When the atomic mass is indicated in the periodic table, it typically refers to the atomic mass of an atom, which includes both the mass of the nucleus and the mass of the electrons.
The atomic mass is often expressed in atomic mass units (AMU) or unified atomic mass units (u). It is an average value that takes into account the different isotopes of an element and their relative abundances.
The atomic mass of an element listed on the periodic table considers the masses of the protons and neutrons in the nucleus, as well as the average mass contribution of the electrons. While the mass of electrons is relatively small compared to protons and neutrons, it is still accounted for in the atomic mass calculation.
The atomic mass is calculated using the following formula:
Atomic mass = (mass of isotope 1 * abundance of isotope 1) + (mass of isotope 2 * abundance of isotope 2) + ...
The abundance refers to the relative occurrence or percentage of each isotope in a naturally occurring sample of the element.
For example, the atomic mass of carbon listed on the periodic table is approximately 12.01 AMU. This value takes into account the average masses of the carbon-12 and carbon-13 isotopes, as well as their respective abundances in nature.
So, to answer your question, the atomic mass indicated on the periodic table includes both the mass of the nucleus and the mass of the electrons.