Band Theory, Defects and Why Some Solids Conduct · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Bands decide who conducts

Science · Chemistry · ages 21-22
Name ______________________   Date ____________

  1. A solid has a partly filled top band. How does it conduct?

    • Like an insulator
    • Not at all
    • Like a metal

  2. Where do energy bands in a solid come from?

    • Billions of atomic levels packed so tightly they blur together
    • Electrons slowing to a standstill
    • Gaps leaking into the levels

  3. In an insulator, electrons exactly fill a band and face a wide gap.

    Circle one:   True   False

  4. Extra levels just below the conduction band give which doped type?

    • p-type
    • Unchanged silicon
    • n-type

  5. Warming silicon raises its conduction, while copper gains nothing. Why?

    • Warmth kicks electrons across silicon's small gap; copper already has a partly filled band
    • Copper melts before it can respond
    • Silicon loses its gap entirely

  6. A crystal with missing atoms shows a new colour. What may explain it?

    • A wider measuring ruler
    • A point defect shifting the levels
    • A heavier sample holder

  7. Adding impurity atoms to silicon can only lower its conduction.

    Circle one:   True   False

  8. A solid conducts a little, and warming raises its conduction. How do you classify it?

    • Metal
    • Semiconductor
    • Insulator
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Bands decide who conducts W1-mt_RuPWyBzGOp-s1

  1. Like a metal · Empty states sit next door, so electrons drift when pushed.
  2. Billions of atomic levels packed so tightly they blur together · Each atom brings its levels, and the crowd of them merges into bands.
  3. True · No nearby empty states means no current can flow.
  4. n-type · Levels near the conduction band donate electrons, which is the n-type pattern.
  5. Warmth kicks electrons across silicon's small gap; copper already has a partly filled band · New carriers appear in silicon, while copper already had all the room it needs.
  6. A point defect shifting the levels · Missing or extra atoms move levels around, and colour can follow.
  7. False · Extra levels near a band edge change conduction sharply, usually raising it.
  8. Semiconductor · Small conduction that grows with warmth is the semiconductor signature.
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