Lab 5: Molecular Geometry
- Page ID
- 514167
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PURPOSE
- To use molecular models to help determine electron and molecular geometries, central atom hybridization, and whether the molecule is polar or nonpolar.
INTRODUCTION
Understanding molecular geometry is essential for predicting the physical and chemical properties of molecules. In this lab, you will use molecular modeling kits to construct three-dimensional representations of small molecules. By examining these models, you will determine electron and molecular geometries, identify the hybridization of central atoms, and assess molecular polarity. This hands-on approach will reinforce concepts from VSEPR (Valence Shell Electron Pair Repulsion) theory and hybridization, providing a visual and interactive way to explore molecular structure.
SAFETY PRECAUTIONS
- Be cautious when assembling and disassembling models to avoid pinching fingers or breaking small parts.
EQUIPMENT AND CHEMICALS NEEDED
- Molecular modeling kits
EXPERIMENTAL PROCEDURE
- Determine the total valence electrons and draw the Lewis Structure for the given compounds.
- Use VSEPR to determine the electron domain geometry, hybridization, number of lone pairs, and the molecular geometry.
- Determine if the molecule is polar or nonpolar from the atoms present and the molecular geometry.
- Be sure to include a picture of an assembled model showing the atoms, bonds, and lone pairs.
When using the molecular modeling kits, do NOT select the ball to use for the central atom according to the key provided in the kits. Instead, select the ball to use according to how many electron domains the central atom has. Pay very close attention to the hole geometry!
Only single bonds
Use this table to determine the central atom ball.
| Number of Electron Domains | Hole Geometry |
|---|---|
| 2 |
linear (you may have to use 6, octahedral and use holes that are opposite each other) |
| 3 |
trigonal planar (you may have to use 5, trigonal bipyramidal and leave the holes that are opposite each other empty) |
| 4 |
tetrahedral |
| 5 |
trigonal bipyramidal |
| 6 |
octahedral |
Multiple Bonds
If there are double bonds, you will have to add a hole for the second bond. For example: 3 electron domains with one double bond use a ball with 4 holes (tetrahedral). If there are triple bonds, you will have to add 2 holes.
Terminal Atoms
For the terminal atoms, use white (one hole) for hydrogen, red (two holes) for oxygen, and green (one hole) for halogens.
PRE-LAB QUESTIONS
- What is the VSEPR theory, and how is it used to determine the electron domain geometry and molecular geometry of a molecule?
- How do you determine the total number of valence electrons for a given molecule or ion, and how does this relate to drawing a Lewis structure?
- Explain the relationship between electron domain geometry and molecular geometry. How do lone pairs of electrons affect molecular geometry?
- Explain how to determine if a molecule is polar or nonpolar. Consider the types of atoms present and the molecular geometry of the molecule.
DATA AND OBSERVATIONS
| Molecular Formula | CH4 | PH3 | SO3 | BCl3 |
|---|---|---|---|---|
| Total Valence Electrons | ||||
| Lewis Structure | ||||
| Electron Domains | ||||
| Electron Domain Geometry | ||||
| Hybridization | ||||
| Lone Pairs | ||||
| Molecular Geometry | ||||
| Polar or nonpolar | ||||
| Picture |
| Molecular Formula | CO | H2S | PCl5 | SF4 |
|---|---|---|---|---|
| Total Valence Electrons | ||||
| Lewis Structure | ||||
| Electron Domains | ||||
| Electron Domain Geometry | ||||
| Hybridization | ||||
| Lone Pairs | ||||
| Molecular Geometry | ||||
| Polar or nonpolar | ||||
| Picture |
| Molecular Formula | BrF3 | XeF2 | SF6 | IF5 |
|---|---|---|---|---|
| Total Valence Electrons | ||||
| Lewis Structure | ||||
| Electron Domains | ||||
| Electron Domain Geometry | ||||
| Hybridization | ||||
| Lone Pairs | ||||
| Molecular Geometry | ||||
| Polar or nonpolar | ||||
| Picture |
| Molecular Formula | XeF4 | CO32− | NO3− | OF2 |
|---|---|---|---|---|
| Total Valence Electrons | ||||
| Lewis Structure | ||||
| Electron Domains | ||||
| Electron Domain Geometry | ||||
| Hybridization | ||||
| Lone Pairs | ||||
| Molecular Geometry | ||||
| Polar or nonpolar | ||||
| Picture |
| Molecular Formula | SCl2 | C2H6 | C2H4 | C2H2 |
|---|---|---|---|---|
| Total Valence Electrons | ||||
| Lewis Structure | ||||
| Electron Domains | ||||
| Electron Domain Geometry | ||||
| Hybridization | ||||
| Lone Pairs | ||||
| Molecular Geometry | ||||
| Polar or nonpolar | ||||
| Picture |
POST-LAB QUESTIONS
- Explain how you used the VSEPR theory to predict the electron domain and molecular geometries of the molecules you modeled in the lab. Were there any molecules for which the predicted geometry differed from the actual model you created? If so, why might that be?
- For the molecules you identified as polar, describe how the molecular geometry and bond polarity contribute to the overall polarity of the molecule. Explain why some molecules with polar bonds are nonpolar overall.
- Reflect on your experience assembling the molecular models. Did you encounter any difficulties or unexpected observations? How did the physical models enhance your understanding of molecular geometry compared to just drawing Lewis structures