Atomic weights

Atomic weight, or atomic mass, is a measure of the mass of an atom, usually expressed in atomic mass units (amu). It reflects the average mass of an element's isotopes, which are atoms with the same number of protons but different numbers of neutrons. Since isotopes occur in varying natural abundances, atomic weight is a weighted average. For example, carbon has an atomic weight of about 12.01 amu, indicating its isotopes, like carbon-12 and carbon-14, vary slightly in weight and proportion in nature. This concept helps understand the composition and behavior of elements in chemical reactions.