DEVELOPING AND DESIGNING NEW CHEMICALS AND MATERIALS - Chemistry: Notable Research and Discoveries - page 9

use the scattered X-ray pattern to deduce the structure. Th is technique
is known as X-ray crystallography. Although the crystal consists of many
atoms or molecules, they are all in the same orientation—the repeating
geometry of the crystal—and so the confi guration of a single unit can be
determined. Ordinary solids that lack repeating geometry could not be
used in this technique since the randomly oriented atoms would fail to
create an interpretable pattern of scattered radiation.
Both graphite and diamond are made of carbon, but in graphite the
bonded carbon atoms are stacked in a plane (a fl at, two-dimensional fi g-
ure), with only weak bonds between planes. Part B of the fi gure illustrates
this structure. Th e carbon bonds within the plane are strong, but the
planes slide past one another, giving graphite its soft , slippery property. A
diamond, illustrated in Part A of the fi gure, has a much diff erent confi gu-
ration. In diamonds, the bonded carbon atoms do not form a plane but
rather a three-dimensional fi gure known as a tetrahedron, and the packing
is tight. As a result, diamonds are hard. Carbon squeezes into diamonds
under high pressures and temperatures, such as in the depths of Earth, or
in special laboratories designed to produce these extreme conditions. Un-
(A) In a diamond, carbon atoms form the shape of tetrahedrons, which
are packed together. A single tetrahedron is shaded. Black dots repre-
sent carbon atoms. (B) Graphite consists of planes of carbon atoms.