What refers to a weighted average of the atomic weights of all naturally occurring isotopes of an element.

Atomic mass of an element refers to a weighted average of the atomic weights of all naturally occurring isotopes of an element.

The atomic mass of an element is the weighted average mass of the atoms of all naturally occurring isotopes of the element. Atomic mass is usually reported in atomic mass units and it can be calculated using the weights of the different isotopes and the relative abundances of the element's naturally occurring isotopes. The atomic mass of each element is usually indicated below the element's symbol in each square in the periodic table. For example, the atomic mass of the element boron is 10.8, while that of neon is 20.8.