Chemistry is taught at all levels of the school curriculum, from early childhood to high school and beyond. The curriculum in the early years focuses on the properties of matter; upper elementary and middle school shifts to looking more closely at the particulate nature of matter; and high school seeks to understand the atom, including its mathematical and chemical models. Ultimately, students are developing understandings of phenomena by simultaneously envisioning the properties of the element, compound, or mixture, the behavior of the particles, and various chemical and mathematical equations.

This progression of learning relates to and contextualizes chemistry’s multiple levels of thought and attributes. The multi levels of thought are content-specific and include:

• macroscopic (macro) – observable properties of matter;
• submicroscopic (submicro) – matter represented by the constituent atoms, molecules, and ions; and symbolic – the mathematical and chemical symbols and models. ^{1 –4}

Contextualizing chemistry at the human element level attends to the real-world applications of science.⁵ The PreK–12 learning progression delves deeper into the subatomic levels; however, all is tied to the observations and descriptions of matter that are introduced in the early grades.

Although one might consider the multiple levels of thought to be the secondary teachers’ concern⁴, argued the difficulties of learning science were based on how it was taught, with little regard to what children understand. Regardless of age, all PreK–12 students hold some form of naïve or alternative understanding of chemistry (matter). Young children until the age of 13 have naïve understandings of matter that include not recognizing all states of matter (i.e., gases) and have difficulty describing matter (for example, basing their description solely on an object’s function). Middle and high school students hold alternative conceptions about the atom that include applying the properties of the element to explain the properties of a single atom. They tend to see models as reality, rather than as tools for understanding; they may also have numerous misunderstandings about the size, structure, and weight of atoms. However, children may experience an overload of their working memory as they struggle with more than one level of thought.⁴

Designing instruction to attend to children’s understandings involves both the teacher and student being aware of the multiple representation levels. To help teachers who are trying to address this challenge, this paper presents the learning progressions for properties of matter in light of the multiple representation levels.

Tetrahedral model of chemistry education

Designing instruction for the PreK–12th grade students involves recognizing the multiple levels of thought and framing the learning in the human element. Johnstone’s levels of thought model ⁴ depicted the chemistry content as a trigonal planar model (see Figure 1). The model operates in the macro level, as students observe a phenomenon (e.g., properties of matter, chemical reactions) but the submicro and symbolic levels explain the visible phenomenon.

Mahaffy argued that non-scientists do not recognize how the molecular world applies to the industrial and real-world applications, and thus introduced the human element.5 In doing so, Mahaffy proposed a tetrahedral model in which to frame the content levels (see Figure 2). Table 1 presents the definitions and examples of each level of thought for the tetrahedral model. Table 2 shows the learning progression for the PreK–12^th grade standards⁶ Next Generation Science Standards (NGSS) Disciplinary Core Idea (DCI) – Structure and Properties of Matter ⁷ and Common Core State Standards for Mathematics ⁸.

Macro level of thinking

The macro level focuses on the observable features of matter including the measurable, quantifiable, and reproducible aspects^9,10. Examples of observation at the macro level can include exploring the properties of matter, watching a demonstration, or engaging in a laboratory experiment. Students are tasked with identifying and classifying matter based on the physical (e.g., color) and chemical (e.g., reactivity) properties. Much of the instruction is based on the features of matter observed by the naked eye, as children classify matter using texture, color, size, shape, and state of matter.

Within the learning progression, the PreK–2^nd grade standards focus on the macro level as children explore the properties of matter (i.e., color, hardness, texture, flexibility) including the states of matter (NGSS DCI: 2-PS1-1). This level includes the observable properties as well as those that are measurable and quantifiable (see Tables 1 and 2). As such, I suggest that educators for the PreK–2^nd grade also introduce the mathematics standards on measurement in conjunction with the properties of matter standards. The development of measurement skills aligns to the upper elementary learning progression for matter (NGSS DCI: 5-PS1-3) continuing through the high school grade level band.

