Isotope is the term used for an atom of an element that differs in atomic mass from other atoms of the same element. The word is derived from the Greek words iso, meaning the same, and topos, meaning place, which refers to the fact that all the isotopes of an element will be in the same place in the periodic table of the elements. In the periodic table the number given for the atomic mass of an element represents the average mass of all the isotopes of that element, weighted by the relative abundance of each isotope. While all atoms of the same element have the same number of protons and electrons, different atoms of the same element often contain different numbers of neutrons. An atom that has a specific number of neutrons and protons is referred to as a nuclide.

Isotopes of the same element exhibit no...