Transcript Molecular Geometry  VSEPR - Valence Shell Electron Pair Repulsion Theory.  In small molecules, electrons and bonds are arranged as far apart as possible.

Molecular Geometry
 VSEPR
- Valence Shell
Electron Pair Repulsion Theory.
 In small molecules, electrons
and bonds are arranged as far
apart as possible.
Molecular Geometry
This
allows for atoms to have
3-D shapes different from
their shapes in 2-D (paper).
Molecular Geometry
 Linear
– the
bonds form a
straight line.
 Example CO2
 Bond Angle
180⁰
[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH10/FG10_02-02d.JPG]
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
Molecular Geometry
 Trigonal
[http://wps.prenhall.com/wps/media/objects/476/488316/Instructo
r_Resources/Chapter_10/FG10_00-66c.JPG]
Planar– The
central atom
has only 3
bonds.
 Example: CH2O
(Formaldehyde)
 Bond angle
120⁰
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
Molecular Geometry
Tetrahedral –The
central atom has
only 4 bonds
 Example: CH4
(methane)
 Bond Angle
109.5⁰

[http://wps.prenhall.com/wps/media/object
s/476/488316/Instructor_Resources/Chapt
er_10/FG10_00-69d.JPG]
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
Molecular Geometry
Trigonal
Pyramidal –
Central atom has
3 bonds and one
lone pair of
electrons that
“pushes” the
bonds away.
 Example: NH3
(ammonia)

[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
Molecular Geometry
 Bent
– Here
there are two
bonds and two
pairs of
electrons on the
central atom.
 Example: H2O
(water)
[http://www.elmhurst.edu/~chm/vchembook/images/206water.gif]
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
[http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter07/Text_Images/FG07_05-01UN.JPG]
Polarity
 When
2 atoms in a bond have
different electronegativity
values, electrons can be
“pulled” more toward one side
of the bond.
 A bond where this occurs is
called a dipole.
[http://www.cybered.net/library/Teaching_Resources/Chemistry/Bonding_II/Image_Gallery/Bonding2--PolarBond.jpg]
[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11.JPG]
Polarity
Showing Polarity
 “Minus” sign above
the high
electronegative
atom.
 “Plus” sign over the
other atom.
 Draw arrow from
plus to minus.

[http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/text_images/CH09/FG09_11-02.JPG]
Compound Polarity
 Draw
H
H
C
H
H
a
correct 2-D
compound
with arrows
along each
bond.
 Example: CH4
Compound Polarity
 Then,
check
to see if any
of the arrows
cancel out.
 To do this
think “tug of
war”
H
H
C
H
H
Compound Polarity
If
all arrows cancel out, the
molecule is non-polar or
covalent.
If the arrows do not cancel
out, the molecule is polar or
polar-covalent.
Compound Polarity
H
H
O
O
H
H
 Remember:
3D shape
determines
2D drawing.
 Example: H2O