3.56. Radioactivity http://www.ck12.org
3.56 Radioactivity
- Define radioactivity and radiation.
- Give examples of radioactive elements.
- Outline the discovery of radioactivity.
The man in this old illustration was an alchemist. Alchemists, who lived during the Middle Ages, were people who
strived to turn lead into gold. They tried all sorts of chemical reactions involving lead, but they were never able
to produce gold. Today, scientists know that one element cannot be changed into another by chemical processes.
However, there is a way that some elements can change into others. You’ll find out what it is when you read this
article.
Elements and Protons
For an atom of one element to change into a different element, the number of protons in its nucleus must change.
That’s because each element has a unique number of protons. For example, lead atoms always have 82 protons, and
gold atoms always have 79 protons.
Q:So how can one element change into another?
A:The starting element must be radioactive, and its nuclei must gain or lose protons.
Radioactive Elements
Radioactivityis the ability of an atom to emit, or give off, charged particles and energy from its nucleus. The
charged particles and energy are called by the general termradiation. Only unstable nuclei emit radiation. They
are unstable because they have too much energy, too many protons, or an unstable ratio of protons to neutrons. For