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
Even and odd atomic nuclei 162, and 165+ can also alpha decay.) This gives a total of 101 stable nuclides with odd mass numbers. There are another 9 radioactive primordial nuclides (which by definition all have relatively long half lives, greater than 80 million years) with odd mass numbers. Odd-mass-number nuclides are fermions, i.e. have half-integer spin. Generally speaking, since odd-mass-number nuclides always have an even number of either neutrons or protons, the even-numbered particles usually form part of a "core" in the nucleus with a spin of zero. The nucleon with the odd number (whether protons or neutrons) then form a second core with