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Solids: Introduction

Structure Types

Crystals may not only be categorized according to their repetitive units (motifs) and bonding, but also according to the orientation of their bonds. For example, bonding may be uniformly strong in all three dimensions, or could be limited to two dimensions. The following examines three types of structure.

Three-dimensional structure
The three-dimensional type of structure is an unlimited lattice structure with strong bonds. The bonds have the same strength in all directions. Examples are NaCl (Abb. 1) and diamond (Abb. 4) .
Layer structure
If the bonds within a crystal are strong in two dimensions but weak in the third, the result is a layer structure. The individual layers are held together by Van der Waals forces (London forces) or oppositely charged ions. Examples include graphite (Abb. 2) and molybdenum disulfide (Abb. 5) .
Chain structure
Crystals in which the repetitive units are strongly bound in only one direction have a chain structure: The building blocks are arranged in a linear fashion. The individual chains are held together by Van der Waals forces (London forces) or by oppositely charged ions. Examples include beryllium chloride (Abb. 3) and copper chloride .

Figures

Tab.1
Figures
Three-dimensional structureLayer structureChain structure
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Fig.1
Sodium chloride, NaCl
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Fig.2
Graphite, C
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Fig.3
Beryllium chloride, [BeCl2]n
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Fig.4
Diamond, C
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Fig.5
Molybdenum disulfide, MoS2

Trigonal prismatic environment of molybdenum disulfide

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