The single atomic mass listed on most periodic tables is the average atomic mass, which takes into account the relative abundance of all naturally occurring isotopes of that element.

Here's how it relates to different isotopes:

* Isotopes are atoms of the same element that have the same number of protons (atomic number) but different numbers of neutrons. This difference in neutrons leads to different atomic masses for each isotope.

* Relative abundance refers to the proportion of each isotope found naturally. Some isotopes are more common than others.

* Average atomic mass is calculated by multiplying the mass of each isotope by its relative abundance, then summing up the results. This gives us a weighted average that represents the typical mass of an atom of that element.

Example:

* Carbon has two main isotopes: carbon-12 (with 6 protons and 6 neutrons) and carbon-13 (with 6 protons and 7 neutrons).

* Carbon-12 has a relative abundance of about 98.9% while carbon-13 has a relative abundance of about 1.1%.

* The average atomic mass of carbon is calculated as:

(12 amu * 0.989) + (13 amu * 0.011) = 12.01 amu

In essence, the single atomic mass on the periodic table is a weighted average that reflects the presence of multiple isotopes and their relative abundances.