http://www.ck12.org Chapter 3. Chemical Interactions
3.60 Alpha Decay
- Explain how and why alpha decay occurs.
- Show how to write a balanced nuclear equation for alpha decay.
- Describe the dangers of alpha decay.
You probably associate the termdecaywith images like the one above. But when it comes to atoms, decay has a
different meaning. Decay in chemistry refers to changes in the nuclei of certain atoms.
Why Some Nuclei Decay
Radioactive elements and isotopes have unstable nuclei. To become more stable, the nuclei undergo radioactive
decay. In radioactive decay, the nuclei give off, or emit, radiation in the form of energy and often particles as well.
There are several types of radioactive decay, including alpha, beta, and gamma decay. Energy is emitted in all three
types of decay, but only alpha and beta decay also emit particles.
What Is Alpha Decay?
Alpha decay occurs when a nucleus is unstable because it has too many protons. TheFigure3.110 shows what
happens during alpha decay. The nucleus emits an alpha particle and energy. An alpha particle consists of two
protons and two neutrons, which is actually a helium nucleus. Losing the protons and neutrons makes the nucleus
more stable.
3.60 Alpha Decay
Radioactive nuclei and particles are represented by nuclear symbols that indicate their numbers of protons and
neutrons. For example, an alpha particle (helium nucleus) is represented by the symbol^42 He, where He is the