Answer:
isotopes
Explanation:
Atomic mass is also called atomic weight, although this denomination is incorrect, since mass is a property of substances and weight depends on gravity. The atomic mass is the mass of an atom corresponding to a certain chemical element. The atomic mass unit (u) is usually used as a unit of measure. This unit is also usually called Dalton (Da) in honor of the English chemist John Dalton.
The atomic masses of the chemical elements are usually calculated as the weighted average of the masses of the different isotopes of each element taking into account the relative abundance of each of them, which explains the non-correspondence between the atomic mass in u, of an element, and the number of nucleons in the nucleus of its most common isotope.
