Single-Crystal Diffraction: From Reflections to a Refined Structure · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Spots into atoms

Science · Chemistry · ages 22-24
Name ______________________   Date ____________

  1. Why are X-rays the right probe for crystal structures?

    • Their wavelength matches atom spacing
    • They pass through crystals without scattering
    • They carry less energy than visible light

  2. What comes out of a diffractometer?

    • A photo of individual atoms
    • Spot intensities and angles
    • The chemical formula in plain text

  3. The unit cell is the smallest repeating block that tiles the whole crystal.

    Circle one:   True   False

  4. What is the phase problem?

    • Spots overlap so badly that no cell can be read
    • Lost phases must be recovered first
    • Refinement runs forever without reaching an answer

  5. Ideal rhodochrosite, MnCO3, has smaller manganese ions where calcite has calcium ions, and its cell measures smaller than calcite's. What does the size change show?

    • That heat damaged the crystal during the run
    • That the space group was assigned wrongly
    • That chemistry shows up as cell size

  6. After phases are recovered, what does refinement do?

    • Tunes the model against the data
    • Takes a direct photo to confirm atom positions
    • Assigns the space group from missing spots

  7. A model posts a neat residual factor. Which finding should still worry you?

    • Cell edges reported to three decimal places
    • Same bonds refining apart for no reason
    • A data set collected at low temperature

  8. In a refined structure, one atom labelled as oxygen has a displacement far smaller than its neighbours', and the residual factor is high. What is the most likely error?

    • The crystal was too small to diffract
    • The site holds a heavier atom than its label
    • The X-ray wavelength was set wrong
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Answer key

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

Spots into atoms W1-mt_7PjfoEu-WE-s1

  1. Their wavelength matches atom spacing · No instrument shows detail finer than about the wavelength it uses.
  2. Spot intensities and angles · The instrument returns a pattern, and the structure must be worked out from it.
  3. True · Edges a, b, and c plus three angles describe that one tile.
  4. Lost phases must be recovered first · Intensities arrive without phases, and a solution step works around the loss.
  5. That chemistry shows up as cell size · Smaller ions shrink the repeating block, and the cell edges record it.
  6. Tunes the model against the data · Refinement tunes the model against measured data, not against a picture.
  7. Same bonds refining apart for no reason · Neat statistics can hide a wrong element or missed disorder, and strange geometry is their trace.
  8. The site holds a heavier atom than its label · A displacement that is too small means the model gave the site too few electrons, so the real atom is heavier than oxygen.
Worksheet · LightMySky