Isotopes of an element are atoms which have the same number of protons but different number of neutrons. Isotopes have same chemical properties since they have same number of electrons and occupy the same place in periodic table. In Greek the ‘isos’ means same and ‘topos’ means place.
Hydrogen has three isotopes with one proton, dutreium one proton and one neutron, and tritium has one proton and two neutrons.
Each form of element is called nuclide.
Nuclides with the same Z but different A are the isotopes.