Summary

In this activity, students will view an animation that explores how metallic bonding contributes to the properties of metals and alloys. Particle diagrams show how mobile valence electrons allow for metals to be easily shaped and to conduct electricity. Examples of alloys are provided starting with ancient people discovering alloys in meteorites and progressing to the use of alloys in modern airplanes.

Grade Level

Middle School, High School

NGSS Alignment

This activity will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-1: Develop models to describe atomic composition of simple molecules and extended structures.
• HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
• Scientific and Engineering Practices:
  • Developing and Using Models
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this activity, students should be able to:

• Identify that metals have mobile valence electrons.
• Describe how mobile valence electrons cause some properties of metals.
• Define alloys and explain why they are useful materials.

Chemistry Topics

This activity supports students’ understanding of:

• Metallic bonding
• Alloys
• Valence electrons

Time

Teacher Preparation: minimal
Lesson: 20-30 minutes

Materials

• Computer and projector with internet access
• https://teachchemistry.org/classroom-resources/bonding-in-metals-and-alloys-animation
• Student handout

Safety

• No specific safety precautions need to be observed for this activity.

Teacher Notes

• All of the animations that make up the AACT Animation collection are designed for teachers to incorporate into their classroom lessons. Intentionally, these animations do not have any spoken explanations so that a teacher can speak while the animation is playing and stop the animation as needed to instruct.
• If you assign this to students outside of class time, you can create a Student Pass that will allow students to view the animation (or any other video or ChemMatters article on the AACT website).
• We suggest that a teacher pause this animation at several points or watch it more than once to give students the opportunity to make notes, ask questions, and test their understanding of the concepts presented. It may be particularly useful to replay the particle diagrams shown at several points throughout the animation. The student activity sheet can help guide students through the animation and focus their attention on key points in the video. The questions on the student activity sheet follow the same order as the information presented in the animation.

Background Information and Animation Notes

• This animation would be useful in a unit on bonding that covers metals, metallic bonding, and alloys. Metallic bonding differs from ionic or covalent bonding, and metals behave differently and have different properties than ionic or molecular compounds.
  • In ionic and covalent bonding, individual atoms exchange or share electrons to make stable compounds by filling or emptying their valence shells.
  • With metallic substances, valence electrons are delocalized, or shared between all metals atoms in a sample and are not associated with one particular atom. Essentially, each atom donates its valence electrons to what is often described as a “sea of electrons” that moves among the lattice of metal atom cores. Since the valence electrons are not attached to a specific atom anymore, the remaining cores of all the atoms are slightly positive, and the negative sea of electrons is attracted to the positive cores. This attractive force holds the whole structure together.
    • The animation references the “moldability” of metals – teachers can choose to introduce the terms malleability and ductility if desired.
  • Because metal atoms in a sample all share delocalized valence electrons in this sea of electrons, they do not need to have specific ratios of elements when they combine to form stable materials. Thus, when metals are combined they typically form mixtures (alloys) where the percentages of each element can vary.
  • In the section of the animation that describes the conductivity of metals, the particle diagram shows a net flow of electrons in one direction due to an electric field. A household outlet uses alternating current, so the electric field, and therefore the direction of flow, reverses at a set frequency. This animation simplifies the particle diagram to emphasize the general principle of conductivity. Emphasize that, because the valence electrons in a metal sample are able to move freely throughout the substance and are not associated with specific atoms, the presence of an electric field will cause them to move in a certain direction.
• An alloy is a material made by mixing a metal with one or more other elements to improve its properties. Generally, alloys can be categorized as substitutional or interstitial. In substitutional alloys, atoms of another element that are similar in size to the base metal atoms replace some of the metal atoms. In interstitial alloys, the other element being added to the metal has significantly smaller atoms, which squeeze into the spaces between the metal atoms rather than replacing them. Some alloys can be described as both, depending on the elements added.
  • The aluminum alloy shown in the animation is a substitutional alloy with zinc, magnesium, and copper atoms replacing some of the aluminum atoms. The iron alloy (steel) shown in the animation is both substitutional, with chromium and nickel atoms replacing some of the iron atoms, and interstitial, with smaller carbon atoms in the spaces between the larger atoms.

Extension Activities and Further Learning

• In the student handout, students are asked to list 3 properties of metals and 3 things that are made of metal before viewing the animation. Consider having a class discussion based on these questions, or make it a competition – set a timer and have students list as many metallic things as they can in a minute, for example. Alternatively, pick an object with a lot of parts (such as a computer, a car, a building, etc.) and have students try to list different parts that are made of metals and discuss what properties are important for that part. For example, in a car, conductivity is important for electronic parts like computers and lights, strength and corrosion resistance are important for structural parts like the frame and doors, etc.
• Compound Interest has a great post and infographic on The Elemental Composition of Alloys with lots of information on the names, compositions, and uses of different alloys, as well as why alloys are often used rather than pure metals. As an extension activity, consider having students research one or more of these alloys in more detail and present their findings to the class in a poster, video, presentation, etc.
• The ability to isolate, manipulate, and use various metals and alloys has marked important technological advances throughout human history. Entire segments of history, such as the Bronze Age and Iron Age (steel), have been named after these materials because the new tools they made possible so significantly altered the course of human development. This is a great opportunity to make connections to social studies and history content students may have learned in other courses and to show the impact that science has on society.
• Classroom resources from the AACT Library that may be used to further teach this topic include:
  • Lesson Plan: Observing Properties of Those Marvelous Metals
  • Lesson Plan: Paper Plate Alloys
  • Lesson Plan: The Captivating Chemistry of Coins
  • Lab: Chemistry of Art through Alloys and Metal Plating
  • Lab: Molding Metal
  • Lab: Investigating Heat Treatments and Properties of Steel
  • Project: Problem Solving with Materials
  • Demonstration: Metallic Bonding & Magnetics