The document discusses molecular geometry, describing its significance in determining the three-dimensional arrangement of atoms in a molecule and its impact on properties and reactivity. It explains the Valence Shell Electron Pair Repulsion (VSEPR) theory, providing methodologies for predicting molecular shapes based on electron pair interactions and includes examples of various molecules, such as BeCl2, CO2, BCl3, ozone, CH4, NH3, H2O, PF5, and SF6. The document highlights the importance of bond pairs and lone pairs in determining molecular geometry and angles.

1. GEOMETRY OF MOLECULES AND
POLARITY OF COMPOUNDS

2. MOLECULAR GEOMETRY
•Molecular geometry pertains to the three-
dimensional arrangement of atoms in a
molecule.
•Geometry affects the physical and chemical
properties of molecules and their reactivity
towards other molecules.

3. MOLECULAR GEOMETRY
• Molecular geometry can be determined by
experiment such as x-ray diffraction. However, the
geometry of simple molecules can be predicted even
without experimentation.
• While the results of the prediction is only qualitative
and not as accurate as experiment, they still help in
explaining the properties of chemical substances.

4. VSEPR THEORY
• The prediction rests on the assumption that all electron
pairs in the valence shell around a central atom repel
one another. They want to be as far apart from one another
as possible.
• These valence shell electron pairs are the ones involved in
bonding. They assume a geometry or orientation that will
minimize the repulsions.This is the stable orientation and the
one with lowest energy.
• This approach in predicting molecular geometry is called the
Valence Shell Electron Pair Repulsion Theory
(VSEPR).

5. HOW DO WE APPLY THE VSEPR THEORY TO
PREDICT MOLECULAR GEOMETRY?
1. Electron pairs stay as far apart from each other as possible to
minimize repulsions.
2. Molecular shape is determined by the number of bond pairs and
lone pairs around the central atom.
3. Treat multiple bonds as if they were single bonds (in making the
prediction).
4. Lone pairs occupy more volume than bond pairs. Lone pair-lone
pair repulsions are greater than lone pair-bond pair repulsions which
in turn are greater than bond pair-bond pair repulsions
5. Molecular geometry is a very important concept.

6. WHAT ARE THE COMMON ORIENTATIONS OF
ELECTRONS PAIRS (BOND PAIRS AND LONE PAIRS)
THAT MINIMIZE REPULSIONS?

10. IS THE ORIENTATION OF THE ELECTRON PAIR THE
SAME AS MOLECULAR GEOMETRY?
They are not necessarily the same.
The molecular geometry is determined by
the position of the nuclei of the atoms. We
do not “see” lone pairs.

11. MOLECULAR GEOMETRY OF
SAMPLE MOLECULES
For this lesson, the following notation is adopted:
• A refers to the central atom and X refers to another
atom bonded to it.
• If there are lone pairs attached to the central atom, this is
indicated by the letter E.
• Hence, AX2E2 means that A has two atoms of X bonded
to it and A also has two lone pairs of electrons.

12. 1. PREDICT THE MOLECULAR GEOMETRY OF THE
MOLECULE BECL2 . THIS IS OF THE TYPE AX2 .
• a. The first thing to do before we can predict the
molecular geometry is to draw the Lewis structure of the
molecule.This is shown below:

13. b. How many bond pairs surround the central atom of Be? Two bond
pairs surround Be.
c. How will two electron pairs orient themselves such that they will
be as far apart from one another as possible? Remember VSEPR
Theory says they repel one another.To minimize repulsion, the
two electron pairs will be arranged in a linear arrangement as
shown above.
d.What is the molecular geometry?
The molecular geometry is determined by the arrangement of the nuclei of
the atoms in the molecule.The molecular geometry of BeCl2 is linear.

14. What is the Cl-Be-Cl bond angle? It will be 180o
.

15. 2. PREDICT THE MOLECULAR GEOMETRY OF CO2 . THIS
IS ALSO OF THE TYPE AX2 BUT WITH DOUBLE BONDS
a. In determining molecular geometry, always start with the
Lewis structure.

