Bonding and Molecular Geometries
CHEM 131L Principles of Chemistry I Laboratory
1
Bonding and Molecular Geometries
Remote Instruction Version
In today’s laboratory activity, you will be using an online simulation to investigate the structure of
several molecules. The shapes of molecules are predicted by VSEPR (valence shell electron pair
epulsion) theory, which states that electron groups are positioned as far from one another as possible
in a molecule. The electron groups considered by the VSEPR theory can be either in the form of lone
pairs of electrons, or shared electrons in a chemical bond. The following shapes are predicted by VSEPR:
Two electron groups
Two bonding pairs: linear
Three electron groups
Three bonding pairs: trigonal planar
Two bonding pairs, one lone pair: bent
Four electron groups
Four bonding pairs: tetrahedral
Three bonding pairs, one lone pair: trigonal pyramidal
Two bonding pairs, two lone pairs: bent
Five electron groups
Five bonding pairs: trigonal bipyramidal
Four bonding pairs, one lone pair: see-saw
Three bonding pairs, two lone pairs: t-shape
Two bonding pairs, three lone pairs: linear
Six electron groups
Six bonding pairs: octahedral
Five bonding pairs, one lone pair: square pyramidal
Four bonding pairs, two lone pairs: square planar
Valence bond theory states that when electron groups are positioned around an atom, they are placed
in hy
idized atomic o
itals. That is, rather than filling in s, p, d, or f o
itals, they occupy o
itals that
are combinations of those simpler atomic o
itals. The number of atomic o
itals used in hy
idization is
equal to the number of electron groups around the atom. For example, in ammonia, the central nitrogen
atom is bonded to three hydrogen atoms and has a single lone pair of electrons. According to VSEPR
theory, the shape of ammonia is trigonal pyramidal, and according to valence bond theory, the nitrogen
is sp3 hy
idized since it uses its 2s and all three 2p o
itals in bonding.
2
The PhET Molecule Shapes simulation provides three-dimensional models of several small molecules as
well as a set of generic models that illustrate the possible geometries of the theory. Each model can be
moved and manipulated. In Part I of the worksheet, you will use the simulation together with your
understanding of Lewis structures to complete the following entries. In Part II of the experiment, you
will use Lewis theory to evaluate the shapes of larger molecules.
Part I: Small molecules
Use the PhET Molecule Shapes simulation to answer the following questions. You can find it at
https:
phet.colorado.edu/sims/html/molecule-shapes/latest/molecule-shapes_en.html.
NOTE: Not all of the following molecules are included in the PhET Molecule Shapes
simulation. If the molecule is not in the simulation, use your knowledge of Lewis, VSEPR, and
hy
idization theories to help you answer the questions.
H2O
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
NH3
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
3
CO2
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
BF3
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
ClF3
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
4
SF6
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
O3
Name: Ozone
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
AsF5
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
5
KrCl4
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
SeCl4
Name:
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
CH2Cl2
Name: Dichloromethane
Lewis Structure: 3-D Sketch:
Hy
idization: Polarity:
Molecular Shape: Bond Angle:
6
Find two molecules from the worksheet above that are bent, but with different hy
idizations:
____________________________________
Do the two bent molecules have the same bond angle? __________________
Why? ______________________________________________________________________________
___________________________________________________________________________________
Compare H2O, NH3, and CH2Cl2. Which has the smallest bond angle? __________________________
Why? ______________________________________________________________________________
___________________________________________________________________________________
Part II: Larger molecules
Answer the following questions about the geometry of larger molecules. You do not need the PhET
simulations.
Alanine is one of the simplest and most common amino acids. The structure of alanine is:
C
C
C
O
O
H
H
H
H
N
H
H
H
structural formula ball-and-stick model
1. Label each internal atom in the structure above with its hy
idization and molecular geometry.
2. How many sigma bonds and how many pi bonds are present in alanine?
______________σ, ______________ π
7
Cyclohexane, C6H12, and benzene, C6H6, are both molecules containing six ca
on atoms a
anged in a
ing. Draw the Lewis structures of the two molecules:
Cyclohexane Benzene
3. What are the hy
idizations of the ca
on atoms in each of the molecules?
Cyclohexane: ______________ Benzene: ______________
4. What are the C-C-C bond angles in each of the molecules?
Cyclohexane: ______________ Benzene: ______________
5. Which of these molecules is likely to be entirely in one plane? ______________
6. How many sigma bonds and how many pi bonds are in each molecule?
Benzene: ______________σ, ______________ π
Cyclohexane: ______________σ, ______________ π