BONDING AND MOLECULAR GEOMETRIES

BONDING AND MOLECULAR GEOMETRIES REMOTE INSTRUCTION ACTIVITY

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 repulsion) 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 hybridized atomic orbitals. That is, rather than filling in s, p, d, or f orbitals, they occupy orbitals that are combinations of those simpler atomic orbitals. The number of atomic orbitals used in hybridization 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 hybridized since it uses its 2s and all three 2p orbitals in bonding.

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.

NH3 Name:

Lewis Structure: 3-D Sketch:

Hybridization:
Polarity:

Molecular Shape:
Bond Angle:

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 hybridization theories to help you answer the questions.
H2O Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

 
CO2 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

BF3 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

ClF3 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:
SF6 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

O3 Name: Ozone
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

AsF5 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:
KrCl4 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

SeCl4 Name:
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

CH2Cl2 Name: Dichloromethane
Lewis Structure: 3-D Sketch:

Hybridization: Polarity:
Molecular Shape: Bond Angle:

Find two molecules from the worksheet above that are bent, but with different hybridizations:
____________________________________
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:

structural formula ball-and-stick model
1. Label each internal atom in the structure above with its hybridization and geometry.
2. How many sigma bonds and how many pi bonds are present in alanine?
______________, ______________ 

Cyclohexane, C6H12, and benzene, C6H6, are both molecules containing six carbon atoms arranged in a ring. Draw the Lewis structures of the two molecules:
Cyclohexane Benzene

3. What are the hybridizations of the carbon 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: ______________, ______________ 
Cyclohexane: ______________, ______________ 