
The bonding electrons are pulled toward the O ends of the
molecule equally because O is more electronegative (EN) than
the C atom.
–
The net result is a nonpolar molecule.

Molecule Polarity
• The bond between the O atom and H atoms in H
2
O molecule is polar.
•
Both sets bonding electrons are pulled toward the O end of the
molecule equally because O is more electronegative (EN) than the
H atom.