Untitled - Kelly Walsh High School

158 CHEMISTRY FOR THE UTTERLY CONFUSED
Get Started
Quick Tip
The goal of this chapter is to help you learn about intermolecular forces.
Intermolecular forces are interactions between atoms, molecules, and/or ions.
We can use these forces to explain both macroscopic and microscopic properties
of matter.
The state of matter in which a substance exists depends upon two factors. One
of these factors is the kinetic energy of the particles. The other factor is the
intermolecular forces between the particles. The average kinetic energy of the
molecules relates directly to the temperature. Kinetic energy tends to move
particles away from each other. As the temperature increases, the average
kinetic energy increases. When the kinetic energy increases, the particles move
faster. In a solid, the intermolecular forces are sufficiently great to minimize
particle movement. When the temperature increases, the kinetic energy
increases and eventually will overcome the intermolecular forces. The substance
might in fact melt. While a substance is melting, the temperature remains
constant even though we are adding energy. The temperature at which the solid
converts into the liquid state is the melting point (mp). Melting is an example
of a change in state. Changes of state, called phase changes, depend on the temperature.
In some cases, the pressure can also influence these changes.
The melting point of a substance and its freezing point (fp) are identical.
In this chapter, we will concentrate on the solid and liquid states. It may be useful
to review the section in Chapter 10 that deals with the polarity of molecules.
And again, Practice, Practice, Practice.
11-1 Types of Intermolecular Forces
Intermolecular forces are attractive or repulsive forces between atoms, molecules,
and/or ions. The attractive forces compete with the randomizing factor of
kinetic energy. The structure that a particular substance exhibits depends on the