question_answer

The atomic mass of an element is the weighted average of the atomic masses of different isotopes of the element. This explains, why atomic masses of many elements show large departures from integer values. However, even if we consider masses of individual isotopes, they are not strictly integer multiples of the mass of a hydrogen atom. How do you account for this fact?

Answer:

                This is because of following reasons: 1. The mass of proton and neutron are not identical. 2. The atomic mass also includes mass of electrons and an atom of mass number A has Z electrons and not A electrons. 3. The mass of nucleus is slightly less than the mass of the constituent nucleons.