The document discusses molecular geometry and polarity, focusing on predicting molecular shapes using the valence shell electron pair repulsion (VSEPR) theory. It outlines key concepts such as bond angles, dipole moments, and the classification of molecular shapes based on electron pair orientations. Exercises are provided to apply the learned concepts on specific molecules.

1. GEOMETRY OF
MOLECULES & POLARITY
OF COMPOUNDS
Prepared by: Mrs. Eden C. Sanchez

2. Learning Objectives
1. Apply the Valence Shell Electron Pair
Repulsion Theory to predict the geometry
of simple molecules.
2. Define dipole moment.
3. Predict the polarity of molecules
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3. Keywords
a. Molecular geometry
b. Valence Shell Electron Pair
Repulsion Theory
c. Bond angle
d. linear
e. trigonal planar
f. tetrahedral
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4. Keywords
g. trigonal bipyramidal
h. octahedral
i. dipole moment
j. polar bond
k. polar molecule
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5. Motivation
▰ What is tetrahedron, a
trigonal bipyramid, and an
octahedron?
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6. Molecular Geometry
▰ pertains to the three-dimensional
arrangement of atoms in a molecule.
▰ affects the physical and chemical properties
of molecules and their reactivity towards
other molecules.
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7. ▰ Molecular geometry can be determined by
experiment such as x-ray diffraction
▰ the geometry of simple molecules can be
predicted even without experimentation
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8. ▰ the results of the prediction is only
qualitative and not as accurate as
experiment, but they still help in explaining
the properties of chemical substances.
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9. ▰ 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.
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10. ▰ 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).
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11. Key ideas of the VSEPR theory
are:
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).
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12. Key ideas of the VSEPR theory
are:
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
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13. Common orientations of electrons
pairs that minimize repulsions
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No. of Electron
Pairs
Orientation of Electron
Pairs
2 Linear
3 Trigonal planar
4 Tetrahedral
5 Trigonal bipyramidal
6 Octahedral

14. Molecular Geometry of Sample
Molecules
▰ For this lesson, 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.
▰ Example: AX2E2 means that A has two atoms
of X bonded to it and A also has two lone
pairs of electrons.
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15. Molecular Geometry of Sample
Molecules
▰ Predict the molecular geometry of the
molecules of
a. BeCl2.
b. CO2
c. BCl3
d. O3
e. CH4
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16. Molecular Geometry of Sample
Molecules
f. H2O
g. PF5
h. SF6
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17. SUMMARY OF MOLECULAR
GEOMETRICS
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18. 18

19. Exercises:
1. Using the VSEPR theory, give the electron pair
orientation and predict the geometry of the
following:
a. CH3I
b. SiH4
c. NF3
d. SCN– (C is the middle atom)
e. H2S
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20. Exercises:
2. The molecule, acetone, has the following Lewis
structure:
a. What is the geometry of the first carbon?
b. What are the bond angles around the first carbon?
c. What is the geometry of the middle carbon?
d. What are the bond angles around the middle carbon?
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21. Dipole Moments and Polarity
of Molecules
 polar covalent bonds, the electrons are not equally
shared by the bonding atoms
 there is a shift in electron density towards the more
electronegative atom.
 shift is symbolized by a crossed arrow with the arrow
pointing toward the direction of the shift.
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22. Dipole Moments and Polarity
of Molecules
 The polarity of the bond can be experimentally
measured in terms of the dipole moment – is
the product of the charge, Q, and the distance
between the charges, r.
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23. Dipole Moments and Polarity
of Molecules
 To maintain neutrality, the charges on
the ends of the molecule must be equal
in magnitude but opposite in sign.
 The unit of the dipole moment is in
terms of the Debye¸D¸
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24. Exercises
1. Is carbon dioxide a polar molecule or not?
2. Is ammonia a polar molecule?
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Thank You!
Any questions?

26. CREDITS
Special thanks to all the people who made
and released these awesome resources for
free:
▰ Presentation template by SlidesCarnival
▰ Photographs by Startup Stock Photos
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