Close Packing, Unit Cells and Ionic Lattice Types · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One small block, repeated

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

  1. How many atoms does a conventional monatomic face-centred cubic cell contain?

    • 1
    • 2
    • 4

  2. A corner atom is shared by eight cells. How much counts toward one cell?

    • One whole atom
    • One half
    • One eighth

  3. An atom on a cell face counts as one half toward that cell.

    Circle one:   True   False

  4. A unit cell has mass 2.0 x 10^-22 g and volume 5.0 x 10^-23 cm3. What is the crystal density?

    • 0.25 g/cm3
    • 4.0 g/cm3
    • 10.0 g/cm3

  5. A body-centred cubic cell has eight corner atoms and one centre atom. How many atoms does it hold? Type the number.

    Answer: ______________

  6. Chloride ions form an FCC array and sodium ions occupy every octahedral hole. Which named structure is described?

    • Zinc blende, with half the tetrahedral holes filled
    • Rock salt, with all the octahedral holes filled
    • An empty FCC metal lattice, with no second ion present

  7. Two ideal close-packed structures repeat ABAB and ABCABC respectively. Which pair identifies them in that order?

    • Hexagonal close packing; cubic close packing
    • Cubic close packing; hexagonal close packing
    • Body-centred cubic packing; simple cubic packing

  8. An ionic radius ratio is 0.55, but measured coordination is 4. Which explanation could account for the discrepancy without changing the supplied radii?

    • Directional bonding can defeat the hard-sphere ionic model
    • A ratio of 0.55 lies in the model's four-neighbour range
    • Choosing a primitive cell changes the actual neighbour count
LightMySky · lightmysky.comW1-mt_LzpVzwrDm3-s1

Answer key

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

One small block, repeated W1-mt_LzpVzwrDm3-s1

  1. 4 · Eight corner contributions give one atom, and six face-centred contributions give three more: four atoms.
  2. One eighth · Divide the atom among its eight cells: each cell claims one eighth.
  3. True · The face is shared by two cells, so each claims one half.
  4. 4.0 g/cm3 · Density is mass divided by volume: (2.0/5.0) x 10 = 4.0 g/cm3.
  5. 2 · Eight eighths make one, plus the centre atom makes two.
  6. Rock salt, with all the octahedral holes filled · NaCl has the rock-salt structure: an FCC chloride array with all octahedral holes occupied by sodium.
  7. Hexagonal close packing; cubic close packing · ABAB defines HCP. ABCABC defines CCP, which is equivalent to FCC.
  8. Directional bonding can defeat the hard-sphere ionic model · 0.55 lies in the approximate six-neighbour range. Directional bonding can defeat that size-only prediction; changing cell description does not change physical neighbours.
Worksheet · LightMySky