Radioactivity: definition in chemistry
Radioactivity: The spontaneous emission of radiation by unstable atomic nuclei as they decay into more stable ones.
The three main types of radiation are alpha particles (helium-4 nuclei), beta particles (fast electrons or positrons) and gamma rays (high-energy electromagnetic waves). Alpha and beta decay change the number of protons, so the atom becomes a different element. Radioactivity was discovered by Henri Becquerel in 1896, and Marie and Pierre Curie went on to discover the radioactive elements polonium and radium. It is used in medicine, smoke detectors and dating rocks and fossils, but the radiation can damage living cells.
Examples
- Americium-241 in smoke detectors gives off alpha particles
- Radon gas seeping from rocks into basements
- Potassium-40, a natural radioactive isotope found in bananas
- Cobalt-60 gamma rays used to sterilize medical equipment
On the periodic table
Radioactive elements are concentrated at the bottom of the table: every element after lead is radioactive, and so are technetium and promethium.