Featured article
Talanquer, V. (2008). Students’ predictions about the sensory
properties of chemical compounds: Additive versus emergent frameworks. In: Science
Education. 92 (1). January 2008. pp.96–114.
This research investigated the reasoning used by students to predict the properties (colour, smell or taste) of the compound formed from the reaction of two substances, each with their own given properties.
The opening of the paper introduces the idea of "commonsense reasoning" that can result in naïve explanations by novice learners. The author shares findings from the research literature relating to the use of this “intuitive thinking”. It is suggested that an intuitive thinker is more likely to create an explanation based on a single mechanistic cause that produces a linear progression of events.
This
study was carried out in the U.S. with
over 400 students in their first year of a general introductory chemistry
course for science and engineering majors. These first-year student
participants were still regarded as “novices” for the purposes of the study.
The focus of the study was on the properties of compounds and so it is still potentially highly relevant to those teaching younger students as the properties of elements and compounds commonly features in the school chemistry curriculum for students aged 11 to 14.
The paper describes one way of reasoning about the predicted properties of a compound (from given information on the properties of the reacting substances) as an additive framework. Using this framework, the properties of a compound are thought of as a
linear combination of the original properties of each component.
This is to be contrasted with the use of emergent framework of thinking in which the properties of a complex system result from an interaction of its parts. This is the framework of thinking that should be applied to the properties of compounds. The properties of a compound arise (or "emerge") from the arrangement of atoms (or ions) and not from the addition of the properties of the substances from which it is formed.
The author devised a series of questionnaires using multiple
choice questions and black and white particle diagrams. The questions asked students to select the answer
that best predicted the colour, taste or smell of the compound resulting from a
reaction between the two substances depicted. Some students also took part in
follow-up interviews to determine the reasons for their answers.
The researchers used a range of examples in the multiple-choice questionnaires including:
- varied ratios of reacting substance particles
- different sizes of reacting substance particles
- reacting substances with no property (e.g. no colour)
- the answer options of “other” and “more information needed to make a prediction”
A student who was confident in using an emergent framework for their thinking would be expected to consistently answer “other” or “more information
needed” across all questions.
Less than 3% of students were found to consistently respond
in this way.
In the initial question in which a blue substance reacted
with a yellow substance with a 1:1 ratio of particles, 90.4% of participants
selected the answer “green” as being the property of the final compound. This suggests that the vast majority of
students in the study were applying additive rather than emergent thinking.
The questions which included a non 1:1 ratio of reacting
substance particles provided further evidence of this additive thinking. In a
similar question to above (but with a 4:1 ratio of particles), 79.6% of students answered blue (rather than
green).
The interviews revealed that even when some students did select “other” it was not necessarily due to emergent thinking. Sometimes students said that there was a need for more information on the “dominance” of a particular property. For example, if a blue substance reacted with yellow substance (in a 1:1 ratio of particles) might the blue dominate over the yellow rather than answering “green”?
If additive thinking is indeed present in other educational contexts,
then this raises questions about the teaching of this topic. The reflective
questions below raise some points to consider about the way in which this topic
is commonly taught which could inadvertently encourage additive thinking.
The final recommendation of the author of the paper is that “helping
students recognise the existence of emergent properties in chemical systems is crucical if
we want them to develop meaningful understandings of a variety of topics”. This raises questions regarding curriculum priorities and the importance of getting
the earlier years (age 11-4) right to provide a sound foundation for later chemistry learning.
BEST Question
A compound Is made up of a combination of atoms from a blue
substance and a yellow substance.
What colour is the compound?
A blue
B yellow
C green
D other
The expected answer is D "other".
The colour of the compound is not related to the colour of substances made from its constituent atoms. This information is not sufficient to predict the colour of the compound.
Students who are using an additive approach are likely to predict that the compound is green (option C). A prediction of blue (option A) may mean that the student thinks that a darker colour may overwhelm the yellow.
Useful links
BEST
Topic 2 Key concept 1: Atoms and molecules
Diagnostic questions to check for student misconceptions
about the atomic model as part of a five-part progression (and including
response activities)
University of York Science Education Group
Reflective questions
This study was undertaken with students in their
first year of a general chemistry course in the U.S. To what extent do you think an additive framework of thinking is applied by students in your school context?
Look at some particle diagrams that you use to teacher
elements and compounds. To what extent could these reinforce additive thinking
and what adjustments to the diagrams or your use of the diagrams could better emphasise the need for emergent thinking?
A compound is often defined as “a substance formed when two
or more different elements are chemically bonded together”. To what extent
could this reinforce additive thinking and what adjustments in the phrasing of
the definition, or clarification when teaching, could reduce this?