How is the atomic mass of an element on the periodic table determined?

The atomic mass of an element on the periodic table is determined by calculating the weighted average of the masses of all of its naturally occurring isotopes. This means that the contribution of each isotope's mass to the overall atomic mass is proportional to its natural abundance.

Each isotope of an element has a different mass due to differences in the number of neutrons in the nucleus, and since isotopes are present in varying amounts, it is most accurate to take into account the abundance of each when calculating the average. This approach provides a more comprehensive and representative value that reflects the typical atomic mass of the element as it exists in nature.

For instance, if an isotope is very abundant, its mass will have a larger effect on the average atomic mass compared to an isotope that is rare. This method of using the average of isotopes rather than just focusing on either the most abundant or the heaviest one ensures a more accurate representation of the element’s atomic mass. It captures the weighted influence of all stable isotopes rather than relying on extremes or outliers.