INTERPRETATION OF PHYSICAL PROPERTIES FROM MOLECULAR STRUCTURE. A COMPARATIVE ANALYSIS AMONG THREE WAYS OF ASSESSMENT: OBJECTIVE ITEMS, OPEN QUESTIONS AND GRAPHIC DESCRIPTIONS

J.A. Llorens-Molina, I. Sanz Berzosa

Universitat Politècnica de València (SPAIN)
The difficulty to coordinate the different description levels concerning physical and chemical change (macroscopic, symbolic and atomic-molecular) is a well known learning difficulty, extensively described in the literature. Indeed, a noteworthy difficulty to interpret physical and chemical properties of substances from atomic and molecular interactions is clearly noticeable even in higher education courses. This fact can be related to a poor understanding of pure substance and chemical change concepts. This way, misconceptions such as the association between phase changes and covalent bond breaking or the ambiguous use of term “stability” referred both physical and chemical context, have a significant occurrence. Some causes have been suggested in the literature to explain them, mainly, the little attention paid to study intermolecular forces in chemical bond introduction and a contradictory and confusing use of terminology concerning these topics.

Given that intermolecular forces and related topics are key contents in introductory organic chemistry, to have reliable tools for their assessment becomes necessary. In order to reach this goal, a triple way to test the understanding how physical changes can be interpreted from intermolecular forces has been carried out. For this purpose, a classroom activity was developed in an introductory organic chemistry for Food Technology students.

This activity consisted of a previous questionnaire which comprises three parts:
(1) a true-false test dealing with the role of chemical bond and intermolecular forces in phase changes, dissolution processes and chemical stability,
(2) opened questions about experimental facts related to the mentioned topics and
(3) drawing tasks about them.

The comparison from these three types of data gives the following results:
(1) a considerable occurrence of a typical misconception consisting of considering the covalent bonds breaking in boiling process interpretation,
(2) the results from true-false test are clearly better than the other two ways of assessment; nevertheless, their lack of consistence leads us to have no great confidence in the sole use of this sort of assessment tools and
(3), the great difficulty to use the atomic-molecular model to make graphic explanations of physical and chemical changes.

As concluding remarks from these results, we argue for the need of implementing several changes concerning both to content and learning methods about these topics:
(1) need of paying more attention to nature and role of intermolecular forces in chemistry curriculum since its beginnings,
(2) diversify the assessment tools so as to bring the maximum number of skills and abilities to bear and
(3) pay much more attention to graphic expression of scientific ideas and particularly, all that concerns to atomic-molecular representations.