This is the new updated edition of the first book in the bestselling Uncovering Student Ideas in Science series. Like the first edition of volume 1, this book helps pinpoint what your students know (or think they know) so you can monitor their learning and adjust your teaching accordingly. Loaded with classroom-friendly features you can use immediately, the book includes 25 “probes”—brief, easily administered formative assessments designed to understand your students’ thinking about 60 core science concepts.

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The purpose of this assessment probe is to elicit students’ ideas about atoms. The probe is specifically designed to determine whether students can use the idea of atoms to explain why a metal expands when heated. Furthermore, older students’ explanations may reveal whether these students use the kinetic molecular theory to explain how heating causes the atoms to vibrate more, thus pushing the atoms apart.

More A-More B

atoms, thermal expansion

The best answer is C: The space between each atom increased. Thermal expansion of metals involves the tendency of a metal to increase in volume in response to an increase in temperature. As a metal object is heated, its atoms vibrate in place more vigorously and, as a result, increase the separation between individual atoms. This slight increase in the empty space between atoms results in a cumulative change in the measurable volume of the object. The object expands. When the object expands, no new atoms are added. Although the length or width of the metal object may increase, the size of the atoms it is made of stays the same. It is the space between the atoms that increases and contributes to an increase in volume. As the atoms of a solid gain energy, they vibrate more in place. Unlike a gas, which is free to move about, the metal atoms maintain their general positions.

Elementary Students

In the elementary grades, students observe macroscopic properties of matter, including changes caused by heating. Their observations focus on objects and materials. Explanations of phenomena that use the idea of atoms should wait until middle school or when students are ready to use this abstract idea.

Middle School Students

In the middle grades, students begin to use atomic and molecular ideas to explain phenomena. They begin to relate the expansion and contraction associated with the heating and cooling of substances to the position and motion of particles. However, students at this level may still confuse the properties of the material or substance with the properties of the atoms or molecules of which they are made.

High School Students

Students at the high school level should be able to use ideas about atomic/molecular motion to explain phenomena from a microscopic view. They should be able to distinguish between the observable properties of a substance and the properties of the atoms making up the substance. However, many students at this stage will attribute expansion of the solid material to an increase in the amount of matter and/or an increase in the size of the atoms rather than to the space between them.

Make sure students understand the phenomenon. Consider providing real-life examples of similar phenomena, such as the space between the metal joints on a bridge expanding in the summer or a metal door that sometimes scrapes against the floor on a hot summer day. The ball and ring apparatus sold in science supply stores can also be used by demonstrating how the metal ball can no longer pass through the ring when it has been heated.

• Students of all ages show a wide range of beliefs about the nature and behavior of particles. For example, they attribute macroscopic properties to particles; do not accept the idea there is empty space between particles; and have difficulty accepting the intrinsic motion of solids, liquids, and gases (AAAS 1993).
• Children frequently consider atoms of a solid to have all or most of the macroproperties they associate with the solid (Driver et al. 1994).
• Some older students (ages 11–16) who had learned about the kinetic molecular theory of matter attempted to explain conductivity phenomena in terms of particulate ideas. However, these ideas were not used spontaneously by most of the students interviewed. When they did use particle ideas, they had a tendency to attribute expanding (getting bigger) to the properties of the atoms (Driver et al. 1994).
• Children’s naive view of particulate matter is based on a “seeing is believing” principle in which they tend to use sensory reasoning. Being able to accommodate a scientific particle model involves overcoming cognitive difficulties of both a conceptual and perceptive nature (Kind 2004).

Association for the Advancement of Science (AAAS). 2001. Atlas of science literacy. Vol. 1. (See “Atoms and Molecules” map, pp. 54–55.) Washington, DC: AAAS.

Michaels, S., A. Shouse, and H. Schweingruber. 2008. Ready, set, science! Putting research to work in K–8 science classrooms. Washington, DC: National Academies Press.

Robertson, W. 2007. Chemistry basics: Stop faking it! Finally understanding science so you can teach it. Arlington, VA: NSTA Press.

• Demonstrate the phenomenon with the ball and ring apparatus sold by most science supply companies. Before heating, the ball easily passes through the ring. After the ball is heated, it expands and will no longer pass through the ring when warm. Ask students to describe what happened to the ball itself. Then ask students to describe what happened to the atoms that make up the ball. Ask them to describe the difference between the phenomenon at the substance level versus the atomic level.
• Encourage students to draw “atomic pictures” of what they think is happening to the atoms as the metal is heated.
• Have students generate a list of other things that expand when heated and describe what is happening to the atoms or molecules.
• Ask students what happens to the metal when it cools down. Have them explain what happens at both the substance and atomic level.
• The PRISMS (Phenomena and Representations for Instruction of Science in Middle Schools) website at http://prisms. mmsa.org has a collection of web-based phenomena and representations aligned to the Benchmarks for Science Literacy (AAAS 1993) and Curriculum Topic Study Guides (Keeley 2005) that can be used to help students understand why metals expand when heated.