The terms "nuclear mass" and "atomic mass" refer to different aspects of an atom's mass:
Nuclear Mass: Nuclear mass specifically refers to the mass of the nucleus of an atom. The nucleus is the central part of an atom that contains protons and neutrons. The nuclear mass is the sum of the masses of all the protons and neutrons within the nucleus. It is typically expressed in atomic mass units (amu) or kilograms (kg).
Atomic Mass: Atomic mass, also known as atomic weight or relative atomic mass, refers to the average mass of all the isotopes of an element, taking into account their natural abundances. Isotopes are variants of an element that have the same number of protons but different numbers of neutrons. Atomic mass is a weighted average of the masses of all the naturally occurring isotopes of an element, where the weighting factor is the relative abundance of each isotope. It is typically expressed in atomic mass units (amu) or grams (g).
The atomic mass listed on the periodic table represents the weighted average of the masses of all the isotopes of an element. It takes into account both the mass and the abundance of each isotope to provide a more accurate representation of the typical mass of atoms in a sample of the element.
In summary, nuclear mass refers specifically to the mass of the nucleus of an atom, whereas atomic mass represents the average mass of all the isotopes of an element, taking into account their natural abundances.