As the teacher designs instruction, it is important to understand that children often do not focus on describing matter in terms of measurability. Instead, children are found to focus on what makes an object useful — properties of materials — using five main criteria:¹¹

• Compositional: What objects are made of;
• Function: What objects could be used for;
• Location: Where objects might be found;
• Perceptual: How objects are perceived to have observable properties; and
• Manufactured: Man-made.

Within these five criteria, the child discusses the different properties that make the material useful for different purposes, which aligns the NGSS DCI: 2-PS1-2 and 2-PS1-3. For an example of properties of material, children may explore which material is best suited for building a house to keep a wolf out, like in The Three Little Pigs¹². In this scenario, properties of matter would be describing the properties of the straw, sticks, and bricks, which might include the strength, color, and weight. Properties of materials involve using the properties of matter to make decisions on when to use a certain material over another. Teachers need to be aware that children may begin discussing properties of materials when presented with items, and thus need guidance to turn their discussion to describing the properties of matter. Macro understandings, within the early childhood curriculum, emphasize both the observable and quantifiable features of matter, along with the states of matter.

Children entering upper elementary through middle school classrooms start distinguishing the intensive and extensive properties of matter. Intensive properties hold true for any sample size and do not change by the sample size (e.g., color). In contrast, extensive properties are dependent on the amount of the substance and can be changed by crushing or dividing (e.g., size). The early childhood matter standards focus on intensive properties, but it is not until the learning progressions from the third grade through middle school that children are tasked with identifying materials based on these observations (NGSS DCI: 5-PS1-3; MS-PS1-2; MS-PS1-3). At these grade bands, intensive properties include: thermal and electrical conductivity, color, hardness, reflectivity, solubility, and magnetic properties. Children explore the identification of matter based on the intensive properties for up to six years in the learning progression. As students enter high school, the curriculum simultaneously emphasizes both the macro and the abstract levels, as will be discussed in the next section.

Working in the macro and abstract levels

Children at the upper elementary through high school levels are tasked with connecting what is observed at the macro level to what is occurring at the submicro level using the symbolic level. With regard to the multiple levels of thought, students have difficulty with the emphasis on the abstract nature of chemistry by focusing on the submicro and symbolic levels (abstract levels), reliance upon mathematical equations (symbolic), and negotiating the different thinking levels simultaneously.

However, teachers are often unaware of students’ difficulties with the multi-levels of thought¹³. We teachers must help students navigate the multiple levels by explicitly relating the macro level to the abstract levels, using consistent language, and showing the strengths and weaknesses of the models used to represent the particulate nature of matter.

Looking closely at the NGSS DCI for each of these grade bands, one might miss the emphasis on the connection between the macro and abstract levels. It is within the performance expectations and the clarification statements, more specifically, that the intentions for students to develop the ability to work between the levels of thought are highlighted (see Table 3). The table identifies the level of thought recognized in brackets, along with any possibilities of interpretations within the vagueness of language. For example, the fifth grade standard [5-PS1-1] states, “develop a model [symbolic] to describe that matter is made of particles too small to be seen. [submicro].” The development of a model is an example of the symbolic level, and the description of the particles at the subatomic level represents a submicro example. The fifth grade criterion emphasizes the ability to expand a basketball, which is an example of the macro level. However, not all state standards may explicitly mention connecting the macro level to the abstract levels. Regardless, teachers need to ensure that instruction emphasizes the connection between the macro level in light of the abstract levels.

For example, the upper elementary performance expectation states that for students to demonstrate their understanding, they must “develop a model to describe that matter is made of particles too small to be seen”.⁷ Here the performance expectation emphasizes the submicro level, in which students describe the behavior of particles using a symbolic level representation of a model. Figure 3 shows a typical example: a circle in which students visually depict the motion of the particles (in this case, a gas). However, the NGSS clarification statement provides examples from the macro level — such as the basketball analogy (Figure 4), sugar in water, or evaporating salt water. As stated before, students need help in making connections between the macro and the abstract levels. Providing examples that are linked to everyday objects (such as basketballs) can help students connect the observable to the behaviors of particles. While seemingly a small difference between Figure 3 and Figure 4, this level of specificity is necessary for students to recognize and connect the levels of thought regarding the matter around them.

