John Dalton in one of his postulations of Atomic Theory stated that atoms of the same element are alike and different from atoms of other elements . This was, however, faulted with the discovery of nucleon mass (mass number) and neutrons by Rutherford and Chadwick respectively. Studies showed that there are atoms of the same element that have the same atomic number, but different mass numbers as a result of the difference in their number of neutrons. These atoms are called isotopes and the phenomenon is known as isotopy. Examples of elements that exhibit isotopy include chlorine (Cl-35 and Cl-37), carbon (C-12, C-13 and C-14), oxygen (O-16, O-17 and O-18) etc. In reality, all elements exhibit isotopy because this explains why the relative atomic masses of elements are not whole numbers . Relative Abundance of Isotopes In a particular element, say chlorine, the two isotopes - Cl-35 (chlorine-35) and Cl-37 (chlorine-37) are present in different quantities of
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