|
Asia-Pacific Forum on Science
Learning and Teaching, Volume 5, Issue 1, Article 3 (Apr., 2004) Daniel Kim Chwee TAN and Kim Seng CHAN An analysis of two textbooks on the topic of intermolecular forces
|
|
|
Asia-Pacific Forum on Science
Learning and Teaching, Volume 5, Issue 1, Article 3 (Apr., 2004) Daniel Kim Chwee TAN and Kim Seng CHAN An analysis of two textbooks on the topic of intermolecular forces
|
Results and Discussion
Electrostatic nature of intermolecular forces
Hill and Holman presented intermolecular forces as a topic separate from chemical bonds. This separation might prevent students from seeing the links between intermolecular forces and the other types of chemical bonds. Although Ramsden integrated intermolecular forces as a section of the topic of chemical bonds, there was no explicit discussion on the similarities and differences between intermolecular forces and other conventional chemical bonds. In addition, there were several statements in the textbooks which could cause difficulties for students. For example,
These weak, short-range forces of attraction between molecules are known as Van der Waals' forces. Van der Waals' bonds are, of course, much weaker than covalent and ionic bonds.
(Hill & Holman, 1989, p. 116)
The above statement might lead to students, who were novices in chemistry, to be confused with the terms "force" and "bond". From the electrostatic perspective (Taber, 1997), intermolecular forces were just another type of chemical bond which differed from other chemical bonds because the types of particles involved were different. Thus, emphasis should be placed on the electrostatic nature of chemical bonds irrespective of the types of bonds. If such a perspective was not emphasised, students would see intermolecular forces as very much different from other chemical bonds, and this might hinder the formation of a more coherent and meaningful conceptual framework (Taber, 1997).
Another problematic statement which required more elaboration was
When molecules pack together in the liquid or solid state, there must be forces of attraction between them. J D van der Waals postulated the existence of forces of attraction and repulsion that are neither ionic or covalent. Such forces arise in a number of ways and are collectively called van der Waals' forces.
(Ramsden, 1994, p. 117)
There was no mention of any force of attraction between gases in the section on van der Waals forces in Ramsden (1994), only between solids and liquids. This could be problematic as students might think that there were no van der Waals forces between gases, and these forces account for the non-ideal behaviour of real gases. In addition, the statements,
"In the liquid state, the molecules of alcohols are associated by hydrogen bonding. Energy must be supplied to break these bonds when the liquid is vaporized..."
(Ramsden, 1994, p. 120)
could give students the impression that when a liquid was boiled, intermolecular forces would be broken resulting in no intermolecular forces between the particles in a gas.
Copyright (C) 2004 HKIEd APFSLT. Volume 5, Issue 1, Article 3 (Apr., 2004). All Rights Reserved.
