1.1 What is Chemistry?

13.2. Liquids and Solids http://www.ck12.org

TABLE13.1:(continued)

Type Connecting Forces Properties Examples

covalent covalent bonds hard, high melting points,

poor conductors

diamond, quartz

metallic metallic bonds variable hardness and

melting points, good

conductors

Cu, Fe, other metals

Ionic crystals have very strong interactions between individual particles, due to the electrostatic attraction between
oppositely charged ions. This is reflected in the very high melting points of most ionic solids. The shape of the solid
depends upon the relative sizes of the ions and the ratio of cations to anions. Although ionic substances are poor
conductors in the solid state, the ions become mobile upon melting, and the resulting liquid is a very good conductor
of electricity.

Molecular solids are held together by weak dispersion forces or other polar interactions. Because these are based on
attractions between partial charges, they are not as strong as ionic forces. Due to the weaker forces involved, this
class of solids will melt at much lower temperatures than ionic crystals.

Covalent solids are composed of atoms connected by covalent bonds in a three-dimensional network. This extensive
series of strong connections produces a very stable structure that is not affected much by changes in temperature.
The hardness and stability of diamond is a reflection of the many strong carbon-carbon bonds that form its covalent
network.

Metallic solids are composed entirely of metallic atoms. In other solid structures, the electrons involved in bonding
tend to be localized, or fixed in place in the covalent bonds. However, the electrons in metallic bonds are delocalized
over the entire crystal. The fact that the electrons are free to move between different atoms causes metallic solids to
be very good conductors of electricity.

Crystalline solids can also be characterized by their shape. TheTable13.2 illustrates some of the common crystal
forms. The crystal shapes are determined by the type and arrangement of the individual atoms, ions, or molecules
from which they are constructed.

TABLE13.2: Seven Basic Crystal Systems

Crystal System Diagram

Cubic

a = b = c;α=β=γ= 90°