Welcome to CHM 102!
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Instructor: Jason Whitehead
Phone (office): 910-962-7602
Phone (cell): 800-NO-WAYYY
Email: jrw7046@uncw.edu
Alternate Email: Jason.Whitehead@Duke.edu
Office Hours: Monday-Thursday, 9:45-11:00 am,
or by appointment (call or email)
The Basics
• Grading Breakdown: 3 exams (50%), lab(15%),
4 quizzes(15%), and the final(20%).
• If you’re more than 10 min late for the first half
8:00 am – 8:50 am, you’ll have to wait for the
second half to start at 9:00 am to come in.
• Attendance will not be taken in lecture. Students
who miss lecture should consult with other class
members to obtain notes.
• ATTEND LAB!?! Miss more than 4 labs and
receive an F for CHM 102!
Part I:
VSEPR Theory and
Lewis Structure
Review
CHM 102 Lecture
Tuesday, June 26th
What does VSEPR stand for?
V
S
E
P
R
- valence
- shell
- electron
- pair
- repulsion
What does it do?
• VSEPR Theory gives us a
3-dimensional idea of how our
molecules are structured.
• The key to VSEPR lies in the
words electron pair repulsion.
Opposites attract, but like
charges repel each other!
Electrons in bonds and lone
pairs (valence electrons) that are
around atoms try and arrange
themselves to get as far away
from each other as possible!
Some shapes to know:
The basics…
• To use VSEPR Theory, we have
to start with these two terms:
• bonding electron domains electrons shared between two
atoms in a bond.
• nonbonding electron domains electrons found located on one
atom (lone pair).
*Multiple bonds, single bonds,
and lone pairs, each count for
one electron domain.
How many domains of each type?
Molecular vs. Electron Domain
Geometry
• There are two types of geometry:
Molecular Geometry - spatial
arrangement of atoms in a molecule (deals
centrally in bonding domains).
Electron Domain Geometry-spatial
arrangement of electron domains (bonding
AND nonbonding) around an atom.
• When no nonbonding domains (lone pairs)
are present, molecular geometry IS THE
SAME as electron domain geometry.
Lewis Structures!
• Lewis Structures such as
the one shown to the right
aid in determining which
electron domains are
bonding and which are
nonbonding.
• Understanding Lewis
structures is an important
piece to solving a
VSEPR puzzle!
4 Steps of Drawing Lewis
Structures
1.
2.
Count up your total
valence electrons. (i.e.
Oxygen has 6, Nitrogen 5,
Carbon 4, Halogens 7,
etc).
If your structure is an ion
and has an overall plus or
minus charge (i.e. NH4+)
you have to subtract an
electron for each (+)
charge and add an
electron for each (-)
charge.
4 Steps… (cont’d)
3.
4.
Write your central atom
down, and arrange the
surrounding atoms
connected to it.
Make sure all of the
atoms have an octet,
save for your noted
exceptions! (i.e. BF3,
SF6, READ THIS
SECTION!!).
Enter the VSEPR Theory
• Does ammonium (NH4)+
really look flat and crossshaped as shown above
to the right?
• NO! You can count 4
bonding electron pairs,
and 0 nonbonding
electron pairs. This gives
ammonium a tetrahedral
molecular geometry AND
tetrahedral electron
domain geometry.
Drawing Ammonia, NH3.
• With 1 Nitrogen and 3
Hydrogens, with no
charge on our
molecule, you should
count up 8 total
valence electrons.
• Following through the
same way as before:
VSEPR Theory Strikes Again
• We’ve got the lewis
structure for ammonia
now.
• How many nonbonding
electron domains?
How many bonding
electron domains?
• This results in
tetrahedral electron
domain geometry (A)
but trigonal pyramidal
molecular geometry (B)
with ~109.5o H-N-H.
Tackling a larger molecule…
• Let’s do carbonate
(CO3)2• Each oxygen has 6
v.e., each carbon has
4 v.e., and we have to
add 2 additional
electrons to the total
count (to account for
the 2- charge. Total
v.e. count: 24.
What’s the geometry of carbonate?
• Once again we have
a lewis structure.
• How many
nonbonding domains?
How many bonding?
• What should the
molecular geometry
be? Electron domain
geometry?
Part II:
Molecular Polarity and
Hybridization
CHM 102 Lecture
Tuesday, June 26th
What is molecular polarity?
• A molecule is considered polar
if it has a non-zero dipole
moment.
• A dipole moment is a measure
of the strength and direction of
the separation of partial
negative and positive charges
in a molecule.
• The molecular dipole moment
for water is shown to the right,
with the arrow pointing towards
the higher electron density
(partial negative) and the tail of
the arrow being the partially
positive “pole.”
How do you determine polarity?
• The two most important contributing factors to finding
molecular polarity are looking at geometry, as well as
individual bond polarity.
• The arrow for a bond dipole works the same way as for a
molecular dipole, with the arrow pointing to the more
electronegative element.
• Shown below is the polar H-F bond, which points to
fluorine, which is the most electronegative element.
Recall the trend in electronegativity
Comparing bond polarities
• Which is more polar…. the C-O, B-O, or N-O
bond?
• When looking at the O-H bond, which direction
does the dipole arrow go?
• Compare the N2, Br2, and Cl2 bonds. Which is
more polar (if they are indeed polar)?
Returning to Water and Polarity
• Note that the bond
dipoles for water point
towards the oxygen.
Because of the way
they are oriented, the
overall dipole ends up
going straight up
through the molecule.
Molecular Polarity and Geometry
• “Polarity Tug o’ War”- Try
and think of the potential
molecular polarity of a
molecule as a tug of war
game.
• If bond dipoles are pulling
with equal and opposite
force, they cancel one
another out.
• The examples shown right,
CO2 (top), and CCl4
(bottom) contain polar
bonds, but are nonpolar
(have an overall zero
dipole moment).
Symmetry and Polarity
• Note the high degrees
of symmetry of atoms
around a central atom
tends to make bond
dipoles “cancel.”
• This is in part what is
meant by the
“Geometry”
consideration in finding
molecular polarity.
Is CCl3F polar or nonpolar?
Is SF5Br polar or nonpolar?
Is SF4Br2 polar or nonpolar?
Is BeClF polar or nonpolar?
Hybridization
• Hybridization is often used to explain
geometries in polyatomic molecules.
• It involves the combination of individual
atomic orbitals upon bonding to form
“hybridized” orbitals.
• The shape and characteristics of the
orbitals change upon hybridization.
sp-hybridization
• Linear molecules such as BeCl2 and CO2
show sp hybridization.
sp2-hybridization
• Molecules or portions of molecules such as the
carbon on the molecule of acetone below, exhibit
trigonal planar electron domain geometry and
have sp2-hybridization.
sp3
• Molecules showing tetrahedral electron domain
geometry such as methane (CH4) have sp3
hybridization.
Do we see a trend here?
• sp3d
• Sp3d2
• Count the electron domains around the
central atom for an easy way to find the
hybridization!!