Academic journal article The Science Teacher

Finding Patterns: A Lesson on Naming Chemical Compounds

Academic journal article The Science Teacher

Finding Patterns: A Lesson on Naming Chemical Compounds

Article excerpt

Students best learn science through a combination of science inquiry and language learning (Stoddart et al. 2002). This article presents a series of chemistry lessons on the naming of compounds. The weeklong unit focuses on patterns across compound names and chemical formulas and addresses several of the Next Generation Science Standards (NGSS Lead States 2013; see box, p. 47).

I first taught these lessons to a summer class of five students who had failed their grade 10 chemistry course. Since then, multiple student teachers have used these pattern-based inquiry lessons successfully with their regular chemistry classes. In this article, I emphasize the inquiry portions of the unit.

Categorizing cards

Before the lesson, I print binary compound names and their corresponding formulas on card stock. Then I cut the names and formulas into individual cards and laminate the cards to protect them for future use (for sample cards, see Figure 1). The number of cards in a set should be informed by students' needs; I generally used 10 to 25 cards in a set.

At the beginning of the first lesson, I ask students, "How can you categorize these compounds based on their names? What patterns can you find?" Working in pairs, students examine their cards. For large classes, students work well in groups of four, as long as each group includes a moderate range in abilities or comfort level. Higher-achieving groups can be given more cards and, before starting, informed that they can move on to creating a graphic representation of their results and associated reasoning.

My cards included a good mix of binary compound types, leaving these categories unidentified and unexplained to students. A Type I binary compound consists of a metal that forms a single type of cation and a nonmetal, based on the pattern of electrons in the outermost energy level of their atoms. A Type II compound consists of a transition metal that can form two or more types of cation and a nonmetal. A Type III compound consists of two nonmetals. (Note: I arrange the compounds by type in Figure 1 to serve as an answer key for the final classification systems.)

I encourage groups to find multiple ways to categorize the compounds by name. This allows some students to initially organize the cards in simple, nonscientific ways, such as alphabetical order, and then consider the specific elements and name structures and components. The activity builds on students' existing abilities to identify patterns and classify items, which increases the degree of students' critical thinking. Throughout the exploration, I remind students that their careful observations of the compound names and their reasoning are more important than their classification systems.

To support their work, I ask questions such as, "What about the word parts? Where is this word part in relation to the main, or root, word?" as I point to prefixes and suffixes. Did anything seem strange in some of these names?" Teachers have reported that all students could identify multiple categorizing possibilities and were comfortable with the components of the compound names.

Groups then share their reasoning and supporting evidence for their different categorization systems and evaluate each system, clarifying and challenging each other's ideas. At least one group commonly focuses on the elements involved in the compound, regardless of their position in the compound. For example, one student justified categorizing all compounds with sulfur together by referencing potential similarities among where the compounds might form. Another student emphasized the Roman numerals in the middle of some of the names. Another highlighted the prefixes on the first word, second word, or both.

After some debate about the merits of the different categorization systems, students generally agree on three main categories, based on the compound names:

* no Roman numeral and no prefixes,

* Roman numeral with no prefixes, and

* prefixes with no Roman numeral. …

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