Question

define fractional atomic mass

Answer 1

The atomic masses of most elements are fractional because they exist as a mixture of isotopes of different masses. Most elements occur as a mixture of isotopes of different masses. The fractional atomic masses arise because of this mixture. Avg. mass = total massof all atoms/number of atoms.

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Answer 2

It is because some elements exist in the form of isotopes thus we take their average atomic mass so sometimes it is fractional