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Lesson Plans Library 6-8 > Physical Science
Metalloids
Grade level: 6-8 Subject: Physical Science Duration: Two class periods
 


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Objectives
Students will
  • Talk about metalloids, their use as semiconductors, and their impact on the computer industry.
  • Work in groups to create a visual timeline showing the evolution of the computer.
  • Consider how today's computers have evolved and might continue to change in the future.
Materials
  • Metalloids program
  • Periodic table
  • Print and online resources about the history of the computer
  • Computer with Internet access
  • Color copier or printer
Procedures
  1. After watching the program, remind students that every element can be classified as a metal, nonmetal, or metalloid. Show students where these elements are found on the periodic table, pointing out that metalloids fall between the metals and nonmetals.
  2. Explain that metalloids share some properties with metals and some with nonmetals. For example, one of the most important distinctions is that metals are good conductors of heat and electricity but nonmetals are not. In other words, metals allow electricity to flow through them, while nonmetals block electric currents. Ask students: How can metalloids share both the properties of metals and nonmetals when it comes to their ability to conduct electricity? (Metalloids are semiconductors: At high temperatures, they conduct electricity as if they were metals, but at lower temperatures, they act as insulators, stopping electric currents from flowing.)
  3. Review how our knowledge of semiconductors has changed the computer industry: Early computers used mechanical on-off switches, then vacuum tubes, to conduct and stop electric currents, creating the ones and zeroes used in the computer's binary code. Then semiconductors were used to create silicon transistors without moving parts-switches were turned on or off depending on temperature. Silicon transistors allowed computers to be smaller, faster, and more reliable.
  4. Have students work in small groups to create a visual timeline that shows the evolution from the earliest computers to the first popular personal computers. Each group should select five computers that they think best reflect the most important advancements from the 1940s to the 1980s. On the timeline, they should include an image of the computer, the date it was released, and one to two sentences describing its significance. Some of the computers they may wish to highlight include (but are certainly not limited to) the following:
    • ENIAC (1946)
    • UNIVAC (1951)
    • IBM 1401 (1961)
    • Nova (1958)
    • Kenbak-1 (1971)
    • MITS Altair 8800 (1975)
    • Apple II (1977)
    • IBM PC (IBM PC 5150) (1981)
    • Osborne I (1981)
    • Apple Lisa (1983)
    • Macintosh (1984)
    • PC Convertible (IBM 5140 PC Convertible) (1986)
  5. Provide any appropriate print resources about early computers and point students to the following Web sites:
  6. After the groups share their timelines with the class, ask students: What were some of the most common choices? How did these computers change the face of the computer industry? How have computers changed since the 1980s?
  7. Challenge students to think of everyday products that include computer chips made with semiconductors, such as PDAs (personal digital assistants), cars, camera phones, coffee makers, even children's toys. Ask students: In the future, what other products might use computer chips?

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Evaluation
Use the following three-point rubric to evaluate students' work during this lesson.
  • Three points: Students were active in class discussions; showed a strong understanding of metalloids and their use as semiconductors; created a complete, engaging visual timeline of the evolution of computers that included a clear, compelling description of the significance of each computer.
  • Two points: Students participated in class discussions; showed a satisfactory understanding of metalloids and their use as semiconductors; created a complete visual timeline of the evolution of computers that included a simple description of the significance of each computer.
  • One point: Students did not participate in class discussions; showed a weak understanding of metalloids and their use as semiconductors; created an incomplete or confusing visual timeline of the evolution of computers that included unclear or incomplete descriptions of the significance of each computer.

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Vocabulary
abacus
Definition: A manual computing device consisting of a frame holding parallel rods strung with movable beads that represent numbers
Context: The abacus, a five-thousand year-old computing system, is considered the earliest version of the digital computer.

central processing unit (CPU)
Definition: The part of a computer that interprets and executes instructions; often referred to as the brains of the computer
Context: More complex operations like adding, subtracting, and comparing data are also a function of the CPU.

conductor
Definition: A substance or body that allows electricity, heat, or sound to pass through it
Context: Silicon acts as an electrical conductor when heated.

electronegative
Definition: Having the tendency to attract valence electrons from other elements during chemical reactions
Context: If an element has more than four valence electrons, as nonmetals do, it is electronegative.

electropositive
Definition: Having the tendency to release valence electrons to other elements during chemical reactions
Context: If an element has less than four valence electrons in its outermost shell, as most metals do, it is electropositive.

metalloid
Definition: An element that has some properties of metals and nonmetals; metalloids include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium
Context: Most metalloids are brittle, somewhat shiny solids that exhibit properties of metals and nonmetals.

microchip
Definition: A tiny complex of electronic components and their connections that is produced in or on a small slice of material (like silicon)
Context: Very pure silicon is used to make semiconductors and microchips for electronic devices.

semiconductor
Definition: An element (like germanium or silicon) that behaves as an insulator at room temperature, but as an electrical conductor when heated
Context: Semiconductors are used in everything from calculators to computer chips.

transistors
Definition: A solid-state electronic device that is used to control the flow of electricity in electronic equipment and consists of a small block of a semiconductor (like germanium) with at least three electrodes
Context: The invention of silicon transistors revolutionized and miniaturized the world of computers.

valence electrons
Definition: The electrons in an atom's outermost electron shell that dictate how elements interact
Context: Boron has three valence electrons and tends to act as a metal by shedding its valence electrons during chemical reactions.

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Academic Standards

Mid-continent Research for Education and Learning (McREL)
McREL's Content Knowledge: A Compendium of Standards and Benchmarks for K-12 Education addresses 14 content areas. To view the standards and benchmarks, visit http://www.mcrel.org/compendium/browse.asp.
This lesson plan addresses the following national standards:

  • Science: Physical Sciences-Understands the structure and properties of matter
  • Technology-Knows the characteristics and uses of computer hardware and operating systems

National Academy of Sciences
National Academy of Sciences provides guidelines for teaching science in grades K-12 to promote scientific literacy. To view the standards, visit this Web site: http://books.nap.edu/html/nses/html/overview.html#content.
This lesson plan addresses the following national standards:

  • Physical Science
  • Science and Technology
  • Science in Personal and Social Perspectives

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