This is a modeling activity designed for pairs of students where students use molecular models to construct a simple 2-carbon alkane, then convert it to a 2-carbon alkene and 2-carbon alkyne. After observing changes in structure among the 2-carbon series, students will use molecular models to investigate the myriad of structures for polyethylene, one of the most common, multipurpose plastics found in their daily lives.
All these items are made from the same basic unit, ethylene. What do you think allows for the wide variety of properties among the materials?
PE HS-PS2-6. Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
No PPE is required for the activity.
Copy or upload student activity page. There is no disposal of waste materials.
Drawings will vary. Guide students toward a long chain, a chain with a couple of branches, a chain with many branches, or a chain with cross-links. Bonding rules still apply.
Moving from ethane to ethyne, describe what happened to the ratio of carbon to hydrogen atoms and how the change affected the structure of the molecule. You may insert your diagrams as evidence of changes.
From ethane to ethene, two hydrogens were lost. The ratio went from 2C:6H (or 1:3) to 2C:4H (or 1:2). From ethene to ethyne another 2 hydrogens were lost making the ratio 2C:2H (or 1:1). Structurally, ethane is a 3-dimensional molecule and looks like 2 pyramids, (tetrahedrons) are stuck together. Ethene has the double bond which flattens the molecule so that it looks planar in the model. Ethyne has the triple bond and 2 less electrons and the structure looks linear.
In a well-written statement, explain why each of your polyethylene structures will function as a foam, film, or rigid solid.
Student answers will vary but they may say a long single chain of monomers should be stretchy, highly cross-linked molecules would be rigid, and structures with lots of open space or pore space will be a foam. They will investigate the actual polymer shapes in assessment 3 and evaluate their own designs.
Check your design skills. Research the types of polyethylene, their structures, and uses then write a detailed explanation of at least three types. Evaluate the design of your ethylene polymers for structure and function based on your research.
Student answers will vary. Check for three different polyethylene variations. Some options include:
Look for an evaluation of all three of their designed polymers.
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