Problem Set Activity: Modeling Intermolecular Forces

Objective: In this activity models of chemicals will be built using molecules-3D program that is downloaded from the internet. Models of the molecule can also be created using molecular modeling kits in class. Using the models and information from the textbook the correlation between structural features and attractive and repulsive forces between molecules (intermolecular forces) will be established.

See activity #7, Building Molecular Model for a review of Molecular-3D.

Go to http://www.chemspider.com/

Use chemfinder to look up structure and properties of the chemicals below.  Your instructor may direct you to other websites or provide you other information on the structure of these chemicals.

Discussion:   The figure below shows the range of the various molecular forces.  Intramolecular forces which covers ionic bonds and covalent bonds.  Shown below are five intermolecular forces, of which dipole-dipole, London Dispersion forces and H-bonding are the most significant. In this activity the nature of intermolecular attraction will be investigated. The different nature of intermolecular forces will be reviewed and virtual chemical models will help explain how intermolecular forces explains the attractive and repulsive properties for different substances.

 

Problem Set Activty: Modeling Intermolecular Forces
___/ ___ Score	Name (Last)_______________(First)_______________ Date _______

1 Ethane, Ethene and Ethyne

Begin by building models of C₂H₆, C₂H₄, and C₂H₂, or download or create the 3-dimensional model of these chemicals. Answer the following questions in your report.

Use the models that you have to explain differences in atom arrangement and bond angles. What are the bond angles in these molecules? How would you describe the shapes of each structure?

Click on each links below to obtain information on Ethane, Ethene and Ethyne.
Fill the table below.

Molecule, Draw structure	Chem Formula, Molar Mass Chemical name, Synonym name	No. of Valence electrons around central atom	Bond angles and shape	Is the chemical soluble in water?  Is the chemical polar or nonpolar?	Physical Properties Melting Pt. Boiling Pt. Density
Ethane
Ethene
Ethyne

Explain the structure for each of the three molecules.

 

2 Methane, Ammonia and Water

Build models of CH₄, NH₃, and H₂O, or click on each links below to obtain informaton.  Answer the following questions in your report.
Using models of CH₄, NH₃, and H₂O develop an explanation for describing shapes of molecules, polarity, and intermolecular forces. Compare the arrangement of the hydrogen around the central atom for each of the structures. What is the arrangement of atoms and valence electron pairs around the central atom? What are the approximate bond angles? What are the shapes of the molecules? Which molecules are polar, and which are nonpolar? Which of the compounds has the highest boiling point? Which molecule has the strongest intermolecular forces? You might consider building multiple structures of the same molecule to consider how multiple molecules interact.

Click on each links below to obtain informaton on Methane, Ammonia and Water. 
Fill the table below.

Molecule, Draw structure	Chem Formula, Molar Mass, Chemical name, Synonym name	No. of Valence electrons around central atom	Bond angles and shape	Is the chemical soluble in water?  Is the chemical polar or nonpolar?	Physical Properties Melting Pt. Boiling Pt. Density
Methane
Ammonia
Water

 

 

3 Ethanol, Propanol and Butanol

To develop your explanations about intermolecular forces further, use models to explain the differences in boiling points for CH₃CH₂OH (ethanol), CH₃CH₂CH₂OH (propanol), and CH₃CH₂CH₂CH₂OH (butanol). The chemical formulas listed in the table are shorthand notations for the arrangement of atoms along the carbon chain. Note that the structural formula as shown is written in two dimensions and does not represent the three-dimensional arrangement of atoms needed to explain the properties of the molecule.

Click on each links below to obtain informaton on Ethanol, Propanol and Butanol.
Fill the table below.

Molecule, Draw structure	Chem Formula, Molar Mass, Chemical name, Synonym name	No. of Valence electrons around central atom	Bond angles and shape	Is the chemical soluble in water?  Is the chemical polar or nonpolar?	Physical Properties Melting Pt. Boiling Pt. Density
Ethanol CH3CH2OH
Propanol CH3CH2CH2OH
Butanol CH3CH2CH2CH2OH

 

 

4 Cyclohexane, Diethyl ether and Ethylene glycol in either carbon tetrachloride or water.

Consider a mixture of carbon tetrachloride (CCl₄) or water, and the chemicals shown below to form solutions that has two components. Based on your models, decide what types of intermolecular forces could be experienced by each of these substances. Explain the importance of why some substances will form a homogenous solution while others form separate layers when mixed.

Click on each links below to obtain informaton on Cyclohexane, Diethylether and Ethylene glycol.  Fill the table below.

Molecule, Draw structure	Chem Formula, Molar Mass, Chemical name, Synonym name	No. of Valence electrons around central atom	Describe the shape around the C atoms Bond angles and shape	Is the chemical soluble in water?  Is the chemical polar or nonpolar?	Physical Properties Melting Pt. Boiling Pt. Density
Cyclohexane C6H12
Diethyl ether CH3CH2OCH2CH3
Ethylene glycol HOCH2CH2OH

 

 

Report    Write a report on how you developed all the structures mentioned in this exercise. Your report should have a minimum of two typed pages and it should address all the questions the discussion posed. It is important to address the type of intermolecular forces that exist for each chemical and how these forces influence the properties, such as boiling point, surface tension, miscibility of these chemical. Your report should also summarize the magnitude of each type of intermolecular force and how the structure of the chemical accounts for such force.