VSEPR

Topics: VSEPR theory, Molecule, Atom Pages: 5 (589 words) Published: September 30, 2013


LARRY COMPTON
CHEMISTRY 151
RIO SALADO COLLEGE
2 NOVEMBER 2012

VALENCE SHELL ELECTRON PAIR REPULSION THEORY

Purpose:

The purpose of this lab is to further our understanding of interactions between molecules. We have to draw Lewis structures during this lab. Describe single, double and triple bonds. We also must predict the structure of a molecule using the VSEPR theory.

Materials:

Balloons
Colored Pencils
Molecular Model Kit

Procedures:

Part 1

1. Blow up all of the balloons in the lab kit and tie them.

2. Blow the three blue ones up slightly larger than you do the five red balloons.

3. The blue balloons will represent the repulsive field created by an unbonded pair of electrons. This field is slightly larger than the repulsive field created by the bonded electron pairs, represented by the red balloons.

Part 2

1. Use the model kit to construct a model of the CH4 molecule. Use the color chart that comes with your kit.

2. Draw a sketch of the CH4 model once constructed.

3. Repeat steps 1 and 2 for H2O, H3O+ , HCl, NH3, Cl2, N2, PCl3, CH3OH, and CO2.

Data:
Molecular Formula
Un-bonded Pairs on Central Atom
Molecular Geometry
Polarity
CH4
2
Tetrahedral
Non-Polar
H2O
2
Bent
Polar
H3O+
1
Trigonal Pyramidal
Polar
HC1
0
Linear
Polar
NH3
1
Trigonal Pyramidal
Polar
Cl2
0
Trigonal Bi-Pyramidal
Non-Polar
N2
1
Bent
Non-Polar
PCl3
1
Trigonal Pyramidal
Polar
CH3OH
2
Tetrahedral
Polar
CO2
4
Linear
Non-Polar

Calculations:

None required for this lab.

Results:
There were multiple bonds observed using the model kit.

Discussion Questions:

1. Explain the difference in polarity between CO2 and SO2 based on their molecular shapes.

SO2 is bent with two dipoles of oxygen bonds. These bonds will not cancel out like in CO2. SO2 has a stronger dipole.

2. Describe the similarities between H3O+ and NH3. Compare/contrast their shapes and polarities within the context of your answer. These molecules are called isoelectronic. Why?

Their shapes are the same except H3O+ is positively charged and much more polar because oxygen is more electronegative than nitrogen. They both are isoelectronic because they have the same structure using the same number of electrons and same orbitals.

3. What information about a molecule can you gain from the Lewis-dot structure? Is it possible to determine molecular geometry based upon a Lewis structure? Explain your response.

Lewis dot structures help predict molecular structure. Take SO2 for example it has a lone pair of electrons on sulfur. The carbon in CO2 does not have the same lone pair of electrons.

4. What is the difference between electron geometry and molecular geometry? How can knowing both assist in determining whether a molecule is polar or nonpolar?

Electron geometry is the arrangement of electron domains about the central atom of a molecule or ion. Molecular geometry is the arrangement of only the atoms in a molecule or ion.

Conclusion:

During this lab we had to identify interactions between molecules. This was accomplished with the aid of the model kit and some balloons. Once we established interactions then Lewis structures were drawn. We also had to identify bonds as single, double or triple.

I had to draw Lewis structures. Electron and Molecular geometry had to be identified as well. We also had to determine if compounds were polar or non-polar.

In conclusion I really enjoyed this lab. Its interesting doing the labs at home with the actual kit. The purpose of this VSEPR lab has been satisfied. I understand more about molecular bonds and my kids got to play with some balloons.

References:

Brown, Theodore (2009). Chemistry: The Central Science (11th ed.) Upper Saddle River: Pearson Prentice Hall


References: Brown, Theodore (2009). Chemistry: The Central Science (11th ed.) Upper Saddle River: Pearson Prentice Hall
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