1.1 What is Chemistry?

http://www.ck12.org Chapter 13. States of Matter

FIGURE 13.6

Vapor Pressure

Vapor pressureis a measure of the pressure exerted by a gas above a liquid in a sealed container. While viscosity
and surface tension increase as the strength of intermolecular forces increase, vapor pressuredecreases. This is
because the stronger the intermolecular forces are, the harder it is for liquid molecules to escape into the gas phase.
Vapor pressure a measure of how much of a substance is in the gas phase when that substance is at equilibrium;
that is, the number of molecules in the gas and liquid phases are not changing. The more molecules that are able
to escape into the gas phase, the higher the vapor pressure. Vapor pressure is also proportional to temperature. As
temperature increases, vapor pressure also increases.

Solids

Solids are materials that have both a defined shape and a defined volume. They do not take on the shape of their
container, as liquids and gases do. Solids can be either amorphous or crystalline. Amorphous solids (such as glass)
do not have a well organized three-dimensional arrangement of molecules or atoms, so they lack a high level of
order. On the other hand,crystalline solidsdisplay a highly ordered and predictable three-dimensional structure. In
this section we will discuss the different types of crystalline solids.

Types of Solids

Solids can be categorized by the forces holding the individual atoms, ions, or molecules together. TheTable13.1
summarizes the properties of different solids:

TABLE13.1:Crystal Types in Solids

Type Connecting Forces Properties Examples

ionic ionic bonds brittle, high melting

points, poor conductors

NaCl, LiBr

molecular intermolecular forces soft, low melting points,

poor conductors

water, glucose