The average atomic mass for each element on the periodic table is representative of the weighted average of the masses of all naturally occurring isotopes of that element. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei, resulting in slightly different masses.
Since many elements have multiple isotopes with varying abundances in nature, the average atomic mass provides a more accurate representation of the typical mass of atoms of that element in the natural environment.
The average atomic mass is calculated by considering the mass of each isotope and its relative abundance. This information is often provided in the periodic table, where the average atomic mass is usually listed beneath the element's symbol.
For example, carbon has two stable isotopes: carbon-12 and carbon-13. Carbon-12 is more abundant, while carbon-13 is less common. The average atomic mass of carbon takes into account the mass of both isotopes and their relative abundances to provide a single value that reflects the average mass of carbon atoms found in nature.
By using the average atomic mass, chemists and scientists can perform accurate calculations and determine precise stoichiometric ratios in chemical reactions involving specific elements.