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. Rhodochrosite swaps some calcium for smaller manganese, and its cell measures smaller than calcite. 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. A refined structure shows a high residual factor and one atom with an implausible displacement. What probably went wrong, and what do you check first?

    • The crystal was too small; grow a bigger one first
    • Wrong label or disorder; check those
    • The X-ray wavelength was wrong; retune the source first
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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 that structure must be worked out from.
  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. Wrong label or disorder; check those · Bad labels and missed disorder inflate residuals and warp displacements together.
Worksheet · LightMySky