16. b. How many electron pairs are around the central atom of
carbon? We have indicated earlier that in applying theVSEPR
theory, we will treat multiple bonds to be like single bonds.
Therefore, there will be two pairs around carbon.
c.What will be the orientation of the electron pairs: Answer:
Linear
d.What will be the molecular geometry of CO2?
Answer: Linear
e.What will be the O – C – O bond angle?
Answer: 180o
.

17. 3. PREDICT THE MOLECULAR GEOMETRY OF THE
MOLECULE BCL3 . THIS IS OF THE TYPE AX3 .
a.Again, the first step is to get the Lewis structure.

18. b. How many bond pairs surround the central atom of boron?
Three bond pairs surround B.
c. How will three electron pairs orient themselves such that they
will be as far apart from one another as possible? To minimize
repulsion, the two electron pairs will be arranged in a trigonal planar
arrangement as shown above.
d.What is the molecular geometry?
The molecular geometry of BCl3 is trigonal planar. This is a flat
molecule as shown in the figure.
e.What is the Cl – B – Cl bond angle?
The bond angle is 120o
.

19. 4. PREDICT THE MOLECULAR GEOMETRY OF
OZONE, O3 . THIS MOLECULE IS OF THE TYPE AX2 E.
a. Lewis structure

20. For predicting geometry, we may use only one of the resonance
structures.
b. Number of electron pairs around central oxygen atom (treat
multiple bonds as single bonds): three electron pairs
c. Orientation of three electron pairs: trigonal planar
d. Molecular geometry: bent
We only use the positions of the nuclei of the atoms.We are unable
to “see” the lone pair.Therefore, the molecular geometry is bent.
The lone pair occupies more volume and
pushes the bond pair closer.
Therefore, the bond angle is
slightly less than 120o
.

21. 5. PREDICT THE MOLECULAR GEOMETRY OF THE
MOLECULE METHANE, CH4 . THIS IS OF THE TYPE AX4 .
a. Draw the Lewis structure of methane.
b. Methane has four bonding pairs of electrons around
C.
c.The four bonding pairs will arrange themselves to be
as far apart from one another as possible.This is
achieved through a tetrahedral arrangement where the
four H atoms are at the corners of a tetrahedron.

22. d.The molecular geometry is tetrahedral.
e.The H-C-H bond angle is 109.5o
.

23. 6. PREDICT THE GEOMETRY AND BOND ANGLES IN
AMMONIA, NH3. THIS MOLECULE IS OF THE TYPE AX3E.
a. Draw the Lewis structure.
b. NH3 has three bond pairs and one lone pair around
nitrogen.
c.The electron pairs are arranged in a tetrahedral
orientation.
d. Since the lone pair is not considered, the molecular
geometry is pyramid.

24. e.Again, since the lone pair occupies more volume, it
will push the bond pair in and the resulting H-N-H
bond angle is slightly less than 109.5. Experimental
results show it is 107o
.

25. 7. PREDICT THE MOLECULAR GEOMETRY OF WATER,
H2O. THIS IS OF THE TYPE AX2E2.
a. Draw the Lewis structure of water.
b.There are four electron pairs around the central atom:
two bond pairs and two lone pairs.
c.The electron pairs are tetrahedrally oriented.
d.The molecular geometry is bent.

26. e. Because there are two lone pairs occupying more volume and
pushing in the bond pairs, the H-O-H bond angle is less than 1200
.
Experiment shows this to be 104.5o
. This is smaller than the bond
angle in NH3. Remember that lone pair-lone pair repulsions > lone
pair-bond pair repulsions > bond pair-bond pair repulsions.

27. 8. PREDICT THE MOLECULAR GEOMETRY OF PF5 . THIS IS OF THE TYPE AX5 .
a. Draw the Lewis structure of PF5.
b.There are five electron pairs around phosphorus.
c.The orientation of the five electron pairs is trigonal
bipyramidal.
d.The molecular geometry is trigonal bipyramidal.
e.The bond angles are 90o
and 120o
.

28. 9. PREDICT THE MOLECULAR GEOMETRY OF SF6 . THIS IS OF THE
TYPE AX6 .
a. Draw the Lewis structure of SF6.
b.There are six electron pairs around S.
c.The electrons pairs are oriented in an octahedral
manner.
d.The molecular geometry is octahedral.
e.The bond angles are 90o
and 180o
.

29. SUMMARY OF MOLECULAR GEOMETRICS