Students also need to recognize the unique attributes of the symbolic level. The first attribute is that the symbolic level is a representation.¹⁴ It has been argued that the symbolic represents real, tangible substances (e.g., Ca for calcium), but to the student, they are just symbols^.15,16 Other authors¹⁴ emphasize the nature of models:

• Description: A depiction that may or may not be accurate but helps to provide a mental image.
• Perception: The model is a tool to help understand the real entity.

Within the NGSS Framework, developing models is a scientific practice in which students by grade 12 should be able to “discuss the limitations and precisions of a model… in which the model might be improved to better fit available evidence.”¹⁶ Engaging students in discussions about the strengths and weaknesses of the symbolic levels provides an opportunity to delve deeper into understanding matter at the macro and submicro levels of thought.

Research has shown that secondary chemistry teachers do not always connect the three content levels of thought. In a study of beginning chemistry teachers, Adams & Luft¹⁸ identified five themes that may impact how the teacher connects the content levels:

1. Primarily lecture with little opportunity for student discussion;
2. Few laboratories and demonstrations used during a lesson or unit;
3. Models and simulations used only to explain the abstract (submicro and symbolic) without connecting to the observable (macro), with little discussion of the strengths and weaknesses of models;
4. Emphasize memorization and skill building for solving chemical and mathematical equations; and
5. Present concepts without discussing and/or connecting the three levels of thought.

These teachers’ classes often began with a lecture about the concept, after which students would finish with a worksheet to practice skills in solving mathematical or chemical equations. The worksheets often provided examples framed in the chemical world, but most emphasized abstract chemicals and ideas whose contexts the student might not understand. Finally, the teachers often emphasized only the content in two levels — atomic structures emphasizing the submicro (subatomic particles) and the symbolic (models of the atom). We, as teachers, must ensure that the learning is both housed in the observable, while also providing contexts of the real world.

Contextualizing learning with the human element

The human element moves the learning away from the abstract to the real-world setting. Contextualized learning includes:

• connecting to the students’ lived experiences;
• nature of science (NOS) — how science is done including levels of uncertainty, biases, societal influences on science, historical advances, and more;
• socio-scientific issues (SSI) — deliberate use of scientific topics, often controversial, that engage students in discussions and debate; and
• industrial applications.

There are many examples of this approach. The idea of real-world applications helps students to answer the question, “where will I use this?” For real-world and industrial applications examples, many high school teachers use the flame test laboratory experiment to connect the atomic structures to the physical and chemical properties of fireworks. A teacher of three-year-olds contextualizes the states of matter through explorations of the solar system — solid and gas planets along with the sun. A NOS element example conveys the idea that scientific knowledge is open to revision in light of new evidence¹⁷ as teachers emphasize the history of the atom. The American Chemical Society’s (ACS) Chemistry in the Community curriculum¹⁹ is designed to frame student learning in societal issues (e.g., water and its contaminants). Meanwhile, the curriculum in Manitoba, Canada has shifted to include the human element.²⁰ Additional ideas for contextualizing the chemistry content can be found in journals such as Chemistry Solutions and ACS ChemMatters.

Conclusion

Learning chemistry begins early as young children explore the world, and then shifts across the grade bands to include abstract understandings about the behavior of particles. However, it is necessary for the teacher to help the student make the connection to both the observable and the abstract features of matter. This is done in part by engaging in explicit discussions about the multi-levels, how the abstract concepts relate to the observable, and the limitations of the symbolic level representations. It can also involve introducing laboratory experiments or explorations of matter to help students navigate the chemistry content at all grade levels. In doing so, we address students’ difficulty of maneuvering between the content levels of thought. Placing the learning experiences in a contextualized setting also helps students recognize how chemistry applies to their world, and not some far-away chemistry laboratory. For the PreK–12 teacher to develop children’s understanding, it is necessary to recognize the multiple representation levels when designing instruction to build the foundation on which to bridge from the observable to the atom.

Table 1. Definitions and examples of the tetrahedral levels of thought.

