Isotope Isotope Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in mass number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom. The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. The number of protons within the atom's nucleus is called atomic number and is equal to the number of
Isobar (nuclide) Isobar (nuclide) Isobars are atoms (nuclides) of different chemical elements that have the same number of nucleons. Correspondingly, isobars differ in atomic number (or number of protons) but have the same mass number. An example of a series of isobars would be S, Cl, Ar, K, and Ca. The nuclei of these nuclides all contain 40 nucleons; however, they contain varying numbers of protons and neutrons. The term "isobars" (originally "isobares") for nuclides was suggested by Alfred Walter Stewart in 1918. It is derived from the Greek word "isos", meaning "equal" and "baros", meaning "weight". The same mass number implies