Question

Why are the atomic mass of most of the element fractional?

Answer 1

The atomic masses of most elements are fractional because they exist of a mixture of Isotopes of different masses. the fractional atomic masses arise because of this mixture... mass =total mass of all atoms/number of atomd

Answer 2

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.

Isotopes vary in abundance in the universe for a variety of reason. The most common isotopes are usually ones that are formed from nuclear fusion in the suns core. Other isotopes aren’t made in as great of concentrations because their production requires more specific conditions that occur less often (generally odd mass isotopes). And still others are radioactive so their concentrations slowly diminish unless there is a continuous source of them. Radioactive isotopes also are not included in the average mass in the periodic table, which is why all the radioactive isotopes have (mass) in parenthesis