We use average atomic mass as a way to represent the mass of an element's atoms. An element can have different isotopes, which are atoms with the same number of protons but different numbers of neutrons. Since isotopes have different masses, the average atomic mass provides a more accurate representation of the mass of the element as a whole.
The average atomic mass is calculated by taking into account the relative abundances of each isotope of an element and multiplying it by the mass of that isotope. The relative abundance is the percentage of each isotope found in a naturally occurring sample of the element. By multiplying the mass of each isotope by its relative abundance and summing up these values, we can obtain the average atomic mass.
The average atomic mass is typically reported in atomic mass units (amu) or unified atomic mass units (u). It is an essential value in many scientific calculations, such as determining the amount of a substance in moles or calculating the molecular weight of a compound.
It's worth noting that the average atomic mass is not always a whole number because it accounts for the presence of isotopes with different masses. For elements with only one stable isotope, the average atomic mass is equal to the mass number of that isotope.