http://www.ck12.org Chapter 13. States of Matter
TABLE13.2:(continued)
Crystal System Diagram Example
Hexagonal
a = b 6 =c;α=β= 90°,γ= 120°BerylUnit Cells
Aunit cellis the smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire crystal.
A crystal can be thought of as the same unit cell repeated over and over in three dimensions. Illustrated below (
Figure13.15) is the relationship of a unit cell to the entire crystal lattice.
FIGURE 13.15
A unit cell is the smallest repeating portion
of a crystal lattice.Unit cells occur in many different varieties. As one example, the cubic crystal system is composed of three different
types of unit cells: (1) simple cubic, (2) face-centered cubic, and (3) body-centered cubic. These are shown in three
different ways below (Figure13.16).
Classes of Crystalline Solids
Crystalline substances can also be described by the types of particles in them and the types of chemical bonding that
take place between the particles. There are four types of crystals: (1) ionic, (2) metallic, (3) covalent network, and
(4) molecular. Properties and several examples of each type are listed and described below (Table13.3).
TABLE13.3: Crystalline Solids –Melting and Boiling Points
Type of Crystalline Solid Examples (formulas) Normal Melting Point
(°C)Normal Boiling Point
(°C)
Ionic NaCl
CaF 2