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(–)
A neutral atom:
(–) + + +2
–2
0 net charge
A
(–)

Removing an electron
produces a positive ion:
(–) + +2
+ –1
+1 net charge
B

(–)
FIGURE 6.1 The importance of electrical power seems obvious
in a modern industrial society. What is not so obvious is the role of Adding an electron produces
a negative ion:
electricity in magnetism, light, chemical change, and as the very (–) ++
basis for the structure of matter. All matter, in fact, is electrical in +2
nature, as you will see. –3
C (–) –1 net charge
Electric charges interact to produce what is called the electrical
FIGURE 6.3 (A) A neutral atom has no net charge because
force. Like charges produce a repulsive electrical force as positive the numbers of electrons and protons are balanced. (B) Removing
repels positive and negative repels negative. Unlike charges pro- an electron produces a net positive charge; the charged atom is
duce an attractive electrical force as positive and negative charges called a positive ion. (C) The addition of an electron produces a
attract one another. You can remember how this happens with the net negative charge and a negative ion.
simple rule of like charges repel and unlike charges attract.
Ordinary atoms are usually neutral because there is a
balance between the number of positively charged protons Static Electricity
and the number of negatively charged electrons. A number of Electrons can be moved from atom to atom to create ions. Th ey can

different physical and chemical interactions can result in an also be moved from one object to another by friction and by other
atom gaining or losing electrons. In either case, the atom is said means that will be discussed soon. Since electrons are negatively
to be ionized, and ions are produced as a result. An atom that charged, an object that acquires an excess of electrons becomes
is ionized by losing electrons results in a positive ion because a negatively charged body. The loss of electrons by another body

it has a net positive charge. An atom that is ionized by gaining results in a deficiency of electrons, which results in a positively

electrons results in a negative ion because it has a net negative charged object. Th us, electric charges on objects result from the
charge (Figure 6.3). gain or loss of electrons. Because the electric charge is confi ned to
an object and is not moving, it is called an electrostatic charge.
Positively You probably call this charge static electricity. Static electricity
Nucleus charged is an accumulated electric charge at rest, that is, one that is not
proton
moving. When you comb your hair with a hard rubber comb, the
Negatively comb becomes negatively charged because electrons are trans-
charged P P
electrons ferred from your hair to the comb. Your hair becomes positively
charged with a charge equal in magnitude to the charge gained
N N
by the comb (Figure 6.4). Both the negative charge on the comb
from an excess of electrons and the positive charge on your hair
from a deficiency of electrons are charges that are momentarily at

rest, so they are electrostatic charges.
Neutral
neutron Once charged by friction, objects such as the rubber comb
soon return to a neutral, or balanced, state by the movement of
FIGURE 6.2 A very highly simplified model of an atom has electrons. This happens more quickly on a humid day because

most of the mass in a small, dense center called the nucleus. water vapor assists with the movement of electrons to or from
The nucleus has positively charged protons and neutral neutrons.

charged objects. Thus, static electricity is more noticeable on
Negatively charged electrons move around the nucleus at a much
greater distance than is suggested by this simplified model. Ordinary dry days than on humid ones.
atoms are neutral because there is balance between the number of An object can become electrostatically charged (1) by
positively charged protons and negatively charged electrons. friction, which transfers electrons from one object to another,
6-3 CHAPTER 6 Electricity 141