Physical Chemistry , 1st ed.

736 CHAPTER 21 The Solid State: Crystals

Cubic

Tetragonal

Orthorhombic

Triclinic Monoclinic

Rhombohedral

Hexagonal

It might seem that 14 lattices are not enough to describe the possible

arrangements of crystals that might exist. However, they do cover all possibil-

ities. By its very definition, a crystal has a specific three-dimensional symme-

try, and these 14 lattice types cover all possible three-dimensional symmetry

arrangements. Also, if you were to add an atom to a center or face of a lattice

in an attempt to define a new Bravais lattice, you would make a crystal whose

true Bravais lattice can be described by a different (and usually smaller!) unit

cell that would be one of the 14 lattices described.

Figure 21.9 The 14 Bravais lattices that are
possible for the seven crystal systems. Some crys-
tal systems have more than one possible lattice;
others have only one.