The terms "atomic mass" and "atomic weight" are often used interchangeably, but they can have slightly different meanings depending on the context. In general, both terms refer to the mass of an atom, but they may focus on different aspects of atomic mass.
Atomic Mass: Atomic mass refers to the mass of a single atom of an element, typically expressed in atomic mass units (amu) or unified atomic mass units (u). It takes into account the masses of all the protons, neutrons, and electrons in the atom. The atomic mass is a characteristic property of an element and is often listed on the periodic table.
Atomic Weight: Atomic weight is a concept that takes into account the average mass of all the naturally occurring isotopes of an element, as well as their relative abundances. Since different isotopes of an element have different numbers of neutrons, they have different masses. The atomic weight is calculated by summing the products of the masses of each isotope and its respective abundance and dividing by the sum of the abundances. Atomic weight is also expressed in atomic mass units (amu) or unified atomic mass units (u).
In summary, atomic mass refers to the mass of a single atom, while atomic weight considers the average mass of all the isotopes of an element. Atomic mass is a fixed value for a specific isotope, whereas atomic weight represents the weighted average of isotopic masses based on their natural abundances.