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Chemistry

Memory Metals: Nitinol, a Shape Memory Alloy

(For Teacher Notes and Student Materials, see Printer-Friendly Version of Lesson Plan )

Standard Statements

3.1.10b - Describe concepts of models as a way to predict and understand science and technology.

3.4.10a - Explain concepts about the structure and properties of matter.

3.4.12a - Apply concepts about the structure and properties of matter.

Content Objectives

Students will know that
  1. Metal atoms in the solid phase are very ordered, closely packed, and held in fixed positions.
  2. It often requires extreme temperatures to both melt and vaporize metals.
  3. The electron sea model depicts metals as a lattice of cations surrounded by a mobile sea of valence electrons.

Process Objectives

Students will be able to
  1. Model the metal atoms in the solid, liquid, and gas phases using marbles and Petri dishes.
  2. Model the sea of valence electrons using BBs.

Assessment Strategies

  1. Evaluation of completed student handout.
  2. Group discussion of key ideas.
  3. Evaluation of a reflective essay describing what they did during the activity, what they feel they learned, what aspects of the lesson they feel they still do not understand, and one question that they are curious about regarding metals.

Suggested Level

Grades 9-12

Standard Category

3.1 - Unifying Themes
3.4 - Physical Science, Chemistry, & Physics

Materials

per group:

  • 3 Petri dishes (at least one should be a square Petri dish)
  • 44 (12 mm size) marbles
  • 40 BBs (shot-gun pellets will also work)
  • Tap or polystyrene glue to seal Petri dishes

Instructional Strategies

Individual or small groups

Procedures

Part 1 (20 min)
  1. Distribute all materials to each group or individual.
  2. Students place 40 marbles in the square Petri dish, 3-4 marbles in another Petri dish, and ~40 BBs in the remaining dish. Each dish (especially the one containing the BBs) should be taped or glued shut.
  3. Explain that in this activity the marbles in the Petri dishes will represent metal atoms, and the BBs will be used to represent electrons in a metal.
  4. Students hold the square Petri dish on a slight tilt so that all the marbles congregate toward one side and are in a closely packed arrangement. While still holding it on a tilt, they gently shake the dish and notice that for the most part, the marbles stay fixed in their original positions. The students sketch a picture of how the marbles look in this configuration and provide a brief written explanation of what they see.
  5. Students vigorously shake the square Petri dish to observe the marbles come out of their fixed positions. They illustrate and describe what they see.
  6. Students observe the behavior of the 3-4 marbles in the second Petri dish as they shake it vigorously. They sketch a picture and describe what they see.
  7. The students predict which of the three tasks models metal atoms in each of the three phases (solid, liquid, or gas). They compare the melting and boiling points of water to the extreme temperatures required to melt and boil various metals from the Periodic Table.
  8. Discuss key ideas about metal atoms in the solid, liquid, and gas phases (see Teacher Notes).
Part 2 (30 min)
  1. Discuss the electron sea model of metals with the class before the students attempt to model it using the BBs (key concepts of this model are included in the Teacher Notes).
  2. Students place the Petri dish with the BBs over top of the diagram in their student handout which depicts a collection of positively charged point particles in fixed positions. The students move the Petri dish back and forth over top of the diagram and record what they observe. They provide a written explanation of how this task illustrates the electron sea model of metal atoms.
  3. Emphasize key components of the electron sea model in light of the visual representation the students now have. Point out that the mobile nature of electrons depicted in this model is useful in explaining many properties of metals (conductivity, ductility, malleability, etc.).