Sub-microscopic representations are more difficult to understand for pupils, which is due to the abstraction of the particle nature of matter. The research results confirm the above argument, since pupils misunderstand the chemical concepts at the sub-microscopic level.
The purpose of the study was to determine whether the ninth graders misunderstand the chemical concepts such as the aggregate state of matter, a mixture, a pure substance, an element, a compound, a physical and a chemical change, and a chemical reaction at the sub-microscopic level.
The survey sample included 188 ninth graders of six elementary schools in Ljubljana and its surroundings. The measurement instrument of the survey was the knowledge test with five authentic problem tasks. The knowledge test is economical, has content validity and is discriminatory.
The survey results show that 48.4% of the ninth graders have difficulties in identifying the sub-microscopic representation of a compound. 67.0% of the pupils do not distinguish between the sub-microscopic distribution of particles in the solid and liquid states of water. More than 75.0% of the pupils recognize a mixture, a pure substance and a physical change from sub-microscopic representations. 99.5% of the pupils are successful in identifying individual elements of the particle distribution schemes.
According to the research results it can be concluded that the ninth graders confuse the distribution of particles in the liquid and solid states of water at the sub-microscopic level, as they are not yet familiar with the hydrogen bonding of water molecules. The majority of the ninth graders (88%) failed to write down the equation of a chemical reaction from a sub-microscopic representation of reactants and products. In elementary school, when teaching chemistry concepts and processes, greater integration of the macroscopic, the sub-microscopic and the symbolic levels of representations of chemistry concepts would be essential a for better understanding of the chemistry concepts and processes.