Chemical Education Today
Chemical Bonding Makes a Difference!
by Mary Harris
Chemical Bonding Makes a Difference! is a brief PowerPoint presentation that shows how sometimes a small difference in bonding can result in a drastic change in the properties of a material. It would be appropriate for high school and college students studying covalent bonding and polymers. The economically significant subject of polymers deserves a larger role in chemistry classes. This year’s National Chemistry Week theme, “Your Home—It’s All Built on Chemistry” is an opportunity to introduce polymers found in the home to the chemistry classroom. Two relevant molecules discussed in the presentation are starch and cellulose. Both consist of chains of glucose molecules, but the linkage between the rings is slightly different. As a result, starch is digestible by humans, while cellulose, a major component of wood, is not (although termites in your home may find it tasty!). High density polyethylene (HDPE) (Figure 1) and low density polyethylene (LDPE) are used in construction materials. The presentation suggests simple activities for students to help them discover the physical difference between these two plastics, which is a result of the difference in the arrangement of their polymer chains. [Further information on polymers used in construction is available on p 1428 of this issue of JCE.] Students may also be interested in real-world polymers such as Kevlar, Nylon, and Nomex fibers, which illustrate the importance of cis- and trans- conformations. The presentation also illustrates the slight difference in molecular structure between sucrose and sucralose, an artificial sweetener commonly identified with the brand name Splenda. Replacing a few –OH groups with –Cl makes sucralose sweeter by a factor of 600!
Figure 1. Example slide from the PowerPoint presentation.
Using this presentation will help your students realize the importance of bonding in some everyday items such as construction materials, artificial sweeteners, plastic bags, bulletproof vests, and PET bottles. We use polymers in all kinds of products every day; including polymer chemistry in our curriculum is important. Visit JCE OnlineW to access the presentation and enjoy! Supplemental Material The 56-page PowerPoint presentation described above is available in this issue of JCE Online. W
Marry Harris teaches chemistry at John Burroughs School, St. Louis, MO; [email protected]
Vol. XX No. XX Month 200X
Journal of Chemical Education