The atomic mass of an element is not a whole number because the atomic mass is the weighted mass of the isotopes of that element, and isotopes have different atomic masses.
Isotopes are defined as substances having same number of protons but different number of neutrons.Number of protons is characteristic for determining position of elements in the periodic table.
Since,all isotopes have the same number of protons and hence have same position.They have similar chemical properties as they have same number of electrons.
They find applications in the field of nuclear medicine and oil and gas research . There are 2 types of isotopes : stable and unstable.
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