# 8.3-Molecular Geometry

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```-Understand how the absence or presence of lone
pairs of electrons affects the geometry of a molecule
-Know what the various geometries are and how to
predict them
-Understand the concept of orbital hybridization and
how it changes the bonding in an atom such as carbon
(NEXT LECTURE)
The arrangement of atoms
within a given molecule.
Valence Shell Electron Pair
Repulsion = VSEPR
( Section 8.3 232-236 in
your textbook)
Assumption: Electron pairs repulse
each other
Consequences
1) This repulsion of electron pairs
causes them to orientate as far from
each other as possible.
2) Atom centers also want to be as far
apart as possible
2 Bonding pairs
0 lone pairs
AX2
..
2 Bonding pairs
2 lone pairs
:AX2:
3 Bonding Pairs
0 lone pairs
AX3
3 bonding pairs
One lone pair
:AX3
4 bonding pairs
0 lone pairs
AX4
Summary of Five Main Geometries
Linear
Bent
Trigonal Planar
Trigonal Pyramidal
Tetrahedral
Formula= AX2
Formula = : AX2 :
Formula = AX3
Formula = : AX3
Formula = AX4
Note: A –represents the central atom
X – represents the attached atom
• 5 cards in your packet … one for each geometry.
• As a group, use your whiteboards to draw the Lewis dot
structure for each one of your compound cards.
• Once you have the Lewis Dot structure, use it as a guide
to construct a model of the compound.
• I will walk around and check your Lewis Dot structures
and models.
• Create a group sheet to record those Lewis Dot
structures/models that you are having trouble with.
• We will have cool down that you will hand in today (exit
slip)
Groupwork norm I will also be
assessing ….
Every student contributes when
every student feels safe to make
mistakes in the group.
What the fudge?!
DON’T JUDGE!
Hybridization
The electron structure of a carbon atom can be
written as:
Based on this model, we would predict that
carbon atoms should form two covalent
bonds??!!
Instead carbon atoms almost
always form 4 bonds.
Why????
Hybridization
Regular Carbon Aufbau Diagram
Hybridized Carbon Aufbau Diagram
hybridization
1 s + 3 p = 4 sp3
(All 4 orbitals are now equal at the 2nd
energy level)
Electrons must be distributed among the new orbitals.
Since these hybrid orbitals are equal in energy, the
electrons must distributed according to Hund’s Rule.
4
3
sp
orbitals
4 sp3 orbitals bond with
4 hydrogen atoms - methane
Overlap here
is known as
sigma bond
sp3 carbon
2
sp
hybridization
2
sp
hybridization
carbon double bond - ethene
sp hybridization
sp hybridization
carbon triple bond - acetylene
sp hybridization
carbon triple bond - acetylene
234-236 in your text
discusses these examples
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