What term is used for the weighted average mass of isotopes of an element?

The term "atomic mass" refers to the weighted average mass of all the naturally occurring isotopes of an element. This value takes into account both the mass of each isotope and their relative abundance in nature. It is expressed in atomic mass units (amu) and represents the average mass of an atom of the element when considering the contributions from its isotopes.

For instance, if an element has two isotopes with different masses and proportions, the atomic mass will reflect the average that corresponds to the isotopes' respective abundances. This distinction is essential in chemistry and physics since it allows for more accurate calculations in stoichiometry and understanding chemical behavior.

Molar mass, while related, is not specifically about isotopes; it represents the mass of one mole of a substance and can include not only atomic masses but also the masses of compounds or molecules. Molecular weight is a term often used interchangeably with molar mass, but it's less precise in terms of whether it accounts for isotopes. Isotopic mass refers to the mass of a specific isotope, not the weighted average of all isotopes that constitutes atomic mass.