http://www.ck12.org Chapter 11. Nuclear Chemistry
11.1 Radioactivity
Lesson Objectives
- Explain radioactivity and how it was discovered.
- Describe source, dangers, and uses of radiation.
Lesson Vocabulary
- radiation
- radioactivity
- radioisotope
Introduction
Some elements naturally change into different elements. To understand how this happens, first recall what an element
is. An element is a unique substance, with a unique number of protons in the nucleus of its atoms. No two elements
have the same number of protons. For example, carbon atoms always have six protons. If an atom has a different
number of protons, it isn’t carbon. For an element to change into a different element, then, it must change the number
of protons in the nucleus of its atoms. This happens only in radioactive elements.
Introduction to Radioactivity
Radioactivityis the ability of an atom to emit, or give off, charged particles and energy from the nucleus. The
charged particles and energy are called by the general termradiation. Only unstable nuclei emit radiation. When
they do, they gain or lose protons. Then the atoms become different elements. (Be careful not to confuse this
radiation with electromagnetic radiation, which has to do with the light given off by atoms as they absorb and then
emit energy.)
Discovery of Radioactivity
Radioactivity was discovered in 1896 by a French physicist named Antoine Henri Becquerel. Becquerel was
experimenting with uranium, which glows after being exposed to sunlight. Becquerel wanted to see if the glow
was caused by rays of energy, like rays of light and X-rays. He placed a bit of uranium on a photographic plate. The
plate was similar to film that’s used today to take X-rays. You can see an example of an X-ray inFigure11.1. As
Becquerel predicted, the uranium left an image on the photographic plate. This meant that uranium gives off rays
after being exposed to sunlight.