Figure 13-28 Some
representations of the crystal
structure of sodium chloride,
NaCl. Sodium ions are shown
in gray and chloride ions are
shown in green. (a) One unit
cell of the crystal structure
of sodium chloride. (b) A
representation of the unit cell of
sodium chloride that indicates
the relative sizes of the Na
and Clions as well as how
ions are shared between unit
cells. Particles at the corners,
edges, and faces of unit cells
are shared by other unit cells.
Remember that there is an
additional Naion at the center
of the cube. (c) A cross-section
of the structure of NaCl,
showing the repeating pattern
of its unit cell at the right.
The dashed lines outline an
alterative choice of the unit cell.
The entire pattern is generated
by repeating either unit cell
(and its contents) in all three
directions. Several such choices
of unit cells are usually possible.
(d) A stereoview of the sodium
chloride structure, extending
over several unit cells.524 CHAPTER 13: Liquids and Solids
Figure 13-29 Crystal structures of some ionic compounds of the MX type. The gray
circles represent cations. One unit cell of each structure is shown. (a) The structure
of cesium chloride, CsCl, is simple cubic. It is notbody-centered, because the point
at the center of the cell (Cs, gray) is not the same as the point at a corner of the cell
(Cl, green). (b) Sodium chloride, NaCl, is face-centered cubic. (c) Zincblende, ZnS, is
face-centered cubic, with four Zn^2 (gray) and four S^2 (yellow) ions per unit cell. The
Zn^2 ions are related by the same translations as the S^2 ions.(a) (b) (c)
NaCl(d)(c) Zincblende
ZnS: Zn^2 , S^2 (b) Sodium chloride
NaCl: Na, Cl(a) Cesium chloride
CsCl: Cs, Cl