Engineering Chemistry S Datta

SOLID STATE CHEMISTRY 485
Crystal lattice
The idea of lattice developed from the internal regularity suggested from the external
appearance of the crystal. A crystal lattice is a highly ordered three dimensional structure,
formed by its constituent atoms or molecules or ions. Thus a lattice may be defined as an
infinite set of points repeated regularly through space.
A set of points that are repeated at a distance ‘a’ along a line form a one-dimensional
lattice. When a set of points occur regularly in a plane, it constitutes a two dimensional
lattice. When the set of points are repeated regularly in three dimensions, the three
dimensional lattice or space lattice is obtained.
(a)
a
b
b
(b)
a
a
(c)
(d)
Fig. 22.5 Lattice arrangement: (a) one dimensional;
(b, c) two dimensional; (d) three dimensional or space lattice.
On the basis of the arrangement of structural units in their crystal lattices, crystalline
substances are classified as in Table 22.1.