The terms "atomic weight" and "mass number" refer to different concepts in atomic physics:
Atomic Weight: Atomic weight is a term that represents the average relative mass of an atom of an element. It takes into account the isotopic composition of the element, considering the masses of different isotopes and their relative abundances. Atomic weight is expressed in atomic mass units (amu) or unified atomic mass units (u).
Mass Number: Mass number, on the other hand, refers to the total number of protons and neutrons in the nucleus of an atom. It is a whole number and is specific to a particular isotope of an element. The mass number is used to identify different isotopes of an element, where isotopes have the same number of protons but different numbers of neutrons.
To summarize:
- Atomic weight is an average value that considers the abundance of different isotopes in a naturally occurring sample of an element.
- Mass number is a whole number representing the sum of protons and neutrons in a specific isotope of an element.
It's important to note that atomic weight is a weighted average of the mass numbers of all isotopes of an element, while mass number refers to the specific number of particles in a given isotope.