Page 291 - Theory and Problems of BEGINNING CHEMISTRY

CHAPTER 19

Nuclear

Reactions

19.1. INTRODUCTION
In all the processes discussed so far, the nucleus of every atom remained unchanged. In this chapter, the
effect of changes in the nucleus will be considered. Reactions involving changes in the nuclei are called nuclear
reactions. They involve great quantities of energy, and this energy is referred to as atomic energy or more precisely
as nuclear energy. In general, nuclear reactions may be either spontaneous or induced. We will consider them in
that order.
Nuclear reactions differ from ordinary chemical reactions in the following ways:
1. Most often, atomic numbers change.
2. Although there is no change in the total of the mass numbers, the quantity of matter does change significantly.
Some matter is changed to energy.
3. The atom reacts independently of other atoms to which it might be bonded.
4. Reactions are those of specific isotopes rather than the naturally occurring mixtures of isotopes.
5. The quantities usually used in calculations are atoms rather than moles of atoms.

19.2. NATURAL RADIOACTIVITY
The nuclei of the atoms of some isotopes are inherently unstable, and they disintegrate over time to yield
other nuclei (Sec. 3.5.). The process is called radioactive decay, and the decay of each nucleus is called an event.
There is nothing that humans can do about this type of radioactivity; as long as these isotopes exist, the nuclei
will decompose. Depending on the isotope involved, some number of existing atoms decompose over a period
of time (Sec. 19.3). Three main types of small particles are emitted from the nuclei during natural radioactive
decay; they are named after the first three letters of the Greek alphabet. Their names and properties are listed in
Table 19-1. When an alpha or beta particle is emitted from the nucleus, the identity of the element is changed
because the atomic number is changed,
A stream of alpha particles is sometimes called an alpha ray. A stream of beta particles is called a beta ray.
A gamma ray is composed of a stream of gamma particles.
We can denote the charge and mass number of these small particles as we denoted atomic numbers and mass
numbers in Sec. 3.5.

280

Copyright © 2005, 1999, 1991 by The McGraw-Hill Companies, Inc. Click here for terms of use.