All isotopes of an atom have the same:

All Isotopes of an atom all have the same number of protons. This number of protons is the number of the atom on the Periodic Table of elements. Since atoms have equal numbers of protons and electrons, all isotopes of an atom have the same number of electrons as well. For the same atom, the number of neutrons is what identifies each isotope. The various isotopes of an atom all share certain properties, but can differ in other properties. One well known example involves isotopes of Hydrogen: protium with a single neutron, deuterium with two neutrons and tritium with three neutrons. Protium is the usual form of Hydrogen. Deuterium is known as "heavy Hydrogen" and was used for atomic weapons research in "heavy water". Another well known example involves Carbon: Carbon-12 is the common isotope, while Carbon-14, with two extra neutrons with a half life of approximately 5700 years, is radioactive, and used in Carbon dating processes.