isotope

/ˈaɪsəˌtoʊp/

Other forms: isotopes

An isotope of a chemical element is an atom that has a different number of neutrons (that is, a greater or lesser atomic mass) than the standard for that element.

The atomic number is the number of protons in an atom's nucleus. Atomic mass adds to that the number of neutrons in the nucleus. Each element has a typical atomic mass, but when the number of protons stays the same and the number of neutrons changes, you have an isotope. These can be stable, like Deuterium, an isotope of Hydrogen that has one extra neutron, or they can be radioactive, like Plutonium-239, which is a component of nuclear waste.

Definitions of isotope

1. noun

   one of two or more atoms with the same atomic number but with different numbers of neutrons
   types:

   radioisotope

   a radioactive isotope of an element; produced either naturally or artificially

   deuterium, heavy hydrogen

   an isotope of hydrogen which has one neutron (as opposed to zero neutrons in hydrogen)

   tracer

   (radiology) any radioactive isotope introduced into the body to study metabolism or other biological processes

   label

   a radioactive isotope that is used in a compound in order to trace the mechanism of a chemical reaction

   iodine-131

   heavy radioactive isotope of iodine with a half-life of 8 days; used in a sodium salt to diagnose thyroid disease and to treat goiter

   iodine-125

   light radioactive isotope of iodine with a half-life of 60 days; used as a tracer in thyroid studies and as a treatment for hyperthyroidism

   type of:

   atom

   (physics and chemistry) the smallest component of an element having the chemical properties of the element