Chemistry Reference
In-Depth Information
3. Spheres, OG and TG exist in a ratio of 1:1:2 in the close-packing of spheres.
The structure of the sodium chloride crystal can therefore be explained
like this: Cl
ions form a cubic close-packing of spheres, all octahedral
gaps are occupied by smaller Na
+
ions. The coordination numbers are 6
and 6, the ion ratio is 1:1, the ratio symbol should be (Na
+
)
1
(Cl
)
1
Explain the cubic shape of the sodium chloride crystal.
M 6.11: Take the elementary cube from M6.5, look for octahedral gaps and fill
them with small red balls.
(a) Complete the model drawing by filling the gaps with small spheres
(see picture).
(b) Draw the crystal structure next to the picture. Draw a perspective
cube: instead of the balls only give the central points of the balls and
connect these points (see M6.4).
M 6.12: Build the cubic close-packing of spheres with the help of the square frame
and with both kinds of spheres. Draw the sequence of the 2-spheres layers.
M 6.13: Convince yourself that the elementary cube can be build into the packing
of spheres beginning with the triangle pattern (M 6.8) as well as the one
beginning with the square pattern (M 6.12). Which position does it take in
both models?
Draw the elementary cube with the help of (a) layers of spheres in the
triangular pattern, (b) layers of spheres in the square pattern.
M 6.14: Amodel for the aluminium oxide structure (corundum structure) may be built:
(a) Stick together three layers with 15 white balls each (see picture).
(b) Add ten small balls in the shown pattern (see picture).