Table 2. Progression of Learning for Structures and Properties of Matter*

*Please reference your state’s guidelines for specifics on the learning progression for structure and properties of matter.

Table 3. NGSS Example Performance Expectations and Clarification Statements for 3^rd–12^th Grade

References

1. Gilbert, J.K., and David F. Treagust. 2009. "Introduction: Macro, submicro, and symbolic representations and the relationship between them: Key models in chemical education." In Mulitple Representations in Chemical Education, edited by J.K. Gilbert and David F. Treagust, 1-8. Springer Science + Business Media B.V
2. Treagust, David F., Gail Chittleborough, and Thapelo Mamiala. 2003. "The role of submicroscopic and symbolic representations in chemical explanations." International Journal of Science Education 25:1353-1368.
3. Andersson, Bjorn. 1986. "Pupils' explanations of some aspects of chemical reactions." Science Education 70:549-563.
4. Johnstone, Alex H. 1991. "Why is science difficult to learn? Things are seldom like they seem."Journal of Computer Assisted Learning 7:75-83.
5. Mahaffy, Peter. 2006. "Moving chemistry education into 3D: A tetrahedral metaphor for understanding chemistry " Journal of Chemical Education 83:49-55.
6. Nebraska Department of Education. 2004. Nebraska Early Learning Guidelines for Ages 3 to 5 Version 2005 ed: Nebraska Department of Education.
7. NGSS Lead States. 2013. Next Generation Science Standards: For states, by states. Washington, DC: National Academy Press.
8. National Governors Association Center for Best Practices, and Council of Chief State School Officers. 2010. Common Core State Standards for Mathematics. Washington, D.C.: Authors.
9. Gabel, Dorothy L. 1999. "Improving teaching and learning through chemistry education research: A look to the future." Journal of Chemical Education 76:548-554.
10. Hinton, Michael E., and Mary B. Nakhleh. 1999. "Students' microscopic, macroscopic, and symbolic representations of chemical reactions." Chemical Educator 4:158-167.
11. Russell, Terry, Ken Longden, and Linda McGuigan. 1998. Materials. In Primary Space Project Research Report . Liverpool.
12. Seibert, Patricia. 2002. The Three Little Pigs. Columbus, OH: School Speciality Publishing: Brighter Child.
    
13. Van Driel, J.H., Onno de Jong, and Nico Verloop. 2002. "The development of preservice chemistry teachers' pedagogical content knowledge." Science Teacher Education 86:572-590.
    Adams, K L, and Julie Luft. Accepted. "Beginning chemistry teachers’ depictions of the chemistry content." International Journal of Environmental and Science Education .
14. Davidowitz, Bette, and Gail Chittleborough. 2009. "Linking the macroscopic and sub-microscopic levels: Diagrams." In Multiple Repersentations in Chemical Education , edited by J.K. Gilbert and David F. Treagust. Springer Science + Business Media B.V.
15. Talanquer, Vicente. 2011. "Macro, submicro, and symbolic: The many faces of the chemistry triplet." International Journal of Science Education 33:179-195.
16. Hoffmann, Roald. 2007. "What might philosophy of science look like if chemists built it?" Synthese 155:321-336.
17. National Research Council. 2011. A Framework for K-12 Science Education: Practices, Crosscutting Concepts, and Core Ideas . Washington, DC: National Academies Press.
18. Adams, K L, and Julie Luft. Accepted. "Beginning chemistry teachers’ depictions of the chemistry content." International Journal of Environmental and Science Education.
19. American Chemical Society. 2006. Chemistry in the Community (ChemCom). New York: W.H. Freeman.
    
20. Manitoba Education Citizenship and Youth. 2006. Grade 11 chemistry: A framework for implementation . Winnipeg: Manitoba Education, Training and Youth.
21. Kern, Anne L., Nathan B. Wood, Gillian H. Roehrig, and James Nyachwaya. 2010. "A qualitative report of the ways high school chemistry students attempt to represent a chemical reaction at the atomic/molecular level." Chemistry Education Research and Practice 11:165-172.