Band Structure: Metals, Insulators and the Gap · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Why some solids conduct

Science · Matter & Materials · ages 23-24
Name ______________________   Date ____________

  1. Where do band gaps open?

    • At the bottom of every band, near zero energy
    • Wherever an atom happens to sit in the crystal
    • At zone edges via Bragg reflection

  2. What happens to atomic levels in a crystal?

    • They spread into bands with gaps between
    • They stay single and unchanged
    • They merge into one continuous band with no gaps

  3. A completely full top band conducts electricity well.

    Circle one:   True   False

  4. Which filling makes an insulator?

    • A full band plus a large gap
    • A half empty top band
    • A full band that overlaps the next band

  5. Which filling makes a metal?

    • A full top band with a large gap above it
    • A partly filled or overlapping top band
    • A full top band with a tiny gap above it

  6. What is a semiconductor?

    • A small-gap insulator crossed by heat or light
    • A metal whose top band is only half full
    • An insulator whose gap is far too wide to cross

  7. Two similar crystals differ in conduction. A student says structure alone decides. What is wrong?

    • Crystals never conduct at all
    • Gaps never open in similar structures
    • Filling and gap size decide alongside structure

  8. What is the free electron gas in band language?

    • The same bands with every gap made twice as wide
    • The picture with gaps switched off
    • A full band with a large gap above it
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Answer key

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

Why some solids conduct W1-mt_9f74Vu6qnW-s1

  1. At zone edges via Bragg reflection · Bouncing at the zone edge splits travelling waves in energy.
  2. They spread into bands with gaps between · A mole of atoms turns each level into a band.
  3. False · No nearby empty spots means electrons cannot respond.
  4. A full band plus a large gap · Full plus gapped strands every electron.
  5. A partly filled or overlapping top band · Room to gain energy means room to move.
  6. A small-gap insulator crossed by heat or light · Small gaps let a few electrons hop across.
  7. Filling and gap size decide alongside structure · Looks match while fillings and gaps differ.
  8. The picture with gaps switched off · Ignoring the ions removes the bounce that opens gaps.
Worksheet · LightMySky