Polymorf - Knowhwere- FCC symmetry

In particular the orientation of the (100) and (111) planes of the FCC lattice can be

modeled to relate the nature of their interpenetration.


	Figure 43 - Interpenetrating FCC
	(100) and (111) layers
	( 72 T, 79 pinges )

	click image to enlarge

Slicing the FCC lattice parallel to each of the (100), (110), and (111) planes also

demonstrates the orientation of these symmetry planes and the geometry of their

sphere (atom) packings. In the following model the red (100) plane is shown to

intersect with the blue (110) plane and the purple (111) plane at a corner.

The atomic packing arrangement of the differently oriented layers in matter

relates to the external forms, or habits, their crystals commonly exhibit as well as the

crystals' cleavage planes and surface physical characteristics. In particular, a

discrete crystal is built up by the sequential layering of atoms on its exposed surface.

Thus the internal structure of its crystal lattice greatly influences its external

appearance. For example the above image can be pictured as a corner of a crystal

with an FCC lattice structure. Also the cleavage planes of crystals often parallel the

closest packed (111) plane. Some crystals even exhibit differential hardness with the

densest packed (111) face being the hardest. Finally, the surface reactivity of some

catalytically important precious metals is dependent on what surface is exposed

when they are cut or etched.

As will be seen in the following section, atoms can avail themselves of the

periodic regularity afforded by the CP, HP, FCC, HCP, BCC, and other uniform lattice

structures to create a rich diversity of inorganic matter which varies widely in

chemical and physical properties.

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Page 30 - Structure matters - FCC symmetry