Why is the atomic mass not a whole number?

The mass quoted on the Periodic Table is the weighted average of the individual isotopes. The element tin, Z=50 , has 10 stable isotopes, and the atomic mass quoted on the Periodic Table, 118.710⋅g⋅mol−1 , is the weighted average of the individual isotopes. read more

Quick Answer. The atomic mass is not given as a whole number because it is a weighted average taken of all of an atom's isotopes found in nature relative to the mass of carbon-12. read more

The mass quoted on the Periodic Table is the weighted average of the individual isotopes. The element tin, Z=50, has 10 stable isotopes, and the atomic mass quoted on the Periodic Table, 118.710*g*mol^-1, is the weighted average of the individual isotopes. read more

An element's atomic mass is not an integer (a whole number) because it is the average mass of all of the element's isotopes (elements that have different amounts of neutrons effecting the mass number of an element). read more