Vsepr Theory & Hybridization Cont. Wood County Schools Page 3
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Common Problems
•
•
Determining the shape of a molecule.
Determining the hybridization state of a molecule.
•
•
Draw the Lewis structure for the molecule.
Draw the Lewis structure for the molecule.
•
•
Determine the number of electron pairs (bonded
Find the number of electron pairs, and match it
and unbonded) around the central atom.
with the correct hybridization state
•
•
Use the table (or your memory) to find the
Determining the polarity of a molecule.
correct shape.
Drawing VSEPR Structures
Basic VSEPR
Example:
Determine the VSEPR Structure of ammonia (NH
).
3
1. Draw the Lewis structure for the molecule.
2. Determine the number of electron pairs (bonded and unbonded) around the central atom.
3. Use the table (or your memory) to find the correct shape.
Figure: (left) Ammonia Lewis structure (right) Ammonia VSEPR shape. The top orbital has a
pair of electrons that fill the orbital.
Ammonia has 4 orbitals, one of which is filled. Thus, it is trigonal pyramidal.
Advanced VSEPR
Example:
Determine the VSEPR structure of sulfur tetrafluoride (SF
).
4
1. Count up the number of valence electrons in the entire molecule
•
Sulfur = 6, Fluorine = 7
•
6 + 4 · 7 = 34
2. Determine how many electron pairs are necessary for the non-central atom. Since sulfur is the central atom, each
fluorine will have 6 non-bonding electrons (3 electron pairs). Deduct these from the electron count.
•
34 – 6 · 4 = 34 – 25 = 10
3. There are now 10 electrons associated with the central atom, fluorine. Four bonds will form, one between the sulfur
and each fluorine. Deduct 2 electrons for each bond formed.
•
10 – 2 · 4 = 10 – 8 =2
4. There are thus 2 non-bonding electrons on the sulfur. Using the VSEPR Chart, 1 electron pair and 4 bonds means
this is seesaw-shaped.
Figure: VSEPR structure of the seesaw-shaped sulfur tetrafluoride.
Polarity & VSEPR
Hybridization & VSEPR
Example:
Example:
Is OF
polar?
What is the hybridization state
2
of xenon in XeF
?
4
1. Draw the VSEPR structure of the molecule following the steps
•
Follow the steps for determining the
above.
VSEPR structure of an atom.
2. Determine the electronegativities of each atom.
•
Xenon is square planar with 2 filled
Fluorine = 4, oxygen = 3.4. Draw dipoles along the bonds, with
orbitals.
the positive ends at the atom with the lower electronegativity.
•
Look up on the chart which hybridization
3. If the arrows cancel each other out, the molecule is not polar. In
this corresponds to. This means xenon
this case, OF
is polar.
2
has a hybridization of sp
d
.
3
2
Figure: Polarity of oxygen difluoride
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