CTS Guide: Elements, Compounds, and the Periodic Table, pp 156-157- Section IV Research Summaries

Elements and Compounds

• Chemistry has a unique language, which can pose difficulties for conceptual understanding. Evidence suggests that difficulties may arise because teachers are unaware of the meanings students have for chemical terms. “Students’ understanding of the differences between elements, compounds, and mixtures in particle terms is poor. It is therefore unsurprising that students find chemistry ‘hard,’ as they do not understand a basic principle providing a foundation for more detailed study” (Kind 2004, p. 22).

• Barker’s study (1994) revealed that only about 3% of 16-year-old students surveyed at the beginning of a general chemistry class could explain how to test whether a substance was an element or compound. The study also revealed that 43% of the students surveyed could define element and compound at the beginning of the course; at the end of the course, this percentage remained relatively unchanged.

• Although chemical compounds are regarded as single substances, several studies have found that children frequently describe compounds as though they are mixtures of elements. This may be due to a lack of conceptual understanding of the chemical combination of elements in a compound (Driver et al. 1994).

• Even though the idea that elements cannot be broken down into simpler substances was introduced at ages 11 and 12, Briggs and Holding’s study (1986) found that only 25% of a sample of 300 British 15-year-old students could apply it to explain how elements differed from other substances. When using particle representations of elements, compounds, and mixtures, they found that many students could not distinguish a particle representation of an element from a compound.

Concept of a Substance

• Ahtee and Varjola (1998) found that students of all ages find the term substance problematic. Students interchanged substance with atom. For example, a 17-year-old student said, “Substances change outer electrons between them.”

Periodic Table, Isotopes, Allotropes

• Schmidt, Baumgärtner, and Eybe (2003) studied secondary school students’ concepts of isotopes and allotropes and how the concepts are linked to the periodic table. Many students who recognized that diamonds and graphite were forms of carbon expected diamond atoms to contain more neutrons than the graphite atoms because diamonds were harder than graphite. Only a few students explained the difference in structure. There was confusion between terms such as isotope, isomer, and allotrope.

• In an analysis of items from a British Examination Board study, students had difficulty understanding why diamond, graphite, and fullerenes are not named in the same spot on the periodic table as carbon (Schmidt 1998).