The atomic mass of an element is not directly related to the physical size of its atoms. The atomic mass represents the average mass of an atom of that element, taking into account the different isotopes and their abundances.
Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. For example, carbon has three naturally occurring isotopes: carbon-12, carbon-13, and carbon-14. Carbon-12 is the most abundant isotope, and carbon-13 and carbon-14 exist in much smaller quantities.
When calculating the atomic mass of an element, scientists take into consideration the mass of each isotope and its abundance in nature. The atomic mass is determined by multiplying the mass of each isotope by its abundance and summing up these contributions for all isotopes.
So, the atomic mass of an element is a weighted average of the masses of its isotopes, not a direct measurement of the physical size of an atom. The size of an atom is typically described by its atomic radius, which represents the distance from the nucleus to the outermost electron orbital. Atomic radius can vary depending on factors such as the number of electron shells and the electron configuration of the atom, but it is not directly related to the atomic mass.